Ultrasensitive chemiluminescent immunoassay of Salmonella with silver enhancement of nanogold labels.

In this paper, silver enhancement of nanogold labels coupled with chemiluminescence detection was developed for ultrasensitive immunoassay of Salmonella based upon antigen-antibody immunoreaction. Polyclonal rabbit anti-Salmonella sp. antibodies (pAb) were employed to establish the analytical protocol. The pAb coated onto ELISA microwell plates and Au nanoparticles (Au NPs) conjugated pAb capture target Salmonella to form a sandwich-type complex. Silver then was in situ deposited around the Au NPs core and resulted in the signal amplification. In consequence, silver was dissolved to form Ag(+) and a sensitive chemiluminescence based on the Ag(+)-K2S2O8-Mn(2+)-luminol system was coupled for further signal amplification. Under the optimized conditions, the chemiluminescent intensity is proportional to target Salmonella over the range of 5-1038 cfu mL(-1) with a detection limit of 5 cfu mL(-1). The relative standard deviation for 11 measurements of about 50-100 cfu/mL target Salmonella is 4.7%. The proposed method was successfully applied to measure Salmonella in food samples and the results are identical to those of the offical standard method of China. These offer us a more powerful tool for ultrasensitive assay of foodborne pathogens.