One-Pot To Synthesize Multifunctional Carbon Dots for Near Infrared Fluorescence Imaging and Photothermal Cancer Therapy

Borylation of Diazonium Salts by Highly Emissive and Crystalline Carbon Dots in Water

Efficient borylation reaction of diazonium salts in water is realized for the first time by using easily prepared, highly emissive and crystalline carbon dots. Electron-donating and electron-withdrawing groups on diazonium salts were well tolerated with moderate to good conversion efficiency. Compared with widely used metal complexes, organic dyes and quantum dots, the approach presented herein uses carbon dots, which are nontoxic and possess good biological and medicinal compatibility and high reactivity. Therefore, this approach presents a new prospective use for carbon dots in green chemistry.

Deep Red Emissive Carbonized Polymer Dots with Unprecedented Narrow Full Width at Half Maximum

Development of high-performance carbon dots (CDs) with emission wavelength longer than 660 nm (deep red emission) is critical in deep-tissue bioimaging, yet it is still a major challenge to obtain CDs with both narrow full width at half maximum (FWHM) and high deep red/near-infrared emission yield. Here, deep red emissive carbonized polymer dots (CPDs) with unprecedented FWHM of 20 nm are synthesized. The purified CPDs in dimethyl sulfoxide (DMSO) solution possess quantum yield (QY) as high as 59% under 413 nm excitation, as well as recorded QY of 31% under 660 nm excitation in the deep red fluorescent window. Detailed characterizations identify that CPDs have unique polymer characteristics, consisting of carbon cores and the shells of polymer chains, and π conjugated system formed with N heterocycles and aromatic rings governs the single photoluminescence (PL) center, which is responsible for high QY in deep red emissive CPDs with narrow FWHM. The CPDs exhibit strong absorption and emission in the deep red light region, low toxicity, and good biocompatibility, making them an efficient probe for both one-photon and two-photon bioimaging. CPDs are rapidly excreted via the kidney system and hepatobiliary system.

Carbon Dots for Intracellular pH Sensing with Fluorescence Lifetime Imaging Microscopy

The monitoring of intracellular pH is of great importance for understanding intracellular trafficking and functions. It has various limitations for biosensing based on the fluorescence intensity or spectra study. In this research, pH-sensitive carbon dots (CDs) were employed for intracellular pH sensing with fluorescence lifetime imaging microscopy (FLIM) for the first time. FLIM is a highly sensitive method that is used to detect a microenvironment and it can overcome the limitations of biosensing methods based on fluorescence intensity. The different groups on the CDs surfaces changing with pH environments led to different fluorescence lifetime values. The CDs aqueous solution had a gradual change from 1.6 ns to 3.7 ns in the fluorescence lifetime with a pH range of 2.6-8.6. Similar fluorescence lifetime changes were found in pH buffer-treated living cells. The detection of lysosomes, cytoplasm, and nuclei in living cells was achieved by measuring the fluorescence lifetime of CDs. In particular, a phasor FLIM analysis was used to improve the pH imaging. Moreover, the effects of the coenzymes, amino acids, and proteins on the fluorescence lifetime of CDs were examined in order to mimic the complex microenvironment inside the cells.

Bone Tissue Engineering via Carbon-Based Nanomaterials

Bone tissue engineering (BTE) has received significant attention due to its enormous potential in treating critical-sized bone defects and related diseases. Traditional materials such as metals, ceramics, and polymers have been widely applied as BTE scaffolds; however, their clinical applications have been rather limited due to various considerations. Recently, carbon-based nanomaterials attract significant interests for their applications as BTE scaffolds due to their superior properties, including excellent mechanical strength, large surface area, tunable surface functionalities, high biocompatibility as well as abundant and inexpensive nature. In this article, recent studies and advancements on the use of carbon-based nanomaterials with different dimensions such as graphene and its derivatives, carbon nanotubes, and carbon dots, for BTE are reviewed. Current challenges of carbon-based nanomaterials for BTE and future trends in BTE scaffolds development are also highlighted and discussed.

Overview of the application of inorganic nanomaterials in cancer photothermal therapy

Cancer photothermal therapy (PTT) has captured the attention of researchers worldwide due to its localized and trigger-activated therapeutic effect.

