Diene-Extended Chalcones Enable Red Fluorescence Detection of Human Serum Albumin Through FA1 Binding

Fluorescent molecular probes for selective and real-time detection of human serum albumin (HSA) protein in urine and blood have important applications in clinical diagnostics for various diseases. The majority of known fluorescent HSA probes give emission in the blue-green spectral region where biological autofluorescence could interfere with the detection. In this study, a series of chalcones with extended conjugation are shown to give red-emission with a large Stokes shift (λ_abs ≈ 430-445 nm, λ_em ≈ 620-640 nm), and low fluorescence in H₂O. Upon addition of HSA protein, the fluorescence of these chalcones is shown to increase significantly, by as high as 30-fold. Potential site-selective binding to HSA has been examined by competitive displacement experiments using various known site-selective drugs. In conjunction with molecular docking experiments, the study further indicates that the chalcones could selectively enter the FA1 (Fatty Acid site 1) binding pocket (Drug Site III).