Redox-Mediated Quantum Dots as Fluorescence Probe and Their Biological Application

Abstract

Semiconductor quantum dots (QDs) as a new class of fluorescent labels have become valuable fluorescent platforms for biological applications due to their unique optical properties. In addition to their well-known size-dependent emission spectra, QDs are extremely sensitive to the presence of additional charges either on their surfaces or in the surrounding environment, which leads to a variety of optical properties and electronic consequences. By using thiols as bridges between QDs and redox-active ligands, the fluorescence effects of functionalized QD conjugates were investigated because QDs are prone to exchange electrons or energy with the attached ligands upon excitation, resulting in their fluorescence change. The recovery/enhancement or quenching of the QD conjugate fluorescence could be reversibly tuned with the transformation with the redox state of surface ligands. Moreover, quenching of the QD emission is highly dependent on the relative position of the oxidation levels of QDs and the redox-active ligand used. Importantly, the utility of these systems could enhance the compatibility of functionalized QDs in biological systems and can be used for monitoring the fluorescence change to trace in vitro and intracellular target analyte sensing. We believe that redox-mediated quantum dots as fluorescence probe are a significant step forward toward biosensing.