Synthesis of Nanowires Using Synthesis of Nanowires Using Dip-Pen NanolithographyDip-Pen Nanolithographyand Biocatalytic Inksand Biocatalytic Inks

14/04/2009 – NanomaterialsGroup 5

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IntroductionIntroduction• What is “nanowire”

Nanowire is a nanostructure, with the diameter of the order of a nanometer (10−9 meters). Alternatively, nanowires can be defined as structures that have a thickness or diameter constrained to tens of nanometers or less and an unconstrained length.

• What is “Dip-Pen Nanolithography”

Dip Pen Nanolithography (DPN) is a scanning probe lithography technique where an atomic force microscope tip is used to transfer molecules to a surface via a solvent meniscus. This technique allows surface patterning on scales of under 100 nanometers. DPN is the nanotechnology analog of the dip pen (also called the quill pen), where the tip of an atomic force microscope cantilever acts as a "pen," which is coated with a chemical compound or mixture acting as an "ink," and put in contact with a substrate, the "paper."

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Group 5 : Synthesis of Nanowires Using Dip-Pen Nanolithography and Biocatalytic Inks

IntroductionIntroduction The similar dimension of biomolecules, such as enzymes or DNA, and

nano-objects, such as nanoparticles or nanotubes, suggests that the conjugation of biomolecules and nano-objects may yield hybrid systems with new functions and properties.

Dip-pen nanolithography (DPN) is already a well-established technology for the deposition of nanostructures on surfaces, and the method has been widely applied to deposit molecular, polymer, biomolecular, and nanoparticular nanostructures on surfaces using a chemical “ink” solution.

Three different biocatalytic systems are characterized:

· Glucose oxidase (GOx),

· Galactose oxidase (GalOx)

· Alkaline phosphatase (AlkPh)

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Group 5 : Synthesis of Nanowires Using Dip-Pen Nanolithography and Biocatalytic Inks

1.Observations and 1.Observations and CharacterizationCharacterization

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The flavoenzymes (oxidases) GOx and GalOx were modified with N-hydroxysuccinimide-functionalized Au NPs (1.4 nm). This method was also used for the modification of AlkPh. The single N-hydroxysuccinimide functionality linked to the NPs ensures the specific linkage of the NPs to a single enzyme unit, without crosslinking aggregation of several enzyme units.

(Figure 1) shows electron microscopy images of the Au-NPmodified GOx, GalOx, and AlkPh

Group 5 : Synthesis of Nanowires Using Dip-Pen Nanolithography and Biocatalytic Inks

2. The biocatalytic activity of 2. The biocatalytic activity of these enzyme–NP hybridsthese enzyme–NP hybrids

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• For the activity of the AlkPh, a photometric system was also used that utilized the color change of p-nitrophenylphosphate after cleavage of the phosphate functionality..• For the flavoenzymes, the corresponding substrate changes its color due to reaction of the in-situ-generated H2O2.

After that the biocatalytic enlargement of these particles in solution was investigated.

For all three enzymes, the activity was not altered by the modification with the NPs

Group 5 : Synthesis of Nanowires Using Dip-Pen Nanolithography and Biocatalytic Inks

2. The biocatalytic activity of 2. The biocatalytic activity of these enzyme–NP hybridsthese enzyme–NP hybrids

A) Absorbance spectra of GOx–Au upon reaction with 80 mM glucose and 0.3 mM AuCl4

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B) Absorbance spectra of AlkPh–Au upon reaction with 20 mM p-aminophenylphosphate and 1 mM AgNO3.

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A slight red-shift => a particle size increase, proving that enlargement takes place

Hydrogen peroxide in the solution is necessary to start the reaction

Spontaneous reaction

Group 5 : Synthesis of Nanowires Using Dip-Pen Nanolithography and Biocatalytic Inks

2.The biocatalytic activity of 2.The biocatalytic activity of these enzyme–NP hybridsthese enzyme–NP hybrids

C) Absorbance of GOx–Au after 14.5 min in a growth solution containing 0.3 mM AuCl4

- and glucose

D) Absorbance of AlkPh–Au after 5 min in agrowth solution containing 1 mM AgNO3 and p-aminophenylphosphate

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For this experiment, the enzymes were incubated with the respective substrates and metal salts for fixed time intervals at which the plasmon absorbance was recorded.

