A-D-A type fluorescent probe with dual quaternary-ammonium-salt anchors for turn on detection of HSA in wide emission gamut.

Human serum albumin (HSA) is a key protein implicates in various physiological and pathological conditions such as renal injury, diabetes mellitus. Herein, we report an AIE-active fluorescent probe (DNI-4) for detection of HSA with a "turn on" response covering visible and near-infrared region (500 - 800 nm). Combining with a triphenylamine and two 1,8-naphthalimide moieties, the chromophore segment of DNI-4 forms a "A-D-A" type molecular architecture with the twisted intramolecular charge transfer property. Two quaternary ammonium salt moieties are introduced into the chromophore to give the probe (DNI-4), which has good hydrophilicity and can interact with HSA to form the dye-HSA aggregates with "turn-on" signal. DNI-4 demonstrates a good linear correlation over a low concentration range of HSA from 0 to 0.2 μM (R = 0.9995), with a limit of detection (LOD) as low as 15 nM. We tested the diameters and potential values of DNI-4 and HSA to disclose the variation in microstructure before and after the recognition event. Furthermore, we test and compare the sensitivity and association constants of DNI-4 and two control compounds, neutral DNI-1 and mono-quaternary-ammonium-salt-substituted DNI-5. The results indicate the electronic interaction is a key factor for recognition and DNI-4 with the most positive groups is the best probe for HSA. At last, DNI-4 is successfully applied to probe HSA in the Hela cells indicating the potential application in fluorescent sensing and bioimaging.