Silver Nanoplates and Gold Nanospheres as Probesfor Revealing an “Interference” Phenomenon in a Simultaneous Quantitative Immunochromatographic Assay

Abstract

Escherichia coli O157:H7 and Salmonella choleraesuis are two important foodborne pathogens that cause illnesses and even deaths. Rapid and convenient methods, such as immunochromatographic assays (ICAs), are useful for detecting these two pathogens. Herein, we developed a highly sensitive ICA for the simultaneous quantitative analysis of these two foodborne pathogens. Silver nanoplates (AgNPs) and gold nanospheres (AuNSs) were synthesized as two probes for simultaneous detection. In this method, Escherichia coli O157:H7 (E. coli O157:H7) and Salmonella choleraesuis (S. choleraesuis) were specifically detected at concentrations as low as 2.16 × 104 and 1.18 × 105 colony-forming units (CFU)/mL, respectively, in 30 min. Subsequently, a method for separately detecting these two targets with the same test strips was developed. The tests achieved specific detections of E. coli O157:H7 and S. choleraesuis, with detection limits of 1.07 × 104 and 9.85 × 104 CFU/mL, respectively. By comparing the intensity of the test lines (T) in the two methods, we found an interesting phenomenon in which the intensity of T in the simultaneous detection method was lower than that in the separate detection method. RGB analysis of the test lines demonstrated that the two probe–target compounds influenced each other. We believe that this phenomenon is an important factor to consider when building a simultaneous quantitative ICA.