Surface modification and chemical functionalization of carbon dots: a review

Surface functional groups strongly affect the properties of carbon dots (CDs). Amino, carboxy, and hydroxy groups are most commonly encountered in CDs, and they can be introduced via covalent and noncovalent modification. This article (with 116 refs.) reviews the progress made in the past few years. Following an introduction into the field, a large section covers methods for covalent modification (via amide coupling reactions, silylation, and other reactions including esterification, sulfonylation and copolymerization). Next section reviews methods for noncovalent modifications (π interactions, complexation/chelation, and electrostatic interactions). The resulting modified CDs are powerful nanomaterials for targeting and extracting analytes, and in drug release. The modification of the surface also affects fluorescence quantum yields, complexation capacity, the color of fluorescence, and their quenching capability. Current challenges are critically assessed in the concluding section. Graphical abstract The modification methods of carbon dots (CDs) includes covalent and noncovalent. Covalent modifications include amidation, silylation, esterification, sulfonylation and copolymerization reaction. Noncovalent modifications include electrostatic interactions, complexation and π interactions.