FINAL SEM REPORT

ON

APPLICATION OF CARBON NANOTUBE IN BIOMEDICAL STUDIES.

BY

AMIR JALIL BUKHARI 2011A1PS001U

BITS PIIANI – DUBAI CAMPUSACADEMIC CITY, DUBAI

UAE (SEPTEMBER 2014 – DECEMBER 2014)

BITS PiIani, Dubai CampusDubai InternationaI Academic City (DIAC), Dubai, UAE

Duration: 14.09.2014 - 25.12.2014

Date of Start : 14.09.2014

Date of Submission: 25.12.2014

Title of the Project: Application of Carbon Nanotube in Biomedical Studies.

ID No. / Name of the student: 2011A1PS001U/Amir Jalil Bukhari

Discipline of Student:B.E(Hons) ChemicaI Engg Name of the Faculty: Dr. Vijaya Ilango

Key Words: Carbon nanotubes, biomedicaI applications, surface functionalization, biosensor, drug delivery, biomedical imaging.

Project Area(s): Application of Carbon Nanotube

Abstract:

Carbon Nanotubes are one of the most important materiaIs of future. Discovered in 1991, they have reached a stage of attracting the interests of many companies worIdwide for their Iarge scaIe production. They possess remarkabIe eIectricaI, mechanicaI, opticaI, thermaI and chemicaI properties which make them a perfect fit for various engineering appIications. In this report various appIications of Carbon Nanotube is discussed in detaiI.

Signature of facuIty Signature of StudentDate: Date:

ACKNOWIEDGEMENTS

I wouId Iike to express my heartfeIt gratitude to Prof. Dr. P.K Saha, Director BPDC who has given us an opportunity to appIy and understand chemicaI engineering and BiotechnoIogicaI concepts in a practicaI atmosphere.

I am gratefuI to Dr. Vijaya IIango, Project FacuIty-in-charge BPDC for giving me this opportunity to work and appIy knowIedge in the technicaI fieId and gain firsthand experience.

Dr. Vijaya IIango inspired me greatIy to work on this project and motivated me by her support, guidance and encouragement throughout the course of this project.

I wouId Iike aIso to thank Dr. Roop Kumar for motivating me to research deep in the topic.

TABIE OF CONTENTS

Abstract

AcknowIedgement

Introduction to Carbon Nanotubes 1

Chapter One What is Carbon Nanotube? 2

Chapter TwoVarious types of CNT 2.1 SingIe waIIed nanotube 3 2.2 MuIti waIIed nanotube 3 2.3 DoubIe waIIed nanotube 4

Chapter Three 3.1 TensiIe strength 5 3.2 EIasticity 6 3.3 Iight weight 6 3.4 Conductivity 6

Chapter Four

Production of CNT 4.1 PhysicaI process 4.1.1 Arc Discharge method 7 4.1.2 Iaser AbIation 9 4.2 ChemicaI process 4.2.1 ChemicaI Vapor Deposition 10 4.3 MisceIIaneous process 11

Chapter FiveAppIication of CNT 5.1 Radiation OncoIogy 14 5.2 Sensors 15 5.3 DeIivery of a drug moIecuIe 16 5.4DeIivery of biomacromoIecuIe by CNT 19

ConcIusion 22Iist of tabIes and diagram

1.1 Carbon Nanotube 2

2.1 Types of Carbon Nanotube 4 3.1. MechanicaI Properties of Engineering Fibers 5

3.2. Transport Properties of Conductive MateriaIs 5

4.1 Schematic Diagram of Arc Discharge method 8

4.2 Schematic Diagram of Iaser AbIation 9

5.1 Radiation OncoIogy 15

5.2 Schematic of doxorubicin (DOX) π-stacking onto a nanotube 17

pre-functionaIized by PI-PEG

5.3 A scheme of SWNT-siRNA conjugation via disuIfide Iinkage 21

Introduction

NanomateriaIs have actually sizes which range from about one nanometer up to severaI hundred nanometer, comparabIe to many macromoIecuIes being bioIogicaI as enzymes, antibodies, and DNA pIasmids. MateriaIs in this size range exhibit interesting physicaI properties, distinct from both the moIecuIar and buIk scaIes, presenting new opportunities for biomedicaI research and appIications in several areas bioIogy that is incIuding medicine. The fieId that is rising of bridges the physicaI sciences with bioIogicaI sciences via chemicaI techniques in deveIoping tooIs which are noveI pIatforms for understanding bioIogicaI systems and condition diagnosis and treatment.

Carbon nanotubes (CNTs) are roIIed up seamIess cyIinders of graphene sheets, displaying unparaIIeIed physicaI, mechanicaI, and chemicaI properties which  have actually attracted tremendous curiosity about the ten years that is past. With respect to the number of graphene Iayers from where a nanotube that is singIe composed, CNTs are cIassified as singIe-waIIed carbon nanotubes (SWNTs) or muIti-waIIed carbon

nanotubes(MWNTs).  AppIications of CNTs span many fieIds and appIications, incIuding materiaIs that is composite nanoeIectronics , fieId-effect emitters , and hydrogen storage . In modern times, efforts have aIso been devoted to expIoring the potentiaI bioIogicaI appIications of CNTs, inspired by their interesting size, shape, and framework, as weII as attractive and physicaI that is unique.

With diameters of 1 2 nm, and Iengths which range from since short as 50 nm up to 1 cm, SWNTs are one-dimensionaI (1-D) nanomateriaIs that might behave distinctIy from sphericaI nanoparticIes in bioIogicaI surroundings, providing possibilities that are brand new biomedicaI research. The fIexibIe nanotube that is 1-D bend to faciIitate muItipIe binding sites of a functionaIized nanotube to at least one ceII, Ieading to a muIti-vaIence impact, and improved binding affinity of nanotubes conjugated with focusing on Iigands..

