An easy and smart way to explore the light-emitting responses of carbon dot and doxorubicin hydrochloride assembly: white light generation and pH-dependent reversible photoswitching

Abstract

The excellent and extensive application of carbon dots (CDs) as drug delivery systems, bioimaging probes as well as in different optoelectronic devices with tunable emission properties influenced us to make a bridge between their drug delivery and light-emitting responses. In this scenario, we synthesized and purified CD from citric acid (CA) and urea using microwave method and thoroughly characterized them using several spectroscopic and microscopic techniques. The interesting pH dependence and pH reversibility of the synthesized CD system was studied. The loading of the anticancer drug doxorubicin hydrochloride (Dox) in CD generated white light (WL) when the pH of the solution changed from pH 12 to 2 and this WL system showed reversible “ON–OFF” photoswitching between pH 2 and 12. The probable mechanism of this WL generation was further explored to be fluorescence resonance energy transfer (FRET) between the respective components and consequently, for pH-dependent reversible photoswitching, the mechanism was established to be the pH responses of both CD and Dox. The WL system also retained its optical properties in the agarose gel matrix. Therefore, this study may open a new horizon in modelling a smart CD-based drug delivery system with interesting light-emitting properties, and thus can be applicable in constructing future drug delivery as well as light-emitting devices.