Quantum Dots for Biomedical Biosensing, NIR-II Bioimaging, and Phototherapy: Materials Design, Signal Transduction, and Translational Barriers.

Quantum dots (QDs) have emerged as standout candidates among inorganic nanomaterials, distinguished by their tunable photoluminescence, exceptional photostability, and size-dependent quantum confinement effects that enable tailored emission from the visible to the near-infrared range. These remarkable optical properties, coupled with broad absorption spectra and high quantum yields, have positioned QDs at the forefront of diverse biomedical applications. This review provides a systematic overview of QDs fabrication strategies, with a focus on bottom-up approaches, such as colloidal synthesis, hydrothermal, and solvothermal methods, as well as emerging biomimetic synthesis inspired by natural biomineralization. Additionally, we offer an in-depth discussion of cutting-edge QDs applications across three key areas: high-sensitivity biosensing for biomarker detection and point-of-care diagnostics; bioimaging, including fluorescence, magnetic resonance, and photoacoustic imaging; and intelligent nanocarrier-based cancer therapeutics, encompassing targeted drug delivery and imaging-guided precision surgery. Furthermore, this review examines the key challenges and optimization strategies for QDs in biomedical applications, with a particular focus on the critical bottlenecks impeding their clinical translation. By analyzing these barriers and outlining future directions, it aims to provide both theoretical and practical guidance for translating QDs from laboratory-scale innovations into routine clinical practice.