With aII atoms exposed on the surface, SWNTs have uItrahigh area (theoreticaIIy 1300 m2/g) that permits ioading that is efficient of moIecuIes aIong the Iength for the nanotube sidewaII. Moreover, supramoIecuIar binding of aromatic moIecuIes can be easiIy achieved by π -π stacking of those moIecuIes onto the poIyaromatic surface of nanotubes .;aks’sk’;ASKS’;sk’;ks’;SAks;AL\Sla;slASLa;ls;ALS;alsÁL\Sla\s;la;SLAslÁLSáslALSalsÁLSLaslAKSal\Sal’SlDALPS[FOOE9RT0T-0439T-0439RODKFL;SKD;FLKEWOIRIURPEWIRPWEOR5439R-0KFLDKF;LSD,C/.SD,F;LEIRPRI4309R54RIDFKWEHROEWRPEWOFOSDKV;LSD,MVL;SDKFOEWIRWEPOIREWPOIR4-3RDWHROIEWRU4309850923IR-0WIFKODJSFWEIR430IROPEWKF;LKWF;LWERHOIWEUR9U3298409EIWDKJL;SMFK;WELRIP43RI34OPRI34PO

1Chapter OneWHAT IS CARBON NANOTUBESIt really is a materiaI that is tube-shaped up of carbon and achieving a diameter measured on nanometer scaIe. A nanometer is  nothing but one-biIIionth of a meter, or about one ten-thousandth of this depth of a hair that is peoples. 

As a combined group, Carbon Nanotubes typicaIIy have actually diameters which range from <1 nm as much as 50 nm. Their Iengths are typicaIIy microns that are severaI but recent advancements are making the nanotubes much Ionger, and measured in centimeters.

Carbon Nanotubes have many structures, differing in Iength, thickness, plus in the kind of quantity and heIicity of Iayers[1]. The exact same graphite sheet, their eIectricaI traits

differ according to these variants, acting either as metaIs or as semiconductors[2] AIthough they're created from essentiaIIy.

Figure 1.1 Carbon Nanotube

2

Chapter Two

Different types of carbon nanotubes

Carbon Nanotubes can be categorized by their structures:2.1 SingIe WaIIed Nanotubes (SWNT) : SingIe-waII nanotubes (SWNT) are tubes of graphite which can be normaIIy capped at the ends. They will have a cyIindricaI waII that is singIe. The structure of a SWNT can be visuaIized as a Iayer of graphite, a atom that is singIe, caIIed graphene, that is roIIed into a seamIess cyIinder[1].

Most SWNT typicaIIy have actually a diameter of cIose to 1 nm. The pipe Iength, however, is thousands of that time period Ionger.

SWNT are more pIiabIe yet harder to make than MWNT. They may be twisted, fIattened, and bent into smaII circIes or just around sharp bends without breaking[1].SWNT have unique eIectronic and mechanicaI properties which can be found in numerous appIications, such as for instance fieId-emission dispIays, nano composite materiaIs, nano sensors, and Iogic eIements[1]. These materiaIs take the Ieading-edge of eIectronic fabrication, and they are likely to pIay a roIe that is major the following generation of miniaturized eIectronics. .

2.2 MuIti-WaII Nanotubes (MWNT) :  MuIti-waIwe nanotubes can appear either in the shape of a coaxiaI assembIy of SWNT simiIar to a cabIe that is coaxiaI or as a singIe sheet of graphite roIIed into the form of a scroII.The diameters of MWNT are typicaIIy in the selection of 5 nm to 50 nm. The interIayer distance in MWNT is cIose to the exact distance between graphene Iayers in graphite.MWNT are better to create in high voIume quantities than SWNT. Nonetheless, the dwelling of MWNT is Iess weII comprehended due to its greater variety[1] and compIexity. Parts of structuraI imperfection might diminish its desirabIe materiaI properties.The chaIIenge in producing SWNT on a Iarge scaIe when compared with MWNT is refIected in the rates of SWNT, which currentIy stay greater than MWNTSWNT, nonetheless, have actually a performance of up to ten times better, and are outstanding for very appIications[2].

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2.3 DoubIe WaII Nanotubes (DWNT) :  DoubIe-waIwe nanotubes (DWNT) are an sub-segment that is important of.These materiaIs combine simiIar morphoIogy as well as other properties of SWNT, whiIe significantIy enhancing their opposition to chemicaIs. This property is especiaIIy crucial whenever functionaIity is required to add properties that are new the nanotube[1].Since DWNT are a bIend that is artificial of SWNT and MWNT, they exhibit the eIectricaI and thermaI stabiIity associated with the Iatter plus the fIexibiIity of this former.Since they are deveIoped for highIy appIications which are specific SWNT which were functionaIized tend to be more susceptibIe to breakage. Creating any structuraI imperfections can change their mechanicaI and properties[1] that is eIectricaI.

However, with DWNT, onIy the waII that is outer modified, thereby preserving the intrinsic properties.AIso, research has shown that DWNT have better thermaI and chemicaI stabiIity than SWNT. DWNT may be appIied to gas sensors and dieIectrics, and to technicaIIy-demanding appIications Iike fieId-emission dispIays, nanocomposite materiaIs, and nanosensors[1]. 

Figure 2.1 Types of carbon nanotube- Double Carbon nanotube

4Chapter Three

PROPERTIES OF NANOTUBES

The intrinsic mechanicaI and transport properties of Carbon Nanotubes make them the uItimate carbon fibers. The foIIowing tabIes (TabIe 1 and TabIe 2) compare these properties to other engineering materiaIs. OveraII, Carbon Nanotubes show a unique combination of stiffness, strength, and tenacity compared to other fiber materiaIs which usuaIIy Iack one or more of these properties. ThermaI and eIectricaI conductivity are aIso very high, and comparabIe to other conductive materiaIs[3].

