A non-enzymatic sensor obtained by direct writing of a AuNP-based ink for monitoring ascorbic acid in sweat

Abstract

Recently, there has been an increasing interest in the development of wearable sensors for monitoring vitamin C (ascorbic acid) in sweat. These sensors can help assess personal nutritional status, prevent vitamin imbalances, and determine the effectiveness of certain medical treatments. This study presents the first example of non-enzymatic ascorbic acid sensor based on the catalytic activity of printed AuNPs. The three-electrode electrochemical system sensor was fabricated by printing a working and counter-electrode from an AuNP-based ink and a pseudo-reference electrode from a silver ink, on a flexible Kapton® substrate. SEM examination of the printed gold layer revealed a highly divided material, which facilitates electron transfer and accelerates the oxidation of ascorbic acid. In vitro amperometry demonstrated a proportional increase in current with ascorbic acid concentration ranging from 10 to 390 μM, with a sensitivity of 14 μA·mM−1·cm−2. The low oxidation potential of +0.2 V vs Ag/AgCl effectively avoided most interfering oxidations. These results pave the way toward evaluation on the body of healthy volunteers, by placing the sensor directly on their skin, for example for tracking the changes in ascorbic acid concentration in sweat when eating Vitamin C tablets or Vitamin C-containing food such as orange juice. The very first results demonstrated good real-time performance in testing in such experimental conditions. This has potential applications in healthcare, not only on skin but also on therapeutic bandages applied to chronic wounds.