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.
Highlights
There has been growing interest in the development of miniaturized sensors for biomedical and environmental applications, both for monitoring biologically significant analytes and environmental conditions such as pH, physiological markers such as oxygen and carbon dioxide content in blood, as well as detection of pathogenic bacteria and viruses
The reference electrode has a pronounced influence on the accuracy of measurements made with such bio-sensors, whether they are electrochemical sensors, biological Field Effect Transistor [7,8] or bio-impedances probes [9,10], as it is present in almost all types of biosensors, and plays an important role in ensuring proper device operation and reliability of the results
In field-effect transistors (FETs) systems, reference electrodes serve to fix a potential at a certain level to provide a bias for the gate of the transistor-based sensor, which is often exposed to an electrolyte solution
Summary
There has been growing interest in the development of miniaturized sensors for biomedical and environmental applications, both for monitoring biologically significant analytes and environmental conditions such as pH, physiological markers such as oxygen and carbon dioxide content in blood, as well as detection of pathogenic bacteria and viruses. Electrochemical biosensors for biomedical and environmental applications have been developed employing various fabrication methods such as photolithography, screen-printing and ink-jet printing In all these biosensors, the electrochemical transducer, which converts the quantity and type of chemical/biological analyte into a distinct electrical signal, is the most important component. All components of the electrode such as metal, salt, filling solutions and interfaces need to be miniaturized Factors such as potential drift, liquid junction effects and solution concentrations are significant factors which could obscure correct results and need to be controlled [5,6]. The reference electrode has a pronounced influence on the accuracy of measurements made with such bio-sensors, whether they are electrochemical sensors, biological Field Effect Transistor (bioFET) [7,8] or bio-impedances probes [9,10], as it is present in almost all types of biosensors, and plays an important role in ensuring proper device operation and reliability of the results. Examples of common uses of electrodes in chemical and biological sensing will be given
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