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A rapid and semiquantitative lateral flow assay has been developed for detection of cephalexin (CFX) in milk. The assay is based on a competitive format using polyclonal antibodies. Antibodies were raised in rabbits against CFX-keyhole limpet hemocyanin. The specificity of antibodies was ascertained by direct enzyme-linked immunosorbent assay. The laboratory prepared gold nanoparticles coupled to anti-CFX antibodies, which competed for free CFX in sample and CFX-bovine serum albumin conjugate on the test line of a lateral flow strip. The control line of the lateral flow strip consisted of species-specific antibody. The assay was validated with spiked milk samples and involved application of skim milk to the adsorbent pad followed by visualization of red color on test and control lines within 8 min. The lower detection limit of CFX was 30 ppb in milk, which is lower than the Codex prescribed maximum residue limit. The storage stability of the prepared strip was also established. PRACTICAL APPLICATIONSA simple method for the detection of cephalexin in milk using lateral flow assay has been described. The applicability of polyclonal antibodies in the development of lateral flow assay has been demonstrated. The method is sensitive to detect 30 ppb cephalexin in milk, which is lower than the Codex prescribed maximum residue limit of 100 ppb. This method can be used for preliminary screening of milk samples for the presence of cephalexin residues in milk.

A lateral flow based detection method for ascertaining the presence of soymilk in whole bovine milk has been described. The method uses commercially available rabbit anti-soy protein antibodies conjugated to gold nanoparticles (AuNPs) wherein soymilk protein in adulterated milk and soymilk protein at test line competes for limited antibodies. At control line, anti-rabbit immunoglobulin was immobilized for ensuring flow properties of antibody-conjugated AuNPs. Absence or diminished intensity of band at test line indicates presence of soymilk in milk. The soymilk detection limit was 1.75% (v/v) in whole bovine milk and results are available in 5 min. Constructed lateral flow device can be used for on-spot examination of soymilk in milk.