A light-based DNA hydrogel valve biosensor for naked-eye sensitive detection of aflatoxin B1.

DNA hydrogels have garnered significant attention in biosensing due to their high programmability and excellent biocompatibility. However, the synthesis of their key building block, DNA-polymer, is typically cumbersome, time-consuming, and involves hazardous reagents, which significantly hinders their broader application. Herein, we report a rapid (<1 min) and green synthesis strategy for DNA-polymer via photo-initiated (405 nm) covalent grafting of DNA strands onto gelatin methacryloyl (GelMA). Based on this DNA-polymer, we constructed a light-based DNA hydrogel integrated with a paper substrate to develop a molecular valve biosensor. The sensing mechanism relies on target-induced conformational change of the aptamer, triggering cleavage of the hydrogel cross-linked network and consequently altering the fluid flow velocity in the paper substrate. Signal readout is achieved by visually monitoring the flow rate change without instrumental assistance, greatly simplifying the detection process. Using aflatoxin B1 (AFB1) as a model target, the sensor demonstrated a detection range of 50-750 pM, a limit of detection (LOD) of 34.22 pM (≈0.01 μg/kg, below the EU regulatory limit), a detection time of 607-1052 s (concentration-dependent), and spike-recovery rates of 81 %-98 % in real samples. The hydrogel volume used per sensor was 0.2 μL. This study efficiently prepares DNA-polymer through photografting technology and constructs a DNA hydrogel valve based on this. By combining the on-site detection advantages of paper substrate platforms, it provides a novel high-sensitivity sensing technology for rapid screening of food safety.