Nanozyme-loaded colorimetric gelatin methacryloyl microneedles for glucose detection in interstitial fluid

The pursuit of portable glucose monitoring has stimulated growing interest in interstitial fluid (ISF) as an alternative diagnostic medium, due to its strong correlation with blood glucose levels and reduced interference from macromolecular substances. However, the transition toward ISF-based sensing technologies, particularly those employing colorimetric microneedle (MN) patches, has been hindered by the inherent instability of natural enzymes such as horseradish peroxidase (HRP), which undergo significant activity loss under fluctuating environmental conditions. To overcome this critical limitation, we engineered a colorimetric MN patch that leverages the copper oxide nanozymes (CuO NPs) with robust peroxidase-mimicking activity and high stability. The patch was fabricated from a gelatin methacryloyl (GelMA) hydrogel matrix co-embedded with glucose oxidase (GOx) and the chromogenic agent 3,3',5,5'-tetramethylbenzidine (TMB). We demonstrated that within the developed microneedle patch, the nanozyme-enabled system enables glucose level assessment suitable for preliminary screening or trend monitoring across the clinical range of 1.7-21 mmol/L by converting ISF glucose levels into colorimetric signals in mice, with performance showing good agreement with commercial assay kits. The CuO nanozyme-based colorimetric MN patch is easy to operate and requires no professional expertise or large-scale equipment, which suggests potential applicability for future clinical diagnosis and daily monitoring pending additional validation.