Gold nanoparticle-decorated covalent organic frameworks as amplified light-scattering probes for highly sensitive immunodetection of in milk

Traditional immunoassays exhibit insufficient screening sensitivity for foodborne pathogens due to their low colorimetric signal intensities. Herein, we propose an ultrasensitive dynamic light scattering (DLS) immunosensor for Salmonella based on a "cargo release-seed growth" strategy enabled by a probe, namely gold nanoparticle-decorated covalent organic frameworks (COF@AuNP). Large amounts of AuNPs in COF@AuNP can be released by acid treatment-induced decomposition of the imine-linked COF, and then they are enlarged via gold growth to generate a dramatically enhanced light-scattering signal, leading to a vast improvement in detection sensitivity. Based on an immunomagnetic microbead carrier, the proposed DLS immunosensor is capable of detecting trace Salmonella in milk in the range of 2.0 × 10 2 -2.0 × 10 5 CFU mL −1 , with a limit of detection of 60 CFU mL −1 . The immunosensor also demonstrated excellent selectivity, good accuracy and precision, and high reliability for detecting Salmonella in milk. An ultrasensitive DLS immunosensing method based on a "cargo release-seed growth" signal amplification strategy was developed for detecting Salmonella , using a probe of gold nanoparticle-decorated covalent organic frameworks (COF@AuNP).