Structure change of mixed shell polymeric micelles and its interaction with bio-targets as probed by the 1-anilino-8-naphthalene sulfonate (ANS) fluorescence

Multicompartment polymeric micelles (MPMs) have attracted broad interest, due to their intriguing advantages. Although a plethora of MPMs have been designed recently, characterization of the fine hierarchical compartmented structure and dynamic conformation change of MPMs are still challenging. In this contribution, we reported a strategy to detect thermo-induced structure rearrangement of one kind of MPMs--mixed shell polymeric micelles (MSPMs) and its interaction with bio-targets such as proteins by the means of the 1-anilino-8-naphthalene sulfonate (ANS) fluorescence. It is found that there exists a specific fluorescent emission phenomena characterized by a strong blue-shifted emission maximum and enhanced quantum yield when ANS interacts with MSPMs with a mixed shell consisting of homogeneously mixed poly(ethylene oxide) (PEG) and poly(N-isopropylacryamide) (PNIPAM). Such emission maximum was exploited to probe the structure evolution of MSPMs during the collapse of the thermo-sensitive PNIPAM component by heating. The variation of the emission behavior of ANS during heating is in line with the structure rearrangement of the MSPMs which critically depends on the nature of the micellar core. Binding of a model protein-carbonic anhydrase B (CAB) during heating induced denaturation to the hydrophobic PNIPAM domains of the MSPMs was also reflected by the change of the emission behavior of ANS.