Synthesis strategies, luminescence mechanisms, and biomedical applications of near-infrared fluorescent carbon dots

Carbon dots (CDs) have attracted significant interest as one of the most emerging photoluminescence (PL) nanomaterials. However, the realization of CDs with dominant near‐infrared (NIR) absorption/emission peaks in aqueous solution remains a great challenge. Herein, CDs with both main NIR absorption bands at 720 nm and NIR emission bands at 745 nm in an aqueous solution are fabricated for the first time by fusing large conjugated perylene derivatives under solvothermal treatment. With post‐surface engineering, the polyethyleneimine modified CDs (PEI‐CDs) exhibit enhanced PL quantum yields (PLQY) up to 8.3% and 18.8% in bovine serum albumin aqueous and DMF solutions, which is the highest PLQY of CDs in NIR region under NIR excitation. Density functional theory calculations support the strategy of fusing large conjugated perylene derivatives to achieve NIR emissions from CDs. Compared to the commercial NIR dye Indocyanine green, PEI‐CDs exhibit excellent photostability and much lower cost. Furthermore, the obtained PEI‐CDs illustrate the advantages of remarkable two‐photon NIR angiography and in vivo NIR fluorescence bioimaging. This work demonstrates a promising strategy of fusing large conjugated molecules for preparing CDs with strong NIR absorption/emission to promote their bioimaging applications.

Toward Strong Near‐Infrared Absorption/Emission from Carbon Dots in Aqueous Media through Solvothermal Fusion of Large Conjugated Perylene Derivatives with Post‐Surface Engineering

Mitochondria-targeted smart AIEgens: Imaging and therapeutics

Carbon dots (CDs), as one new class of carbon nanomaterials with various structure and extraordinary physicochemical properties, have attracted tremendous interest for their potential applications in tumor theranostics, especially in targeted bioimaging and therapy. In these areas, CDs and its derivatives have been employed as highly efficient imaging agent for photoluminescence bioimaging of tumors cells. With unique structure, optical and/or dose attention properties, CDs have been harnessed in various nanotheranostic strategies for diverse tumors through integrating with other functional nanoparticles or utilizing their inherent physical properties. Up to now, CDs have been approved as novel biomaterials by their excellent performances in precise targeted bioimaging and therapy for tumors. Herein, the latest progress in the development of CDs in targeted bioimaging and tumor therapy are reviewed. Meanwhile, the challenges and future prospects of the application of CDs in promising nanotheranostic strategies are discussed and proposed.

Recent progress of carbon dots in targeted bioimaging and cancer therapy

As a new solution-processable laser material, carbon dots (CDs) offer advantages of non-toxicity, low cost, and high stability, which are conducive to the sustainable development of miniaturized lasers. We prepared full-color CDs (FC-CDs) with bright-blue, green, yellow, red, deep-red, and near-infrared (NIR) fluorescence. Their photoluminescence emission ranged from 431 to 714 nm. The FC-CDs showed narrow full widths at half maximum in the range of 44-76 nm, with concurrent high radiative transition rates (KR ) of 0.54-1.74 × 108 s-1 ; their performance is comparable to that of organic laser dyes, indicating their good gain potential for lasers. Laser pumping of the FC-CDs gave laser outputs at 467.3, 533.5, 577.4, 616.3, 653.5, and 705.1 nm, spanning from blue to NIR region, and covering 140% of the NTSC color gamut. The FC-CDs showed high Q-factors (2000-5500), appreciable gain coefficients (9-21.5 cm-1 ), and better stability (∼100%@4-7 h) than commercial laser dyes. These excellent properties make them suitable for high-quality, colorful, speckle-free laser imaging and dynamic holographic display. Our findings will be helpful in promoting the practical applications and development of solution-processable CD-based lasers. This article is protected by copyright. All rights reserved.

Carbon Dots with Blue-to-Near-Infrared Lasing for Colorful Speckle-Free Laser Imaging and Dynamical Holographic Display.

