Review Article The Development of Silicon Nanowire as...

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2013 Article ID 328093 16 pageshttpdxdoiorg1011552013328093

Review ArticleThe Development of Silicon Nanowire as Sensing Materialand Its Applications

Jahwarhar Izuan Abdul Rashid12 Jaafar Abdullah3 Nor Azah Yusof13 and Reza Hajian1

1 Functional Devices Laboratory Institute of Advanced Technology Universiti Putra Malaysia (UPM) 43400 SerdangSelangor Malaysia

2 Department of Chemistry and Biology Centre for Defense Foundation Studies National Defense University of MalaysiaSungai Besi Camp 57000 Kuala Lumpur Malaysia

3 Department of Chemistry Faculty of Science Universiti Putra Malaysia (UPM) 43400 Serdang Selangor Malaysia

Correspondence should be addressed to Nor Azah Yusof azahyupmedumy and Reza Hajian rezahajianputraupmedumy

Received 4 September 2013 Accepted 3 November 2013

Academic Editor Artde Donald Kin-Tak Lam

Copyright copy 2013 Jahwarhar Izuan Abdul Rashid et al This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

The application of silicon nanowire (SiNW) as a sensing nanomaterial for detection of biological and chemical species has gainedattention due to its unique properties In this review a short description is also demonstrated on the synthesis techniques of SiNWsand recent progress on sensor development based on electrochemical methods fluorescence field-effect transistors (FET) andsurface-enhanced Raman scattering (SERS) spectroscopy We also discussed the challenges of SiNW-based sensors in the future

1 Introduction

In the last decades biological and chemical sensor technolo-gies have received a tremendous interest among researchareas in various applications due to their efficiency inmonitoring and regulating many areas such as toxicologytesting [1 2] food industry [3 4] medical diagnostics [5ndash7] environmental monitoring [8 9] and drug industries[10 11] Biosensors or chemical sensors can be defined asanalytical devices that incorporated with sensing materialsand molecular recognition elements (enzyme protein anti-body nucleic acid hormone chemical compounds etc) thatget integrated within transducers [12ndash16] The basic principleof sensor detection is based on interaction between therecognition molecule (biological or chemical molecule) andits target and the change of the biochemical reaction wouldbe catalyzed by the sensing material as well as translatedinto a quantifiable signal via the transducer whether in theform of electrochemical [17 18] electrical [19] optical [20]piezoelectric [21] thermometric [22] and so forth Theimportant criterion in the construction of sensors is theperformance in terms of sensitivity that is able to achievelow detection limits Hence the choice of the sensingmaterial

is the fundamental prerequisite step in the development ofultrasensitive sensors [23 24]

With the fast growth and development of advancednanotechnology many sensing nanomaterials with uniqueproperties desired size and chemical compositions havebeen fabricated to be incorporatedwithin the transducerOneof them is the application of one-dimensional (1D) nanos-tructures (nanotubes nanowires nanorods nanobelts andheteronanowires) within the transducers in previous studiesthat can enhance the sensor performance for example TiO

2

nanowires [25] carbon nanotubes [26] CuS nanowires [27]NiO-Au nanobelts [28] CuS nanotubes [27] and grapheneoxide-modified vanadium nanoribbons [29]

Silicon nanowire is one of the 1D nanostructures andhas emerged as the promising sensing nanomaterial upon itsunique mechanical electronical and optical properties [30ndash34] The main reason why SiNWs have attracted attention inthe development of ultrasensitive sensors is due to their highsurface to volume ratios [35 36] thus greatly enhancing thedetection limit to fM concentrations and giving high sensi-tivity In addition the dimension of SiNW is in the range ofasymp1ndash100 nm hence making it very comparable and compatible

2 Journal of Nanomaterials

Si Si Si Si

Au AuAu

Au

Si + 2H2

(I) Aunanoparticledeposition

(II) Silane gas reducedinto Si vapor

(III) Si vapor diffusedthrough droplet of Aunanoparticles

(IV) Supersaturatedwith Si(precipitation)forming SiNWs

Catalyst H2

Si wafer

SiCl4

Figure 1 The SiNWs synthesis using VLS method via CVD method

to the dimensional scale of biological and chemical species[37 38] Having the smallest dimension SiNWs exhibitedgood electron transfer in detection because the accumulationof charge in SiNWsdirectly occurs within the bulk ofmaterialresulting in fast response of detection In this review webriefly elaborate on the synthesis of silicon nanowires andthe application of chemical and biological sensors based onSiNWs

2 SiNWs Synthesis Techniques

In general two techniques have been developed for fab-rication of SiNWs such as bottom-up approach (Vapourliquid solid (VLS) oxide assisted growth (OAG) and metalassisted chemical etching) and top-down approach Bottom-upmethod is a growth or synthesized technique of the SiNWsfrom bulk silicon wafer either metal catalyzed-assisted ormetal catalyzed-free Meanwhile top-down approach startsfrom bulk silicon wafer and scales down to the desired sizeand shape of SiNWs using a lithographic process

21 Vapour Liquid Solid (VLS) Wagner and Ellis havereported for the first time silicon wire synthesis in vaporphase condition using silicon substrate coated with liquidAu droplet [39] In VLS metal-catalyzed (Au Fe Pt Aletc) would be deposited on the silicon wafer first and thenthe SiNWs growth is enhanced either by chemical vapordeposition (CVD) technique [40ndash42] or by laser ablationmethods [43] Principally Si wafer coated metal catalystsare placed at the center of the horizontal tube furnaceand introduced with a Si gas source such as silane (SiH

4)

or tetrachlorosilane (SiCl4) and passed over metal catalyst

deposited on Si wafer in the chamber at above eutectic tem-perature [44] The silane (SiH

4) gas would be decomposed

into silicon vapor and diffuses throughmetal catalyst formingmetal-silicon alloy droplets As silicon diffuses throughmetalnanoparticle catalyst resulting in a supersaturate conditionthe silicon will precipitate out from droplets of metal-Siforming silicon nanowires [45] With establishing a uniformdistribution ofmetal nanoparticles catalyzed on the substratewe can possibly manage to control the diameter and growthalignment of SiNWs (Figure 1)

22 Oxide Assisted Growth (OAG) via Thermal EvaporationIn recent years many researchers have successfully fabri-cated SiNWs using bottom-up approach called oxide assistedgrowth (OAG) via thermal evaporation due to its advantagesin producing a large quantity of SiNWs [46ndash49] In thisOAG method the growth of SiNWs was greatly enhancedusing SiO as starting material to induce the nucleation andthe growth of SiNWs without assisted catalyzed metal thusproducing high purities SiNWs free of metal contamination[50] The fabrication of SiNWs using OAG method has beendescribed in detail by the group of Shao et al [50] Intheir experiment the alumina boat containing the mixtureof SiO powder (10 g) and Si powder (005 g) was placed atthe center of an alumina tube inside horizontal tube furnaceWith certain pressure Argon as a carrier gas was introducedand the furnace heated to 1250ndash1300∘C for 10 hours SiNWswith diameter of 85 nm were collected around the aluminatube surface (Figure 2) One of the characteristics of SiNWsproduced by OAG method is the presence of oxide layer atthe outer surface of SiNWs which is chemically inert Thisoxide layer was usually removed by treatment of hydrofluoricacid (HF) to improve the electrical and optical properties ofSiNWs According to Zhang et al [51] the advantage of thismethod is capability to produce different morphologies inchains rods wires ribbons and coaxial structures and theuse of dangerous precursor gases such as silane (SiH

4) or

tetrachlorosilane (SiCl4) can be avoided The main similarity

between VLS and OAGmethods is in the final SiNWs grownproduct in the form of suspended nanowires [52]

23 Metal Assisted Chemical Etching Metal assisted chemicaletching was reported as a low-cost and simple technique forSiNWs array fabrication [53]Thismethod involves twomainsteps which are electroless metal (silver nickel platinumgold) deposition on silicon wafer followed by chemical etch-ing in Fluoride-ion-based solution [54ndash56] Simultaneousreaction of electroless deposition and chemical etching canbe seen in the work of Brahiti et al [57] when they soakedcleaned Si wafer in a solution containing NH

4HF2and

AgNO3 In this process Ag+ ion would attract electrons

from the silicon substrate (1) that resulted from deposition

Journal of Nanomaterials 3

Argon gaspowder in alumina boat

Mixture of SiO and Si

SiNWs were collectedaround alumina tube

surface1200ndash1300∘C

(a) (b)

Figure 2 (a) Schematic diagram of synthesis SiNWs using OAGmethod (b) SEM image of SiNWs synthesis using OAGmethod (Reprintedwith permission from [50])

(IV) SiNWs array

(III) The sinkingof AgNPs leads to

SiNWs arrayformation

(II) Holesgenerated as the

result ofoxidation siliconand etched by HF

(I) Deposition ofAgNPs on silicon

surface

(a) (b)

Figure 3 (a) Ag assisted chemical etching mechanism (b) view SEM image of Au-assisted electroless etched silicon in 15 g NH4HF2 40mL

H2O2 50mL H

2O solution of pH-1 in room temperature for 30min (Reprinted with permission from [59])

of Ag nanoparticle on silicon surface as Si electronegativity ishigher than silicon [58] Consider

Ag + eminus 997888rarr Ag0 (s) (1)Meanwhile silicon beneath the Ag nanoparticle is oxi-

dized and then etched by HF etchant causing the holesformationThe remaining of the Ag nanoparticles would sinkinto holes and longitudinal and lateral dissolution of silicontriggering the formation of SiNWs arrays [59] (Figure 3)According to Zhang et al [60] different morphologies ofSiNWs arrays could be obtained with the manipulationparameters of etching conditions (temperature depositiontime and concentration etchant) surface orientation anddoping level

24 Top-Down Approach Generally fabrication of SiNWsvia a top-down approach which employed the application

of advanced nanolithography tools on silicon-on insulator(SOI) is mostly compatible with conversional complemen-tary metal oxide-semiconductor (CMOS) technology thattypically consist of deposition etching and patterning stepsBasically the SiNWs fabrication started from the bulk mate-rial and scaled down into a single SiNW or SiNW arraythat can be formed with the help of nanolithography tech-niques such as electron beam lithography (EBL) [61] lithog-raphy patterned nanowires electrodeposition nanoimprintlithography [62] and photolithography For example Parket al [61] applied a top-down approach using electron beamlithography and reactive ion etching on SOI wafer producinghigh control of the geometry and alignment of SiNWs aswell as showing good electrical properties High arrays ofSiNWs with width down to 20 nm and height of 60 nm havebeen demonstrated by the group of Vu et al [62] whichcombined the attributes of the nanoimprint lithography and


SiN Fox

Deposit (ebeam) metal mask Ion beam milling metal mask

RIE SiN

RIE Si device layer

Top view

Remove SiN Top view

Top viewTop view

Wet etch SiO2

Box

Undercut region

Metal mask

Contact regions

Metal mask

Si devicelayer

Si handle

(a)

(d)

(g) (h)

(e) (f)

(b) (c)

Angleddeposition

Contact regionsSiNW

L

Si-Nw

minus45∘45∘

Iw

LPCVD deposit SiO2SIN

Remove SiO2

Figure 4 Single mask silicon nanowires DEA fabrication process (Reprinted with permission from [63])

TMAH wet anisotropic etching Pham et al [63] utilized theDEA technology and photolithography technique to realizea single SiNW with diameter below 100 nm and height of1mm (Figure 4) SiNWarrayswhich consist of 250 nanowireswith 150 nm width 20120583m length and equal space size ofapproximately 32 nm have been successfully fabricated bythe group of Kulkarni et al [64] using top-down approachIn their work they approached 4 steps of photolithographytechniques deep reactive ion etching (DRIE) TMAH wetanisotropic etching and thermal oxidation for developmentof SiNW FET sensor

