Novel fluorescent amphiphilic copolymer probes containing azo-tetraphenylethylene bridges for azoreductase-triggered release

Abstract

Enzyme-sensitive amphiphilic polymers play an important role as smart materials in drug delivery and biological detection. Azobenzene, an azoreductase active site, has received significant attention in recent years. Herein, we synthesized a novel aggregation-induced emission (AIE) fluorescent probe of amphiphilic block copolymer PCL-TPE-Azo-PEG based on an azoreductase response, in which tetraphenylethylene (TPE) conjugated to an azo group provides the junction between the hydrophilic and hydrophobic (PEG and PCL) chain segments. In phosphate buffer solution, the resulting amphiphilic polymers self-assembled into rod-like micelles that are non-fluorescent owing to the quenching effect of the azo moieties on the AIE activity of TPE. In the presence of a reducing agent (such as azoreductase or Na₂S₂O₄), the azo bond was broken and the assemblies fragmented into PEG and PCL chain segments. Following disassembly of the micelles, the AIE effect of TPE was activated because the TPE moiety is encapsulated in the resulting PCL aggregation. Furthermore, the amphiphilic polymer could encapsulate drugs, such as DOX, to form drug-loaded micelles in PB solution. And the micelles indicated an increasing fluorescence with drug release under the action of reducing agent. This amphiphilic block copolymer could potentially be applied in biosensing and controlled drug delivery for colonic conditions.