Generating long-wavelength absorption bands with enhanced deep red fluorescence and photothermal performance in fused carbon dots aggregates

Obesity is a major global health problem that significantly increases the risk of many other diseases. Herein, a facile method of suppressing lipogenesis and obesity using L-arginine-functionalized carbon dots (L-Arg@CDots) is reported. The prepared CDots with a negative surface charge form stronger bonds than D-arginine and lysine with L-Arg in water. The L-Arg@CDots in the aqueous solution offer a high photoluminescence quantum yield of 23.6% in the red wavelength region. The proposed L-Arg functionalization strategy not only protects the red emission of the CDots from quenching by water molecules but also enhances the intracellular uptake of L-Arg to reduce lipogenesis. Injection of L-Arg@CDots can reduce the body weight increase in ob/ob mice by suppressing their food intake and shrinking the white adipose tissue cells, thereby significantly inhibiting obesity.

L-Arginine-Functionalized Carbon Dots with Enhanced Red Emission and Upregulated Intracellular L-Arginine Intake for Obesity Inhibition.

Abstract：As a new type of photothermal nanomaterial， carbon dots (CDs) have attracted extensive attention in tu• mor therapy.However， limited carbon dots can achieve high photothermal conversion efficiency， especially in the deep red (DR)/near-infrared (NIR) region.Beyond that， the targeting of carbon dots to tumors is also an important issue that we urgently need to solve.In this review， some practical strategies， including size tuning， elemental dop• ing， surface engineering， semiconductor coupling， and biomacromolecule coating， are introduced to enhance the deep red or near-infrared absorption and photothermal conversion efficiency of carbon dots.Based on these strate• gies， suitable carbon dots or their complexes are constructed to achieve targeted therapy for tumors.Finally， we hope to establish an efficient tumor identification and photothermal therapy system to realize the clinical application of car• bon dots.We hope this integrated system has important scientific significance and application value in solving tumorrelated problems and promoting health development. Key words： carbon 

Research Progress on Photothermal Property of Deep Red to Near-infrared Carbon Dots

A key challenge to enhance the therapeutic outcome of photothermal therapy (PTT) is to improve the efficiency of passive targeted accumulation of photothermal agents at tumor sites. Carbon dots (CDs) are an ideal choice for application as photothermal agents because of their advantages such as adjustable fluorescence, high photothermal conversion efficiency, and excellent biocompatibility. Here, we synthesized polylysine-modified near-infrared (NIR)-emitting CDs assemblies (plys-CDs) through post-solvothermal reaction of NIR-emitting CDs with polylysine. The encapsulated structure of plys-CDs was confirmed by determining morphological, chemical, and luminescent properties. The particle size of CDs increased to approximately 40 ± 8 nm after polylysine modification and was within the size range appropriate for achieving superior enhanced permeability and retention effect. Plys-CDs maintained a high photothermal conversion efficiency of 54.9 %, coupled with increased tumor site accumulation, leading to a high efficacy in tumor PTT. Thus, plys-CDs have a great potential for application in photothermal ablation therapy of tumors. 

Polylysine-modified near-infrared-emitting carbon dots assemblies: Amplification of tumor accumulation for enhanced tumor photothermal therapy.

Carbon nanodots (CDs) with high photothermal performance are ideal candidates for tumor photothermal therapy (PTT). Herein, we investigated the photothermal performance of CDs synthesized from urea and citric acid via solvothermal method in dimethyl sulfoxide (DMSO) at different temperatures. Photothermal conversion efficiency (PCE) of up to 61.3% was obtained in the CDs synthesized at 150 °C (150-CDs), which is much better than the CDs synthesized at 180 °C (180-CDs). By analyzing the morphologies, chemical structures, and absorption spectra of these CDs, we found that the photothermal effect of the CDs was due to the lattice vibration of their carbonized cores, in which moderate carbonization with high content of surface carbonyl group (C=O) contributed for enhanced absorption band in deep red region with improved photothermal performance. Moreover, we also demonstrated that 150-CDs with moderate carbonized cores exhibit much better tumor PTT performance in vivo than 180-CDs with higher carbonized cores. Appendix S1: Supporting Information Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. 

Toward Rational Design of Carbon Nanodots with High Photothermal Efficiency for Tumor Photothermal Therapy

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