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The quality and authenticity of milk are of paramount importance. Cow milk is more allergenic and less nutritious than ewe, goat, or donkey milk, which are often adulterated with cow milk due to their seasonal availability and higher prices. In this work, a silicon photonic dipstick sensor accommodating two U-shaped Mach–Zehnder Interferometers (MZIs) was employed for the label-free detection of the adulteration of ewe, goat, and donkey milk with cow milk. One of the two MZIs of the chip was modified with bovine κ-casein, while the other was modified with bovine serum albumin to serve as a blank. All assay steps were performed by immersion of the chip side where the MZIs are positioned into the reagent solutions, leading to a photonic dipstick immunosensor. Thus, the chip was first immersed in a mixture of milk with anti-bovine κ-casein antibody and then in a secondary antibody solution for signal enhancement. A limit of detection of 0.05% v/v cow milk in ewe, goat, or donkey milk was achieved in 12 min using a 50-times diluted sample. This fast, sensitive, and simple assay, without the need for sample pre-processing, microfluidics, or pumps, makes the developed sensor ideal for the detection of milk adulteration at the point of need.

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.