Dependence of phthalocyanine-based fluorescence on albumin structure: A fluorescent probe for ascorbic acid

[Display omitted] •An albumin-encapsulated fluorescence probe for ascorbic acid: the probe consists of an SiPc fluorophore and TEMPO radicals.•The fluorescence intensity reflects the structural changes of serum albumin, such as folding ↔ unfolding and α-helix ↔ β-sheet.•Usefullness for developing fluorescent probes using the structural change of albumin. In this study, we have investigated the environmental dependence of the fluorescent probe for detecting ascorbic acid. The fluorescent probe used herein, R2c, consists of silicon phthalocyanine and two 2,2,6,6-tetramethyl-1-piperidinyloxy radicals, and is encapsulated by the dimer of bovine serum albumin (BSA). Due to this encapsulation, the R2c@(BSA)2 complex was prevented from reacting with various redox species in biological systems, but reacted selectively with ascorbic acid. The fluorescence of R2c@(BSA)2 after ascorbic acid addition depended on the pH: the fluorescence intensity increased in the order pH 6