Abstract
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.
Highlights
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
Despite the extensive research into synthesis and characterization of carbon dots (CDs) for a variety of applications, there is a clear gap in the literature as CDs with both red emission fluorescence and two-photon absorption (TPA) capabilities (RTCDs) have not been extensively reported
Most synthesized Red-emissive two-photon excitable CDs (RTCDs) still have some downsides in some aspects and further modifications are required for practical requirements
Summary
CDs have proved to be useful for various applications owing to their excellent photophysical, physiochemical, and biological properties[12]. To guarantee the effectiveness of PDT, the photosensitizer should be targeted to the nucleus or mitochondria, regions of the cell most susceptible to ROS damage[114], as well as a large absorption coefficient in the NIR is required to ensure sufficient tissue penetration[49] In this regard, RTCDs possess an excellent NIR absorption coefficient with ability to excite and emit in red/NIR regions under exposure to low power laser irradiation resulting in their high efficiency at deeper tissue depths[33]. Nitrogen-doped RTCDs prepared from paminoazobenzene showed nucleolar targeting, intracellular ROS generation under laser irradiation, and the capacity for real-time fluorescence monitoring of dynamic changes in the nucleolus during PDT49 These characteristics encouraged the researchers to investigate the capability of the RTCDs for use in PDT. These properties include (i) optimal optical specifications, (ii) enhanced tumor targetability and therapeutic effect on the deep tumors, (iii) regulate the catalytic activity of RTCDs to overcome tumor hypoxia and to achieve higher treatment efficiency; all need to be addressed in future studies
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