Tong et al [65] presented a new low-cost top-downnanowire fabrication technology without using nanolithog-raphy This technique is suitable for any conventionalmicrotechnology clean room facility This novel wafer-scaletechnology process uses a combination of angled thin-filmdeposition and etching of a metal layer in a precisely definedcavity with a single micrometer-scale photolithography stepThe key factor to provide an improved dimensional controlcompared to other methods is a precisely defined cavity thatpermits controlled removal of the metal layer with an angledwafer level ion beam that resembles a nanostencil structurepatterned directly on the wafer surface which minimizeslateral spread of the deposited metal

Chen et al [66] presented a new simple Si-NWs fab-rication technology that requires only two microlithogra-phy steps and conventional microfabrication processes on

silicon-on-insulator wafers to form long (ranging from a fewmicrometers up to asymp100120583m) Si-NWs with scalable lateraldimensions ranging from 200 nm down to 10ndash20 nm withnear-perfect crystalline cross sections atomically smoothsurfaces and wafer-scale yields greater than 90 using anovel size reduction method where nanowires can be con-trollably scaled to any dimension and doping concentrationindependent of large contacting regions from a continuouslayer of crystalline silicon

In some circumstances instead of the following ldquobottom-up synthesis first assembly and top-down fabrication nextrdquoit is desirable to grow nanowires precisely and rationally ina predetermined device architecture [67] Direct integrationof growth into fabrication will markedly simplify proce-dures and avoid deterioration of nanowires in some micro-nanofabrication processes In the study reported by He et al[68] Si nanowires have been grown laterally inmicrotrenchesthat were prefabricated on silicon-on-insulator wafers whichdemonstrated that nanowire growth and device fabricationcan be achieved simultaneously Lateral bridging growth wasfirst demonstrated for GaAs nanowires [69] and recentlyfor Si nanowires [70] However well controlled growth anddevice operation were not achieved He et al demonstratedexcellent epitaxial growth of bridging Si nanowires andeffective control of diameters lengths and densities [68]Table 1 shows a brief description on the SiNW synthesis asreported above


Table 1 SiNWs synthesis techniques

Technique Material Reference

Bottom-up approach

Vapour liquid solid (VLS)Coating catalyzed metals on silicon substrate-CVD [39ndash42]Coating catalyzed metals on silicon substrate-laser ablation [43]Si wafer coated metal catalyst introduced with Si gas source [44 45]

Oxide assisted growth (OAG) OAG-thermal evaporation [46ndash50]OAG-HF [51]

Metal assisted chemical etching Electroless metal deposition-chemical etching [54ndash60]

Top-down approach

Electron beam lithography [61]Nanoimprint lithography [62]DEA technology and photolithography [63]Photolithography-DRIE-TMAH-thermal oxidation [64]Angled thin-film deposition-micrometer scale photolithography [65]Lateral bridging growth [70]

3 Applications of SiNW-Based Sensor forChemical and Biological Molecule Detection

In this section we demonstrate the latest applications ofSiNWbased sensor using different detectionmethods includ-ing surface-enhancedRaman scattering (SERS) fluorescenceelectrochemical methods and field-effect transistors (FET)that have been fabricated

31 Surface-Enhanced Raman Scattering (SERS) SpectroscopySensor Utilized SiNWs Surface-enhanced Raman scatteringspectroscopy based on a metal nanostructure has gainedattention due to the enhancement of Raman signal thatreached 1012ndash1015 compared to normal Raman signals Inrecent years most studies reported the utilization of SiNWsfunctionalized Ag nanoparticles to enhance SERS detectionSilver coated SiNW arrays are described as ultrasensitiveSERS sensor for Amoxicillin (an antibiotic medicine thatalways exists in milk and dairy product) and calciumdipicolinate (CaDPA) marker compound of B anthracisspore detection [71] The author explained that silver coatedSiNW arrays as SERS sensor are suitable to detect residualamoxicillin in the milk since they are capable of detectingthe concentration down to 10minus9M The developed sensoralso could achieve detection limit of 4 times 10minus6M for calciumdipicolinate which is 15 times lower than an infectious doseof spore (6 times 10minus5M) suggesting that it is extremely suitablefor detecting B anthracis sporeThe authors further exploredthe application of SiNW arrays coated with Ag nanoparticleas SERS substrate for protein and immunoglobulin detec-tion [72] The results showed that Raman signals of 50 ngmouse immunoglobulinG (migG) and 50 ng goat anti-mouseimmunoglobulin G (gamIgG) were effectively enhancedusing SiNWs-AgNPs in different SERS substrates (silicon(III)wafer SiNWs arrays and Ag coated silicon wafer) Inter-estingly when the concentration of immunoreagents (migGand gamIgG) was down to 10 ng it produced weak Ramansignals but in the presence of the same concentrations ofmigG-gamIgG complex the Raman signal is strongThis maybe due to the fact that the immune reaction between migG

and gamIgG changed the conformation structure in terms ofamino acid residue functional group and orientation bondsthus displaying different Raman signals The detection limitof 4 ng immunocomplex is obtained using SiNWs-AgNPs asSERS substrate Zhang et al [72] concluded that each of theAgNPs that were distributed on the surface of the SiNWsproduced the own electromagnetic wave and SiNWs playeda role to transfer couple and resonate the entire surface ofAgNPsSiNWs which afforded a strong Raman signal

Study of Shao et al [50] also demonstrated good resultsfor achieving high sensitivity for SERS sensor based on siliconnanowires decorated Ag nanoparticles approach to achievedetection limit of 25120583L of 1times 10minus16M 1times 10minus16M 1times 10minus14Mand 1 times 10minus8mgmL for Rhodamine crystal violet nicotinein methanol and calf thymus DNA respectively They alsoestablished inorganic ion SO

4

2minus SERS sensor using the sameSiNWs-AgNPs nanomaterial which allowed detection limitof 1 times 10minus9M Furthermore the group of Jiang et al [73]have fabricated SiNW decorated AgNPs via metal assistedchemical etching technique based sandwich structural DNASERS sensor for multiplex DNA detection In their studiesthey demonstrated the immobilization of thiolated single-stranded DNA probe functionalized with AgNPs via Ag-S bonding and followed by hybridization with the targetreporter probe labeled with Rhodamine 6G before SERSdetection (Figure 5) This remarkable strategy showed highreproducibility and specifically for DNA detection wherethis SERS sensor is capable of discriminating single basemismatched DNA at lower concentrations of 1 pM

Han et al [74] introduced the optimized single SiNWs-AgNPs for SERS detection of pesticide residues (carbaryl)on cucumber surface which was featuring the advantagesin terms of simplicity flexibility high resolution in situdetection fast response (within one second) and enhancedattachment of sensor on rough surface of probe The authorsalso studied the detection of E coli-based SERS sensor byassembling the AgNPs-SiNWs on the commercial filter aswater contaminated with E coli was filtered first beforecharacterization by Raman spectroscopy (Figures 6(a) and6(b))


SH

Step 1 Step 2

600 1000

Target DNA

1400 1800

SERS

SERS

Inte

nsity

Step

3

SH capture DNAReporter DNA

Target DNA DNANC

DNANC

S S S S S S S S S S S S

S S S S S S

Raman shift (cmminus1)

Figure 5 The development of SERS sensor based SiNWsAgNPs for DNA detection (Reprinted with permission from [73])

32 Fluorescencersquos Sensor Utilized SiNWs Su et al [75]recently developed novel AuNP-SiNW-based molecular bea-cons (MBs) for high-sensitivity multiplex DNA detection(Figure 7) Interestingly the authors found that AuNPs-SiNWs based MBs showed robust stability in wide saltconcentrations (001ndash01M) and thermal stability (10∘Cndash80∘C) AuNPs-MBs gradually aggregated due to salt inducedreduction of electrostatic between AuNPs at the high con-centration of salt [76] In principle both ends through thestem loop structured oligonucleotide were modified withorganic dyes carboxyfluorescein and thiol group assembledat AuNPsSiNWs via Au-S bonds Since the position ofcarboxyfluoresceine is close proximity with AuNPs-SiNWsin terms of stem loop conformation structure leadingfeeble intensity of fluorescence When DNA hybridizationhappened the stem loop of MBs underwent conformationchanges resulting in spatial separation of the carboxyfluo-rescein and AuNPs-SiNWs thus enhancing the fluorescenceintensity The study found that when the concentration oftarget DNA increased from 50 pM to 10 nM the fluorescenceintensity was significantly enhanced The authors concludedthat AuNPs-SiNWs based on MBs are able to detect DNAtarget at low concentrations down to pM level and also showhigh selectivity in the presence of noncomplementary DNAand single base mismatch

There is another research by Maxwell et al [77] whodesigned a simple method of fluorescence detection forDNA hybridization events through fabrication of SiNWnetwork modified DNA probe The complementary targetDNA labeled with a fluorescence dye cyanine (Cy3) wouldhybridize with SiNW networks and detected using OlympusBX41MmicroscopeThe authors made a comparison of threedifferent regions of the sample (DNA-grafted SiNWsDNA-grafted Si

3N4surface Si

3N4surface) and as expected the

SiNW networks enhanced the fluorescence signal It wasfound that the optical sensor has high selectivity as it has the

lower fluorescence signal with no complementary DNA dueto the absence of Cy3 labeled target DNA which is more than30 lower than complementary DNA

Another application of SiNWs has been reported by Hanet al [78] for fluorescence protein immunosensor devel-opment The authors reported the fabrication of vertically-aligned SiNW arrays (8120583m in height and 150 120583M in diam-eter) via electroless etching (AEE) process and protein werecovalently immobilized onto (aminopropyltriethoxysilane)APTES modified SiNWs Due to the high aspect ratio ofSiNWs generated high surface of SiNWs that enhanced theimmobilization of loaded BSA protein which is approx-imately 14 times (5733 plusmn 476 120583gcm2) more than planarsilicon substrates (410 plusmn 476 120583gcm2) Based on the positiveresult of BSA immobilization using modified SiNWs-BSAthe authors continued to construct two types of immunosen-sor assays between IgG and FITC-anti-Ig-G (Fluoresceinisocyanate) and IgM and Cys3-anti IgM Their findingdemonstrated that fluorescence intensity as the result of thebinding of both anti-Ig G and anti-IgMwas greatly enhancedusing SiNWs compared with planar substrates (Figure 8)

New type of optical sensor based on SiNWs forCu(II) detection an important element for hematopoiesismetabolism growth and immune system was constructedby the group of Mu et al [79] Here the authors modified thesurface of SiNWs via reaction of the outer hydroxyl groupwith silanol group of fluorescence ligand N-(quinoline-8-yl)-2(3-triethoxysilyl-propylamino)-acetamide (QIOEt) pro-duced highly sensitive for Cu(II) detection down to 10minus8Mhigher than unmodified with QIOEt The presence of othermetal ions such as mercury zinc cadmium ferrum cobaltand plumbum in this study did not have significant inter-ference effect on the selectivity of an optical sensor basedon QIEOT-SiNWs Miao et al [80] reported the applica-tion of SiNWs in the development of fluorescence sensorfor detection of nitride oxide (NO) from liver extract It


1156 1522

1378

(IV)

(a)

(b)

(III)

(II)

(I)

O

NH

O

1000 1200 1400 1600


Inte

nsity

(au

)

600 800 1000 14001200 1600 1800


Inte

nsity

(au

)

