Xanthine determination in food samples using a carbon veil-based bi-enzyme amperometric sensor.

An innovative bi-enzyme sensor system for the determination of xanthine - a marker of fish freshness - is presented. The sensor is based on a glassy carbon electrode modified with composite of carbon veil/pillar[5]arene, xanthine oxidase, and uricase, integrated into a flow-through electrochemical cell manufactured by 3D printing and optimized for use with both planar and solid-state electrodes. The carbon veil, which has a highly developed specific surface area, provided a multiple increase in the effective electrode surface area, and facilitates efficient mass transfer of the substrate to the active sites of immobilized enzymes. Pillar[5]arene acts as an electron transfer mediator. The flow-through cell enabled the implementation of a cascade mechanism for analytical signal generation: enzymatic reactions produce hydrogen peroxide. The developed system demonstrated outstanding analytical and metrological characteristics. The limit of detection for xanthine is 0.9 nM. Testing of the sensor on real cod fillet samples showed its ability to detect the dynamics of xanthine accumulation under different storage temperature conditions, which clearly correlates with the organoleptic signs of product spoilage. The developed biosensor opens up broad prospects for application in quality control of fish and meat products, clinical diagnosis of metabolic disorders.