Abstract
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 (i.e., watermelon and apple) with a low content of vitamin C. HRCM and the functionalized working electrodes (WEs) were characterized by SEM and TEM. The increases in the electroactive area and in the diffusion of AA molecules towards the WE surface were evaluated by cyclic voltammetry (CV) and chronoamperometry. The performance of HRCM-SPEs were evaluated by CV and constant potential amperometry compared with the non-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, the 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 to 0.15 and 0.28 μM, respectively. Finally, the functionalization of the SPEs proved to be indispensable for determining the AA concentration in the watermelon and apple samples.
Highlights
The scientific community has long recognized the concentration of ascorbic acid (AA)as an effective indicator of quality depletion in fresh-cut produce, since it is an effective radical scavenger of ROS produced by oxidative stress and quickly changes according to non-optimal post-harvest conditions [1,2,3]
Corresponds to the magnification; SE1 indicates that the images were collected with the secondary corresponds to theImages magnification; that were collected with the secondary electron detector
We demonstrated that the functionalization of screen-printed sensors (SPEs) with nanomaterials allowed for AA detection in species characterized by a low content of vitamin C
Summary
The scientific community has long recognized the concentration of ascorbic acid (AA)as an effective indicator of quality depletion in fresh-cut produce, since it is an effective radical scavenger of ROS produced by oxidative stress and quickly changes according to non-optimal post-harvest conditions [1,2,3]. Previous works have focused on monitoring systems built to alert producers or sellers of small variations in the AA concentration caused by unexpected interruptions in the cold chain. Such a variations can have different kinetics in minimally processed fruit and vegetables, but an AA decay always corresponds to a decline in their nutritional value, even in correct storage conditions [1,3,4,5,6,7,8]. Electrochemical sensors have been demonstrated to be reliable for real-time AA detection, and for the evaluation of the oxidative stability and nutritional quality of fruit and vegetables [9,10]. Carbon electrodes do not always have the necessary requirements to achieve certain objectives; this was the case in [11], where the authors were not able to completely separate the AA and the polyphenol signals and had to resort to the use of fullerenes and nanotubes to increase the sensitivity and specificity of the working electrode [12]; or as in [13], where carbon nanotubes (CNTs) were used to obtain a lower-potential electrocatalytic detection and, a higher selectivity by minimizing the contributions from co-existing electroactive constituents in glucose analysis
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