From Thick Films to Monolayer Recognition Layers in Amperometric Enzyme Electrodes

Abstract

Theoretical models of the conventional thick‐film enzyme electrode and monolayer electrodes are used to determine the important parameters in defining the response of both types of biosensors with regard to their reproducible fabrication. The response of the thick‐film biosensors are very sensitive to the thickness of the enzyme layer and therefore highly precise methods of depositing the enzyme layer are required if reproducible biosensors are to be manufactured. Covalent attachment of an enzyme to a monolayer of alkanethiols self‐assembled onto a gold electrode could potentially provide this more precise fabrication method. A model for monolayer enzyme electrodes gives an excellent fit to an experimental calibration plot for a monolayer of glucose oxidase attached to a self‐assembled monolayer. The model showed the response was highly dependent on the amount of enzyme immobilized and therefore the reproducibility of monolayer enzyme electrodes will be limited by the reproducibility of the enzyme immobilization. The model predicts the response of the monolayer biosensor is limited by the turnover rate of the enzyme rather than the supply of substrate as is the case with thick‐film biosensors.

A Biosilification Fusion Protein for a ‘Self‐immobilising’ Sarcosine Oxidase Amperometric Enzyme Biosensor

“…The mathematical model developed previously by us for enzyme film layers in the amperometric enzyme electrode, was used to compare the current response of different mSOx biosensor constructs. The reaction mechanism of the enzyme follows a mediated Ping‐Pong mechanism as refered to later in section 3.2, where the model is described.…”

“…In thick enzyme layer electrodes, the layer properties can affect the response and dynamic range of the enzyme. From the mathematical models developed by us previously , for an enzyme electrode, diffusion and reaction in the enzyme layer are important in determining the electrode current and the available dynamic range. This can be categorised according to the thiele modulus, =(d 2 k cat [E T ])/(D med [Med] b ).…”

The Influence of the Underlying Gold Substrate on Glucose Oxidase Electrodes Fabricated Using Self-Assembled Monolayers

“…Most studies in which a monolayer of enzyme is immobilized onto a gold surface using self-assembled monolayers have employed short chain alkanethiols; commonly three carbon atoms in the alkyl chain [1, 5,[11][12][13][14][15][16]. The length of such SAMs are well within the range of surface roughness of the underlying gold surface.…”

“…The purpose of this study is to investigate the effect of different gold surfaces on the electrochemical response of an enzyme electrode. The model enzyme electrode used is the system we have studied previously where glucose oxidase (GOD) covalently attached to a 3-mercaptopropionic acid SAM using carbodiimide coupling [10][11][12]22]. The response of the enzyme electrode to glucose is tested in an oxygen free environment using p-benzoquinone as a redox mediator.…”

The rise of self‐assembled monolayers for fabricating electrochemical biosensors—an interfacial perspective

“…Our rationale for doing so was initially to improve the reproducibility of such devices. Modelling of polymer based enzyme electrodes by us18–20 and others21,22 showed that a big determinant in the difficulties in developing highly reproducible enzyme electrodes, where precise quantitative measurements were required, was to be able to deposit an enzyme layer over an electrode with reproducible thickness. This is a considerable challenge because the response of an enzyme electrode had a square dependency on the thickness of the layer, and, at least at the time, the only methods for fabricating such layers with sufficient precision was by electrodeposition 23.…”