Pipette

AgNPsSiNWsthin film sensor

E coli detection

AgNPsSiNWs thin film

(c)

(d)

Figure 6 (a) Photograph of the detection of pesticide residues on a cucumber surface experiment (left) and the microscope image of asingle AgNPSiNW transferred to the rough cucumber surface (right) (b) Raman spectra recorded from the rough cucumber surface with1 s acquisition time and 50x objective Curve I clean cucumber surface curve II carbaryl contaminated surface curve III SERS spectraof a carbaryl contaminated surface modified by a single AgNPSiNW curve IV SERS spectra of pure carbaryl (c) Photograph of SiNWsassembled on a commercially available filter film (with a pore size of 022120583m) and schematic of the E coli detection (d) Raman spectrarecorded from a blank thin film and five different sites on the E coli contaminated AgNPSiNWs thin film with 10 s acquisition time and50x objective (Reprinted with permission from [74])

was found that the modified SiNWs fluorescence sensor(MsiNWs) showed a rapid fluorescence response towardsNOin a few seconds and was stable for days at room temperatureBesides showing high stability rapid responses and highselectivity in the presence of reactive species including O

2

NO2minus NO3minus H2O2 O2minus OH ClOminus and Fe2+ were also

achieved Interestingly the fluorescence images of singleMSiNW before and after reacting with NO showed a finespatial resolution when it was combined with microscopytechniques In the presence of metal nanoparticleSiNWsnanomaterial showed a larger surface-enhanced fluorescence(SEF) for Ln3+ Pr3+ Nd3+ Ho3+ and Er3+ [79 80]

In the study of Zhuo et al [81] the authors explainedthat the application of AuSiNWs nanomaterial enhancedthe fluorescence intensity of Ln3+ which was about 169-fold67-fold and 58-fold for Nd3+ Ho3+ and Er3+ respectivelySimilar results were obtained when using different metalnanoparticles such as silver and copper modified SiNWswhich were approximately twofold of SEF for Ln3+ ioncompared with unsupported silver and copper nanoparticles[82] This is because metal nanoparticle deposited firmly onthe surface of SiNWs without aggregation and the fieldsoverlapped thus resulted in an optimum for enhancement offluorescencersquos signals and caused a great SEF effect Mean-while unsupported metal nanoparticle without SiNWs waseasily aggregated due to the high surface energy of the small

nanoparticle and the large particles were expected to meetstronger steric hindrances in the coupling

33 Electrochemical Sensor Utilized SiNWs The basic prin-ciple of electrochemical detection is based on redox reac-tion as a result of chemical reaction between immobilizedbiomolecule or chemical species on working electrode andtarget analyte which finally produces measurable electricalcurrent [83] The novel nonenzymatic method for detectionof hydrogen peroxide (H

2O2) with high sensitivity and selec-

tivity based on electrochemical method using nanostructureof Ni (OH)

2-SiNWs was reported by Yan et al [84] In their

study the SiNW array was prepared using a chemical etchingprocess followed by deposition of nickel film through electro-less technique The combination of Ni(OH)

2and SiNWs as

working electrode exhibited high catalytic effect for (H2O2)

detection which achieved sensitivity of 331mAsdotmMminus1sdotcmminus1with detection limit of 32120583M and high stability Based onprevious studies there is a great interest in the applicationof SiNWs functionalized with metal nanoparticle due toenhancement of electron transfer of enzyme activity andelectrical conductivity

Su et al [47] have fabricated SiNWs via oxide assistedgrowth technique and treated with 5 HF to produce H-terminated layer This H-terminated layer acts as a strongreducing agent which can reduce 1 HAuCl

4to AuNPs on


SS

S

SS

S

SS

S

SS

S

SH FAMStem-loop DNA

Step 1 Step 2

Target DNA

AuNPs-decorated SiNWs

(a)

BG NC 50pM 100pM 1nM 10nM

13

12

11

10

DNA

Background (BG)

ComplementaryNoncomplementary (NC)

I

times105

(b)

I

10

08

06

04

02

0

BackgroundSingle-base mismatchComplementary

500 520 540 560

120582 (nm)

(c)

Figure 7 (a) Schematic preparation of silicon-based nano-MBs for DNA analysis (b) Fluorescence intensity of different concentrationsof complementary target DNA Background and noncomplemetary sequence are presented as control (c) Photoluminescence spectra ofFAM-tagged probes in the absence and presence of 10 nM complementary target DNA and single-based mismatched DNA (Reprinted withpermission from [75])

the surface of SiNWsThe authors demonstrated that SiNWs-AuNPs modified carbon electrode exhibits high sensitivitycomparedwith the unmodified carbon electrode (Figure 9) Itwas clearly shown that SiNWs enable to increase the electricalconductivity of modified electrode and facilitate electrontransfer of acetylcholinesterase (AChE) for organophosphatepesticide detection The authors found that the SiNWsmodified electrode showed rapid response in the detection ofacetylcholine in the range of 10 120583Mndash10mM and was highlysensitive down to 8 ng Lminus1

According to Su et al [85] the electron transfer gotgreatly enhanced when the surfaces of SiNWs were coatedwith Au nanoparticles for detection of dopamine (DA) aneurotransmitter in brain The author found that SiNWselectrode produced a weak peak current Meanwhile themodified AuNPsSiNWs electrode showed a pair of well-defined quasireversible peaks at 023V and 009V for oxi-dation and reduction potentials respectively (Figure 10)However the application of SiNW arrays functionalizedwith Au nanoparticle enhanced the sensitivity of dopaminedown to 40 nM which was lower than AuAuNP-modifiedelectrode (220 nM) The enrichment of dopamine on the

surface of SiNWs was assisted with the negative charge onSiNWsAuNPs electrode via electrostatic interaction Theauthors also reported the detection of ascorbic acid by cyclicvoltammetry (CV) method using the same AuNPsSiNWselectrode with a detection limit of 500 nM The suc-cess of SiNWsAuNPs electrode is due to the advan-tages of SiNWsAuNPs electrode in terms of increasingmass transport and enhancing electron transfer ThereforeSiNWsAuNPs electrode can be one of the vast applicableelectrodes for electrochemical detection in the future

Moreover SiNWsAuNPs based biosensor for gluta-thione (GSH) was fabricated and showed a fast response tothe GSH concentration in the range of 033ndash297 120583M [86]There are also some studies using single SiNWs strands(height in 2mm and diameter of 35mm) decorated withAu nanoparticles as working electrode for Bovine SerumAlbumin (BSA) detection which achieved detection aslow as 02120583M [87] Kwon et al [88] who fabricated thevertical SiNW arrays decorated with AuNPs using self-assembled monolayer (SAM) of APTES demonstrated detec-tion of BSA protein in the range of 10ndash70 120583M Moreoverthe nafionGoxSiNWsAuNPsGCE was fabricated by the


(a) (b)

160

140

120

100

80

60

40

20

0minus1 0 1 2 3 4

SiNW substrateFlat silicon substrate

Fluo

resc

ence

inte

nsity

(au

)

log[anti-IgG (ngmL)]

(c)

160

180

140

120

100

80

60

40

20

0minus1 0 1 2 3 4


Fluo

resc

ence

inte

nsity

(au

)

log[anti-IgM (ngmL)]

(d)

Figure 8 Immunoassays withmicropatterned SiNWs Fluorescent images obtained from reaction (a) between IgG and FITC-anti IgG and (b)between IgM and Cy3-anti IgM Change in fluorescence intensity with concentration of (c) FITC-anti IgG and (d) Cy3-anti IgM (Reprintedwith permission from [78])

6

4

2

0

00 02 04 06 08 10

ab

c

d

I(120583

A)

E (V)

Figure 9 Cyclic voltammetry for a serial of electrodes (a) bareGCE (b) AChE modified GCE (c) NafionAChEAuNPs modifiedGCE and (d) NafionAChEAuNPsSiNWsmodified GCE in pH 74PBS containing 10mMATCl (scan rate 50mV sminus1) (Reprintedwithpermission from [47])

research group of Su et al [89] to enhance biocatalyticactivity of glucose oxidase (Gox) for high sensitivity glucosedetection which led to detection limit of 50 120583M enoughto monitor blood-glucose levels typically ranging in 44ndash66mM Since the enzyme based biosensor exposed the lossof activity of enzyme which is affected by temperature pHhumidity and toxic chemicals [90] there was also an attempt

of development of glucose sensor based Pd-NiSiNWs with-out immobilization with other mediators or enzymes [91]The authors investigated the electrocatalytic behavior of Pd-NiSiNWs electrode viaCVmethod in 01MKOHcontaining10mM glucose and found that two well oxidation peakswere observed at the potential of minus027V and minus007 dueto glucose oxidation process The developed Pd-NiSiNWselectrode was tested with different concentrations of glucoseand achieved sensitivity of 1907120583AsdotmMminus1 with detectionlimit of 288120583M

34 Field-Effect Transistors (FET) Sensor Utilized SiNWsSiNWs-FET sensor consists of three electrodes which aresource drain and gate electrode and its work is based onconductive change of the carrier on the surface of SiNWseither accumulation or depletion charge When negativecharged molecules bind on n-type SiNW surface it resultsin accumulation of the negative carriers thus increasing theresistance reading and vice versa if using p-type SiNWs [92]Gao et al [93] have developed high performance of label freeand direct time for DNA detection using SiNWs-FET sensorusing top-down approach In this work they managed toimprove the sensitivity of SiNWs-FET sensor by optimizationof probe concentration buffer ionic strength and the gatevoltage SiNW surface was first modified by the amine group


160

120

80

40

0

minus40

minus80

00 02 04 06

A

BI

(120583A

)

E (V) versus SCE

(a)

25

20

15

10

5

0

minus01 00 01 02 03 04 05

I(120583

A)

E (V) versus SCE

(b)

12

10

8

6

4

2

00 200 400 600 800 1000

I(120583

A)

CDA (120583M)

(c)

22

21

20

1900 02 04 06 08 10

I(120583

A)

CDA (120583M)

(d)

5

4

3

20 20 40 60 80 100

I(120583

A)

CDA (120583M)

(e)

Figure 10 (a) Cyclic voltammograms of AuNPsSiNWsAr electrode (A) In the absence and (B) in the presence of 50 120583MDA in pH 70 PBSScan rate was 01 V sminus1 (b) Differential pulse voltammograms at different concentrations of DA ((d) and (e)) Linear relationship between thepeak current and the concentration of DA (Reprinted with permission from [85])

of APTES and functionalized with carboxyl (COOHndash) groupmodified targetDNAviaN-hydroxysuccinimide (NHS) and 1ethyl 3-(3-dimethylaminopropyl)carbodiimide (EDC) SinceDNA probe possesses a negative charge due to the phosphategroup that binds on SiNW surfaces via SAM layer of aminegroup and carboxyl group as described before leading toan increase of resistance and same observation obtainedwhen hybridization occurred The authors found that theoptimized SiNWs-FET sensor presented detection limit of01 fM for DNA target (Figure 11) Moreover the currentchange displayed around 40 when DNA probe hybridizedwith full complementary target DNA and only 20 and 5upon the introduction of single and second base mismatchedDNA

