MXene catalytic amplification-fluorescence/absorption dimode aptamer sensor for the detection of trace Pb²⁺ in milk

Lead ion (Pb²⁺) is a toxic heavy metal, which is very harmful to organisms. Therefore, the establishment of a rapid, simple, and sensitive method is of great significance to food safety and human health. It was found that MXeneTi₃C₂ nanosheet (NS) has a strong catalytic effect on the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) via H₂O₂ to form the oxidized product (TMB_OX); it has a strong fluorescence peak at 415 nm and an absorption (Abs) peak at 295 nm. The aptamer of Pb²⁺ (Apt_pb) can be adsorbed on the surface of an NS to form MXene-Apt conjugates, which reduces its catalytic active sites and inhibits its catalytic activity. When the target Pb²⁺ is added, it specifically binds with Apt_pb to release MXene NSs to enhance the dimode signals. Therefore, a new MXene catalytic fluorescence/absorption dimode aptamer biosenering platform was fabricated for the determination of trace Pb²⁺ in milk and water samples, with the fluorescence assay linear range (LR) of 5.0 × 10^-2-2.0 nmol/L.