Microfabricated Reference Electrodes and their Biosensing Applications

Abstract

Over the past two decades, there has been an increasing trend towards miniaturization of both biological and chemical sensors and their integration with miniaturized sample pre-processing and analysis systems. These miniaturized lab-on-chip devices have several functional advantages including low cost, their ability to analyze smaller samples, faster analysis time, suitability for automation, and increased reliability and repeatability. Electrical based sensing methods that transduce biological or chemical signals into the electrical domain are a dominant part of the lab-on-chip devices. A vital part of any electrochemical sensing system is the reference electrode, which is a probe that is capable of measuring the potential on the solution side of an electrochemical interface. Research on miniaturization of this crucial component and analysis of the parameters that affect its performance, stability and lifetime, is sparse. In this paper, we present the basic electrochemistry and thermodynamics of these reference electrodes and illustrate the uses of reference electrodes in electrochemical and biological measurements. Different electrochemical systems that are used as reference electrodes will be presented, and an overview of some contemporary advances in electrode miniaturization and their performance will be provided.

Microstructure, surface chemistry and electrochemical response of Ag|AgCl sensors in alkaline media

“…For instance, in the case of screen printing, a Ag-AgCl paste is deposited on a metallic surface (e.g., Pt) to produce the Ag/AgCl electrode. The adhesive properties of the paste to the supporting electrode might not be very good; hence, the reliability of the sensor will depend on the homogeneity of the Ag-AgCl paste used [14]. In general, the relatively small contact area, i.e., weak adhesion between the Ag rod and AgCl layer, may lead to oxidation of AgCl at Ag/AgCl interface by hydroxide ions from the alkaline medium at a relatively fast rate [15].…”

Electrochemical Methods in Analysis of Biofuels

“…Reference electrode is the key to achieve controlled potential conditions and therefore it is a very important component in voltammetric analysis. The literature presents some works totally devoted to reference electrodes including discussions about practical problems associated to them [98] and new techniques for the fabrication of more robust all solid state and miniaturized reference electrodes [99].…”

Recent advances in microfluidic techniques for single-cell biophysical characterization

“…Nonetheless, integrating Ag/ AgCl electrodes into microfluidic channels is complex, and Ag/ AgCl electrodes have a limited lifetime. 100,101 Although other metal electrodes can be more readily integrated into microfluidic channels, the electrical double layers formed between the interface of electrodes and the liquid, which are mainly capacitive, pose difficulties in applying DC signals. Methods for minimizing the electrical double layer effect include the modification of the electrode surface roughness in order to increase the surface area 102 and the utilization of polyelectrolytic salt bridges (PSBEs) 103 or polyelectrolyte gel electrodes (PGEs).…”