Biosensors can be developed using quantum dots (QDs). An inorganic nucleus with organic molecules attached to its surface is referred to as a QD, and they are a type of new fluorescent nanomaterial. QDs possess unique excellent optical properties and chemical properties, including broad excitation spectra, adjustable particle sizes, confined emission spectra, emission of multiple fluorescence colors, superior signal brightness, and extended fluorescence lifetime. QDs have abundant functional groups, which make it easy to form hybrid nanomaterials that perform analytically well. With functionalized sensing systems, we can detect metal ions, biomarkers, and antibiotics sensitively and selectively through the hybridization of QDs with nanomaterials. In this chapter, we first introduce the research trends in the application of QDs and then discuss their surface modification for biological applications.