How to Improve the Performance of Electrochemical Sensors via Minimization of Electrode Passivation

Jiri Barek

doi:10.3390/chemosensors9010012

Abstract

It follows from critical evaluation of possibilities and limitations of modern voltammetric/amperometric methods that one of the biggest obstacles in their practical applications in real sample analysis is connected with electrode passivation/fouling by electrode reaction products and/or matrix components. This review summarizes possibilities how to minimise these problems in the field of detection of small organic molecules and critically compares their potential and acceptability in practical laboratories. Attention is focused on simple and fast electrode surface renewal, the use of disposable electrodes just for one and/or few measurements, surface modification minimising electrode fouling, measuring in flowing systems, application of rotating disc electrode, the use of novel separation methods preventing access of passivating particles to electrode surface and the novel electrode materials more resistant toward passivation. An attempt is made to predict further development in this field and to stress the need for more systematic and less random research resulting in new measuring protocols less amenable to complications connected with electrode passivation.

Highlights

The immense potential of modern electroanalytical methods in monitoring of organic compounds is generally recognized and appreciated [1,2,3,4,5,6,7] because of their low investment and running costs, reasonable and in many cases “fit for the purpose” sensitivity and selectivity, easy automatization, easy miniaturization resulting in portability of corresponding instrumentation, user friendliness, and environmental friendliness (“green electroanalytical chemistry”)
The heart of any electrochemical sensors is a working electrode on which the electrical signal is generated via an electrochemical process and which serves as a transduction element
It is obvious that the main reason for electrode passivation is adsorption/deposition of a passivating compound on working electrode surface

Summary

Introduction

The immense potential of modern electroanalytical methods in monitoring of organic compounds is generally recognized and appreciated [1,2,3,4,5,6,7] because of their low investment and running costs, reasonable and in many cases “fit for the purpose” sensitivity and selectivity, easy automatization, easy miniaturization resulting in portability of corresponding instrumentation, user friendliness, and environmental friendliness (“green electroanalytical chemistry”). To use measurements in flowing systems minimizing passivation [33,34,35] or to use RDE (rotating disc electrode) [36,37,38,39,40,41,42,43,44,45,46] or hydrodynamic electrodes [37] In all these cases, products/intermediates of electrochemical reaction are washed away from the electrode surface minimizing their deposition on working electrode. To use intentional electrode fouling by adding strongly adsorbable organic compounds (e.g., mercapto-hepta(ethylenelycol) forming SAM (self-assembled monolayer) on electrode surface), minimising further electrode fouling by analytes/electrode reaction products This “fighting fire with fire” approach results in the decreased signal of an analyte after formation of SAM but the signal remains stable after multiple repetition of voltammetric scans, enabling standard addition of calibration curve evaluation.

Importance of Electrode Passivation—Reasons and Consequences

How to Minimise Electrode Passivation

Methodology for Electrode Passivation Investigation and Minimisation

The Structural and Phase Characterization of the Electrode Surface

Advantages and Disadvantages of Different Antifouling Approaches

Conclusions