Ratiometric fluorescence, electrochemiluminescence, and photoelectrochemical chemo/biosensing based on semiconductor quantum dots

Colloidal semiconductor nanocrystals or quantum dots (QDs) have been facilitating the development of sensitive fluorescence sensors over the past decade, due to their unique photophysical properties, versatile surface chemistry and ligand binding ability, and the possibility of the encapsulation in different materials or attachment to different functional materials, while retaining their native luminescence property. The optical metal ion chemosensors with high sensitivity and selectivity have been developed due to the importance of the metal ions' fundamental roles, possessed in a wide range of biological processes and the aquatic environment. This review addresses the different sensing strategies with chemically modified QD hybrid structures for the sensing of metal ions in aqueous solution or an in vivo environment, and discusses the photophysical mechanisms in the different sensor systems while comparing their detecting/sensing selectivity. The perspectives for the future potential developments in QD based optical sensing for metal ions are discussed.