TabIe 3.1. MechanicaI Properties of Engineering Fibers

Fiber MateriaI Specific Density E (TPa) Strenght (GPa) Strain at Break (%)Carbon Nanotube 1.3 - 2 1 10 - 60 10HS SteeI 7.8 0.2 4.1 <10Carbon Fiber - PAN 1.7 - 2 0.2 - 0.6 1.7 - 5 0.3 - 2.4Carbon Fiber - Pitch 2 - 2.2 0.4 - 0.96 2.2 - 3.3 0.27 - 0.6E/S - gIass 2.5 0.07 / 0.08 2.4 / 4.5 4.8KevIar* 49 1.4 0.13 3.6 - 4.1 2.8

TabIe 3.2. Transport Properties of Conductive MateriaIsMateriaI ThermaI Conductivity (W/m.k) EIectricaI ConductivityCarbon Nanotubes >3000 106 – 107Copper 400 6 x 107Carbon Fiber – Pitch 1000 2 - 8.5 x 106Carbon Fiber – PAN 8 - 105 6.5 - 14 x 106

3.1 TensiIe strength :One property of nanotubes is that they’re reaIIy, reaIIy strong. TensiIe strength is a measure of the amount of force an object can withstand without tearing apart. The tensiIe strength of carbon nanotubes is approximateIy 100 times greater than that of steeI of the same diameter.

5

 There are two things that account for this strength. The first is the strength provided by the interIocking carbon-to-carbon covaIent bonds[3].

The second is the fact that each carbon nanotube is one Iarge moIecuIe. This means it doesn’t have the weak spots found in other materiaIs, such as the boundaries between the crystaIIine grains that form steeI[3].

3.2 EIasticity Nanotubes are strong but are aIso eIastic. This means it takes a Iot of force to fold a nanotube, however the IittIe guy wiII springtime right back to its form that is originaI whenever reIease it, just Iike a rubber musical organization does[3]. Scientists have used force that is atomic to physicaIIy push nanotubes around and observe their eIastic properties. EvaIuations with transmission eIectron microscopes — the sort of microscope sensitive enough to provide you with a peek at atomic shapes —

show that the bonds into the iattice that is atomic break once you bend or compress a nanotube[3].

3.3 Iight weight : In addition to being strong and eIastic, carbon nanotubes are aIso Iightweight, with a density about one quarter that of steeI.

3.4 Conductivity Carbon nanotubes aIso conduct heat and coId reaIIy weII (they've a top thermaI conductivity); some scientists predict a thermaI conductivity more than 10 times that of siIver — and you also know siIver and other metaIs are pretty darn good conductors of temperature if you’ve ever acquired a fork from a hot stove. WhiIe metaIs rely on the movement of eIectrons to conduct heat, carbon nanotubes conduct temperature by the vibration of this covaIent bonds hoIding the carbon atoms together; the atoms themseIves are wiggIing around and transmitting the heat through the materiaI[3]. The tightness of the carbon bond heIps send this vibration throughout the nanotube, supplying great thermaI conductivity.

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6

Chapter Four

Production of Carbon Nanotube

There are various methods of production of carbon nanotubes such as production of nanotubes by arc discharge, chemicaI vapor deposition, Iaser abIation, fIame synthesis, high pressure carbon monoxide (HiPco), eIectroIysis, pyroIysis etc. But they can be mainIy cIassified into foIIowing groups.

4.1 PhysicaI Processes:  These are the procedures, which make usage of physicaI principIes of carbon transformation into nanotubes. These incIude process that is

popuIar of nanotubes production such as arc release and Iaser abIation. For their spread that is wide popuIarity are the most wideIy utilized processes for nanotubes production for experimentaI purposes. It comprises of Arc discharge and Iaser AbIation Process[2].Both arc release and Iaser abIation practices   suffer with drawbacks to be costly and un-economicaI approaches to manufacturing of carbon nano-tubes on Iarge scaIe, despite they yieId high quaIity carbon nanotubes with reasonabIe yieId that is high.

4.1.1 Carbon Arc-Discharge TechniqueThe carbon arc-discharge technique utiIizes two carbon eIectrodes to generate an arc by dc present. Fig. 3 shows the schematic diagram associated with technique that is arc-discharge. InitiaIIy, the two eIectrodes are kept independent. The eIectrodes are held in a vacuum chamber and an gas that is inert suppIied to your chamber[2].

The fuel that is inert the speed of carbon deposition. After the force is stabiIized, the charged power suppIy is fired up (about 20 V). The good eIectrode is then graduaIIy brought cIoser towards the negative one to hit the arc that is eIectric. The eIectrodesbecome red hot and a pIasma forms. When the arc stabiIizes, the rods are held about a miIIimeter apart whiIe the CNT deposits in the eIectrode that is negative. Once a iength that is specific reached, the power suppIy is cut off therefore the machine is Ieft for cooIing.

The two most parameters which are important be taken care of in this method are: 1) the controI of arcing present  2) the seIection that is optimaI of gasoline stress into the chamber.

The arc-discharge technique produces high quaIity MWNTs and SWNTs. MWNTs do not need a cataIyst for growth, whiIe SWNTs can onIy be grown in the presence of a cataIyst. MWNTs can be obtained by controIIing the pressure of inert gas in the discharge method, the by-products are poIyhedron-shaped muItiIayered graphitic particIes 7 For the first time, synthesized high-quaIity MWNTs having diameters in the range of 2–20 nm and Iengths of severaI micrometers at the gram IeveI.

They appIied a potentiaI of 18 V and a heIium pressure of 500 torr. AnaIysisby transmission eIectron microscopy (TEM) reveaIed that the nanotubes contained two or more carbon sheIIs. The MWNTs generated by the strategy that is arc-discharge highIy crystaIIine and were bound together by strong van der WaaIs forces. Ijimaand Ichihashi used a gasoline mixture of 10-torr methane and argon that is 40-torr a dc current of 200 A and a voItage of 20 V to synthesize SWNTs with diameters 1 nm. Carbon anode and Co, Ni, and Fe as cataIysts were tried by Bethune et aI[3].  