Chen et al [94] studied the utilization of electricallyneutral ethylated DNA (E-DNA) and general DNA as aprobe target on the performance of SiNWs-FET sensor Theauthors found that E-DNA probe helps to enhance sensi-tivity of hybridization signal in terms of resistance changewhich was 233 higher than general DNA Surface plasmaresonance (SPR) response also proved that the amount ofcomplementary DNA hybridized with E-DNA is higher thangeneral probe DNA This can be explained such that E-DNAused in their work does not have an anionic backbone ofthe phosphate group Therefore there is less electrostaticrepulsion between E-DNA and c-DNA thanDNAand cDNAZhang et al [95] also utilized neutral charge DNA analoguepeptide nucleic acid (PNA) as probe immobilization on

the surface of SiNWs-FET sensor which was able to detectmiRNA concentration as low as 1 fM Furthermore SiNWs-FET sensor based PNA-miRNA demonstrated high sequencespecific of full complementary single base mismatchedmiRNA and noncomplemetary miRNA

A novel detection method for DNA-protein interactionrelated to breast cancer estrogen receptor alpha (ER120572)reported by Zhang et al [96] using SiNWs-FET sensorIn their work the amines group modified ER120572 (wild typemutant and noncomplementary) probe was functionalizedon SiNWsurface via vinyl terminated of self-assemblymono-layer (SAM) process and showed high sequence specificity ofER120572 detection which produced 33 of conductance changeupon the interaction of wild type of ERE and ER120572The resultsshowed a smaller conductance change of 84 for detectionof ER120572 using mutant ERE and a negligible charge alsoobserved for bonding to the scrambled DNA The authorsexplored the detection of ER120572 in a crude extract from breastcancer cells and found the change of conductance around234 and 56 when ER120572 bound to the wild-type EREand negative ERE respectively They concluded that DNAprotein functionalized SiNWs-FET sensor produced 103 ofconductance with detection limits of 10 fM for ER120572

C-reactive protein (CRP) and prostate-specific antigen(PSA) were simultaneously detected based on antigen-antibody interaction using SiNW array chip FET sensor [97]The authors utilized sol-gel approach to immobilize anti-CRP and anti-PSA on SiNW arrays instead of using chemical


10

08

06

04

0 25 50 75 100 125

Time (s)

01 fM

1 fM

10 fM

10nM

1pMI DSI 0

(a)

60

45

30

15

0

10minus15 10minus13 10minus11 10minus9 10minus7

Target DNA (M)

ΔI D

SI 0

()

(b)

20

16

1 2

12

08

04

0 15 30 45 60 75

Curr

ent (120583

A)

Time (s)

(c)

078

072

066

060

054

1

2

3

0 25 50 75 100

Time (s)

Curr

ent (120583

A)

(d)

Figure 11 (a) Plots of normalized current change versus time with target DNA at a series of concentrations (01 fM 1 fM 10 fM 1 pM and10 nM) for probe DNA modified SiNW device Hybridization was demonstrated by 05 120583M probe DNA functionalized SiNW biosensor in001 times PBS The length of all SiNWs was 6 120583m (b) Normalized current change as a function of the logarithm of target DNA concentration(c) Plot of current versus time for unmodified SiNWs-FET where region 1 stands for the presence of buffer solution and region 2 for theaddition of 1 nM of fully target DNA The error marks the point when the solution was changed (d) Hybridization specificity demonstratedby 10 nM target DNAs (Reprinted with permission from [93])

modification to avoid loss of protein activity and maintainconformation of antibody It was found that integration ofsol-gel method exhibited high sensitivity with a low amountof serum for simultaneous detection of CRP and PSA in therange of 012ndash10 ngmL and 018ndash881 ngmL respectively

Moreover Zhang et al [98] demonstrated for thefirst time the fabrication of SiNWs-FET sensor basedcarbohydrate-protein interaction where unmodified carbo-hydrate is immobilized via formation of an oxime bond-ing (reaction of amine group from APTES and BOC-aminooxyacetic acid) Their finding on the new developedsensor exhibited high specificity of lectin EC detectionthrough galactose-modified SiNW sensor which is capable ofdetecting as low as 100 fgm four times higher than any othersensors reported previously (Figure 12)

The application of SiNWs-FET sensor for biomarkerdetection also demonstrated by Wu et al [99] who managedto fabricate high sensitivity of interleukin-1120573 genes indicatorfor breast colon lung head and neck cancers To increasethe sensitivity of SiNWs-FET device the authors investigatedthe effect of oxygen (O

2) and nitrogen oxide (N

2O) treatment

on SiNW surface in order to enhance the capture DNAimmobilization efficiency They found out that one-minuteN2O plasma treatment was the optimum time to capture

DNA immobilization and at the same time maintain the

electrical performance of SiNWs-FET Under the optimalcapture DNA functionalized SiNWs-FET via N

2O treatment

20-mer fragment of IL-1120573 was hybridized with capture DNAshowing the sensitivity and detection limit of 012decade and252009fM respectively The direct and real time detection ofinfluenza virus (H

3N2 H1N1 and 8 iso PGF 2a biomarker)

from exhaled breath condensate (EBC) based on antibodyfunctionalized SiNWs-FET sensor was established by Shen etal [100] EBC samples were collected from human subjectswith and without flu and diluted (100-fold) before beingdelivered to the virus antibody functionalized SiNWs-FETdevice which resulted in detection as low as 29 viruses120583LThe authors made a conclusion that 90 of the EBC samplestested with negative or positive results by standard methodof RT-qPCR showed similar patterns when applied withSiNWs-FET detection They also introduced virus antibodymodified magnetic beads to enhance the sensitivity in lowlevel of virus in EBC before direct detection of SiNWs-FET sensor Svendsen et al [101] demonstrated approximately50 resistance change using virus antibody functionalizedSiNWs-FET devices when applied on infected serum samplewith the aleutian disease virus (ADV) from mink thanhealthy mink

Besides the application of SiNWs-FET sensor in detectingmolecule heavy-metal detection based SiNWs-FET sensor


D

Si

Protein

Si

CarbohydrateCarbohydrate

SiNW SiNW DS SSiO2SiO2

(a) (b)

Figure 12 (a) Schematic diagram of the SiNW biosensor for free detection of carbohydrate-protein interaction (b) Optical image of a SiNWsensor chip with four clusters (Reprinted with permission from [98])

has also received great attention recently For exampleBi et al [102] have designed ultrasensitive SiNWs-FET sensorfor simultaneous detection of Cu2+ and Pb2+ in two differentchannels using oligopeptide modified SiNW arrays Theysuggested thatmodified SiNWswith Pb2+ probe oligopeptideconsisted of Cys-Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leuand Cu2+ probe oligopeptide consisted of Gly-Gly-His wereimmobilized independently on SiNW surfaces and exhibitedhigh selectivity also capability of achieving low detection lim-its for Cu2+ and Pb2+ as low as 1 nM and 10 nM respectively

Detection of toxic heavy-metal cations such as Cd2+and Hg2+ based on single-SiNWs-FET sensor has beenfabricated by the group of Luo et al [103] SiNW surfaceswas functionalized with mercaptopropyl silane (MPTES) asthe chelating agent to bind Cd2+ and Hg2+ ions leading tothe accumulation of positive charge of SiNW surface andresulting in the increase of current This developed sensoris based on interaction between thiol groups and Cd2+ andHg2+ The developed FET sensor based SiNWwas enabled todetect Cd2+ and Hg2+ as low as 10minus4 and 10minus7M respectively

Table 2 summarized the applications of SiNW in differenttechniques as described above

4 Conclusions and Perspective

We noticed that the hybrid of SiNWs with metal nanoparti-cles such as gold nanoparticles (AuNPs) and silver nanopar-ticles (AgNPs) presents a new generation of sensing materialelectrodes with excellent catalytic activity and high conduc-tivity that can greatly enhance the performance of sensors interms of sensitivity and selectivity We believe that the inte-gration of SiNWs as sensing nanomaterials has great interest-ing in future for fabrication of of miniaturized sensor devicesdue to their unique properties In our opinion the electro-chemical and electrical detection showed a great promisein realizing a miniaturized sensor based on SiNWs dueto its advantages including high detection portability andsimplicity of the procedure However a few challenges mustbe overcome Firstly the fabrication technique of SiNWseither bottom-up approach or top-down approach must bestrongly developed to ensure the reliable electrochemical andelectrical SiNW sensor Highly controlled SiNW fabrication

Table 2 Application of SiNWs in sensor technologies

Technique Applicationdetection Reference

Surface-enhancedRamanscattering

Amoxicillin calciumdipicolinate [71]

Proteinimmunoglobulin [72]

Rhodamine crystalviolet nicotine calf

thymus DNA[50]

Fluorescencesensor

Multiplex DNAdetection [73]

DNA hybridization [77]Protein immunosensor [78]

Cu (II) detection [79]NO detection [80]

Ln (III) detection [81]

Electrochemicalsensor

H2O2 detection [84]Organophosphatepesticide detection [47]

Dopamine [85]Glutathione [86]

BSA [87 88]Glucose [89 91]

Field effecttransistors

DNA detection andhybridization [93 94]

miRNA determination [95]ER120572 detection [96]

CRP and PSA detection [97]Lectin EC detection [98]Interleukin-I120573 genes [99]

Influenza virus [100]Aleutian disease virus [101]Cu2+ Pb2+ Cd2+ Hg2+ [102 103]

in terms of surface diameter length alignment and so forthshould become the main barrier in the bottom-up techniqueand therefore the parameter manipulation of SiNW synthesishas to be established as the initial step for development of


reproducible sensor based SiNWs Secondly sincemost of thebottom-up techniques produce SiNW suspension followedby dispersing method for the SiNW integration in sensorsystem it is quite hard to control the distribution (align)and identical desired direction Therefore there is a needfor the development technique of casting or alignment ofSiNWs in order to control their distribution and quantityIn contrast top-down approach can provide high controlof SiNW synthesis and alignment however the high costof fabrication of SiNW sensors became the main barrierto develop a low cost portable sensor involving advancedlithography tools For the top-down approach there are greatefforts to find another low costing and effective method forfabrication of reliable sensors In summary SiNW is thepromising nanomaterial sensing in the future

References

[1] G Wang A H Dewilde J Zhang et al ldquoA living cell quartzcrystal microbalance biosensor for continuous monitoring ofcytotoxic responses of macrophages to single-walled carbonnanotubesrdquo Particle and Fibre Toxicology vol 8 article 4 2011

[2] Q Zhang J Ding L Kou and Q Wei ldquoPotentiometricflow biosensor based on ammonia-oxidizing bacteria for thedetection of toxicity in waterrdquo Sensors vol 13 pp 6936ndash69452013

[3] X Xu and Y Ying ldquoMicrobial biosensors for environmentalmonitoring and food analysisrdquo Food Reviews International vol27 no 3 pp 300ndash329 2011

[4] J Lukasiak C A Georgiou K Olsen and D G Georgakopou-los ldquoDevelopment of an L-rhamnose bioluminescent microbialbiosensor for analysis of food ingredientsrdquo European FoodResearch Technology vol 235 pp 573ndash579 2012

[5] J Yuan R Duan H Yang X Luo and M Xi ldquoDetectionof serum human epididymis secretory protein in patientswith ovarian cancer using a label-free biosensor based onlocalized surface plasmon resonancerdquo International Journal ofNanomedicine vol 7 pp 2921ndash2928 2012

[6] Y Cao J Yu B Bo Y Shu and G Li ldquoA simple andgeneral approach to assay protease activity with electrochemicaltechniquerdquo Biosensors and Bioelectronics vol 45 pp 1ndash5 2013

[7] J Y Wu C L Tseng Y K Wang Y Yu K L Ou and CC Wu ldquoDetecting interleukin-1b genes using a N

2O plasma

modified silicon nanowire biosensorrdquo Journal of Experimentaland Clinical Medicine vol 5 pp 12ndash16 2013

