Light scattering intensity as signal transducer to enhance the performance of immunoassay for Cronobacter detection in powdered infant formula

Herein, we propose the light scattering intensity of silver and gold alloy as signal transducer to enhance the sensitivity and dynamic linearity of immunoassay for quantitative detection of Cronobacter muytjensii (C. muytjensii) in powered infant formula (PIF). Silver and gold alloy, namely, silver-coated gold nanocomposite (AuNF@Ag), was obtained by growing silver on the surface of multi-dendritic colloidal gold. The silver growth was triggered by the hydrolysis of urease to urea in the presence of silver nitrate and glucose. Owing to integrating the advantages of light scattering of AuNF@Ag and enzyme-catalyzed mediated signal amplification, the developed light scattering based immunoassay shows high sensitivity for detection of C. muytjensii, with a detection limit of 51 CFU/mL, which is three orders of magnitude lower than that of conventional enzyme-linked immunosorbent assay (ELISA, 6.39 × 104 CFU/mL). In addition, the proposed method also exhibits wide dynamic curve from 3.4 × 102 CFU/mL to 3.4 × 109 CFU/mL for quantitative detection of C. muytjensii, and is significantly superior conventional ELISA (3.4 × 105 CFU/mL to 3.4 × 109 CFU/mL). The accuracy and precision of the proposed immunoassy were evaluated by analysis of C. muytjensii-fortified PIF samples. The average recoveries of the intra- and inter-assays are within 87.90 %–107.91 %, and the coefficient of variation ranges from 2.72 %–9.32 %. This finding indicates an acceptable accuracy for quantitative detection of C. muytjensii in real PIF samples.