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.
Copyright © 2010 John Wiley & Sons, Ltd.