Detection of Aflatoxin M1 in Milk with a Mach–Zehnder Interferometric Immunosensor

Aflatoxin M1 (AFM1) is the hydroxylated form of Aflatoxin B1 (AFB1) and is expelled in the milk of both humans and animals following the consumption of AFB1-contaminated food. AFM1 has been categorized as a Group 1 carcinogen by the International Agency for Research on Cancer. Consequently, the European Commission has established a maximum allowable concentration of 50 pg/mL for AFM1 in dairy products and milk. Here, a rapid and sensitive approach for detecting AFM1 in bovine milk is presented. The analytical setup comprises a broad-band white LED, a spectrophotometer, and a silicon photonic probe, all interconnected by a bifurcated optical fiber [1]. Additionally, a laptop powers the system and facilitates signal monitoring through specialized software. The silicon photonic probe is equipped with two Mach–Zehnder interferometers: one functionalized with AFM1-bovine serum albumin conjugate, and the other with bovine serum albumin to serve as a blank. The analysis involves immersing the probe directly into a mixture of anti-AFM1 antibodies and the sample, followed by sequential immersion into biotinylated anti-rabbit IgG antibody and streptavidin solutions. The entire assay process takes 12 min, and the limit of detection in undiluted milk is 20 pg/mL, below the EU maximum allowable limit of 50 pg/mL. The assay demonstrates accuracy, with %recovery values ranging from 87.5 to 112%, and repeatability, with intra/inter-assay coefficients of variation below 7.6%. Given its analytical performance and compact instrumentation, the proposed immunosensor proves to be an ideal solution for precise on-site determination of AFM1 in milk samples.