Ultrasmall Near‐Infrared Non‐cadmium Quantum Dots for in vivo Tumor Imaging

The high tumor uptake of ultrasmall near‐infrared quantum dots (QDs) attributed to the enhanced permeability and retention effect is reported. InAs/InP/ZnSe QDs coated by mercaptopropionic acid (MPA) exhibit an emission wavelength of about 800 nm (QD800‐MPA) with very small hydrodynamic diameter (<10 nm). Using 22B and LS174T tumor xenograft models, in vivo and ex vivo imaging studies show that QD800‐MPA is highly accumulated in the tumor area, which is very promising for tumor detection in living mice. The ex vivo elemental analysis (Indium) using inductively coupled plasma (ICP) spectrometry confirm the tumor uptake of QDs. The ICP data are consistent with the in vivo and ex vivo fluorescence imaging. Human serum albumin (HSA)‐coated QD800‐MPA nanoparticles (QD800‐MPA‐HSA) show reduced localization in mononuclear phagocytic system‐related organs over QD800‐MPA plausibly due to the low uptake of QD800‐MPA‐HSA in macrophage cells. QD800‐MPA‐HSA may have great potential for in vivo fluorescence imaging.     

A Red Emissive Two‐Photon Fluorescence Probe Based on Carbon Dots for Intracellular pH Detection

Intracellular pH is closely related with many biological processes, including cellular proliferation, apoptosis, endocytic processes, signal transduction, and enzymatic activity. The use of fluorescent probes has become an essential method for intracellular pH detection, but existing fluorescent probes have substantial limitations, such as requiring tedious synthetic preparation, suffering from an inappropriate response range and insufficiently long emission wavelength. In this work, a red emissive two‐photon fluorescence probe based on carbon dots (pH‐CDs) is fabricated using a facile one‐pot hydrothermal method for the monitoring of intracellular pH. pH‐CDs possess a variety of superior properties, including high selectivity, excellent photostability, and low cytotoxicity. Furthermore, they exhibit a pH‐sensitive response in the range of 1.0–9.0 and a linear range of 3.5–6.5, which is desirable for tracking the pH value in living cells. It is demonstrated that the pH‐dependent fluorescence signal is regulated via switching between aggregation and disaggregation of CDs. More importantly, pH‐CDs can be successfully applied to sense and visualize pH fluctuation in cells, tissue, and zebrafish. These findings suggest that the as‐prepared pH‐CDs probe has significant potential for practical application in living systems.     

Near‐Infrared Excitation/Emission and Multiphoton‐Induced Fluorescence of Carbon Dots

Carbon dots (CDs) have significant potential for use in various fields including biomedicine, bioimaging, and optoelectronics. However, inefficient excitation and emission of CDs in both near‐infrared (NIR‐I and NIR‐II) windows remains an issue. Solving this problem would yield significant improvement in the tissue‐penetration depth for in vivo bioimaging with CDs. Here, an NIR absorption band and enhanced NIR fluorescence are both realized through the surface engineering of CDs, exploiting electron‐acceptor groups, namely molecules or polymers rich in sulfoxide/carbonyl groups. These groups, which are bound to the outer layers and the edges of the CDs, influence the optical bandgap and promote electron transitions under NIR excitation. NIR‐imaging information encryption and in vivo NIR fluorescence imaging of the stomach of a living mouse using CDs modified with poly(vinylpyrrolidone) in aqueous solution are demonstrated. In addition, excitation by a 1400 nm femtosecond laser yields simultaneous two‐photon‐induced NIR emission and three‐photon‐induced red emission of CDs in dimethyl sulfoxide. This study represents the realization of both NIR‐I excitation and emission as well as two‐photon‐ and three‐photon‐induced fluorescence of CDs excited in an NIR‐II window, and provides a rational design approach for construction and clinical applications of CD‐based NIR imaging agents.     

