Au nanospheres and nanorods for enzyme-free electrochemical biosensor applications

By: Nur Fatihah bt Abas(154120)Journal’s Author: Yu-Ho Won, Keon Huh, Lia A. Stanciu

OBJECTIVES:• To prepare Au nanocrystals with different morphologies and use for enzyme-free electrochemical biosensor applications.• To investigate the electrocatalytic properties of Au nanocrystals as a function on their morphologies.• To investigate the stability in time of each of the Au nanocrystal-based enzyme-free biosensors.

EXPERIMENTAL

Materials:HAuCl4, NaBH4, polyvinyl pyrrolidone (PVP), tetraethyl orthosilicate (TEOS), ammonium hydroxide,2-propanol, ethanol,Au NRs,dispersed in deionized(DI) water with 0.1% ascorbic acid, <0.1% cetyl trimethylammonium bromide(CTAB) surfactant capping agents, Hydrogen peroxide (H2O2,30% w/v solution), K4Fe(CN)6, K3Fe(CN)6, KH2PO4, K2HPO4 and KCl.

Apparatus and measurements:-Transmission electron microscopy(TEM) images of Au nanocrystals->Tecnai 20(FEI) operating at 200kV.-Ultraviolet visible(UV-Vis) absorption spectra-> SpectraMax M5 spectrometer.-Electrochemical measurements of biosensor for detection of hydrogen peroxide-> BASi epsilon C3 cell stand.-A conventional three-electrode system consists of screen printed electrode as a working electrode, Pt wire as counter electrode and Ag/AgCl electrode as reference electrode->biosensor measurements

Synthesis of Au Nanocrystals:

Au NS- decorated silica spheres were synthesized by using hydrolysis and condensation of sol-gel precursor.TEOS(precursor) and ammonium hydroxide(catalyst) were reacted in 2-propanol solution.As-synthesized silica spheres were washed several times and re-dispersed in DI water.Au NSs were formed on silica spheres via nodified approach.>HAuCl4 solution (2.5mM,100μl) was added to the silica solution(100μl) while stirred.10μl of NaBH4 solution (0.03wt%) was added to mixed solution for reduction of [AuCl4]- solution was washed to remove unreactants.Au NSs were synthesized via method reported by Lim. HAuCl4

solution (0.05mM) was prepared and fast injected into PVP solution(10mg in 10ml DI water) at 100ºC Mixed solution was heated at same temperature for 1h and cooled to 25ºC. Then, solution was washed to remove excessive PVP and re-dispersed in DI water.

Preparation and characterization of biosensor:

Au nanocrystals-based enzyme-free biosensor were fabricated by coating Au nanocrystals on SPEs.

Au nanocrystals dispersed in DI water were dropped on SPEs surface and dried for 2h at 25ºC.

PBS solution (0.05M,pH 7) containing KH2PO4 and K2HPO4 was prepared and pH values were adjusted from 4-7 by using HCl.

Amperometric responses of biosensors were obtained in 3ml PBS(0.05M,pH7) containing 10mM [Fe(CN)6]³¯∕ ⁴⁻, under magnetic stirring (150rpm) at applied potential of 200mV.

RESULTS AND DISCUSSION

Preparation and characterization of

biosensors:

Figure 1. a) Au NSs on silica, b) Au NSs, c) Au NRs(ratio 1:3) and d) Au NRs (ratio 1:5).(1)-(3) are a schematic, a TEM image and UV-

Vis spectrum, respectively

Au nanocrystals-based enzyme-free biosensor

Figure 2: Schematic of enzyme-free hydrogen peroxide biosensor and reaction on electrode (SPE: screen printed electrode, WE: working

electrode, CE: counter electrode, RE: reference electrode).

Figure 3: Stability test of Au nanocrystal-based enzyme-free biosensors over 68days

in the PBS (0.05,pH5) containing 10mM [FE(CN)6]³⁻⁄ ⁴⁻ at 200mV to 0.33mM

hydrogen peroxide.

Stability of biosensors

CONCLUSION: Au nanocrystal-based enzyme-free biosensors for detection of hydrogen peroxide were prepared.Electrocatalytic properties depending on morphologies of Au nanocrystals were prepared and characterized.The sensitivity of biosensors was influenced by morphologies of Au nanocrystals.

ACKNOWLEDGEMENTS:I would like to thank to: Pn. Ruzniza Md Nawi for the guidance in completing this poster.Fellow friends for guidance and also moral support .