Photo-to-thermal conversion: effective utilization of futile solid-state carbon quantum dots (CQDs) for energy harvesting applications

Dominant non-radiative electronic de-excitation in fluorescence quenched CQDs in the solid state results in excellent photo-to-thermal transduction in the system.

Theranostic applications of stimulus-responsive systems based on carbon dots

Over recent years, many different nanoparticle-based drug delivery systems (NDDSs) have been developed. Recently the development of stimulus-responsive NDDSs has come into sharper focus. Carbon dots (CDs) possess outstanding features such as useful optical properties, good biocompatibility, and the ability for easy surface modification. Appropriate surface modification can allow these NDDSs to respond to various chemical or physical stimuli that are characteristic of their target cells or tissue (frequently malignant cells or tumors). The present review covers recent developments of CDs in NDDSs with a particular focus on internal stimulus response capability that allows simultaneous imaging and therapeutic delivery (theranostics). Relevant stimuli associated with tumor cells and tumors include pH levels, redox potential, and different enzymatic activities can be used to activate the CDs at the desired sites.

Evolution and Synthesis of Carbon Dots: From Carbon Dots to Carbonized Polymer Dots

Despite the various synthesis methods to obtain carbon dots (CDs), the bottom-up methods are still the most widely administrated route to afford large-scale and low-cost synthesis. However, as CDs are developed with increasing reports involved in producing many CDs, the structure and property features have changed enormously compared with the first generation of CDs, raising classification concerns. To this end, a new classification of CDs, named carbonized polymer dots (CPDs), is summarized according to the analysis of structure and property features. Here, CPDs are revealed as an emerging class of CDs with distinctive polymer/carbon hybrid structures and properties. Furthermore, deep insights into the effects of synthesis on the structure/property features of CDs are provided. Herein, the synthesis methods of CDs are also summarized in detail, and the effects of synthesis conditions of the bottom-up methods in terms of the structures and properties of CPDs are discussed and analyzed comprehensively. Insights into formation process and nucleation mechanism of CPDs are also offered. Finally, a perspective of the future development of CDs is proposed with critical insights into facilitating their potential in various application fields.

N-Doped Carbon Quantum Dot (NCQD)-Deposited Carbon Capsules for Synergistic Fluorescence Imaging and Photothermal Therapy of Oral Cancer

Use of nanomaterials blessed with both therapeutic and diagnostic properties is a proficient strategy in the treatment of cancer in its early stage. In this context, our paper reports the synthesis of uniform size N-rich mesoporous carbon nanospheres of size 65-70 nm from pyrrole and aniline precursors using Triton-X as a structure-directing agent. Transmission electron microscopy reveals that these carbons spheres contain void spaces in which ultrasmall nitrogen-doped quantum dots (NCQD) are captured within the matrix. These mesoporous hollow NCQD captured carbon spheres (NCQD-HCS) show fluorescence quantum yield up to 14.6% under λ_ex = 340 nm. Interestingly, samples calcined at >800 °C clearly absorb in the wavelength range 700-1000 nm and shows light-to-heat conversion efficiency up to 52%. In vitro experiments in human oral cancer cells (FaDu) show that NCQD-HCS are internalized by the cells and induce a substantial thermal ablation effect in FaDu cells when exposed under a 980 nm near-infrared laser.

A carbon dot based theranostic platform for dual-modal imaging and free radical scavenging