Excitation‐Dependent Photoluminescence from Single‐Carbon Dots

Carbon dots (CDs) are carbon‐based fluorescent nanoparticles that can exhibit excitation‐dependent photoluminescence (PL) “tunable” throughout the entire visible range, interesting for optoelectronic and imaging applications. The mechanism underlying this tunable emission remains largely debated, most prominently being ascribed to dot‐to‐dot variations that ultimately lead to excitation‐dependent ensemble properties. Here, single‐dot spectroscopy is used to elucidate the origin of the excitation‐dependent PL of CDs. It is demonstrated that already single CDs exhibit excitation‐dependent PL spectra, similar to those of the CD ensemble. The single dots, produced by a facile one‐step synthesis from chloroform and diethylamine, exhibit emission spectra with several characteristic peaks differing in emission peak position and spectral width and shape, indicating the presence of distinct emission sites on the CDs. Based on previous work, these emission sites are related to the sp² subregions in the carbon core, as well as the functional groups on the surface. These results confirm that it is possible to integrate and engineer different types of electronic transitions at the nanoscale on a single CD, making these CDs even more versatile than organic dyes or inorganic quantum dots and opening up new routes toward light‐emission engineering.     

Integration of Indocyanine Green Analogs as Near‐Infrared Fluorescent Carrier for Precise Imaging‐Guided Gene Delivery

Codelivery of diagnostic probes and therapeutic molecules often suffers from intrinsic complexity and premature leakage from or degradation of the nanocarrier. Inspired by the “Y” shape of indocyanine green (ICG), the dye is integrated in an amphiphilic lipopeptide (RNF). The hydrophilic segment is composed of arginine‐rich dendritic peptides, while cyanine dyes are modified with two long carbon chains and employed as the hydrophobic moiety. They are linked through a disulfide linkage to improve the responsivity in the tumor microenvironment. After formulation with other lipopeptides at an optimized ratio, the theranostic system (RNS‐2) forms lipid‐based nanoparticles with slight positive zeta potential enabling efficient condensation of DNA. The RNS‐2 displays glutathione responded gene release, activatable fluorescence recovery, and up to sevenfold higher in vitro transfection than Lipofectamine 2000. Compared with a Cy3 and Cy5 labeled fluorescence resonance energy transfer indicator for gene release, the “turn‐on” indocyanine green analogs exhibit longer emission wavelength and better positive correlation with the dynamic processes of gene delivery. More importantly, the RNS‐2 system enables efficient near infrared imaging guided gene transfer in tumor‐bearing mice and thus provides more precise and accurate information on location of the cargo gene and synthesized carriers.     

One‐Step Synthesis of Silica‐Coated Carbon Dots with Controllable Solid‐State Fluorescence for White Light‐Emitting Diodes

Carbon dots (CDots)‐based solid‐state luminescent materials have important applications in light‐emitting devices owing to their outstanding optical properties. However, it still remains a challenge to develop multiple‐color‐emissive solid‐state CDots, due to the serious self‐quenching of the CDots in the aggregation or solid state. Herein, a one‐step synthesis of multiple‐color‐emissive solid‐state silica‐coated CDots (silica/CDots) composites by controlling CDots loading fraction and composite morphology to realize the adjustment of emitting color is reported. The emission of resultant silica/CDots composites shifts from blue to orange with the photoluminescence quantum yields of 57.9%, 34.3%, and 32.7% for blue, yellow, and orange emitting, respectively. Furthermore, the yellow emitting silica/CDots composites exhibit an excellent fluorescence thermal stability, and further have been applied to fabricate white‐light‐emitting devices with a high color rendering index of above 80.     

荧光碳量子点的制备及其在生物医用领域的研究进展

近年来,碳量子点(CQDs)因具有尺寸可控、易于修饰、低毒性、优异的水溶性及生物相容性等优点吸引了生物医学领域科学家的广泛关注。重点综述了CQDs的制备方法、表面修饰及在生物医用领域的最新进展,总结和展望了CQDs在未来制备中需要解决的问题和研究方向。     

Chemically Tailoring Coal to Fluorescent Carbon Dots with Tuned Size and Their Capacity for Cu(II) Detection

