Biofouling of indwelling electrochemical sensors

Abstract

Provision of clean drinking water is regarded as being the most significant positive intervention in human health and it plays a significant role in supporting global health. Population growth, economic development and climate change all drive urbanisation and increase demand for clean water and the infrastructure for its delivery. As demand for clean water increases, so will the pressure to ensure its safety. Indwelling sensor networks offer real-time, long-term and intelligent monitoring system, and would enable optimisation of networks for quality. Electrochemical sensors are inexpensive and simple to construct and operate. However, prolonged exposure of the sensors to water causes biofouling which compromise their performance even in weeks or days, making early detection of performance failure critical. Fouling of sensors due to biofilm formation is very common in indwelling situations and it is a major drawback in the development of sensor networks. Owing to our incomplete understanding of the chemistry, physics and biology of bacterial cell and surface interaction, solutions become ineffective. Understanding how biofilms affect electrochemical sensor performance is important to enable detection of malfunction in situ and can inform the development of methodology to restore the performance in situ. Networks can consist of hundreds of sensors and automated restoration of function in biofouled sensors is thus essential. Hence, the fundamentals on how biofilms affect electrochemical sensor performance, specifically electrode reactions, should be a starting point in the design of a robust indwelling sensors network. A novel electrochemical rapid biofilm formation protocol has been successfully developed to facilitate this investigation. The electrochemical rapid biofilm can form in just 2 hours, instead of days or weeks, and has been shown to be able to replicate key characteristics !" ⁄# of a naturally forming 3 weeks old biofilm. Physico-chemical effects of ! biofouling to diffusional mass transport towards electrode surface and electron transfer kinetics at the surface of electrode can be quantified by using a combination of electroanalytical techniques such as cyclic voltammetry, chronoamperometry, impedance spectroscopy and hydrodynamic techniques, but hydrodynamic voltammetry and amperometry using rotating disk electrode (RDE) and Koutecký-Levich analysis are particularly robust and useful in assessing these effects. Electrochemical reduction of oxygen, or oxygen reduction reaction (ORR), is used as the paradigm to elucidate the nature of electrochemical sensor biofouling. The oxygen paradigm is also used as a means to assess an electrochemical in situ restoration method for biofouled electrode which is based on electrochemical advanced oxidative processes (EAOPs) and pulsed amperometric detection (PAD).