Design principles and biological applications of red-emissive two-photon carbon dots

Carbon dots have been gaining attention in the field of nanobiotechnology due to their superior photostability, high water solubility, ease of synthesis and surface functionalization, chemical inertness, low toxicity, and excellent biocompatibility. They also exhibit good two-photon absorption and unique tunable optical properties across a wide range of wavelengths, from ultraviolet to near infrared endowing them with potential for a variety of biological applications. Recently, there has been a growing interest in the synthesis and development of red-emissive two-photon carbon dots. Here we present recent progress in the design requirements for red-emissive two-photon carbon dots, and review current state-of-the-art systems, covering their applications in bioimaging, biosensing, and photothermal and photodynamic therapy. Carbon dots are suitable for a range of biological applications due to their unique physicochemical properties and biological behavior. This Review summarizes research related to the emerging field of red-emissive two-photon carbon dots for bioimaging, biosensing, and phototherapeutic applications.