Abstract
A flexible sensor is presented for electrochemical detection of ascorbic acid in sweat based on single-step modified gold microelectrodes. The modification consists of electrodeposition of alginate membrane with trapped CuO nanoparticles. The electrodes are fabricated at a thin polyimide support and the soft nature of the membrane can withstand mechanical stress beyond requirements for skin monitoring. After characterization of the membrane via optical and scanning electron microscopy and cyclic voltammetry, the oxidative properties of CuO are exploited toward ascorbic acid for amperometric measurement at micromolar levels in neutral buffer and acidic artificial sweat, at ultralow applied potential (− 5 mV vs. Au pseudo-reference electrode). Alternatively, measurement of the horizontal shift of redox peaks by cyclic voltammetry is also possible. Obtaining a limit of detection of 1.97 μM, sensitivity of 0.103 V log (μM)−1 of peak shift, and linear range of 10–150 μM, the effect of possible interfering species present in sweat is minimized, with no observable cross-reaction, thus maintaining a high degree of selectivity despite the absence of enzymes in the fabrication scheme. With a lateral flow approach for sample delivery, repeated measurements show recovery in few seconds, with relative standard deviation of about 20%, which can serve to detect increased loss or absence of vitamin, and yet be improved in future by optimized device designs. This sensor is envisioned as a promising component of wearable devices for e.g. non-invasive monitoring of micronutrient loss through sweat, comprising features of light weight, low cost, and easy fabrication needed for such application.Graphical Schematic depiction of the cyclic voltammetry signal change as the sweat flows over the sensor surface.
Highlights
IntroductionMicrochim Acta (2020) 187: 520 requirements of a continuous monitoring for preventive healthcare application
The long-time known essential ascorbic acid is a water-soluble molecule that, like other water-soluble vitamins, cannot be stored in the body for a long time [1]; it can be foundElectronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.Taking into account modern day lifestyle and needs, the sensor design principles should evolve correspondingly [7]
scanning electron microscopy (SEM) imaging of backscattered electrons showed the contrast between the membrane material and the trapped CuO (Fig. 1b)
Summary
Microchim Acta (2020) 187: 520 requirements of a continuous monitoring for preventive healthcare application. In this context, micro- and nanofabrication techniques play an important role by helping to perform detection processes in a small and low-cost chip [8, 9] with the potential to include flexible characteristics to withstand mechanical stress produced by the movement of the end user [10,11,12,13]. Some recent examples of such rapid fabrication include galvanostatic electrodeposition of hydrogels containing enzymes [17], stamping of electrode material with further simple enzyme cross-linking [18], or material vacuum filtration through a mask [19] followed by layer-by-layer or potentiodynamic deposition of receptor layers.
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