The desired control of size, structure, and optical properties of fluorescent carbon dots (CDs) is critical for understanding the fluorescence mechanism and exploring their potential application. Herein, a top‐down strategy to chemically tailor the inexpensive coal to fluorescent CDs by a combined method of carbonization and acidic oxidation etching is reported. The size and optical properties of the as‐made CDs are tuned by controlling the structures of graphitic crystallites in the starting precursor. The coal‐derived CDs exhibit two different distinctive emission modes, where the intensity of the short‐wavelength emission is significantly enhanced by partial reduction treatment. The evolution of the electronic structure and the surface states analysis show that two different types of fluorescence centers, nano‐sized sp² carbon domains and surface defects, are responsible for the observed emission characteristics. The reduced CDs are demonstrated as an effective fluorescent sensing material for label‐free and selective detection of Cu(II) ions with a detection limit as low as 2.0 nm , showing a great promise for real‐world sensor applications.     

Oxidized Quasi‐Carbon Nitride Quantum Dots Inhibit Ice Growth

Antifreeze proteins (AFPs), a type of high‐efficiency but expensive and often unstable biological antifreeze, have stimulated substantial interest in the search for synthetic mimics. However, only a few reported AFP mimics display thermal hysteresis, and general criteria for the design of AFP mimics remain unknown. Herein, oxidized quasi‐carbon nitride quantum dots (OQCNs) are synthesized through an up‐scalable bottom‐up approach. They exhibit thermal‐hysteresis activity, an ice‐crystal shaping effect, and activity on ice‐recrystallization inhibition. In the cryopreservation of sheep red blood cells, OQCNs improve cell recovery to more than twice that obtained by using a commercial cryoprotectant (hydroxyethyl starch) without the addition of any organic solvents. It is shown experimentally that OQCNs preferably bind onto the ice‐crystal surface, which leads to the inhibition of ice‐crystal growth due to the Kelvin effect. Further analysis reveals that the match of the distance between two neighboring tertiary N atoms on OQCNs with the repeated spacing of O atoms along the c‐axis on the primary prism plane of ice lattice is critical for OQCNs to bind preferentially on ice crystals. Here, the application of graphitic carbon nitride derivatives for cryopreservation is reported for the first time.     

Bright Single‐Chain Conjugated Polymer Dots Embedded Nanoparticles for Long‐Term Cell Tracing and Imaging

Single‐chain conjugated polymer (CP) dots embedded nanoparticles (NPs) bearing cell penetration peptide (TAT) as surface ligands are synthesized for long term cancer cell tracing applications. The CPNPs are fabricated by matrix‐encapsulation method and the embedded CPs can be modulated into spherical dots with different size upon alteration of feed concentrations. Single‐chain CP dots are formed upon decreasing feed concentration to 0.2 mg/mL, where CPNPs exhibit highest fluorescence quantum yield of 32%. Maleimide is introduced as the new NP surface functional group, which favors easy conjugation with cell penetration peptide via click chemistry to preserve its biofunctions. The obtained CPNPs show high brightness and good biocompatibility, which allow cell tracing for over 9 generations, superior to commercial cell tracker Qtracker 585.     

Solid‐State Carbon Dots with Red Fluorescence and Efficient Construction of Dual‐Fluorescence Morphologies

Stable solid‐state red fluorescence from organosilane‐functionalized carbon dots (CDs) with sizes around 3 nm is reported for the first time. Meanwhile, a novel method is also first reported for the efficient construction of dual‐fluorescence morphologies. The quantum yield of these solid‐state CDs and their aqueous solution is 9.60 and 50.7%, respectively. The fluorescence lifetime is 4.82 ns for solid‐state CDs, and 15.57 ns for their aqueous solution. These CDs are detailedly studied how they can exhibit obvious photoluminescence overcoming the self‐quenching in solid state. Luminescent materials are constructed with dual fluorescence based on as‐prepared single emissive CDs (red emission) and nonfluorescence media (starch, Al₂O₃, and RnOCH₃COONa), with the characteristic peaks located at nearly 440 and 600 nm. Tunable photoluminescence can be successfully achieved by tuning the mass ratio of CDs to solid matrix (such as starch). These constructed dual‐fluorescence CDs/starch composites can also be applied in white light‐emitting diodes with UV chips (395 nm), and oxygen sensing.