Smartphone analysis and dark-field microscopy observation for aflatoxin B1 detection based on the disintegration of core-shell Ag@Au nanoparticles

Aflatoxin B1 (AFB1), one of the most toxic mycotoxins, is commonly found in various food. This study develops a dual-mode biosensor integrating smartphone analysis and dark-field microscopy (DFM) observation for AFB1 detection based on the disintegration of core-shell Ag@Au nanoparticles (Ag@Au NPs). Employing a sandwich assay format, AFB1 aptamer assembled Ag@Au NPs are anchored on 96-well plate and disintegrated by nitric acid. Thereafter, the Ag core is etched, releasing Ag + that serve as colorimetric signal regulators upon the introduction of the glutathione-manganese dioxide nanosheets-3,3′,5,5′-tetramethylbenzidine substrate. The color signal is analyzed using a smartphone based on red-green-blue value analysis. Furthermore, the collapsed Au shell releases individual Au NPs that serve as dark-field scattering nanoprobes, producing a high-intensity green dark-field scattering signal under DFM observation. The detection limit (3.67 fg/mL) is 199/8174/2180-fold lower than those of colorimetric signal, commercial enzyme-linked immunosorbent assay kit, and high-performance liquid chromatography, respectively. Overall, smartphone analysis enables on-site preliminary screening without sophisticated instrumentation. DFM observation allows the ultra-sensitive quantitative detection in a laboratory. The proposed dual-mode biosensor will not only reduce false-positive/negative rate through the bidirectional signal readout, but also offer a practical, stable, and ultrasensitive strategy for AFB1 detection in food.