Multiplex binding assays for the detection of antibiotic residues in food

Although multiresidue detection seems like the ideal screening test for antibiotic residues, just a few platforms that accomplish this are actually available. Advantages and limitations of the commercially available systems are hereby presented.     Although multiresidue detection in food and feed seems like the ideal screening test, and although a hundred million euros have been spent in the past 30 years to develop a high-sensitivity biosensor capable of detecting all chemical contaminants in a single test, just a few platforms that accomplish this are actually available. Advantages and disadvantages of the commercially available system are hereby presented.   Why is multi-target screening for antimicrobials needed? As described in the first paper of this issue, antimicrobials have been and continue to be widely used—and sometimes abused — both in livestock and seafood farming. Residue concerns arose in the 1970s in some European countries but it wasn’t until the end of the 1980s that the US and the EU established maximum residue levels (MRLs). Food Business Operators (FBO) in every food chain have the responsibility to guarantee that their products are compliant with these limits (EU Commission 1990). During the “tech era” (1970-1990), control of antibiotic residues was generally driven by technological issues (e.g. residues in milk hinder the fermentation in the cheese production process) but then, during the “regulatory era” (1990-2020), a need to cope with legal limits arose and the list of target molecules became much longer. With the exception of a few cases, during the “tech era”, Microbial Inhibition Assays (MIAs), like the well known Delvotest, were fit for the purpose. After 1990, residue control became necessary even when milk was sold as such, not just for cheese production. A huge market for rapid diagnostic tests was created quickly. Lac-tek, a simplified ELISA seven-minute assay in a test tube and then SNAP, both by IDEXX, made milk controls fast enough to be used in milk production facilities. Of course, the end-users were looking not only for speed, but also for simplicity. Moving the Lateral Flow ImmunoAssay (LFIA) from clinical applications to the food sector, a Belgium company, UCB Bioproducts, launched the first Lateral Flow Device (LFD) for milk testing in 1996. In the subsequent 20 years, many other manufacturers developed similar products (ROSA by Charm, Tetrasensor by Unisensor, many Chinese brands). Because this occurred during the “regulatory era”, many of these products incorporated 2 or more binding reagents in order to enlarge the number of classes of residues detected. However, with the established LFD technology, it was difficult to accommodate more than three or four groups of molecules on a single test. In the meat, seafood, and honey sectors, the interest in residue screening only arose during the “regulatory era”. In this case, however, particularly for seafood and honey, the main target was not represented by beta-lactams and turnaround time (TAT) was less important so ELISA kits have generally been used for screening (the only exception was Charm II, a battery of radio-immunoassays and radio-receptor assays). Manufacturers offered an increasing number of “broad-range” test kits, but often such assays suffered from an increase in matrix effects. Moreover, it is