Rational Design of Capping Ligands of Quantum Dots for Biosensing

Quantum dots have been widely applied in biosensing due to their outstanding optical properties. The emissions of quantum dots are mainly determined by their composition and size, as described by the Brus's equation. Somehow, in this case, their emissions are hardly regulated reversibly and responsively, which are unsuitable for biosensing and biodetection. In the last decade, capping ligands have been used for designing biosensors because of their responsive regulation on the photoluminescence of quantum dots. Here, we first summarize the advances in characterization and calculation specific for ligands, which have helped to provide insights into the photoluminescence process and energy band theory of quantum dots. We then review two ways of ligand design that influence the optical properties of quantum dots: affecting the process of photoluminescence, or the orbital/electronic structure. In the latter case, the atoms on both the ligand and the surface of the quantum dot interact to affect the energy band structure of the quantum dot core. Examples are presented of how these quantum dots that possess responsive properties due to the design of the ligands have been applied to sensing. With further exploration, we hope to see advances in the fundamental understanding of the energy band structures and practical applications of these quantum dots.