Development of a Broad-Spectrum Fluorescent Lateral Flow Immunoassay for Rapid Screening of Walnut and Hazelnut Protein Residues in Foods

A broad-spectrum fluorescent LFIA was developed for the rapid group-selective screening of walnut and/or hazelnut protein residues in foods, with positive results indicating the presence of walnut and/or hazelnut protein residues but not distinguishing between the two sources. Under optimized conditions, the assay was completed within 10 min. The visual limits of detection for walnut and hazelnut proteins were 25 and 250 ng/mL, respectively, while the instrumental limits of detection were 12 and 156 ng/mL. The assay showed no obvious cross-reactivity with 20 nontarget food ingredients. In biscuit, sausage, and soymilk, the minimum detectable levels were 0.5 mg/kg for walnut protein and 5 mg/kg for hazelnut protein. These results indicate that the proposed assay is a rapid, sensitive, and practical tool for group-selective screening of walnut and/or hazelnut protein residues in complex food matrices.