Albumin-induced large fluorescence turn ON in 4-(diphenylamino)benzothiazolium dyes for clinical applications in protein detection

A series of [4-(diphenylamino)]styrylbenzothiazolium-based fluorescent probes 1a -1f have been synthesized to investigate their albumin binding properties. The probe 1 was found to be nearly non-fluorescent in both aqueous and organic solvents and exhibited a very large fluorescence turn ON at λem ≈ 630–650 nm (фfl ≈0.38–0.40) upon addition of serum albumin in aqueous solution. Probes exhibited high sensitivity towards detecting albumin in aqueous solution with a limit of detection (LOD) below 7–14 ng/mL. The stability constants for the probe-albumin interactions were calculated by Stern-Volmer method. The stability of the probe-albumin complexes was further investigated during this study to understand the role of the substituents of the probe's structure towards the observed selectivity. Spectrometric fluorescence titrations were conducted to investigate selectivity, sensitivity, and stability of the probe-albumin complex. Probe's binding specificity was further studies in the presence of known site-specific drug molecules via competitive displacement method. The large fluorescence response exhibited towards HSA and BSA found to be highly useful for visualizing albumin content in SDS-PAGE up to nanogram scale. The probe 1 was successfully utilized for analysing albumin content in urine samples, showing good linear correlation and indicating the probe's suitability in clinical diagnostics.