[8] G L Turdean ldquoDesign and development of biosensors forthe detection of heavy metal toxicityrdquo International Journal ofElectrochemistry vol 2011 Article ID 343125 15 pages 2011

[9] Y Huang L Wieck and S Tao ldquoDevelopment and evaluationof optical fiber NH

3sensors for application in air quality

monitoringrdquo Atmospheric Environment vol 66 pp 1ndash7 2013[10] M Minunni S Tombelli M Mascini A Bilia M C Bergonzi

and F F Vincieri ldquoAn optical DNA-based biosensor for theanalysis of bioactive constituents with application in drug andherbal drug screeningrdquoTalanta vol 65 no 2 pp 578ndash585 2005

[11] L G Zamfir L Rotariu and C Bala ldquoAcetylcholinesterasebiosensor for carbamate drugs based on tetrathiafulvalenetetra-cyanoquinodimethaneionic liquid conductive gelsrdquo Biosensorsand Bioelectronics vol 46 pp 61ndash67 2013

[12] A Kaur M Verma and S Kamaljit ldquoBiosensor and its clinicalapplicationrdquo International Journal of Advanced Research vol 1pp 108ndash118 2013

[13] A Zhang S You C Soci Y Liu D Wang and Y-H LoldquoSilicon nanowire detectors showing phototransistive gainrdquoApplied Physics Letters vol 93 no 12 Article ID 121110 2008

[14] F Lucarelli S Tombelli M Minunni G Marrazza and MMascini ldquoElectrochemical and piezoelectric DNA biosensorsfor hybridisation detectionrdquo Analytica Chimica Acta vol 609no 2 pp 139ndash159 2008

[15] Y Lei W Chen and A Mulchandani ldquoMicrobial biosensorsrdquoAnalytica Chimica Acta vol 568 no 1-2 pp 200ndash210 2006

[16] S Rodriguez-Mozaz M-P Marco M J Lopez De Alda andD Barcelo ldquoBiosensors for environmental applications futuredevelopment trendsrdquo Pure and Applied Chemistry vol 76 no 4pp 723ndash752 2004

[17] E B Setterington andECAlocilja ldquoElectrochemical biosensorfor rapid and sensitive detection of magnetically extractedbacterial pathogensrdquo Biosensors vol 2 pp 15ndash31 2012

[18] K Chen Z L Zhang Y M Liang and W Liu ldquoA graphene-based electrochemical sensor for rapid determination of phe-nols in waterrdquo Sensors vol 13 pp 6204ndash6216 2013

[19] M B Lerner J Daileya D Brisson and A T Johnson ldquoDetect-ing Lyme disease using antibody-functionalized single-walledcarbon nanotube transistorsrdquo Biosensors and Bioelectronics vol45 pp 163ndash167 2013

[20] X Xu X Liu Y Li and Y Ying ldquoA simple and rapid opticalbiosensor for detection of aflatoxin B1 based on competitivedispersion of gold nanorodsrdquo Biosensors and Bioelectronics vol47 pp 361ndash367 2013

[21] L Su L Zou C C Fong et al ldquoDetection of cancer biomarkersby piezoelectric biosensor using PZT ceramic resonator as thetransducerrdquo Biosensors and Bioelectronics vol 46 pp 155ndash1612013

[22] Y Zheng X Liu Y Ma Y Xu and F Xu ldquoResearch anddevelopment of a new versatile thermal biosensorrdquo Sensors vol9 pp 1033ndash1053 2009

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nanowire bundle arrays use as Pt support for counter electrodesin dye-sensitized solar cellsrdquo Journal of Power Sources vol 238pp 350ndash355 2013

[26] F Shahdost-fard A Salimi E Sharifi and A Korani ldquoFabrica-tion of a highly sensitive adenosine aptasensor based on cova-lent attachment of aptamer onto chitosan-carbon nanotubes-ionic liquid nanocompositerdquo Biosensors and Bioelectronics vol48 pp 100ndash107 2013

[27] L Qian J Mao X Tian H Yuan and D Xiao ldquoIn situ synthesisof CuS nanotubes on Cu electrode for sensitive nonenzymaticglucose sensorrdquo Sensors and Actuators B vol 176 pp 952ndash9592013

[28] Y Ding Y Liu J Parisi L Zhang and Y Lei ldquoA novel NiO-Au hybrid nanobelts based sensor for sensitive and selectiveglucose detectionrdquo Biosensors and Bioelectronics vol 28 no 1pp 393ndash398 2011


[29] Y Sun S H Yang L P Lv et al ldquoA composite film of reducedgraphene oxidemodified vanadium oxide nanoribbons as a freestanding cathode material for rechargeable lithium batteriesrdquoJournal of Power Sources vol 241 pp 168ndash172 2013

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semiconductor photodetectors as efficient light harvestersrdquoNanotechnology Article ID 095502 p 21 2010

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[37] K-I Chen B-R Li and Y-T Chen ldquoSilicon nanowire field-effect transistor-based biosensors for biomedical diagnosis andcellular recording investigationrdquo Nano Today vol 6 no 2 pp131ndash154 2011

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[40] H Suzuki H Araki M Tosa and T Noda ldquoFormation ofsilicon nanowires by CVD using gold catalysts at low temper-aturesrdquo Materials Transactions vol 48 no 8 pp 2202ndash22062007

[41] T W Ho and F C Nan Hong ldquoA novel method to growvertically aligned silicon nanowires on Si (111) and their opticalabsorptionrdquo Journal of Nanomaterials vol 2012 Article ID274618 9 pages 2012

[42] I P Jamal K C Su W Kee Chan M Othman S AbdulRahman and Z Aspanut ldquoFormation of siliconcarbon core-shell nanowires using carbon nitride nanorods template andgold catalystrdquo Journal of Nanomaterials vol 2013 Article ID784150 7 pages 2013

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[44] V Schmidt J V Wittemann S Senz and U Gosele ldquoSiliconnanowires a review on aspects of their growth and theirelectrical propertiesrdquoAdvancedMaterials vol 21 no 25-26 pp2681ndash2702 2009

[45] P R Bandaru and P Pichanusakorn ldquoAn outline of the synthesisand properties of silicon nanowiresrdquo Semiconductor Science andTechnology vol 25 no 2 Article ID 024003 2010

[46] L Yang H Lin T Wang S Ye and M Shao ldquoTellurium-modified silicon nanowires with a large negative temperaturecoefficient of resistancerdquo Applied Physical Letters Article ID133111 p 101 2012

[47] S Su Y He M Zhang et al ldquoHigh-sensitivity pesticidedetection via silicon nanowires-supported acetylcholinesterase-based electrochemical sensorsrdquo Applied Physics Letters vol 93no 2 Article ID 023113 2008

[48] S D Hutagalung K A Yaacob and A F A Aziz ldquoOxide-assisted growth of silicon nanowires by carbothermal evapora-tionrdquo Applied Surface Science vol 254 no 2 pp 633ndash637 2007

[49] N Wang Y H Tang Y F Zhang C S Lee I Bello and S TLee ldquoSi nanowires grown from silicon oxiderdquo Chemical PhysicsLetters vol 299 no 2 pp 237ndash242 1999

[50] M-W Shao M-L Zhang N-B Wong et al ldquoAg-modifiedsilicon nanowires substrate for ultrasensitive surface-enhancedraman spectroscopyrdquo Applied Physics Letters vol 93 no 23Article ID 233118 2008

[51] R-Q Zhang Y Lifshitz and S-T Lee ldquoOxide-assisted growthof semiconducting nanowiresrdquo Advanced Materials vol 15 no7-8 pp 635ndash640 2003

[52] W Chen H Yao C H Tzang J Zhu M Yang and S-TLee ldquoSilicon nanowires for high-sensitivity glucose detectionrdquoApplied Physics Letters vol 88 no 21 Article ID 213104 2006

[53] Z Huang N Geyer P Werner J De Boor and U GoseleldquoMetal-assisted chemical etching of silicon a reviewrdquoAdvancedMaterials vol 23 no 2 pp 285ndash308 2011

[54] F Bai M Li D Song H Yu B Jiang and Y Li ldquoOne-step synthesis of lightly doped porous silicon nanowires inHFAgNO

3H202solution at room temperaturerdquo Journal of

Solid State Chemistry vol 196 pp 596ndash600 2012[55] K Peng YWu H Fang X Zhong Y Xu and J Zhu ldquoUniform

axial-orientation alignment of one-dimensional single-crystalsilicon nanostructure arraysrdquo Angewandte Chemie vol 44 no18 pp 2737ndash2742 2005

[56] K W Kolasinski ldquoSilicon nanostructures from electrolesselectrochemical etchingrdquo Current Opinion in Solid State andMaterials Science vol 9 no 1-2 pp 73ndash83 2005

[57] N Brahiti S-A Bouanik and T Hadjersi ldquoMetal-assistedelectroless etching of silicon in aqueous NH4HF2 solutionrdquoApplied Surface Science vol 258 no 15 pp 5628ndash5637 2012

[58] N Megouda R Douani T Hadjersi and R BoukherroubldquoFormation of aligned silicon nanowire on silicon by electrolessetching inHF solutionrdquo Journal of Luminescence vol 129 no 12pp 1750ndash1753 2009

[59] S-C Shiu S-B Lin S-C Hung and C-F Lin ldquoInfluence ofpre-surface treatment on the morphology of silicon nanowiresfabricated by metal-assisted etchingrdquo Applied Surface Sciencevol 257 no 6 pp 1829ndash1834 2011

[60] M-L Zhang K-Q Peng X Fan et al ldquoPreparation of large-area uniform silicon nanowires arrays through metal-assistedchemical etchingrdquo Journal of Physical Chemistry C vol 112 no12 pp 4444ndash4450 2008

[61] I Park Z Li A P Pisano and R S Williams ldquoTop-downfabricated silicon nanowire sensors for real-time chemicaldetectionrdquoNanotechnology vol 21 no 1 Article ID015501 2010

[62] X T Vu R GhoshMoulick J F Eschermann R Stockmann AOffenhausser and S Ingebrandt ldquoFabrication and application


of silicon nanowire transistor arrays for biomolecular detec-tionrdquo Sensors and Actuators B vol 144 no 2 pp 354ndash360 2010

[63] V B Pham X Thanh T Pham et al ldquoDetection of DNA ofgenetically modified maize by a silicon nanowire field-effecttransistorrdquo Nanoscience and Nanotechnology vol 2 Article ID025010 2011

[64] A Kulkarni Y Xu C Ahn et al ldquoThe label free DNA sensorusing a silicon nanowires arrayrdquo Journal of Biotechnology vol160 pp 91ndash96 2012

[65] H D Tong S Chen W G Van Der Wiel E T Carlen and AD Van Berg ldquoNovel top-down wafer-scale fabrication of singlecrystal silicon nanowiresrdquo Nano Letters vol 9 no 3 pp 1015ndash1022 2009

[66] S Chen J G Bomer W G Van der Wiel E T Carlen and AVanDen Berg ldquoTop-down fabrication of sub-30 nmmonocrys-talline silicon nanowires using conventional microfabricationrdquoACS Nano vol 3 no 11 pp 3485ndash3492 2009

[67] L Gangloff E Minoux K B K Teo et al ldquoSelf-aligned gatedarrays of individual nanotube and nanowire emittersrdquo NanoLetters vol 4 no 9 pp 1575ndash1579 2004

[68] R He D Gao R Fan et al ldquoSi nanowire bridges inmicrotrenches integration of growth into device fabricationrdquoAdvanced Materials vol 17 no 17 pp 2098ndash2102 2005

