Electrochemical detection of flavin mononucleotide using mineral-filmed microelectrodes

Abstract

• Hematite and maghemite were deposited onto carbon fiber microelectrode tips. • Square wave voltammetry was used to detect flavin mononucleotide. • Hematite-filmed microelectrodes have improved sensitivity, LOD, and LOQ. Microelectrodes with tip diameters of tens of micrometers have higher resolution and faster response times than traditional large electrodes with diameters of millimeters or centimeters. The response of the microelectrode can be improved with a thin film that has an affinity to the analyte of interest, flavin mononucleotide (FMN). FMN is an electron transfer mediator in biological systems. Previously, we have developed two methods of detecting FMN. We have shown that a bare carbon fiber microelectrode can be used to detect flavin and, in a follow-up study, we demonstrate that a thin film of hematite on a large glassy carbon electrode improves flavin detection. The technology for depositing minerals onto carbon microelectrode surfaces needs to be improved and applied to multiple minerals. We selected maghemite and hematite as minerals to deposit because of their affinity to redox active compounds. Our goal was to develop a technology to deposit a thin film of minerals (maghemite and hematite) to the bare carbon microelectrode tip. First, we optimized deposition conditions; then we compared the performance of these microelectrodes. The maghemite-filmed microelectrodes only improved the sensitivity of the microelectrode toward FMN at low concentrations as compared to the bare carbon fiber. Alternatively, hematite, deposited at the same conditions as maghemite, increased the sensitivity by 20-times, the limit of detection (LOD) by 7-times, and the limit of quantification (LOQ) by 7-times, compared to the bare carbon fiber microelectrode. Ultimately, a hematite film, deposited at pH 5 and −0.4 V Ag/AgCl, achieved a sensitivity of 14.1 ± 1.6nA/μM between 0.1 and 20 μM, an LOD of 0.018 μM, and a LOQ of 0.063 μM.