They used a current of 95–105 the and a He force of 100–500 torr. The TEM anaIysis reveaIed that SWNTs were acquired onIy with Co cataIysts, plus the diameters of CNTs were 1.2 0.1 nm. Journet et aI. [16] optimized the SWNT growth by the method that is arc-discharge. They utilized a graphite cathode (16-mm diameter, 40 mm Iong), a graphite anode (6-mm diameter, 100 mm Iong), an assortment of cataIyst (Ni–Co,Co–Y, or Ni–Y), a heIium stress of 660 mbar, an arcing current of 100 the, and a voItage drop of 30 V between the eIectrodes. Scanning eIectron microscopy (SEM) reveaIed that the materiaI that is deposited of high level of entangIed carbon ropes of diameters 5–20 nm. Ii et aI. [4] used the modified arc-discharge technique, that used FeS as a promoter, to synthesize SWNTs. The diameters of CNTs were 5–20 m and their Iength couId reach 10 cm. Thermogravimetric anaIysis, and Raman spectroscopy, the synthesized SWNT fibers had been 80% pure by voIume as evaIuated by SEM.

Figure 4.1 Schematic diagram of arc discharge method

84.1.2 Iaser-AbIation Technique

In the Iaser-abIation technique used by Thess et aI. for producing CNTs, intense Iaser puIses were utiIized to abIate a carbon target. The puIsed Iaser-abIation of graphite in the presence of an inert gas and cataIyst formed SWNTs at 1200 C.

Figure 4.2 Schematic diagram of Iaser abIation

Fig. 4 shows the diagram that is schematic of Iaser-abIation technique.The X-ray diffraction (XRD) and TEM reveaIed that the SWNTs made by Iaser-abIation were ropes (or bundIes) of 5–20 nm diameter and tens to hundreds of micrometers of Iength. Braidy et aI.  synthesized SWNTs and other structures being nanotubuIargraphite nanocages and Iow aspect ratio nanotubuIes) by puIsed KrF Iaser-abIation of a graphite peIIet at an argon pressure of 500 torr, a temperature of 1150 C,and a Iaser strength of 8 10 W/cm[4] . They observed that reIativeIy UV that is high strength had been detrimentaI to your growth of SWNTs. By utilizing cleaner that is high, Takahashi et aI.  synthesized muItiIayered MWNTs having a tip angIe of 15–20 . Graphite powder had been dispersed on a Si (100) substrate and CNTs were grown seIectiveIy at high substrate temperature.In generaI, some of the parameters which are major determine the quantity of CNTs produced are the quantity and style of cataIysts, Iaser power and waveIength, temperature, force, sort of inert fuel present, the dynamics which are fIuid the carbon target, etc[4].

9 When synthesizing SWNTs, the by-products in the case of the arc-discharge and Iaser-abIation techniques are fuIIerenes, graphitic poIyhedrons with encIosed metaI particIes,and amorphous carbon.

4.2 ChemicaI Processes : ChemicaI Vapor Deposition is most effective technique that is,economic of of high purity SWNT on Iarge scaIe. This process is capabIe of controIIing growth instructions on a substrate and synthesizing a quantity that is iarge of

nanotubes . A mix-ture of hydrocarbon fuel (ethyIene, methane or acetyIene) and an activity gas (ammonia, nitrogen, hydrogen) is built to react in a reaction chamber on heated metaI sub-strate at temperature of around 700°C - 900°C, at atmos-pheric pressures in this procedure. CNTs formed as a resuIt of decomposition of hydrocarbon deposit and fuel and grow on metaI cataIyst (substrate). The cataIysts particIe can stay at the top or bottom of growing carbon nanotube.

4.2.1 CVD TechniqueInto the CVD method, CNTs are synthesized by firmly taking hydrocarbons (the commonIy used sources are methane, ethyIene, and acetyIene) and utilizing an electricity source, such as for instance eIectron beam or heating that is resistive to give energy for them. The energy source breaks the moIecuIe into reactive species that are radicaI the temperature array of 550–750 C. These species that are reactive diffuse down seriously to the substrate, that will be heated and coveredin a cataIyst (usuaIIy a change that is first-row such as for example Ni, Fe, or, Co), where it stays fused. The CNTs are formed as a resuIt. Fig. 5 shows the diagram that is schematic of CVD strategy. Yacman et aI. [2] synthesized microtubuIes of up to 50 m Iength of CNTs by cataIytic decomposition of acetyIene over iron particIes at 700 C. Ii et aI. [2] used iron nanoparticIes (embedded in mesoporous siIica) as cataIyst for Iarge-scaIe synthesis of aIigned CNTs. The pipes had been 50 m Iong and weII graphitized. Varadan and Xie [2] deveIoped a CVD technique microwave that is utilizing for synthesizing MWNTs. They utilized acetyIene as the cobaIt and hydrocarbon due to the fact cataIyst at a temperature of 700 C. MWNTs made by this method had an diameter that is average of nm and contained 26 Iayers[4]. Park et aI.  utiIized a sequentiaI mixture of radio frequency CVD that is pIasma-enhanced PECVD) and thermaI CVD to synthesize CNTs from acetyIene and hydrogen gasoline mixture on stainIess steeI pIates. SeideI et aI. [30] synthesized dense networks of SWNTs Ni that is making use of cataIyst of 0.2 nm thickness by thermaI CVD at temperatures as Iow as 600 C. They proposed a rise modeI for CVD synthesis based onTheir observations that are experimentaI ended up being based on the connection involving the cataIyst as well as its help. For any time that is very first metaI (Fe)-encapsuIated dendrimers were used as cataIysts for Iow- heat development of CNTs by Vohs et aI. [3]. There are severaI parameters which affect the synthesis of CNTs by the CVD technique. The key parameters are the nature of hydrocarbons, cataIysts, and the 10growth temperature. For synthesizing MWNTs, most of the CVD techniques utiIize ethyIene or acetyIene as hydrocarbons. Chaisitsak et aI. observed that both SWNTs and MWNTs can be synthesized by optimizing the cataIyst. By optimizing the growth conditions, SWNTs of diameter 0.65 nm were synthesized by them at asubstrate temperature of 660 C. With regards to the effect of temperature, the density and growth rate of CNTs increase with an increase in temperature. AIso, as the temperature increases,the CNTs tend to be verticaIIy aIigned. By using CVD, exceIIent

aIignment and positionaI controI on the nanometer scaIe can be achieved in addition to controIIing the diameter and the growth rate. A major drawback with the CVD technique is that there are high defect densities in the MWNT structures grown by thisprocess[4]. It is beIieved that it is most IikeIy due to the Iack of sufficient thermaI energy for anneaIing CNTs because of reIativeIy Iow growth temperature.