[69] K Haraguchi K Hiruma T Katsuyama K Tominaga MShirai and T Shimada ldquoSelf-organized fabrication of planarGaAs nanowhisker arraysrdquo Applied Physics Letters vol 69 no3 pp 386ndash387 1996

[70] M S Islam and W C Ellis ldquoHeteroepitaxial ultrafine wire-likegrowth of InAs on GaAs substratesrdquoApplied Physics Letters vol58 no 10 pp 1080ndash1082 1991

[71] B Zhang H Wang L Lu K Ai G Zhang and X ChengldquoLarge-area silver-coated silicon nanowire arrays for molec-ular sensing using surface-enhanced raman spectroscopyrdquoAdvanced Functional Materials vol 18 no 16 pp 2348ndash23552008

[72] M-L Zhang C-Q Yi X Fan et al ldquoA surface-enhancedRaman spectroscopy substrate for highly sensitive label-freeimmunoassayrdquo Applied Physics Letters vol 92 Article ID043116 2008

[73] Z Y Jiang X X Jiang S Su X P Wei S T Lee and YHe ldquoSilicon-based reproducible and active surface-enhancedRaman scattering substrate for sensitive specific and multiplexDNA detectionrdquo Applied Physics Letters vol 100 Article ID203104 2012

[74] X Han H Wang X Ou and X Zhang ldquoHighly sensitivereproducible and stable SERS sensors based on well controlledsilver nanoparticle-decorated siliconnanowire building blocksrdquoJournal of Materials Chemistry vol 22 pp 14127ndash14132 2012

[75] S Su XWei Y Zhong et al ldquoSilicon nanowire-basedmolecularbeacons for high-sensitivity and sequence-specific DNAmulti-plexed analysisrdquo ACS Nano vol 6 no 3 pp 2582ndash2590 2012

[76] P Serre C Ternon V Stambouli et al ldquoFabrication of siliconnanowire networks for biological sensingrdquo Sensors and Actua-tors B vol 182 pp 390ndash395 2013

[77] D J Maxwell J R Taylor and S Nie ldquoSelf-assembled nanopar-ticle probes for recognition and detection of biomoleculesrdquoJournal of the American Chemical Society vol 124 no 32 pp9606ndash9612 2002

[78] S W Han S Lee J Hong E Jang T Lee and W GKoh ldquoMultiscale substrated based on hydrogel-incorporatedsilicon nanowires for protein patterning and microarray-based

immunoassaysrdquo Biosensors and Bioelectronics vol 45 pp 129ndash135 2013

[79] L Mu W Shi J C Chang and S T Lee ldquoSilicon nanowires-based florescence sensor forCu (II)rdquoNanoletters vol 8 pp 104ndash109 2007

[80] R Miao L Mu H Zhang et al ldquoModified silicon nanowiresa fluorescent nitric oxide biosensor with enhanced selectivityand stabilityrdquo Journal of Materials Chemistry vol 22 no 8 pp3348ndash3353 2012

[81] S ZhuoM ShaoHXu T ChenDDDMa and S T Lee ldquoAu-modified silicon nanowires for surface-enhanced fluorescenceof Ln3+ (Ln 5 Pr Nd Ho and Er)rdquo Journal Material Science vol24 pp 324ndash330 2013

[82] S-J Zhuo M-W Shao L Cheng R-H Que D D D Ma andS-T Lee ldquoSilversilicon nanostructure for surface-enhancedfluorescence of Ln3+(Ln=Nd Ho and Er)rdquo Journal of AppliedPhysics vol 108 no 3 Article ID 034305 2010

[83] R Monosık M Stredrsquoansky and E Sturdık ldquoBiosensors-classification characterization and new trendsrdquo Acta ChimicaSlovaca vol 5 pp 109ndash120 2012

[84] Q Yan Z Wang J Zhang et al ldquoNickel hydroxide modifiedsilicon nanowires electrode for hydrogen peroxide sensor appli-cationsrdquo Electrochimica Acta vol 61 pp 148ndash153 2012

[85] S Su X Wei Y Guo et al ldquoA silicon nanowire-based elec-trochemical sensor with high sensitivity and electrocatalyticactivityrdquoMaterial Views vol 30 pp 326ndash331 2013

[86] K Yang H Wang K Zou and X Zhang ldquoGold nanoparticlemodified silicon nanowires as biosensorsrdquoNanotechnology vol17 no 11 pp S276ndashS279 2006

[87] M-W Shao H Yao M-L Zhang N-B Wong Y-Y Shan andS-T Lee ldquoFabrication and application of long strands of siliconnanowires as sensors for bovine serum albumin detectionrdquoApplied Physics Letters vol 87 no 18 Article ID 183106 2005

[88] D H Kwon H H An H-S Kim et al ldquoElectrochemicalalbumin sensing based on silicon nanowires modified by goldnanoparticlesrdquo Applied Surface Science vol 257 no 10 pp4650ndash4654 2011

[89] S Su Y He S Song et al ldquoA silicon nanowire-based electro-chemical glucose biosensor with high electrocatalytic activityand sensitivityrdquo Nanoscale vol 2 no 9 pp 1704ndash1707 2010

[90] Y Shimizu and K Morita ldquoMicrohole array electrode as aglucose sensorrdquo Analytical Chemistry vol 62 no 14 pp 1498ndash1501 1990

[91] S Hui J Zhang X Chen et al ldquoStudy of an amperometricglucose sensor based on Pd-NiSiNW electroderdquo Sensors andActuators B vol 155 no 2 pp 592ndash597 2011

[92] G J Zhang and Y Ning ldquoSilicon nanowire biosensor and itsapplication in disease diagnosticsrdquo Analytica Chimica Acta vol749 pp 1ndash15 2012

[93] A Gao N Lu YWang P Dai X Gao and YWang ldquoEnhancedsensing of nucleic acids with silicon nanowires field effecttransistor biosensorsrdquoNano Letters vol 12 pp 5262ndash5268 2012

[94] W Y Chen H C Chen Y S Yang C J Huang H WH C Chan and W P Hu ldquoImproved DNA detection byutilizing electrically neutral DNAprobe in field-effect transistormeasurements as evidenced by surface plasmon resonanceimagingrdquo Biosensors and Bioelectronics vol 41 pp 795ndash8012013

[95] G-J Zhang J H Chua R-E Chee A Agarwal and S MWong ldquoLabel-free direct detection of MiRNAs with siliconnanowire biosensorsrdquo Biosensors and Bioelectronics vol 24 no8 pp 2504ndash2508 2009


[96] G-J Zhang M J Huang J J Ang E T Liu and K V DesaildquoSelf-assembled monolayer-assisted silicon nanowire biosensorfor detection of protein-DNA interactions in nuclear extractsfrom breast cancer cellrdquo Biosensors and Bioelectronics vol 26no 7 pp 3233ndash3239 2011

[97] H M Lee K Lee and S W Jung ldquoMultiplexed detection ofprotein markers with silicon nanowire FET and sol-gel matrixrdquoin Proceedings of the 34th Annual International Conference of theIEEE EMBS San Diego Calif USA 2012

[98] G J Zhang M J Huang J A Ang et al ldquoLabel free detectionof carbohydrate-protein interaction using nanoscale field-effecttransistor biosensorsrdquo Analytical Chemistry vol 85 pp 4392ndash4397 2013


2O plasma


[100] F Shen J Wang Z Xu et al ldquoRapid flu diagnosis using siliconnanowire sensorrdquo Nano Letters vol 12 pp 3722ndash3730 2012

[101] W E Svendsen M Joslashrgensen L Andresen et al ldquoSiliconnanowire as virus sensor in a total analysis systemrdquo in Proceed-ings of the 25th Eurosensors Conference pp 288ndash291 AthensGreece September 2011

[102] X Bi A Agarwal and K-L Yang ldquoOligopeptide-modifiedsilicon nanowire arrays as multichannel metal ion sensorsrdquoBiosensors andBioelectronics vol 24 no 11 pp 3248ndash3251 2009

[103] L Luo J Jie W Zhang et al ldquoSilicon nanowire sensors for Hg2+and Cd2+ ionsrdquoApplied Physics Letters vol 94 no 19 Article ID193101 2009

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


Si Si Si Si

Au AuAu

Au

Si + 2H2

(I) Aunanoparticledeposition

(II) Silane gas reducedinto Si vapor

(III) Si vapor diffusedthrough droplet of Aunanoparticles

(IV) Supersaturatedwith Si(precipitation)forming SiNWs

Catalyst H2

Si wafer

SiCl4

Figure 1 The SiNWs synthesis using VLS method via CVD method

to the dimensional scale of biological and chemical species[37 38] Having the smallest dimension SiNWs exhibitedgood electron transfer in detection because the accumulationof charge in SiNWsdirectly occurs within the bulk ofmaterialresulting in fast response of detection In this review webriefly elaborate on the synthesis of silicon nanowires andthe application of chemical and biological sensors based onSiNWs

2 SiNWs Synthesis Techniques

In general two techniques have been developed for fab-rication of SiNWs such as bottom-up approach (Vapourliquid solid (VLS) oxide assisted growth (OAG) and metalassisted chemical etching) and top-down approach Bottom-upmethod is a growth or synthesized technique of the SiNWsfrom bulk silicon wafer either metal catalyzed-assisted ormetal catalyzed-free Meanwhile top-down approach startsfrom bulk silicon wafer and scales down to the desired sizeand shape of SiNWs using a lithographic process

21 Vapour Liquid Solid (VLS) Wagner and Ellis havereported for the first time silicon wire synthesis in vaporphase condition using silicon substrate coated with liquidAu droplet [39] In VLS metal-catalyzed (Au Fe Pt Aletc) would be deposited on the silicon wafer first and thenthe SiNWs growth is enhanced either by chemical vapordeposition (CVD) technique [40ndash42] or by laser ablationmethods [43] Principally Si wafer coated metal catalystsare placed at the center of the horizontal tube furnaceand introduced with a Si gas source such as silane (SiH

4)

or tetrachlorosilane (SiCl4) and passed over metal catalyst

deposited on Si wafer in the chamber at above eutectic tem-perature [44] The silane (SiH

4) gas would be decomposed

into silicon vapor and diffuses throughmetal catalyst formingmetal-silicon alloy droplets As silicon diffuses throughmetalnanoparticle catalyst resulting in a supersaturate conditionthe silicon will precipitate out from droplets of metal-Siforming silicon nanowires [45] With establishing a uniformdistribution ofmetal nanoparticles catalyzed on the substratewe can possibly manage to control the diameter and growthalignment of SiNWs (Figure 1)

22 Oxide Assisted Growth (OAG) via Thermal EvaporationIn recent years many researchers have successfully fabri-cated SiNWs using bottom-up approach called oxide assistedgrowth (OAG) via thermal evaporation due to its advantagesin producing a large quantity of SiNWs [46ndash49] In thisOAG method the growth of SiNWs was greatly enhancedusing SiO as starting material to induce the nucleation andthe growth of SiNWs without assisted catalyzed metal thusproducing high purities SiNWs free of metal contamination[50] The fabrication of SiNWs using OAG method has beendescribed in detail by the group of Shao et al [50] Intheir experiment the alumina boat containing the mixtureof SiO powder (10 g) and Si powder (005 g) was placed atthe center of an alumina tube inside horizontal tube furnaceWith certain pressure Argon as a carrier gas was introducedand the furnace heated to 1250ndash1300∘C for 10 hours SiNWswith diameter of 85 nm were collected around the aluminatube surface (Figure 2) One of the characteristics of SiNWsproduced by OAG method is the presence of oxide layer atthe outer surface of SiNWs which is chemically inert Thisoxide layer was usually removed by treatment of hydrofluoricacid (HF) to improve the electrical and optical properties ofSiNWs According to Zhang et al [51] the advantage of thismethod is capability to produce different morphologies inchains rods wires ribbons and coaxial structures and theuse of dangerous precursor gases such as silane (SiH

