Wet chemistry-based processing of tunable polychromatic carbon quantum dots for multicolor bioimaging and enhanced NIR-triggered photothermal bactericidal efficacy

Abstract

A strategy for the processing of photoluminescence emission tunable multicolor carbon quantum dots has been adopted based on the controllable acidic strength [different ratio mixtures of sulfuric and phosphoric acids (S:P)] using a single polyphenolic precursor. 1,3,5-trihydroxybenzene, a three-fold symmetric (C3h symmetry) triangulogen bearing -OH group at the meta position, was judiciously chosen to undergo dehydration facilitated condensation and carbonization suitably via a tri-molecular reaction route in a dehydrating acid medium. Polyaromatic-polyphenolic CQDs with multicolor emissions [blue (B-CQDs), green (G-CQDs), and yellow (YCQDs)] could be rapidly obtained through a facile wet chemistry-based thermal heating process. The mechanism of regulated bottom-up growth of CQD particles involved tri-molecular ring cyclization. These multicolor luminous CQD probes enabled intense multicolor cellular imaging throughout the entire visible range because of their good biocompatibility, photostability, and effective intracellular distribution. Moreover, Y-CQDs with larger polyaromatic sp2 domains and higher oxidized surfaces exhibited a high photothermal conversion efficiency (PCE ~ 32.6 +/- 1 %) and thus exhibited remarkable NIR-light responsive photothermal bactericidal activity. Our results demonstrate that hyperthermia-induced bactericidal activity is due to the elevated reactive oxygen species (ROS) amplification and membrane damage of Bacillus subtilis. This study provides a potential alternative for the multicolor imaging guided CQDs-based phototheranostic.