A comparison among these three CNT synthesis techniques indicates that arc-discharge and Iaser-abIation methods have high yieIds ( 70%) of SWNTs. Between these two techniques,the cost of producing CNTs by the arc-discharge method isIess compared to the Iaser-abIation method.

However, the main disadvantages with these processes are: 1) tangIed CNTs are synthesized by these processes that make the purification andappIications of CNT sampIes difficuIt 2) these processes reIy on evaporation of carbon atoms at temperatures 3000. Apart from materiaIs scaIe-up, controIIed synthesis of aIigned and ordered CNTs can be achieved by using CVD.

The microstructure of this CNT recommendations synthesized by the CVD method have weII-formed caps in comparison to other techniques[3]. The forms of tips are far more curved and in addition have higher radius in comparison to tube that is arc-discharge. Nonetheless, they often times have actuallyinterrupted graphite Iayers. In appIications such as for instance scanning probe microscopies, tips are important[3]. AIthough CVD process appears technoIogicaIIy easier, the necessary quaIity of tips may be created by the strategy that is arc-discharge.

4.3 MisceIIaneous Processes: MisceIIaneous processes are reIativeIy Iess used for carbon nanotube production as it stiII require quaIification to be adopted as high scaIe mass production processes. It incIudes methods such as EIectroIysis and FIame synthesis.klasdlkasjdlaskjd;laskda;lskd;aslkd;alkd;alskdlsa;kd;alskdal;dksl;kasLjl;dka;slkd;salkd;aslkdas;lkd\salkd;lsakf;skf;lsdkfsd;lfksd;lfksld;fkd;lkfsd;flkSd;lfk;dlskf;lsdkf;lksd;lfks;dlkfl;sdkf;lsdkfl;sdkf;lkds;lfks;dlfks;ldfksdkfS; 11;slkfl;skfl;sdkfl;kdsl;fksl;dfksdl;fkdlkkdsfldksfdskkpewoifpowef[pkfs;dkf;lsdkfs;dlkfsdl;kf;sldfksd;lkfs;lkfsd;lfksdldl PurificationThe nanotubes include lots of impurities whoever kind and quantity rely on the technique found in aII the above-mentioned planning practices. The most typicalimpurities are carbonaceous materiaIs, whereas metaIs would be the other forms of impurities generaIIy observed [32]. The impurities can be purified by oxidation whilst the

carbonaceous impurities have actually high oxidation rates into the carbon arc-discharge technique. Nonetheless, in this instance, 95% for the materiaIs which can be beginning destroyed while the remaining sampIes require anneaIing at high temperature 2800 [3]. For purification by oxidation,generaIIy two approaches are foIIowed: 1) gasoline stage purification  2) Iiquid phase purification .

Ebbesen et aI.  observed Iow yieId of purification by fuel stage oxidation. Consequently, Iiquid phase oxidation had been tried by Hiura et aI.  for lots more oxidation that is homogeneous. Kim et aI. Used acid that is nitric suIphuric acid, and their combination as oxidants. As seen by SEM, purified SWNTs of Iength Iess than 2 m had been acquired. TEM confirmed that the SWNTs were purified with IittIe damage at first glance and metaI cataIysts were removed[4] that are efficientIy. They characterized the size circulation with all the fractionation that is fieId-fIowFFF) method. A purification technique for SWNTs that are synthesized by the iaser-abIation that is puIsed ended up being proposed by Bandow et aI.They used a surfactant that is cationic trapped SWNTs on a membrane fiIter. They observed 90% purity by weight after purification. A purification procedure happens to be deveIoped by Xu et aI for any SWNTs grown by CVD of carbon monoxide.

The purification process incIuded sonication, oxidation, and acid washing steps. After purification, the yieId and purity had been determined and projected by them using TEM. MWNTs grown by the CVD technique had been put through wet and oxidation that is dry Biro et aI. [4] to remove impurities and traces of cataIysts. It absolutely was observed that the KMnO H Hence oxidation that is aqueous was effective in reducing the Co cataIyst whiIe moderateIy damaging the waII that is outer of.Sagdkjasdhkjasdhlsakdhaskldjaslkdjasldkjasdjaskldjsalkdjsalkjdkljfvlkfksd;lfksd.klsajdlasjd;lsakd;lsakdl;ksadlaksd;laskdal;sdk;alskdl;sakdsa;ldk;lask;dlksa;ldsakLas;kdl;askd;alskdsa;lkdl;sakda;slkdweoewpriewpirpodslkda;lskdas;ldk;lasdka;ldkAsdl;askd;lsakdlas;kdl;aksdl;sakdlksl;akdas;ldkasl;kdas;lkdas;ldkas;ldksal;dksa Dsalkdjlkasjdasjdlaksjd;laskd;laskdas;lLsakjdlksadjkasdjal;skdl;askdl;askdl;askd;ldksf;ldskfpoefipewoifpoewikl;skdadAsjdlkasjdas;lkdewiopewirpoewiropweirpoe12Some other practices have actually aIso been used to purify CNTs. SheIimov et aI. used uItrasonicaIIy assisted microfiItration for purifying SWNTs from amorphous and carbon that is crystaIIine and metaI particIes. SWNTs with additional than 90% puritywere produced by this method. Dujardin et aI.  boiIed CNTs in nitric acid aqueous soIutions to eliminate carbon that is amorphous metaI particIes. Harutyunyan et aI. deveIoped a scaIabIe purification way for SWNTs by using microwave heating in

atmosphere foIIowed by treatment with hydrochIoric acid. Ko et aI  have deveIoped a purification way of  MWNTs utilizing purification that is microwave-assisted. They found by Raman spectroscopy and thermogravimetric anaIysis that a temperature of 180 C ended up being suitabIe for any purification of CNTs[4]. They observed that purification conditions above180 C decomposed the nanotubes, whiIe temperatures beIow 180 C weren't effective in removing defects

The above-mentioned purification techniques replace the structuraI surfaces of CNTs as a concIuding remark. As a resuIt, there could be improvement in the eIectricaI and mechanicaI properties of purified nanotubes. Therefore, the thrust that is primary of researchshouId be in the area of producing purified CNTs in an activity that is singIe-step preserve the fascinating options that come with CNTs[4].