4) or

tetrachlorosilane (SiCl4) can be avoided The main similarity

between VLS and OAGmethods is in the final SiNWs grownproduct in the form of suspended nanowires [52]

23 Metal Assisted Chemical Etching Metal assisted chemicaletching was reported as a low-cost and simple technique forSiNWs array fabrication [53]Thismethod involves twomainsteps which are electroless metal (silver nickel platinumgold) deposition on silicon wafer followed by chemical etch-ing in Fluoride-ion-based solution [54ndash56] Simultaneousreaction of electroless deposition and chemical etching canbe seen in the work of Brahiti et al [57] when they soakedcleaned Si wafer in a solution containing NH

4HF2and

AgNO3 In this process Ag+ ion would attract electrons

from the silicon substrate (1) that resulted from deposition






(a) (b)


(IV) SiNWs array






surface

(a) (b)


H2O2 50mL H








SiN Fox


RIE SiN

RIE Si device layer

Top view

Remove SiN Top view

Top viewTop view

Wet etch SiO2

Box

Undercut region

Metal mask

Contact regions

Metal mask

Si devicelayer

Si handle

(a)

(d)

(g) (h)

(e) (f)

(b) (c)

Angleddeposition

Contact regionsSiNW

L

Si-Nw

minus45∘45∘

Iw


Remove SiO2










Bottom-up approach




Top-down approach







4




SH

Step 1 Step 2

600 1000

Target DNA

1400 1800

SERS

SERS

Inte

nsity

Step

3


Target DNA DNANC

DNANC


S S S S S S





3N4surface Si







1156 1522

1378

(IV)

(a)

(b)

(III)

(II)

(I)

O

NH

O

1000 1200 1400 1600


Inte

nsity

(au

)

600 800 1000 14001200 1600 1800


Inte

nsity

(au

)

Pipette


E coli detection


(c)

(d)



2










2and SiNWs as




4to AuNPs on


SS

S

SS

S

SS

S

SS

S

SH FAMStem-loop DNA

Step 1 Step 2

Target DNA


(a)


13

12

11

10

DNA

Background (BG)


I

times105

(b)

I

10

08

06

04

02

0


500 520 540 560

120582 (nm)

(c)







(a) (b)

160

140

120

100

80

60

40

20

0minus1 0 1 2 3 4


Fluo

resc

ence

inte

nsity

(au

)


(c)

160

180

140

120

100

80

60

40

20

0minus1 0 1 2 3 4


Fluo

resc

ence

inte

nsity

(au

)


(d)


6

4

2

0

00 02 04 06 08 10

ab

c

d

I(120583

A)

E (V)






160

120

80

40

0

minus40

minus80

00 02 04 06

A

BI

(120583A

)

E (V) versus SCE

(a)

25

20

15

10

5

0

minus01 00 01 02 03 04 05

I(120583

A)

E (V) versus SCE

(b)

12

10

8

6

4

2

00 200 400 600 800 1000

I(120583

A)

CDA (120583M)

(c)

22

21

20

1900 02 04 06 08 10

I(120583

A)

CDA (120583M)

(d)

5

4

3

20 20 40 60 80 100

I(120583

A)

CDA (120583M)

(e)








10

08

06

04

0 25 50 75 100 125

Time (s)

01 fM

1 fM

10 fM

10nM

1pMI DSI 0

(a)

60

45

30

15

0


Target DNA (M)

ΔI D

SI 0

()

(b)

20

16

1 2

12

08

04

0 15 30 45 60 75

Curr

ent (120583

A)

Time (s)

(c)

078

072

066

060

054

1

2

3

0 25 50 75 100

Time (s)

Curr

ent (120583

A)

(d)






2O) treatment




2O treatment






D

Si

Protein

Si



(a) (b)













thymus DNA[50]

Fluorescencesensor








BSA [87 88]Glucose [89 91]









References








2O plasma










































































































2O plasma













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials








(a) (b)


(IV) SiNWs array






surface

(a) (b)


H2O2 50mL H








SiN Fox


RIE SiN

RIE Si device layer

Top view

Remove SiN Top view

Top viewTop view

Wet etch SiO2

Box

Undercut region

Metal mask

Contact regions

Metal mask

Si devicelayer

Si handle

(a)

(d)

(g) (h)

(e) (f)

(b) (c)

Angleddeposition

Contact regionsSiNW

L

Si-Nw

minus45∘45∘

Iw


Remove SiO2










Bottom-up approach




Top-down approach







4




SH

Step 1 Step 2

600 1000

Target DNA

1400 1800

SERS

SERS

Inte

nsity

Step

3


Target DNA DNANC

DNANC


S S S S S S





3N4surface Si







1156 1522

1378

(IV)

(a)

(b)

(III)

(II)

(I)

O

NH

O

1000 1200 1400 1600


Inte

nsity

(au

)

600 800 1000 14001200 1600 1800


Inte

nsity

(au

)

Pipette


E coli detection


(c)

(d)



2










2and SiNWs as




4to AuNPs on


SS

S

SS

S

SS

S

SS

S

SH FAMStem-loop DNA

Step 1 Step 2

Target DNA


(a)


13

12

11

10

DNA

Background (BG)


I

times105

(b)

I

10

08

06

04

02

0


500 520 540 560

120582 (nm)

(c)







(a) (b)

160

140

120

100

80

60

40

20

0minus1 0 1 2 3 4


Fluo

resc

ence

inte

nsity

(au

)


(c)

160

180

140

120

100

80

60

40

20

0minus1 0 1 2 3 4


Fluo

resc

ence

inte

nsity

(au

)


(d)


6

4

2

0

00 02 04 06 08 10

ab

c

d

I(120583

A)

E (V)






160

120

80

40

0

minus40

minus80

00 02 04 06

A

BI

(120583A

)

E (V) versus SCE

(a)

25

20

15

10

5

0

minus01 00 01 02 03 04 05

I(120583

A)

E (V) versus SCE

(b)

12

10

8

6

4

2

00 200 400 600 800 1000

I(120583

A)

CDA (120583M)

(c)

22

21

20

1900 02 04 06 08 10

I(120583

A)

CDA (120583M)

(d)

5

4

3

20 20 40 60 80 100

I(120583

A)

CDA (120583M)

(e)








10

08

06

04

0 25 50 75 100 125

Time (s)

01 fM

1 fM

10 fM

10nM

1pMI DSI 0

(a)

60

45

30

15

0


Target DNA (M)

ΔI D

SI 0

()

(b)

20

16

1 2

12

08

04

0 15 30 45 60 75

Curr

ent (120583

A)

Time (s)

(c)

078

072

066

060

054

1

2

3

0 25 50 75 100

Time (s)

Curr

ent (120583

A)

(d)






2O) treatment




2O treatment






D

Si

Protein

Si



(a) (b)













thymus DNA[50]

Fluorescencesensor








BSA [87 88]Glucose [89 91]









References








2O plasma










































































































2O plasma













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




SiN Fox


RIE SiN

RIE Si device layer

Top view

Remove SiN Top view

Top viewTop view

Wet etch SiO2

Box

Undercut region

Metal mask

Contact regions

Metal mask

Si devicelayer

Si handle

(a)

(d)

(g) (h)

(e) (f)

(b) (c)

Angleddeposition

Contact regionsSiNW

L

Si-Nw

minus45∘45∘

Iw


Remove SiO2










Bottom-up approach




Top-down approach







4




SH

Step 1 Step 2

600 1000

Target DNA

1400 1800

SERS

SERS

Inte

nsity

Step

3


Target DNA DNANC

DNANC


S S S S S S





3N4surface Si







1156 1522

1378

(IV)

(a)

(b)

(III)

(II)

(I)

O

NH

O

1000 1200 1400 1600


Inte

nsity

(au

)

600 800 1000 14001200 1600 1800


Inte

nsity

(au

)

Pipette


E coli detection


(c)

(d)



2










2and SiNWs as




4to AuNPs on


SS

S

SS

S

SS

S

SS

S

SH FAMStem-loop DNA

Step 1 Step 2

Target DNA


(a)


13

12

11

10

DNA

Background (BG)


I

times105

(b)

I

10

08

06

04

02

0


500 520 540 560

120582 (nm)

(c)







(a) (b)

160

140

120

100

80

60

40

20

0minus1 0 1 2 3 4


Fluo

resc

ence

inte

nsity

(au

)


(c)

160

180

140

120

100

80

60

40

20

0minus1 0 1 2 3 4


Fluo

resc

ence

inte

nsity

(au

)


(d)


6

4

2

0

00 02 04 06 08 10

ab

c

d

I(120583

A)

E (V)






160

120

80

40

0

minus40

minus80

00 02 04 06

A

BI

(120583A

)

E (V) versus SCE

(a)

25

20

15

10

5

0

minus01 00 01 02 03 04 05

I(120583

A)

E (V) versus SCE

(b)

12

10

8

6

4

2

00 200 400 600 800 1000

I(120583

A)

CDA (120583M)

(c)

22

21

20

1900 02 04 06 08 10

I(120583

A)

CDA (120583M)

(d)

5

4

3

20 20 40 60 80 100

I(120583

A)

CDA (120583M)

(e)








10

08

06

04

0 25 50 75 100 125

Time (s)

01 fM

1 fM

10 fM

10nM

1pMI DSI 0

(a)

60

45

30

15

0


Target DNA (M)

ΔI D

SI 0

()

(b)

20

16

1 2

12

08

04

0 15 30 45 60 75

Curr

ent (120583

A)

Time (s)

(c)

078

072

066

060

054

1

2

3

0 25 50 75 100

Time (s)

Curr

ent (120583

A)

(d)






2O) treatment




2O treatment






D

Si

Protein

Si



(a) (b)













thymus DNA[50]

Fluorescencesensor








BSA [87 88]Glucose [89 91]









References








2O plasma










































































































2O plasma













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






Bottom-up approach




Top-down approach







4




SH

Step 1 Step 2

600 1000

Target DNA

1400 1800

SERS

SERS

Inte

nsity

Step

3


Target DNA DNANC

DNANC


S S S S S S





3N4surface Si







1156 1522

1378

(IV)

(a)

(b)

(III)

(II)

(I)

O

NH

O

1000 1200 1400 1600


Inte

nsity

(au

)

600 800 1000 14001200 1600 1800


Inte

nsity

(au

)

Pipette


E coli detection


(c)

(d)



2










2and SiNWs as




4to AuNPs on


SS

S

SS

S

SS

S

SS

S

SH FAMStem-loop DNA

Step 1 Step 2

Target DNA


(a)


13

12

11

10

DNA

Background (BG)


I

times105

(b)

I

10

08

06

04

02

0


500 520 540 560

120582 (nm)

(c)







(a) (b)

160

140

120

100

80

60

40

20

0minus1 0 1 2 3 4


Fluo

resc

ence

inte

nsity

(au

)


(c)

160

180

140

120

100

80

60

40

20

0minus1 0 1 2 3 4


Fluo

resc

ence

inte

nsity

(au

)


(d)


6

4

2

0

00 02 04 06 08 10

ab

c

d

I(120583

A)

E (V)






160

120

80

40

0

minus40

minus80

00 02 04 06

A

BI

(120583A

)

E (V) versus SCE

(a)

25

20

15

10

5

0

minus01 00 01 02 03 04 05

I(120583

A)

E (V) versus SCE

(b)

