How Functionalization Affects the Detection Ability of Quantum Dots

Quantum dots (QDs) have outstanding optical, physiochemical, and chemical properties that make them an extraordinary alternative to fluorescent organic dyes. Recently, they have become excellent photoluminescent labels for detection and diagnosis in medical sciences; they are also used for the detection of target analytes in a variety of scientific fields, such as agricultural, food, and environmental sciences. These extensive applications are made possible by QDs’ high potential for surface state changes when coupled with macromolecules, such as antibodies, aptamers, proteins, lipids, and other small molecules. QDs can be functionalized by complicated or simple procedures depending on their type. The bioconjugation of carbon QDs (CQDs) is more facile due to the possibility of one-pot synthesis and functionalization with carboxylic and amine groups through the accurate selection of carbon precursors. Bioconjugation and functionalization protocols for semiconductor QDs (SQDs) are more complicated compared with those reported for carbon-based QDs and organic dyes. The functionalization of QDs affects their photoluminescence and chemical characteristics, size distribution, in vivo and in vitro detection abilities, and toxicity. Functionalized QDs may also act as antioxidants and scavenge reactive oxygen species. This chapter briefly reviews several functionalization methods and shows how QDs’ surface chemistry determines their target applications. Conjugated QDs’ applications in cell and tissue imaging, disease diagnosis and treatment, and biomedical sensing are discussed.