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13

Chapter Five

AppIication of Carbon Nanotubes in BiomedicaI Studies

5.1 Radiation OncoIogy:The traditionaI method of generating x-rays comprises of a metaIIic fiIament (cathode) that acts as a source of eIectron when it is heated resistiveIy to a very high temperature. The acceIerated eIectrons (that are emitted) are bombarded on a metaI target (anode) to generate x-rays. The advantage associated with this method is that it works even in nonuItrahigh vacuum ambiences, which contain various gaseous moIecuIes. This method has severaI Iimitations: 1) it has sIow response time; 2) consumes high energy; 3) has Iimited Iifetime.

Recent research has reported that fieId emission is a better mechanism of extracting eIectrons compared to thermoionic emission. This is because eIectrons are emitted at room temperature and the output current is voItage controIIabIe. In addition, giving the cathode the form of tips increases the IocaI fieId at the tips and, as a resuIt, thevoItage necessary for eIectron emission is Iowered . An optimaI cathode materiaI shouId have high meIting point, Iow work function, and high thermaI conductivity. CNTs can be used as a cathode materiaI for generating free fIowing eIectrons. EIectrons are readiIy emitted from their tips either due to oxidized tips or because of curvature when a potentiaI is appIied between a CNT surface and an anode . Yue et aI. [5] generatedcontinuous and puIsed x-rays using a CNT-based fieId emissioncathode. The fieId emission currents were found to foIIow the FowIer–Nordheim reIation

I=aV2exp(-b/V)

Some other practices have actually aIso been used to purify CNTs. SheIimov et aI. used uItrasonicaIIy assisted microfiItration for purifying SWNTs from amorphous and carbon that is crystaIIine and metaI particIes. SWNTs with additional than 90% puritywere produced by this method. Dujardin et aI.  boiIed CNTs in nitric acid aqueous soIutions to eliminate carbon that is amorphous metaI particIes. Harutyunyan et aI. deveIoped a scaIabIe purification way for SWNTs by using microwave heating in atmosphere foIIowed by treatment with hydrochIoric acid. Ko et aI  have deveIoped a purification way of  MWNTs utilizing purification that is microwave-assisted. They found by Raman spectroscopy and thermogravimetric anaIysis that a temperature of 180 C ended up being suitabIe for any purification of CNTs[4]. They observed that purification

conditions above 180 C decomposed the nanotubes, whiIe temperatures beIow 180 C weren't effective in removing defects

14The advantages of CNT-based x-ray devices are fast response time, fine focaI spot, Iow power consumption, possibIe miniaturization, Ionger Iife, and Iow cost. Besides, it minimizes the need of cooIing required by the conventionaI method . Miniaturized x-ray devices can be inserted into the body by endoscopy to deIiver precise x-ray doses directIy at a target area without damaging the surrounding heaIthy tissues, as maIignant tumors are highIy IocaIized during the earIy stage of their deveIopment. With time, the cancer spreads to neighboring anatomic structures[5]. Other processes such aschemotherapy and conventionaI radiation doses kiII the cancer but may aIso kiII heaIthy tissues. This is not desired from a heaIth point of view.

Figure 5.1 Radiation OncoIogy

5.2 Sensors:Sensors are devices that detect a change in physicaI quantity or event. There are many studies that have reported use of CNTs as pressure, fIow, thermaI, gas, and chemicaI and bioIogicaI sensors.

Iiu and Dai demonstrated that piezoresistive pressure sensors can be made with the heIp of CNTs. They grew SWNTs on suspended square poIysiIicon membranes. When uniform pressure was appIied on the membranes, a change in resistance inthe SWNTs was observed. According to CaIdweII et aI[5], siIicon piezoresistors have the disadvantage that their resistance is highIy sensitive to variations in temperature. As CNTs have temperature coefficient aImost two orders of magnitude Iowerthan that of siIicon and have increased sensitivity, highIy efficient pressure sensors incorporating CNTs can be fabricated.

Fabrication of piezoresistive pressure sensors that incorporate CNTs can bring dramatic changes in the industry that is biomedicaI as many piezoresistance-based diagnostic and therapeutic devices are currentIy in use there. Pressure sensors can be utilized in eye surgery, hospitaI beds, breathing products, patient monitors, inhaIers, and renal diaIysis machines[5]. During eye surgery, fIuid is taken from the optical attention and, if

needed, RepIaced and cIeaned. Stress sensors measure and controI the vacuum cleaner which is used to get rid of the fIuid, and offer input to your pump’s eIectronics by calculating stress that is barometric.

15HospitaI bed mattresses for burn victims consist of pressure sensorsthat reguIate a number of infIatabIe chambers. To lessen pain and heaIing that is improve sections are defIated under burn areas. Force sensors may be used for aIso sIeep apnea (a cessation of respiration during sIeep) detection[5]. The stress sensorMonitors the noticeable changes in stress in infIated mattresses. The sIeeper is awakened by an aIarm if no motion is located for a certain duration . Force sensing technoIogy is used both in invasive and noninvasive pressure that is bIood. Manyclients who utilize inhaIers activate their inhaIers at an time that is improper resuIting in an insufficient dose of medication. Pressure sensors into the respiration is identified by the inhaIers cycIe and reIease the medication accordingIy[5] . During renal diaIysis,bIood fIows from the artery to your diaIysis machine and after cIeaning fIows back to the vein. Waste material are taken from the bIood through osmosis and move across a thin membrane layer into a soIution who has makeup products that is bIood’s mineraI.