Magnetofluorescent carbon dots (Cdots) doped with both P³⁺ and Mn²⁺ (abbreviated as PMn@Cdots) have been synthesized in an aqueous solution via a microwave-assisted pyrolysis method. In this system, a P³⁺ dopant was introduced to enhance the emission efficiency of the Cdots, while the presence of a Mn²⁺ dopant granted magnetic resonance imaging (MRI) capability. To the best of our knowledge, the present work is the first attempt to regulate red-emission and free radical scavenging of PMn@Cdots to serve as a dual-modal imaging nanoprobe and an antioxidant agent. Unlike most red-emitting Cdots, the as-prepared PMn@Cdots can be readily purified from unreacted precursors through antisolvent precipitation instead of by time-consuming purification methods. The whole synthetic procedure is rapid, facile, efficiently reproducible, and scalable. More importantly, further conjugation of the PMn@Cdots with hyaluronic acid (termed PMn@Cdots/HA) gives them good in vivo and in vitro biocompatibility as well as the capability to selectively target CD44-overexpressing cancer cells, as investigated by flow cytometry, fluorescence, and MRI. Meanwhile, PMn@Cdots exhibit antioxidant activity against multiple DPPH, hydroxyl, and superoxide radicals, which is comparable to that for ascorbic acid. Favorably, PMn@Cdots/HA showed a dose-dependent cytoprotective capability against H₂O₂-induced oxidative stress in B16F1, HeLa, and HEL cells. Therefore, the Cdot based theranostic platform can simultaneously function as a potential therapeutic candidate and as a dual-modal probe for enabling accurate diagnosis in future clinical applications.

Carbon dots derived from lychee waste: Application for Fe3+ ions sensing in real water and multicolor cell imaging of skin melanoma cells

Exploit of biomass as an inexhaustible resource has accepted much more curiosity to the present research world. Herein, a simple, one-step solvothermal action has been used to synthesize an ascendable amount of fluorescent carbon dots (CDs) with an average size of~3.13 nm, from Low-reasonable and green source lychee waste. The excitation/emission maxima of CDs have 365/443 nm with high quantum yield (23.5%). The present ingredient predominantly contained carboxylic acid and hydroxyl group that acted as a passive agent for stabilizing the CDs. The structural and optical properties were evaluated through HRTEM, FTIR, UV-vis, zeta potential, XPS, fluorescence, and fluorescence lifetime experiments. We investigated the manoeuvre of our synthesized CDs as a probe for detection of Fe³⁺ ions in water bodies; This sensing approach showed impressive selectivity and sensitivity towards Fe³⁺ions with LOD 23.6 nM. The sensing mechanism took place through static quenching which was entrenched through fluorescence lifetime measurements. Fe³⁺ ions detection was basically carried out with efficacy in real water. For its lofty Photo-stability, low cytotoxicity and cell viability the probe were substantially applied for bio-imaging experiment i.e. intracellular multi-color cell imaging in skin melanoma cells (A375 cells) with and without Fe³⁺ ions exemplifying its real applications in living cells.

Synthesis of Multicolor Carbon Dots Based on Solvent Control and Its Application in the Detection of Crystal Violet

The adjustment of the emitting wavelength of carbon dots (CDs) is usually realized by changing the raw materials, reaction temperature, or time. This paper reported the effective synthesis of multicolor photoluminescent CDs only by changing the solvent in a one-step solvothermal method, with 1,2,4,5-tetraaminobenzene as both the novel carbon source and nitrogen source. The emission wavelengths of the as-prepared CDs ranged from 527 to 605 nm, with quantum yields (QYs) reaching 10.0% to 47.6%, and it was successfully employed as fluorescence ink. The prepared red-emitting CDs (R-CDs, λ_em = 605 nm) and yellow-emitting CDs (Y-CDs, λ_em = 543 nm) were compared through multiple characterization methods, and their luminescence mechanism was studied. It was discovered that the large particle size, the existence of graphite Ns, and oxygen-containing functional groups are beneficial to the formation of long wavelength-emitting CDs. Y-CDs responded to crystal violet, and its fluorescence could be quenched. This phenomenon was thus employed to develop a detection method for crystal violet with a linear range from 0.1 to 11 µM and a detection limit of 20 nM.

Far-Red to Near-Infrared Carbon Dots: Preparation and Applications in Biotechnology

As novel fluorescent nanomaterials, carbon dots (CDs) exhibit excellent photostability, good biocompatibility, and high quantum yield (QY). Their superior properties make them promising candidates for biomedical assays and therapy. Among them, the red-emission (>600 nm) CDs have attracted increasing attention in the past years due to their little damage to the biological matrix, deep tissue penetration, and minimum autofluorescence background of biosamples. This Review, summarizes the recent progress of far-red to near-infrared (NIR) CDs from the preparation and their biological applications. The challenges in designing far-red and NIR CDs and their further applications in biomedical fields are also discussed.

