G-SNAP: A gelation-based single-step naked-eye assay platform mediated by biomarker-triggered enzymatic quinone tanning

Here, we report a novel strategy for rapid and convenient biomarker detection through the naked eye by temporally controlling nature-inspired quinone tanning in a biomarker-specific manner. Quinone tanning is one of the smartest strategies for crosslinking biopolymers chosen by living organisms because of its high efficiency under ambient conditions, arising from the low redox potential of catechol moieties and the high reactivity of the quinone states. However, this efficient mechanism ironically makes it difficult to control the reaction temporally under the desired conditions. Herein, we suggest a dual-enzyme system triggered by biomarker metabolism that can temporally switch on quinone tanning, resulting in rapid sol-gel transition of catechol-conjugated biopolymers. Gelation is a visible indication of the presence of biomarkers, even when dissolved in colored media such as blood and urine. As a demonstration, we established a gelation-based single-step naked-eye assay platform (G-SNAP) for rapid and convenient glucose sensing. The optimized system could detect up to 7 mM glucose in human serum within 1 h by a simple capillary test visualized with the naked eye. The dual enzyme cascade G-SNAP, one for biomarker recognition and the other for quinone tanning, not only allows for signal amplification due to a high turnover rate but also ensures high intrinsic specificity for biomarkers without interference even in complex bio-fluids.