Development of colloidal gold immunochromatographic signal-amplifying system for ultrasensitive detection of Escherichia coli O157:H7 in milk

A colloidal gold immunochromatographic signal-amplifying test strip with a sandwich format was successfully developed to detect Escherichia coli O157:H7. The detection signal was improved by addition of enhancers (HAuCl4 and NH2OH center dot HCl) to the nitrocellulose membrane of a conventional immunochromatographic strip. The detection sensitivities of the test strip before and after signal amplification were 4 x 10(4) and 5 x 10(3) CFU mL(-1), respectively, as determined by a colloidal gold strip reader. An 8-fold increase in sensitivity after signal amplification was accomplished within 20 min. No cross-reactivity with 27 non-target strains was observed, and the time for detecting E. coli O157:H7 in spiked milk samples was shortened by 1.5 h. The colloidal gold immunochromatographic signal-amplifying test strip thus provides a novel method for determining E. coli O157:H7 and is rapid, sensitive, convenient, and suitable for on-site detection.