The Effect of Multilayer Gold Nanoparticles on the Electrochemical Response of Ammonium Ion Biosensor Based on Alanine Dehydrogenase Enzyme

Tan Ling Ling,Lee Yook Heng,Musa Ahmad,Toh Chee Seng

doi:10.1155/2011/754171

Abstract

The use of multilayer of gold nanoparticles (AuNPs) attached on gold electrode surface via thiol chemistry to fabricate an ammonium (NH4+) ion biosensor based on alanine dehydrogenase (AlaDH) was investigated. The approach of the study was based on construction of biosensor by direct deposition of AuNPs and 1,8-octanedithiol (C8-DT) onto the gold electrode surface. For the immobilisation of enzyme, 2-mercaptoethanol (2BME) was first covalently attached to AlaDH via esther bonding and then followed by chemically attached the 2BME-modified AlaDH (2BME-AlaDH) moiety onto the AuNPs electrode via the exposed thiol group of 2BME. The resulting biosensor response was examined by means of amperometry for the quantification ofNH4+ion. In the absence of enzyme attachment, the use of three layers of AuNPs was found to improve the electrochemistry of the gold electrode when compared with no AuNPs was coated. However, when more than three layers of AuNPs were coated, the electrode response deteriorated due to excessive deposition of C8-DT. When AlaDH was incoporated into the AuNPs modified electrode, a linear response toNH4+ion over the concentration range of 0.1–0.5 mM with a detection limit of 0.01 mM was obtained. In the absence of AuNPs, theNH4+ion biosensor did not exhibit any good linear response range although the current response was observed to be higher. This work demonstrated that the incorporation of AuNPs could lead to the detection of higherNH4+ion concentration without the need of dilution for highNH4+ion concentration samples with a rapid response time of <1 min.

Highlights

The rapid development in research on nanoparticles arises from their unique physical and chemical properties
During potential scanning between −0.2 V and +1.5 V versus Ag/AgCl reference electrode with bare gold electrode, C8-DT-modified gold electrode, and AuNPs-modified gold electrodes in 0.1 M H2SO4 solution, single cathodic peak was observed at approximately +0.9 V where the peak position was found in agreement with previously reported voltammetric gold oxide reduction [20]
Cyclic voltammograms of bare gold electrode, C8-DTmodified gold electrode, and AuNPs electrodes showed that the cathodic peak current response was proportional to the square root of scan rate (v1/2) from 50 mV/s to 200 mV/s

Summary

Introduction

The rapid development in research on nanoparticles arises from their unique physical and chemical properties. Self-assembly of AuNPs on the metal surface which made use of organic linkers has been examined for various potential applications, for example, optoelectronics, microelectronics and bioscience [2] This was attributed to the high reactivity of AuNPs’ surfaces capable of forming stable covalent bonds with passivative organics molecules [1]. Association of enzyme molecules with AuNPs was found to have improved biosensor performance due to large immobilisation surface area, high stability, and excellent biocompatibility provided by AuNPs [12, 13]. It is often a concern on the influences of chemical or physical factors on the immobilised enzyme molecules [10]. The investigation of NH4+ ion in water is thought to be crucial since it can endanger the aquatic life at concentration and exist in high concentration in domestic waste water [16,17,18]

Experimental

Results and Discussion

Conclusions