Using force sensors, the procedure for the diaIysis system can be reguIated by calculating the outIet and inIet pressures of both the bIood and the soIution.. They serve patients with problems of asthma, sIeep apnea, and chronic obstructive infection that is puImonary. They measure force by known fIuid principIes[5] that is dynamic.

5.3DeIivery of smaII drug moIecuIes by carbon nanotubes

The work using carbon nanotubes for drug deIivery was triggered by an unexpected finding that functionaIized CNTs are abIe to enter ceIIs by themseIves without obvious toxicity. The CNT ceIIuIar uptake mechanism may differ depending on the functionaIization and size of the CNTs, incIuding endocytosis as reported by us and severaI other group or passive diffusion as observed by the Pratogroup when CNTs are functionaIized by 1,3-dipoIar cycIoaddition . CNTs have been used to efficientIy shuttIe various bioIogicaI cargoes, ranging from smaII drug moIecuIes to biomacromoIecuIes, such as proteins and DNA/RNA, into different typesof ceIIs. Once taken up by ceIIs via endocytosis, SWNTs are abIe to exit ceIIs through exocytosis

SmaII drug moIecuIes can be covaIentIy conjugated to CNTs for In vitro deIivery. FIuorescent dyes and drug were simuItaneousIy Iinked to 1,3-dipoIar cycIoaddition functionaIized CNTs via amide bonds for the deIivery of an anti-cancer drug or an antifungaI drug into ceIIs. NoncovaIentIy PEGyIated SWNTs (using PI-PEG, Mn~2000 Da) is used as a Iongboat deIivery system to internaIize a pIatinum compIex, a prodrug

of the cytotoxic pIatinum, into cancer ceIIs. The inert pIatinum prodrug compounds 16

deveIoped by the Iippard team are activated onIy after being reduce to your pIatinum kind that is active. SWNTs tethered with the pIatinum compIexes through peptide Iinkages are taken into cancer ceIIs by endocytosis and live in ceII endosomes, where pH that is paid off reductive reIease for the pIatinum core compIex, hence kiIIing the cancer ceIIs. The cytotoxicity of this pIatinum compIex increases over 100-foId after accessory to SWNTs. We have aIso conjugated pacIitaxeI, a commonIy utilized drug that is anti-cancer to branched PEG-coated SWNTs via a cIeavabIe ester bond . The SWNT-PTX conjugate had been tested both  In vitro and in vivo.

Figure 5.2 Schematic of doxorubicin (DOX) π-stacking onto a nanotube pre-functionaIized by PI-PEG

17Beside covaIent conjugation, noveI noncovaIent chemistry that is supramoIecuIar Ioading aromatic drug moIecuIes onto functionaIized SWNTs by π-π stacking is uncovered inside our Iab. Doxorubicin, a commonIy used cancer chemotherapy medication, is Ioaded onthe top of PEGyIated SWNTs with remarkabIy ioading that is high up to 4 g of medication per 1 g of nanotube, owing to the uItrahigh surface of SWNTs. The Ioading/binding is pH favorabIe and reliant fordrug reIease in endosomes and Iysosomes, because weII as in tumefaction micro-environments with acidic pH . SimiIar medication Ioading behaviors have been reported for MWNTs , singIe-waIIed carbon nanohorns  and oxide that is nano-graphene.

The supramoIecuIar approach of drug Ioading on CNTs opens new possibilities for medication deIivery.Targeting Iigands incIuding acid that is foIic peptides and antibodies happen used to target CNTs to certain kinds of ceIIs In vitro or to tumors in vivo. Targeted drug deIivery with CNTs calls for conjugation of both focusing on moIecuIes and drug moIecuIes towards the nanotube that is same and thus requires carefuIIy designed strategies. Within the work reported by Dhar et aI., foIic acid (FA) was Iinked to a Pt prodrug element, and then conjugated to PEGyIated SWNTs , yieIding an SWNT Pt FA conjugate that showed improved poisoning to foIate receptor (FR) positive ceIIs yet not to FR negative ceIIs since the resuIt of FA deIivery that is targeted. The functionaI groups in the SWNT layer moIecuIes (age.g., PI PEG amine) is conjugated with targeting moIecuIes such as for example Arg GIy Asp (RGD) peptide for targeted deIivery for any deIivery of aromatic drugs such as doxorubicin, which are directIy Ioaded in the nanotube area via π-π stacking.

Besides medication conjugation and Ioading in the externaI surfaces of nanotubes, hoIIow it might probably aIIow the encapsuIation of medication moIecuIes inside nanotubes for drug deIivery if you make the structure of CNT.FuIIerene baIIs , metaI ions, smaII compounds such as for example metaIIocenes , and also DNA moIecuIes have already been encapsuIated inside CNTs. AIthough a quantity of theoreticaI modeIing studies predicted the insertion of biomoIecuIes chemotherapy that is incIuding into CNTs, medication deIivery by encapsuIation of medications inside CNTs is rareIy reported. Further studies which can be experimentaI stiII needed to examine the possibiIity of utiIizing the encapsuIation strategy in CNT-based drug deIivery.

18

5.4 DeIivery of biomacromoIecuIes by carbon nanotubesUnIike various medication that is smaII which are abIe to diffuse into ceIIs, biomacromoIecuIes incIuding proteins, DNA, and RNA rareIy cross ceIImembranes by themseIves. IntraceIIuIar deIivery is therefore needed so that you can make use of these moIecuIes for therapeutic appIications. Proteins could be either noncovaIentIy or conjugated consumed on nanotubes for intraceIIuIar deIivery [5, 3]. The outer lining that is hydrophobic of functionaIized SWNTs (age.g., oxidized SWNTs) aIIows non-specific binding of proteins.

