Dual signal insight: field-efficient qualitative/quantitative detection of sulphamethazine in raw milk

A novel lateral flow assay (LFA) was developed by introducing magnetic beads with colloidal gold nanoparticles (AuMB) to LFA test strips for the qualitative and quantitative detection of sulphamethazine (SM 2 ) in raw milk. In the proposed assay, test samples are qualitatively judged yes (positive) or no (negative) on the basis of naked-eye signals from the colloidal gold and fluorescence quenching is used to quantitatively determine the level of SM 2 in positive samples. Results indicated that the threshold concentration for determining whether a test sample is positive or negative is 5 ng/mL. The limit of detection and linear range of the proposed AuMB-LFA for quantitative detection were 0.39 and 0.5-200 ng/mL, respectively, and its recovery for detecting SM 2 in raw milk was 97.4-110.2%. The developed AuMB-LFA provides novel insights into efforts to maintain a balance between the efficient screening of targets in large samples and saving time and money.