Carbon Dots, Unconventional Preparation Strategies, and Applications Beyond Photoluminescence

Carbon dots (C-dots) are generally separated into graphene quantum dots (GQDs) and carbon nanodots (CNDs) based on their respective top-down and bottom-up preparation processes. However, GQDs can be prepared by carbonization of small-molecule precursors as revealed with unconventional preparation strategies. Thus, it is their structures rather than their precursors and preparation strategy that govern whether C-dots are GQDs or CNDs. Here, the composites, structure, and electronic properties of C-dots are discussed. C-dots generally consist of a graphite-like core and amorphous oxygen-containing shell. When graphite becomes C-dots, its conduction and valence bands are separated, and the quantum confinement effect appears. Combined with the light-harvesting ability inherited from graphite, electrons in the core of C-dots are transferred from conduction to valence bands, leading to electron-hole pair formation upon light excitation. The photoexcitation activities, such as photovoltaic conversion, photocatalysis, and photodynamic therapy, are influenced by the electronic properties of the core. Different to the semiconductor properties of core, the C-dot shell is electrochemically active, leading to electrochemiluminescence (ECL). The oxygen-containing groups in shell can conjugate to functional species for use in imaging and therapy. The applications of C-dots beyond photoluminescence, including ECL, solar photovoltaics, photocatalysis, and theranostics, are reviewed.

A convenient and universal platform for sensing environmental nitro-aromatic explosives based on amphiphilic carbon dots

2,4,6-trinitrophenol (TNP) is environmentally deleterious substance that has been of pressing societal concern. Therefore, developing a convenient and reliable platforms for its fast and efficient detection is of paramount importance from security point of view. Herein, amphiphilic fluorescent carbon dots (CDs) were prepared by a simple solvothermal method. CDs exhibit high selectivity and sensitivity on TNP in the polar and apolar solvent and even natural water samples. Moreover, the simple and portable indicator paper can be prepared conveniently and used for sensing TNP visually with high sensitivity and fast response. Research findings obtained from this study would assist in the development of portable devices for the on-site and real-time detection of environmental hazards.

Small molecules derived carbon dots: synthesis and applications in sensing, catalysis, imaging, and biomedicine

Carbon dots (CDs) are the new fellow of carbon family having a size less than 10 nm and attracted much attention of researchers since the last decade because of their unique characteristics, such as inexpensive and facile synthesis methods, easy surface modification, excellent photoluminescence, outstanding water solubility, and low toxicity. Due to these unique characteristics, CDs have been extensively applied in different kind of scientific disciplines. For example in the photocatalytic reactions, drug-gene delivery system, in vitro and in vivo bioimaging, chemical and biological sensing as well as photodynamic and photothermal therapies. Mainly two types of methods are available in the literature to synthesize CDs: the top-down approach, which refers to breaking down a more massive carbon structure into nanoscale particles; the bottom-up approach, which refers to the synthesis of CDs from smaller carbon units (small organic molecules). Many review articles are available in the literature regarding the synthesis and applications of CDs. However, there is no such review article describing the synthesis and complete application of CDs derived from small organic molecules together. In this review, we have summarized the progress of research on CDs regarding its synthesis from small organic molecules (bottom-up approach) via hydrothermal/solvothermal treatment, microwave irradiation, ultrasonic treatment, and thermal decomposition techniques as well as applications in the field of bioimaging, drug/gene delivery system, fluorescence-based sensing, photocatalytic reactions, photo-dynamic therapy (PDT) and photo-thermal (PTT) therapy based on the available literature. Finally, the challenges and future direction of CDs are discussed.

PEGylated cyanine dye nanoparticles as photothermal agents for mosquito and cancer cell control

Conversion of light energy to heat via photothermal conversion agents (PTCAs) is of great interest and has potential applications. Here, we described a heptamethine cyanine (Cy7) dye nanoparticles (Cy7-PEG NPs) prepared from heptamethine cyanine and poly(ethylene glycol) (PEG400) via a simple solvothermal process as novel PTCA. Cy7-PEG NPs have absorption maximum at about 808 nm and good photothermal conversion ability. Upon irradiation, Cy7-PEG NPs can effectively kill living mosquito larva (Aedes albopictus) through heat generation. Furthermore, Cy7-PEG NPs have excellent phototoxic activity to Sf9, HeLa and MCF-7 cells. Our results indicated that Cy7-PEG NPs can be used as controlling agent for mosquito larvae and cancer cells.

