Aggregation-induced emission (AIE) dye-polymer nanoformulations via electrostatic complexation

Introduction
Aggregation-induced emission (AIE) dyes are a newly discovered class of molecules that have gained significant research attention. AIE dyes present enhanced emission intensity upon their aggregation with other molecules.
Methods
In this research, the sodium tetraphenylethylene 4,4′,4″,4‴-tetrasulfonate dye was electrostatically complexated with a series of poly(2-(diisopropylamino)ethyl methacrylate-co-2-(dimethylamino)ethyl methacrylate-co-oligoethylene glycol methyl ether methacrylate), P(DIPAEMA-co-DMAEMA-co-OEGMA) multiresponsive terpolymers. Different ratios of terpolymers to dye were used to investigate the aggregation-induced emission phenomenon and its dependence on dye concentration. All experiments were performed in aqueous solutions, while interaction with fetal bovine serum (FBS) proteins was also tested.
Results
Dynamic light scattering (DLS) measurements and Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy confirmed the successful complexation of dye with all terpolymers and their stability. Ultrasmall nanoparticles with a hydrodynamic radius of 5-7 nm were achieved across various formulations. As the polymers utilized are thermoresponsive, temperature-induced DLS measurements showcased the thermoresponsiveness of the polymer-dye nanosystems. Photophysical studies using ultraviolet-visible (UV-Vis) and fluorescence (FS) spectroscopy revealed the aggregation-induced emission phenomenon and enhanced emission intensity compared to that of the pure dye. All nanoformulations presented no significant interactions with FBS. Finally, the fluorescence emission intensity of nanoformulations in FBS medium was retained.
Conclusions
Polymer-dye thermoresponsive nanoformulations presenting the AIE phenomenon were fabricated via an easily scalable method. Further biocompatibility and in vivo tests can confirm the stealthiness and the ability of such nanoparticles to penetrate the blood-brain barrier. These promising ultrasmall nanosystems can find applications in photochemistry and bioimaging, where enhanced emission intensity is required.