Designing and photophysical properties of optically active coacervate droplets

Abstract

Coacervate droplets have tremendous importance in various fields. Here, we have investigated the synthesis, characterization, and functional applications of the distinct coacervate systems: ATP droplets, MSAcapped CdTe QD droplets, and CD droplets. Using spectroscopic techniques, including UV-visible spectroscopy and confocal laser scanning microscopy (CLSM), coupled with quantitative equilibrium partition coefficient (K) measurements, we demonstrated the spontaneous sequestration of pyranine, a photoacid, within all the droplet systems. Notably, pyranine exhibited varying partition coefficients: 7.58 ± 1.2 in ATP droplets, 56.32 ± 5.6 in QD droplets, and 14.8 ± 2.1 in CD droplets, with the highest values observed in QD droplets indicating superior sequestration efficiency. Furthermore, we demonstrated preferential sequestration of the anticancer drug-DOX in pyranine-loaded CD droplets with a partition coefficient of 2.56 ± 0.3. The carbon dot-based coacervates proved particularly advantageous for therapeutic applications due to their biocompatibility, low toxicity, and chemical inertness compared to the potentially toxic QD-based systems. The sequestration mechanism was attributed to the hydrophobic and electrostatic interactions between the guest molecules and droplet matrices, allowing for efficient drug loading without chemical modification of the carriers. The most significant finding was the photo-responsive assembly and disassembly of these coacervate droplets in the presence of pyranine, as characterized by CLSM. This lighttriggered behaviour, combined with the differential sequestration capabilities across droplet systems, positions these materials as promising candidates for diverse biomedical applications, particularly targeted drug delivery to tumor cells. This work advances the fundamental understanding of stimuli-responsive coacervate systems while demonstrating their practical utility in controlled therapeutic release.