A particle counting immunosensor for the sensitive detection of ochratoxin A via click chemistry-mediated signal amplification

The existence of ochratoxin A (OTA) in agricultural products poses significant threats to human health and environment, underscoring the critical need for its prompt and precise quantification. A particle counting immunosensor for the highly sensitive detection of OTA was presented, employing SiO₂@CuO₂ nanoparticles to facilitate click chemistry. The quantity of SiO₂@CuO₂ nanoparticles, and consequently the Cu²⁺ concentration, can be directly altered through the immune response involving OTA. All Cu²⁺ underwent reduction to Cu⁺, resulting in numerous alkyne-functionalized 4 μm polystyrene microspheres (alkyne-PS_4μm) attaching to the surface of individual azide-modified 1 mm polystyrene microspheres (azide-PS_1mm). This attachment occurred via a Cu⁺-mediated click chemistry reaction between the azide and alkyne functionalities. Finally, a handheld cell counter was employed to measure the number of remaining alkyne-PS_4μm, allowing for the calculation of OTA concentration. It showed a wide linear detection range of 50 pg/mL to 500 ng/mL, with the detection limit of 34 pg/mL and recoveries ranging from 82.60 % to 113.00 %. This assay combined the nimbleness of PS_1mm with the precise reading capacity of a handheld cell counter to discern variations in the number of petite microspheres, offering a promising, expedient analytical solution for the portable detection of minute contaminants in agricultural products.