Fluorescence Patterns from Supramolecular Polymer Assembly and Disassembly for Sensing Metallo- and Nonmetalloproteins

Abstract

Critical aggregation concentration (CAC) of surfactants is lowered when polyelectrolytes act as counterions. At a concentration in between the CACs of the surfactant and the polymer−surfactant complex, protein-induced disassemblies can be achieved. This is because, when proteins competitively bind to the polyelectrolytes, the surfactants are not capable of sustaining a micelle-type assembly at this concentration. Since these amphiphilic aggregates are capable of noncovalently sequestering hydrophobic guest molecules, the protein binding induced disassembly process also results in a guest release from these assemblies. We show here that the change in fluorescence with different proteins is dependent not only on the nature of the polymer−surfactant complex, but also on the fluorescent transducer. Two processes can be responsible for the observed fluorescence change: fluorophore guest release from the hydrophobic interior of the assembly and excited state quenching due to complementary components in the analyte. The latter mechanism is especially possible with metalloproteins. We show here that an excited state quenching is possible at nanomolar concentrations of the proteins, while the disassembly based fluorescence reduction is the dominant pathway at micromolar concentrations.