Multifunctional water soluble fluorescent sensor for monitoring HSA, viscosity, and sulfite/bisulfite

We report the design and synthesis of SDHC-1, a water-soluble multifunctional fluorescent probe that can detect human serum albumin (HSA), sulfite/bisulfite (SO₃^2-/HSO₃^-), and viscosity through distinct fluorescence signals. SDHC-1 exhibits very weak fluorescence due to twisted intramolecular charge transfer (TICT). Interaction with HSA or in high-viscosity environments suppresses TICT, producing a strong far-red emission at 670 nm (λ_ex = 550 nm), while sulfite/bisulfite undergoes a Michael addition with the probe's CC bond, disrupting π-conjugation and yielding blue fluorescence at 486 nm (λ_ex = 420 nm). The probe demonstrates high sensitivity with detection limits of 14.7 nM for HSA and 42.3 nM for sulfites, excellent selectivity over potential interfering analytes, and shows rapid response times (∼ 40 s for HSA, ∼ 600 s for sulfites). SDHC-1 functions efficiently across a wide pH range (5.0-10.0), in real samples (urine, water, sugar, wine, biscuits), and enables naked-eye or paper-strip-based detection. Its large Stokes shift minimizes spectral overlap, ensuring precise multi-analyte quantification.