Dual-Channel Recognition of Human Serum Albumin and Glutathione by Fluorescent Probes with Site-Dependent Responsive Features

Design of chemical probes with high specificity and responses are particularly intriguing. In this work, a fluorescent probe (M–OH–SO₃) with dual-channel spectral responses toward human serum albumin (HSA) is presented. By employing dinitrobenzenesulfonate as a recognition site as well as a fluorescence quencher, probe M–OH–SO₃ displayed weak fluorescence, which, nevertheless, exhibits extensive yellow (575 nm) and red (660 nm) fluorescence emissions toward HSA under excitations at 400 and 500 nm, respectively. Interestingly, M–OH–SO₃ displayed the best performance toward HSA with distinctly higher selectivity than that of its counterparts M–SO₃, M–H–SO₃, and M–F–SO₃, which were prepared simply by modulating the functional group at the ortho position of the dicyanoisophorone core. Molecular docking results revealed that M–OH–SO₃ possesses the lowest binding energy among the tested derivatives and accordingly the strongest binding affinity. Probe M–OH–SO₃ showed a good linear relationship toward HSA in a range of 0.5–18 μM with a limit of detection of 35 nM. Cell imaging results demonstrated that probe M–OH–SO₃ could visualize the variation HSA levels in hepatocarcinoma cells. In addition, probe M–OH–SO₃ could also be employed for the recognition of glutathione through the cleavage of the dinitrobenzenesulfonate group along with an enhancement of emission at 575 nm. The site-dependent properties inspired a novel paradigm for design of fluorescent probes with optimized selectivity and responses.