Detection of Aflatoxin M1 in milk using Mach-Zehnder optoelectronic immunosensors

Aflatoxin M1 (AFM1) is excreted in milk of animals after ingestion of food contaminated with Aflatoxin B1 (AFB1). AFM1 has been considered as group I carcinogen since 2002, so the consumption of even low concentrations of AFM1 pose a major threat for human health. In this work, a silicon-based optoelectronic immunosensor for the detection of AFM1 in milk is developed. The immunosensor consists of ten Mach–Zehnder silicon nitride waveguide interferometers (MZIs) monolithically integrated along with their respective light sources onto the same chip. The recording of transmission spectrum is achieved through an external spectrophotometer. The MZIs are bio-functionalized through aminosilane activation and AFM1-bovine serum albumin conjugate immobilization. For AFM1 detection, a 3-step competitive immunoassay configuration is employed, including the primary reaction with rabbit anti-AFM1 antibody, followed by biotinylated anti-rabbit IgG antibody, and streptavidin. The assay is completed in 15 min. The limit of detection is 0.03 ng/mL in undiluted milk, which is below the maximum allowable limit set by European Union (0.05 ng/mL). The assay is accurate (% Recovery values: 91-112) and repeatable with intra-/inter-assay coefficients of variation <8%. The excellent analytical performance of the proposed immunosensor paves the way for accurate AFM1 determination in milk samples at the point-of-need.