블록 공중합체 마이셀을 이용한 금 나노입자와 유기염료의 자가 정렬 구조 제어와 pH 센서 응용

Abstract

Block copolymers can produce periodic nanostructures, the size and morphology of which can be tuned by the molecular weight of each block. For instance, in a selective solvent, diblock copolymers self-associate into spherical micelles consisting of soluble coronas and insoluble cores. Since the chemical structures of core and corona are quite different, one can selectively place a number of functionalities such as inorganic NPs into core, interface, or coronas of micelles by adjusting their chemical affinity with each block. In this regard, particularly interesting phenomena can be found from the micellar assemblies with metal NPs and fluorophores such as dye molecules because the fluorescence of dyes can be strongly engineered by the plasmonic effect of metal NPs. In this study, we prepared NP-fluorophore assemblies by employing micelles of polystyrene-block-poly(acrylic acid), PS-PAA copolymers in an aqueous solution. In water, that is a selective solvent for PAA block, PS-PAA diblock copolymers self-associate into spherical micelles of PS core and PAA corona. We first encapsulated surface-modified Au NPs into the PS core of micelles. Then, positively charged fluorescent dyes of rhodamine 123 (R123) were further conjugated to the negatively charged PAA corona of micelles by electrostatic interaction. Since carboxylate anions in PAA block are weak acid, the degree of binding of R123 to PS-PAA micelles can be adjusted by pH of the solution. Furthermore, Au NP in the core can strongly quench the fluorescence of R123 by the plasmonic effect. Therefore, by changing pH value, we were able to control the fluorescence intensity of R123 in the micellar structure, the principle of which can be applicable to pH sensor.