An on-site colorimetric sensor for glucose in sweat based on a hydrogel embedded with GOx@Co-HHTP

Owing to their stable signal response and facile readout, enzymatic reaction and hydrogel based colorimetric sensors have received widespread attention for on-site sweat glucose detection. Developing enzymes with high stability and activity is an important research direction. Herein, a glucose oxidase-loaded cobalt-2,3,6,7,10,11-hexahydroxytriphenylene composite (GOx@Co-HHTP) has been designed to be incorporated into a carrageenan matrix to construct a hydrogel-based colorimetric sensor for glucose detection. The hydroxyl-rich HHTP surface provides potential sites for noncovalent interfacial association with carrageenan chains, which may facilitate the retention and dispersion of the catalytic composite within the hydrogel matrix. GOx catalyzes glucose oxidation to generate H₂O₂, which is subsequently utilized by the peroxidase-like Co-HHTP to oxidize 3,3',5,5'-tetramethylbenzidine, thereby producing a visible color change of the hydrogel, and this phenomenon can be easily recorded using a smartphone. Under the optimized conditions, the developed system exhibits a linear response to glucose over the concentration range of 5-600 μM, with a limit of detection of 3.02 μM. The sensing system also shows high selectivity against common potential interferents. The concentration-dependent color change of the hydrogel is quantified using smartphone imaging and ImageJ-assisted gray-value analysis, enabling visual and image-assisted glucose determination. This work provides a practical strategy for constructing hydrogel-supported enzyme-nanozyme colorimetric platforms for on-site glucose monitoring.