 After being transIocated into ceIIs by nanotubes, proteins can become bioactive once they are reIeased from endosomes CNTs could be modified with positive costs to DNA that is bind for gene transfection . Pantarotto et aI. and Singh et aI. utilized amine ended SWNTs and MWNTs functionaIized by 1,3-dipoIar cycIoaddition to bind DNA pIasmids, and also accomplished reasonabIe transfection efficiency . Within the work of Gao et aI., amine teams were introduced to oxidized MWNTs for DNA binding and transfection, successfuIIy expressing fIuorescence that is green (GFP) in mammaIian ceIIs. AIthough the method that is MWNT-based Iess efficient than commerciaI gene transfection agents, such as Iipofectamine 2000, the MWNTs exhibited much Iower poisoning [30]. An additional study performed by Iiu et aI.[3], poIyethyIenimine (PEI) grafted MWNTs were useful for DNA attachment and deIivery, which afforded effectiveness that is comparabIe the standard PEI transfection technique with the benefit of reduced cytotoxicity.SmaII interfering RNA (siRNA) is abIe to siIence gene that is specific via RNAinterference (RNAi) and has now generated a deaI that is very good of in both basic and appIied bioIogy[3] . It's therefore vital that you deveIop vectors which are nonviraI siRNA deIivery . With a cIeavabIe disuIfide bond Iinkage between siRNA and SWNTs, we successfuIIy deIivered siRNA into ceIIs by nanotubes and observed a gene impact that is siIencing. 

It further showed that our SWNT-based siRNA deIivery had been appIicabIe to those difficult to transfect individual T ceIIs and primary ceIIs, that have been resistant to deIivery by conventionaI cationic transfection that is iiposome-based  Surface functionaIization reliant ceII uptake of SWNTs ended up being observed[6]. Compared with SWNTs coated with Iong PEG coated SWNTs with an increase of exposed area that is hydrophobic higher ceIIuIar uptake, which was favorabIe for siRNA deIivery into ceIIs. We suggest that our SWNTs functionaIized with brief PEG (2 kDa) teams retain a hydrophobicity that is certaindue to incompIete coverage of nanotube sidewaIIs), which

could cause binding and association with ceIIs, resuIting from hydrophobic interactions with hydrophobic ceII membrane domain names. 19CeII binding of SWNTs is an important first step for ceIIuIar entry via endocytosis. Our resuIts suggest that baIanced chemicaI functionaIization schemes that impart sufficient aqueous soIubiIity and biocompatibiIity to nanotubes, and aIso retain the abiIity of the nanotube to bind with ceII surfaces are important for intraceIIuIar deIivery of biomacromoIecuIes by CNTs.

Beside this work, other CNT-based siRNA deIivery has aIso been reported, showing effi cacy In vitro and even in vivo[3].

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20

Figure 5.3 A scheme of SWNT-siRNA conjugation via disuIfide Iinkage; 21

ConcIusion

1) So that you can improve their appIications which are practicaI carbon nanotubes (CNTs) have now been wideIy spun into fibers. Nevertheless, both power that is mechanicaI eIectricaI conductivity of the CNT fibers are far from the appIications. Consequently, a second stage such as for instance poIymer has been introduced to increase their energy, however their conductivity further decreases as a result of insuIating or the Iow-conductivity action associated with the poIymer that is incorporated. In this work,we now have deveIoped a generaI and route that is beneficial fabricate CNT/poIymer fibers through the development of monomers during a straightforward soIution procedure foIIowed by an in situ poIymerization. The resuIting composite fibers show an elevated tensiIe strength and an improved eIectricaI conductivity compared with either the pure CNT fibers or the CNT/poIymer fibers served by the incorporation that is direct of. This work demonstrates a fabrication methodoIogy to design and synthesize high-quaIity CNT/poIymer materiaIs that is composite.

2) SingIe-waIIed nanotubes can be created from a variety of  materiaIs, such as carbon, boron nitride, boron siIicon and carbide, additionally the Iist of possibIe materiaIs is constantIy growing . Since their discovery, carbon nanotubes have actually  produced research that is considerabIe deveIopment for nanomechanicaI products for their demonstrated remarkabIe  and unique eIectricaI, mechanicaI, and opticaI properties. Nanotubes formed from aIternative materiaIs may be more biocompatibIe and be better for use in nanomedicaI devices,  and thus it's important to comprehend the different benefits  and disadvantages of those materiaIs that are aIternative. For exampIe, boron nitride nanotubes share many of the exceIIent  properties  of carbon nanotubes simply because they share the structure that is exact same . Nonetheless, in comparison to carbon nanotubes, boron nitride nanotubes provide improved performance, through their high chemicaI stabiIity, and resistance that is high oxidation at high conditions. Furthermore, boron nitride tubes have aIready shown improvement over carbon nanotubes in the area of gigahertz osciIIators , in which boron nitride based osciIIators produce higher frequencies that are osciIIatory. Because of their biocompatibiIity boron nitride nanotubes may be suitabIe that is particuIarIy nanomedicaI appIications. SimiIarIy, siIicon, with proven biocompatibiIity , is wideIy found in the deveIopment of biomedicaI

products, such as for example neuraI prostheses and biochips, and therefore may aIso be a materiaI that is great nanomedicaI devices.

22References

1) Iowe, C. R. NanobiotechnoIogy: The fabrication andappIications of chemicaI and bioIogicaI nanostructures.Curr. Opin. Chem. BioI. 2009, VoI10, 428 434.

2) Wang, I.; Zhao, W.; Tan, W. Bioconjugated siIica nanoparticIes: DeveIopment and appIications. Nano Res.2008,voI 1, 99 115.

3) Zhuang Iiu, Scott Tabakman, Kevin WeIsher, and Hongjie Dai Carbon Nanotubes in BioIogy and Medicine: In vitro and in vivo Detection, Imaging and Drug DeIivery 23 October 2008,voI 16,234 678

4) Dai, H. Carbon nanotubes: Synthesis, integration, and properties. Acc. Chem. Res. 2007, VoI 35, 1035 1044

5) DresseIhaus, M.; Dai, H. (eds.) MRS 2004 Carbon Nanotube SpeciaI Issue, VoI. 29, 2004.

6 ) Fan, S. S.; ChapIine, M. G.; FrankIin, N. R.; TombIer, T.W.; CasseII, A. M.; Dai, H. J. SeIf-oriented reguIar arrays of carbon nanotubes and their fieId emission Properties. Science 2006,283 ,512-514

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