Slow kinetics for low concentrations

=> H2O2 is required for the reaction to occur

This is a biocatalytic reaction

No changes in the spectrum

Group 5 : Synthesis of Nanowires Using Dip-Pen Nanolithography and Biocatalytic Inks

3.Patterning using GOx or GalOx3.Patterning using GOx or GalOx

A) General scheme for the generation of a Au nanowire by the biocatalytic enlargement of a Au-NP-functionalized GOx line deposited on a silicon support by DPN

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The enzymes are fully covered with a metallic shell, inhibiting further metallization reactions.

The enzyme-generated H2O2 acts as a reducing agent for the deposition of gold on the Au NPs associated with the enzyme.

Group 5 : Synthesis of Nanowires Using Dip-Pen Nanolithography and Biocatalytic Inks

3.Patterning using GOx or GalOx3.Patterning using GOx or GalOx

B) Atomic force microscopy (AFM) image of the DPN pattern of GOx–Au before enlargement

C) AFM image of the DPN pattern of GOx–Au after enlargement with glucose/AuCl4

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Group 5 : Synthesis of Nanowires Using Dip-Pen Nanolithography and Biocatalytic Inks

3.Patterning using GOx or GalOx3.Patterning using GOx or GalOx

D) Line section through DPN patterns of a) fresh GOx–Au, b) two-month-old GOx–Au, and c) pattern without enzyme and without Au NPs, after enlargement with glucose/AuCl4

-E) SEM images of GalOx–Au pattern after enlargement with galactose/AuCl4

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The bottom image is an enlargement of the area in the top image marked by the white rectangle

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To confirm that the enlargement is really due to the biocatalytic process

The expected loss of activity due to a long-term storage .

Group 5 : Synthesis of Nanowires Using Dip-Pen Nanolithography and Biocatalytic Inks

4.Patterning using AlkPh4.Patterning using AlkPh

A) General reaction scheme for the biocatalytic silver enhancement of AlkPh–Au

B) AFM image of Ag nanowires generated on two parallel AlkPh–Au templates deposited on the silicon support byDPN after enlargement in the Ag growth solution

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The particles are limited in growth by their proximity to the surface and can only grow in one direction: away from the surface.

Group 5 : Synthesis of Nanowires Using Dip-Pen Nanolithography and Biocatalytic Inks

4.Patterning using AlkPh4.Patterning using AlkPh

C) SEM images of an AlkPh–Au pattern after enlargement in the Ag growth solution. The bottom image is an enlargement of the area in the top image marked by the white rectangle

D) AFM image of Au and Ag nanowires generated by deposition and Au enlargement of the Au-NP–GOx, passivation with thiol, and subsequent deposition and Ag enlargement of the Au-NP–AlkPh

12The line is made up of silver

The passivation step is essential. Without the thiolate monolayer, the p-aminophenol, generated by the AlkPh, was found to diffuse and enlarge the Au nanowire with the reduced Ag

Group 5 : Synthesis of Nanowires Using Dip-Pen Nanolithography and Biocatalytic Inks

5.The conductivity properties of the 5.The conductivity properties of the nanowiresnanowires

(Figure 5A) AFM image of a Au nanowire in a 10 lm gap separating two Au “finger microelectrodes using GOx–Au as the “biocatalytic ink” after enlargement with glucose/HAuCl4

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(Figure 5B) depicts the current–voltage (I–V) curve obtained by tunneling AFM (TUNA) not fully understood =>need more studies

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Group 5 : Synthesis of Nanowires Using Dip-Pen Nanolithography and Biocatalytic Inks

ConclusionConclusion

Successfully employed Au-NP-modified enzymes as biocatalytic inks for the generation of metallic nanowires.

Prove the possibility of orthogonal deposition of lines of different metals in a sequential fashion.

The present study has introduced the use of “biocatalytic inks” and DPN as a new posibilitie for generating metallic nanowires.

The possibility to selectively grow tailored metallic patterns and to design nanocircuits of variable compositions by the application of different enzymes and the respective developing solutions paves the way for the generation of complex nanocircuitry.

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Group 5 : Synthesis of Nanowires Using Dip-Pen Nanolithography and Biocatalytic Inks