Microfluidic Microbial Fuel Cell Based Biosensors for Copper Ion and Formaldehyde in Water Monitoring

In this abstract, we present microfluidic microbial fuel cell (MFC) biosensors, which are based on biohybrid materials of microorganisms living on electrodes, for monitoring toxic chemical in water. We have built microfluidic MFCs with anode and cathode chambers of 100μL. Start-up process of the microfluidic MFC biosensors takes 3-5 days and we utilize the MFCs for copper ion and formaldehyde in water monitoring. It is found that for copper ion in water monitoring characterization, a linear relationship between the output current and the copper ion concentration is observed, while the MFC biosensor can recover after the initial current drop caused by the copper ion in water. However, when the MFC biosensor is exposed to formaldehyde in water, a sigmoid relationship is observed and the MFC biosensor cannot recover after formaldehyde causes the current to drop. The experimental results may further the development of microfluidic MFCs for toxic chemical in water monitoring.<br/>Water pollution is a global health threat affecting 2 billion people, causing significant health issues. Traditional non-real-time methods such as atomic spectrometry are time-consuming and expensive. Therefore, many studies have been performed to monitor toxic substances in water with MFCs due to their real-time measurement and low cost. However, the state-of-the-art MFC biosensors are non-reusable and take at least 3 minutes. Therefore, a real-time MFC biosensor for toxic chemical in water monitoring is needed.<br/>The microfluidic MEMS MFC biosensor is composed of anode, cathode and proton exchange membrane (PEM) with a chamber volume of 100 μL. The anode/cathode are 100nm-thick Pt thin films deposited by magnetic sputtering. The start-up process of the MFC biosensor takes approximately 3-5 days and the polarization curve confirms its normal operation. Firstly, we measure the response of the MFC biosensors to copper ion in water. The MFC biosensors are exposed to 0.2-1.6mg/L copper ion respectively. The current is first inhibited and then recovers, demonstrating the reusability of the MFC biosensor for copper ion in water monitoring. The biosensor linearity characterization demonstrates a strong linear correlation between the current inhibition percentage and copper ion concentration with an <i>R² </i>of 0.997. The accuracy of the biosensor is calculated as 3.54% by testing a concentration of 1.3 mg/L, which is the EPA standard for the maximum allowable copper ion concentration in water. The average measurement time for the MFC biosensor is only 48 seconds. Afterwards, we measure the response the MFC biosensor to formaldehyde. When the MFC biosensor is exposed to a large formaldehyde concentration range from a low concentration of 1x10^-3 mg/L to a high concentration of 3 mg/L in water, a sigmoid dose–response relationship of normalized current inhibition percentage versus formaldehyde concentration in water is observed, in agreement with traditional toxicology dose–response curve obtained by other measurement techniques. In addition, the current cannot recover after the inhibition due to the toxicity of the formaldehyde. We believe the different response of the MFC biosensors to copper ion and formaldehyde in water can help to improve the specificity of the MFC biosensors for toxic chemical in water monitoring.