Detection of casein in milk by bilobate-like dyes quinaldine red and thioflavin T

Abstract

Casein is one of the major components in cow's milk, which is found as a suspension of micelles. We describe here two bilobate-like dyes, quinaldine red (QR) and thioflavin T (ThT), both of which supramolecularly interact with casein to fluoresce as shown by various technologies. Specifically, the fluorescence intensity of QR shows a linear relationship with casein in the range of 5∼100 μg mL⁻¹ and 100–1000 μg mL⁻¹, respectively, with a detection limit (LOD) of 10.80 μg mL⁻¹. On the other hand, the linear range of the ThT-based approach is from 5 to 200 μg mL⁻¹ with a LOD of 0.15 μg mL⁻¹. The spiked recoveries for QR-based approach (or ThT-based approach) are 90.4%–107.7% (or 92.9%–104.8%) in the detection of actual milk samples obtained from the local market. Overall, these bilobate probes show good selectivity and sensitivity, and several advantages as compared to canonical approaches. Therefore, we propose these two bilobate dyes as alternative practical fluorescent probes for casein detection.