Researchers at Shanghai University and Shanghai General Hospital at Shanghai Jiao Tong University School of Medicine have developed an electrochemical biosensor that combines a three-dimensional graphene framework with a heat-denatured casein interlayer to detect uric acid in sweat at femtomolar concentrations - a sensitivity the team says surpasses prior sweat-based uric acid sensors.
Uric acid is a key biomarker for conditions like gout, hyperuricemia, kidney dysfunction, and cardiovascular disease, and is conventionally measured through blood tests that require trained personnel and aren't suited to frequent or continuous monitoring. Sweat-based sensing offers a non-invasive alternative, but the low concentration of uric acid in sweat and the complexity of the sweat matrix have made reliable detection difficult, and conventional two-dimensional graphene sensing platforms are limited by restricted surface area for enzyme loading and slow analyte diffusion to active sites.
The team addressed this by mildly heat-treating casein to convert it into a conformal, bioadhesive protein film anchored directly onto the 3D graphene scaffold. This interlayer enhances loading and retention of the enzyme uricase (UOx) through multivalent interfacial interactions while preserving its catalytic activity - avoiding the harsher chemical functionalization methods (covalent bonding via carboxyl, amino, or hydroxyl groups) that can compromise enzyme activity in conventional immobilization approaches. The interconnected, porous architecture of the 3D graphene framework provides a large electroactive surface area and supports rapid mass transport between uric acid and the immobilized enzyme.
Under optimized conditions, the sensor achieved a dynamic range from 1 femtomolar to 10 micromolar with a detection limit of 1 femtomolar (signal-to-noise ratio of 3), along with good selectivity and negligible sensitivity to pH variation within the physiological sweat range. The researchers validated the platform in both artificial and real human sweat samples, finding that its readings showed a positive association with paired clinical blood uric acid measurements in a pilot cohort.
The authors position heat-denatured casein as a broadly useful bioadhesive interlayer strategy for enzyme immobilization on 3D graphene, with potential application in wearable, real-time sweat-analysis platforms for personalized health monitoring.
