On-Site AFB1 detection in food via dual-equipped NH2-ZIF-8@Cu2+ and core-shell UCNPs embedded in SA-PAM hydrogel

The increasing presence of Aflatoxin B 1 (AFB 1 ) residues in food continues to raise significant public health concerns. Herein, we designed an upconversion-based sensor integrated into an alginate-polyacrylamide (SA-PAM) hydrogel for on-site AFB 1 detection in food. First, core-shell upconversion nanoparticles (CSUCNPs) with enhanced fluorescence were modified with complementary DNA (cDNA), forming signal probes known as CSUCNPs-cDNA. Simultaneously, NH 2 -ZIF-8@Cu 2+ with a high surface area and specific affinity for aptamer was synthesized using a one-pot method. This was then modified with an AFB 1 -specific aptamer, forming the capture probe Apt-ZIF-8@Cu 2+ . Using base pairing, CSUCNPs-cDNA and Apt-ZIF-8@Cu 2+ were hybridized into sensing probes (CSUCNPs-ZIF-8@Cu 2+ ), which were embedded into SA-PAM hydrogels as stable sensor carrier. Furthermore, the SA-PAM hydrogel showed a reduced swelling ratio of 1.68–1.80 in water and phosphate buffer solution(s) (PBS), which improves stability. In the presence of AFB 1 , the aptamer selectively binds the AFB 1 , increasing electrostatic repulsion between CSUCNPs-cDNA and Apt-ZIF-8@Cu 2+ . This disrupts Förster resonance energy transfer (FRET), resulting in a pronounced “signal-on” fluorescence. This sensor achieves AFB 1 diffusion through the SA-PAM hydrogel, FRET disruption and upconversion signal stabilization within 18 min, faster than traditional methods. Under optimized conditions, the sensor exhibited a clear linear correlation between fluorescence intensity and the logarithm of AFB 1 concentration ranging from 0.1 to 100 µg/kg ( R ² = 0.994), with a detection limit as low as 0.08 µg/kg. Besides, its performance was further validated through tests on spiked wheat, corn, peanut, and water, demonstrating high accuracy and reproducibility with relative standard deviation (RSD) below 3.63 % and recoveries of 85.88–98.04 %.