An instrument-free height readout biosensing device based on gold nanobipyramid-loaded hydrogel for point-of-care detection of acid phosphatase and the BRCA1 gene.

Point-of-care testing (POCT) is crucial for disease diagnosis, especially in resource-limited settings with inadequate laboratory infrastructure. Although visual distance-based readout sensors present a promising approach for instrument-free quantification, their widespread application is hindered by complex fabrication processes and dependence on external driving mechanisms. Here we developed a universal, instrument-free visual quantification platform based on a gold nanobipyramid -loaded agarose (AuNBP/agarose) hydrogel encapsulated in a polycarbonate (PC) tube. The iodine-mediated etching of AuNBPs transduced target recognition into a measurable color-changing hydrogel height. The addition of acid phosphatase (ACP) initiated the enzymatic production of ascorbic acid (AA), driving the etching process and generated a height signal proportional to ACP concentration in the range of 0.1-1000 mU/mL, with a detection limit of 9.72 μU/mL. Moreover, it exhibited high selectivity and satisfactory recoveries for ACP in human serum samples. For DNA detection, target hybridization introduced horseradish peroxidase (HRP), which effectively inhibited etching by consuming H2O2. This strategy enabled sensitive detection of the BRCA1 gene within a concentration range of 100-1500 nM, with a detection limit of 270 nM. Both assays enabled quantitative readout using a simple ruler, without the need for complex instrumentation, demonstrating a universal and cost-effective strategy for POCT detection.