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Here, a facile hydrothermal method was used to synthesize highly photoluminescent N-doped carbon dots, and the quantum yields reached 97.1%. Then, a label-free immunosensor based on the inner filter effect of carbon dots was developed for ultrasensitive detection of aflatoxin M 1 residues in milk. The detection limit was 0.0186 ng/mL (equivalents to 18.10 ng/kg), which satisfied the most stringent maximum tolerable limit value of 25 ng/kg. Besides, the immunosensor showed a good linear relationship from 0.003 ng/mL to 0.81 ng/mL, and the average recoveries ranged from 79.6% to 112.5% for spiked milk samples, with relative standard deviations ranging from 6.7% to 13.3%. Compared with other immunoassays, the inner filter effect-based immunosensor incorporating fluorescent detection into conventional enzymatic cascade amplification systems and could be a reliable on-site screening method for aflatoxin M 1 residue analysis., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Mycotoxins and antibacterial agents are the main chemical hazards that lead to several health problems. Nowadays, multiplex immunoassay is a primary goal throughout the world. Here, aflatoxin M 1 and pirlimycin were selected as models, and a novel dual colorimetric encoded frit-based immunoassay was developed for simultaneously screening of aflatoxin M 1 and pirlimycin residues in milk. This multiplex frit-based immunoassay combined two monoclonal antibodies to extend the spectrum of analytes and to enable detection of two classes of analytes in a single test. The cutoff values were 0.02 μg/kg for aflatoxin M 1 and 0.5 μg/kg for pirlimycin, which satisfied the requirement to measure the maximum residue levels. The novel colorimetric frit-based immunoassay has the advantage of high throughput, short analysis time, reduced overall cost per assay, and can be used as a rapid screening technique for simultaneously detecting aflatoxin M 1 and pirlimycin residues in milk.