Functionalization of screen-printed sensors with a High Reactivity Carbonaceous Material for ascorbic acid detection in fresh-cut fruit with low vitamin C content

In this study, carbon screen-printed sensors (C-SPEs) were functionalized with a High Reactivity Carbonaceous Material (HRCM) to measure the ascorbic acid (AA) concentration in fresh-cut fruit, watermelon and apple, having low content of vitamin C. HRCM and the functionalized working electrodes (WEs) were characterized by SEM and TEM. The increase in the electroactive area, and in the diffusion of AA molecules towards the WE surface, was evaluated by CV and chronoamperometry. The performance of HRCM-SPEs were evaluated by cyclic voltammetry (CV) and constant potential amperometry, in comparison with the not-functionalized C-SPEs and MW-SPEs nanostructured with multi-walled carbon nanotubes. The results indicated that SPEs functionalized with 5 mg/ml of HRCM and 10 mg/ml of MWCNTs had the best performances. HRCM and MWCNTs increased the electroactive area by 1.2 and 1.4 times, respectively whereas, after functionalization, AA diffusion rate towards the electrode surface increased by an order of 10. The calibration slopes of HRCM and MWCNTs improved from 1.9 to 3.7 times, thus reducing the LOD of C-SPE from 0.55 μM to 0.15 and 0.28 μM, respectively. Finally, the functionalization of the SPEs was proved to be indispensable for determining the AA concentration in the watermelon and apple samples.