Differentiation of HSA and BSA and Instantaneous Detection of HSO(3)(–) Using Confined Space of Serum Albumins and Live Cell Imaging of Exogenous/Endogenous HSO(3)(–)

[Image: see text] The limitations of prevailing probes for the detection of human serum albumin (HSA) and HSO(3)(–) make it challenging to apprehend the cooperative effect of both HSA and HSO(3)(–) in biological systems. Herein, we present a multi-responsive fluorescent probe MGTP, which distinguishes HSA from bovine serum albumin (BSA) through an ∼104-fold fluorescence enhancement at an emission maximum of 595 nm with HSA and only an ∼10-fold increase at an emission maximum of 615 nm with a shoulder at 680 nm with BSA. The absorbance spectrum of MGTP also discriminates HSA and BSA with the respective absorption maxima at 543 nm and at 580 nm. MGTP in the confined space of HSA or BSA undergoes instantaneous conjugate addition of HSO(3)(–) and results in a ratiometric change in fluorescence intensity with diminishing of red fluorescence (600 nm) and emergence of green fluorescence (515 nm). MGTP in the absence of SAs does not react with HSO(3)(–) in phosphate-buffered saline buffer and reacts sluggishly in the dimethyl sulfoxide–water 1:1 mixture. The limit of detection values for the detection of HSA and HSO(3)(–) are 4 and 6.88 nM, respectively. The drug binding studies reveal that MGTP preferably confines itself at the bilirubin site of HSA. In MCF-7 cancer cells, MGTP is localized into mitochondria and reveals both exogenous and endogenous visualization of HSO(3)(–) through a change in fluorescence from the red to green channel.