Diversely positive-charged gold nanoparticles based biosensor: A label-free and sensitive tool for foodborne pathogen detection.

Gold nanoparticles (AuNPs)-based lateral flow strip (LFS) enables a quick screening of foodborne bacteria in point-of-care (POC) diagnostics but suffers from the cumbersome labeling of antibodies and poor sensitive performance. Here, we innovated a label-free immunoassay to detect pathogenic bacteria by introducing diversely positive charges functionalized AuNPs ((+) AuNPs). The (+) AuNPs can be loaded on negatively charged bacteria via electrostatic interaction, leading to a color labeling to target bacteria. Afterward, the (+) AuNPs-bacteria complex can be specifically captured by monoclonal antibody (McAb) immobilized on test (T)-line. Under optimum conditions, the proposed LFS exhibited a lowest detectable concentration of 103 CFU/mL for Salmonella enteritidis (S. enteritidis) and could be well applied in drinking water, lettuce and pork samples. Moreover, this novel (+) AuNPs-LFS possessed a universal applicability, which could also be used for detecting Escherichia coli O157 (E. coli O157) with a superior sensitivity (104 CFU/mL) and specificity.