Portable visual quantitative detection of aflatoxin B-1 using a target-responsive hydrogel and a distance-readout microfluidic chip

Aflatoxin B-1 (AFB(1)), as the secondary metabolite of molds, is the most predominant and toxic mycotoxin that seriously threatens the health of humans and animals. In this work, an AFB(1)-responsive hydrogel was synthesized for highly sensitive and portable detection of AFB(1). The AFB(1)-responsive hydrogel was prepared using an AFB(1) aptamer and its two short complementary DNA strands as cross-linkers. For visual detection of AFB(1), the hydrogel is preloaded with gold nanoparticles (AuNPs). Upon introduction of AFB1, the AFB(1) aptamer binds with AFB1, leading to the disruption of the hydrogel and release of the AuNPs with a distinct color change of the supernatant from colorless to red. In order to lower the detection limit and extend the method to quantitative analysis, a distance-readout volumetric bar chart chip (V-chip) was combined with an AFB(1)-responsive hydrogel preloaded with platinum nanoparticles (PtNPs). In the presence of AFB(1), the hydrogel collapses and releases PtNPs which can catalyze the decomposition of H2O2 to generate O-2. The increasing gas pressure moves a red ink bar in the V-chip and provides a quantitative relationship between the distance and the concentration of AFB(1). The method was applied for detection of AFB(1) in beer, with a detection limit of 1.77 nM (0.55 ppb) where an immunoaffinity column (IAC) of AFB(1) was used to cleanup and pre-concentrate the sample, which satisfies the testing requirement of 2.0 ppb set by the European Union. The combination of an AFB(1)-responsive hydrogel with a distance-based readout V-chip offers a user-friendly POCT device, which has great potential for rapid, portable, selective, and quantitative detection of AFB(1) in real samples to ensure food safety and avoid subsequent economic losses.