12

10

8

6

4

2

00 200 400 600 800 1000

I(120583

A)

CDA (120583M)

(c)

22

21

20

1900 02 04 06 08 10

I(120583

A)

CDA (120583M)

(d)

5

4

3

20 20 40 60 80 100

I(120583

A)

CDA (120583M)

(e)








10

08

06

04

0 25 50 75 100 125

Time (s)

01 fM

1 fM

10 fM

10nM

1pMI DSI 0

(a)

60

45

30

15

0


Target DNA (M)

ΔI D

SI 0

()

(b)

20

16

1 2

12

08

04

0 15 30 45 60 75

Curr

ent (120583

A)

Time (s)

(c)

078

072

066

060

054

1

2

3

0 25 50 75 100

Time (s)

Curr

ent (120583

A)

(d)






2O) treatment




2O treatment






D

Si

Protein

Si



(a) (b)













thymus DNA[50]

Fluorescencesensor








BSA [87 88]Glucose [89 91]









References








2O plasma










































































































2O plasma













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




SH

Step 1 Step 2

600 1000

Target DNA

1400 1800

SERS

SERS

Inte

nsity

Step

3


Target DNA DNANC

DNANC


S S S S S S





3N4surface Si







1156 1522

1378

(IV)

(a)

(b)

(III)

(II)

(I)

O

NH

O

1000 1200 1400 1600


Inte

nsity

(au

)

600 800 1000 14001200 1600 1800


Inte

nsity

(au

)

Pipette


E coli detection


(c)

(d)



2










2and SiNWs as




4to AuNPs on


SS

S

SS

S

SS

S

SS

S

SH FAMStem-loop DNA

Step 1 Step 2

Target DNA


(a)


13

12

11

10

DNA

Background (BG)


I

times105

(b)

I

10

08

06

04

02

0


500 520 540 560

120582 (nm)

(c)







(a) (b)

160

140

120

100

80

60

40

20

0minus1 0 1 2 3 4


Fluo

resc

ence

inte

nsity

(au

)


(c)

160

180

140

120

100

80

60

40

20

0minus1 0 1 2 3 4


Fluo

resc

ence

inte

nsity

(au

)


(d)


6

4

2

0

00 02 04 06 08 10

ab

c

d

I(120583

A)

E (V)






160

120

80

40

0

minus40

minus80

00 02 04 06

A

BI

(120583A

)

E (V) versus SCE

(a)

25

20

15

10

5

0

minus01 00 01 02 03 04 05

I(120583

A)

E (V) versus SCE

(b)

12

10

8

6

4

2

00 200 400 600 800 1000

I(120583

A)

CDA (120583M)

(c)

22

21

20

1900 02 04 06 08 10

I(120583

A)

CDA (120583M)

(d)

5

4

3

20 20 40 60 80 100

I(120583

A)

CDA (120583M)

(e)








10

08

06

04

0 25 50 75 100 125

Time (s)

01 fM

1 fM

10 fM

10nM

1pMI DSI 0

(a)

60

45

30

15

0


Target DNA (M)

ΔI D

SI 0

()

(b)

20

16

1 2

12

08

04

0 15 30 45 60 75

Curr

ent (120583

A)

Time (s)

(c)

078

072

066

060

054

1

2

3

0 25 50 75 100

Time (s)

Curr

ent (120583

A)

(d)






2O) treatment




2O treatment






D

Si

Protein

Si



(a) (b)













thymus DNA[50]

Fluorescencesensor








BSA [87 88]Glucose [89 91]









References








2O plasma










































































































2O plasma













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




1156 1522

1378

(IV)

(a)

(b)

(III)

(II)

(I)

O

NH

O

1000 1200 1400 1600


Inte

nsity

(au

)

600 800 1000 14001200 1600 1800


Inte

nsity

(au

)

Pipette


E coli detection


(c)

(d)



2










2and SiNWs as




4to AuNPs on


SS

S

SS

S

SS

S

SS

S

SH FAMStem-loop DNA

Step 1 Step 2

Target DNA


(a)


13

12

11

10

DNA

Background (BG)


I

times105

(b)

I

10

08

06

04

02

0


500 520 540 560

120582 (nm)

(c)







(a) (b)

160

140

120

100

80

60

40

20

0minus1 0 1 2 3 4


Fluo

resc

ence

inte

nsity

(au

)


(c)

160

180

140

120

100

80

60

40

20

0minus1 0 1 2 3 4


Fluo

resc

ence

inte

nsity

(au

)


(d)


6

4

2

0

00 02 04 06 08 10

ab

c

d

I(120583

A)

E (V)






160

120

80

40

0

minus40

minus80

00 02 04 06

A

BI

(120583A

)

E (V) versus SCE

(a)

25

20

15

10

5

0

minus01 00 01 02 03 04 05

I(120583

A)

E (V) versus SCE

(b)

12

10

8

6

4

2

00 200 400 600 800 1000

I(120583

A)

CDA (120583M)

(c)

22

21

20

1900 02 04 06 08 10

I(120583

A)

CDA (120583M)

(d)

5

4

3

20 20 40 60 80 100

I(120583

A)

CDA (120583M)

(e)








10

08

06

04

0 25 50 75 100 125

Time (s)

01 fM

1 fM

10 fM

10nM

1pMI DSI 0

(a)

60

45

30

15

0


Target DNA (M)

ΔI D

SI 0

()

(b)

20

16

1 2

12

08

04

0 15 30 45 60 75

Curr

ent (120583

A)

Time (s)

(c)

078

072

066

060

054

1

2

3

0 25 50 75 100

Time (s)

Curr

ent (120583

A)

(d)






2O) treatment




2O treatment






D

Si

Protein

Si



(a) (b)













thymus DNA[50]

Fluorescencesensor








BSA [87 88]Glucose [89 91]









References








2O plasma










































































































2O plasma













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




SS

S

SS

S

SS

S

SS

S

SH FAMStem-loop DNA

Step 1 Step 2

Target DNA


(a)


13

12

11

10

DNA

Background (BG)


I

times105

(b)

I

10

08

06

04

02

0


500 520 540 560

120582 (nm)

(c)







(a) (b)

160

140

120

100

80

60

40

20

0minus1 0 1 2 3 4


Fluo

resc

ence

inte

nsity

(au

)


(c)

160

180

140

120

100

80

60

40

20

0minus1 0 1 2 3 4


Fluo

resc

ence

inte

nsity

(au

)


(d)


6

4

2

0

00 02 04 06 08 10

ab

c

d

I(120583

A)

E (V)






160

120

80

40

0

minus40

minus80

00 02 04 06

A

BI

(120583A

)

E (V) versus SCE

(a)

25

20

15

10

5

0

minus01 00 01 02 03 04 05

I(120583

A)

E (V) versus SCE

(b)

12

10

8

6

4

2

00 200 400 600 800 1000

I(120583

A)

CDA (120583M)

(c)

22

21

20

1900 02 04 06 08 10

I(120583

A)

CDA (120583M)

(d)

5

4

3

20 20 40 60 80 100

I(120583

A)

CDA (120583M)

(e)








10

08

06

04

0 25 50 75 100 125

Time (s)

01 fM

1 fM

10 fM

10nM

1pMI DSI 0

(a)

60

45

30

15

0


Target DNA (M)

ΔI D

SI 0

()

(b)

20

16

1 2

12

08

04

0 15 30 45 60 75

Curr

ent (120583

A)

Time (s)

(c)

078

072

066

060

054

1

2

3

0 25 50 75 100

Time (s)

Curr

ent (120583

A)

(d)






2O) treatment




2O treatment






D

Si

Protein

Si



(a) (b)













thymus DNA[50]

Fluorescencesensor








BSA [87 88]Glucose [89 91]









References








2O plasma










































































































2O plasma













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)

160

140

120

100

80

60

40

20

0minus1 0 1 2 3 4


Fluo

resc

ence

inte

nsity

(au

)


(c)

160

180

140

120

100

80

60

40

20

0minus1 0 1 2 3 4


Fluo

resc

ence

inte

nsity

(au

)


(d)


6

4

2

0

00 02 04 06 08 10

ab

c

d

I(120583

A)

E (V)






160

120

80

40

0

minus40

minus80

00 02 04 06

A

BI

(120583A

)

E (V) versus SCE

(a)

25

20

15

10

5

0

minus01 00 01 02 03 04 05

I(120583

A)

E (V) versus SCE

(b)

12

10

8

6

4

2

00 200 400 600 800 1000

I(120583

A)

CDA (120583M)

(c)

22

21

20

1900 02 04 06 08 10

I(120583

A)

CDA (120583M)

(d)

5

4

3

20 20 40 60 80 100

I(120583

A)

CDA (120583M)

(e)








10

08

06

04

0 25 50 75 100 125

Time (s)

01 fM

1 fM

10 fM

10nM

1pMI DSI 0

(a)

60

45

30

15

0


Target DNA (M)

ΔI D

SI 0

()

(b)

20

16

1 2

12

08

04

0 15 30 45 60 75

Curr

ent (120583

A)

Time (s)

(c)

078

072

066

060

054

1

2

3

0 25 50 75 100

Time (s)

Curr

ent (120583

A)

(d)






2O) treatment




2O treatment






D

Si

Protein

Si



(a) (b)













thymus DNA[50]

Fluorescencesensor








BSA [87 88]Glucose [89 91]









References








2O plasma










































































































2O plasma













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




160

120

80

40

0

minus40

minus80

00 02 04 06

A

BI

(120583A

)

E (V) versus SCE

(a)

25

20

15

10

5

0

minus01 00 01 02 03 04 05

I(120583

A)

E (V) versus SCE

(b)

12

10

8

6

4

2

00 200 400 600 800 1000

I(120583

A)

CDA (120583M)

(c)

22

21

20

1900 02 04 06 08 10

I(120583

A)

CDA (120583M)

(d)

5

4

3

20 20 40 60 80 100

I(120583

A)

CDA (120583M)

(e)








10

08

06

04

0 25 50 75 100 125

Time (s)

01 fM

1 fM

10 fM

10nM

1pMI DSI 0

(a)

60

45

30

15

0


Target DNA (M)

ΔI D

SI 0

()

(b)

20

16

1 2

12

08

04

0 15 30 45 60 75

Curr

ent (120583

A)

Time (s)

(c)

078

072

066

060

054

1

2

3

0 25 50 75 100

Time (s)

Curr

ent (120583

A)

(d)






2O) treatment




2O treatment






D

Si

Protein

Si



(a) (b)













thymus DNA[50]

Fluorescencesensor








BSA [87 88]Glucose [89 91]









References








2O plasma










































































































2O plasma













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




10

08

06

04

0 25 50 75 100 125

Time (s)

01 fM

1 fM

10 fM

10nM

1pMI DSI 0

(a)

60

45

30

15

0


Target DNA (M)

ΔI D

SI 0

()

(b)

20

16

1 2

12

08

04

0 15 30 45 60 75

Curr

ent (120583

A)

Time (s)

(c)

078

072

066

060

054

1

2

3

0 25 50 75 100

Time (s)

Curr

ent (120583

A)

(d)






2O) treatment




2O treatment






D

Si

Protein

Si



(a) (b)













thymus DNA[50]

Fluorescencesensor








BSA [87 88]Glucose [89 91]









References








2O plasma










































































































2O plasma













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




D

Si

Protein

Si



(a) (b)













thymus DNA[50]

Fluorescencesensor








BSA [87 88]Glucose [89 91]









References








2O plasma










































































































2O plasma













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





References








2O plasma










































































































2O plasma













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



















































































2O plasma













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials












































2O plasma













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials








2O plasma













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



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