Paper-based microfluidic electrochemical sensor for chloride ion and uric acid detection in sweat

Chloride ions and uric acid are two key biomarkers that play a crucial role in oxidative stress, a pathological condition that can lead to serious diseases if not monitored and identified on time. In this work, we focus on developing an innovative device based on an electrochemical sensor and a paper microfluidic system for the early detection of these biomarkers in sweat. The electrochemical sensor consists of a silicon chip containing thin-film gold electrodes modified by electrodeposition with silver and a composite of reduced graphene oxide and gold nanoparticles for the detection of chloride ions and uric acid, respectively. An initial performance assessment of the sensors in batch in buffer and artificial sweat solutions was conducted using chronoamperometry. Calibration curves were obtained in both media. Chloride ions were detectable in the range of 1–100 mM with a sensitivity of 1.40 μA mM−1 in buffer, while the range and sensitivity in artificial sweat were 1–100 mM and 1.44 μA mM−1. Uric acid was detectable with a sensitivity of 1.610 μA mM−1 and a linear range of 10–500 μM in buffer. The corresponding values in artificial sweat were 1.583 μA mM−1 and 10–500 μM). These analytical values indicate minimal interference and a very small matrix effect when measurements were conducted in artificial sweat. The sensors were integrated with a paper microfluidic component to assess the effectiveness of the device in monitoring chloride ion and uric acid levels in sweat with a very low sample volume (7 μL) for non-invasive and low-cost evaluation of oxidative stress.