Enhanced sensitivity of lateral-flow test strip immunoassays using colloidal palladium nanoparticles and horseradish peroxidase

•Development of highly sensitive lateral-flow test strip immunoassays against pathogens.•Colloidal palladium nanoparticles(PdNPs) and horseradish peroxidase(HRP) were key materials.•Both PdNPs and HRP showed catalytic activity of 3,3′-diaminobenzidine(DAB) oxidation.•The sensitivity of newly developed assays was 5-10-fold higher than that of conventional ones.•Listeria monocytogenes, Escherichia coli O157:H7 and Yersinia enterocolitica was targeted.

Although lateral-flow test strip (LFTS) immunoassays are rapid and require no specialized equipment, they are less sensitive than culture and polymerase chain reaction (PCR)-based methods for detecting bacteria. This study compared the sensitivity of LFTS assays based on colloidal palladium nanoparticles (PdNPs) and colloidal gold nanoparticles (AuNPs). PdNPs demonstrated a time and concentration dependent oxidation of the horseradish peroxidase (HRP) substrate 3,3′,5,5′-tetramethylbenzidine (TMB), whereas AuNPs did not. PdNPs labeled HRP-conjugated antibody lateral flow test strip (PdNPs-HRP LFTS) assays were tested with 3,3′-diaminobenzidine (DAB), a water insoluble substrate. The sensitivity of PdNPs-HRP LFTS assays in detecting Listeria monocytogenes, Escherichia coli O157:H7 and Yersinia enterocolitica was 5-10-fold higher than that of AuNPs-based LFTS (AuNPs LFTS) assays. PdNPs-HRP LFTS assays of reduced milk inoculated with L. monocytogenes were more than 10-fold more sensitive than conventional AuNPs LFTS assays. These results suggest that the PdNPs-HRP LFTS immunoassay is a promising tool for ensuring food safety.