Improved formation of electrically-deposited enzyme-embedded chitosan coatings onto carbon fiber microelectrodes
A significant challenge in the preparation of enzyme modified electrodes is the immobilization of enzyme near the electrode surface. Traditionally, the polysaccharide chitosan can be electrodeposited around an electrode by the application of a moderately negative voltage, causing an increase in the local pH, triggering its precipitation onto the electrode and immobilizing enzyme in the process. Unfortunately, the production of hydrogen gas bubbles during film deposition is well known to result in the formation of incomplete or non-uniform coatings. In this technical note, the simple addition of a redox-active proton consumer into the chitosan deposition solution is shown to improve the uniformity, reproducibility, and throughput of glucose oxidase-embedded chitosan-coated carbon fiber microelectrodes (GOX/CHIT-CFMs) appropriate for fast scan cyclic voltammetry. GOX/CHIT-CFMs produced through the reduction of benzoquinone and chloramphenicol showed no significant difference in enzyme performance, sensitivity, limit of detection, or time response as compared to those produced through the traditional approach, though throughput was much higher and film morphology was more uniform and reproducible. Benzoquinone displayed some reactivity when added to the coating solution which resulted in slightly thicker coatings that were morphologically distinct from those produced by either the traditional approach or with chloramphenicol. The addition of the antibiotic chloramphenicol, however, showed no such effect and is amenable for preparing GOX/CHIT-CFMs with high throughput. Overall, this work enables the production of more robust enzyme-embedded chitosan electrode films onto carbon fiber microelectrodes without sacrificing their performance.