Carbon Dots for In Vivo Bioimaging and Theranostics

Carbon dots (CDs), a kind of carbon material discovered accidentally, exhibit unexpected advantages in fluorescence imaging/sensing such as photostability, biocompatibility, and low toxicity. For emerging theranostics, an interdiscipline created by integrating therapy and diagnostics, CDs are good candidates when they are combined with targeted chemo/gene/photodynamic/photothermal therapeutic moieties. Here, the development of CDs in nanomedicine is reviewed from their use as original imaging agents and/or drug carriers to multifunctional theranostic systems. Finally, the challenges and prospects of the next-generation of CD-based theranostics for clinical applications are also discussed.

Carbon dots, a powerful non-toxic support for bioimaging by fluorescence nanoscopy and eradication of bacteria by photothermia

Carbon Dots (CDs) are innovative materials which have potential applications in many fields, including nanomedicine, energy and catalysis. Here CDs were produced by the alkali-assisted ultrasonic route and characterized by several techniques to determine their composition and properties. Fluorescence nanoscopy using single-molecule localization microscopy shows that they have very good photophysical properties and a remarkable blinking behaviour at 405 nm. Moreover, these CDs are a safe material, non-toxic towards different cell lines (cancer and non-cancer cells) even at very high concentration, reflecting an excellent biocompatibility. Photothermia, i.e. their heating capacity under laser irradiation, was evaluated at two wavelengths and at several power densities. The resulting temperature increment was high (5 < ΔT < 45 °C) and appropriate for biomedical applications. Bioimaging and photothermia were then performed on E. coli, a Gram(-) bacterium, incubated with CDs. Remarkably, by photothermia at 680 nm (0.3, 1 and 1.9 W cm^-2) or 808 nm (1.9 W cm^-2), CDs are able to eradicate bacteria in their exponential and stationary phases. Images obtained by 3D super-resolution microscopy clearly show the different CD distributions in surviving bacteria after mild photothermal treatment. These results confirm that CDs are multifunctional materials with a wide range of biomedical applications.

N-doped carbon dots under Xenon lamp irradiation: Fluorescence red-shift and its potential mechanism

Despite extensive research on carbon dots (CDs), rare studies have been performed on the photostability of CDs. Here, the photostability of CDs synthesized with 3-aminobenzoic acid were systematically investigated under different pH conditions (5.0, 7.4 and 9.0). The results showed that under Xenon lamp irradiation, the fluorescence (FL) intensity of the CDs exhibited an increase first and then a decrease, with a gradual shift of the maximum emission wavelength to longer wavelength. Further investigation indicated that the irradiation induced the change of the CD surface functional groups and gave rise to aggregation, resulting in the formation of larger particles. This study provided important reference value towards research on CDs properties.

Highly Homogeneous Biotinylated Carbon Nanodots: Red-Emitting Nanoheaters as Theranostic Agents toward Precision Cancer Medicine

Very recent red-emissive carbon nanodots (CDs) have shown potential as near-infrared converting tools to produce local heat useful in cancer theranostics. Besides, CDs seem very appealing for clinical applications combining hyperthermia, imaging, and drug delivery in a single platform capable of selectively targeting cancer cells. However, CDs still suffer from dramatic dot-to-dot variability issues such that a rational design of their structural, optical, and chemical characteristics for medical applications has been impossible so far. Herein, we report for the first time a simple and highly controllable layer-by-layer synthesis of biotin-decorated CDs with monodisperse size distribution, well established polymeric shell thickness, and degree of surface functionalization, endowed with strong red luminescence and the ability to convert NIR light into heat. These CDs, henceforth named CDs-PEG-BT, consist of a carbonaceous core passivated with biotin-terminated PEG₂₀₀₀ chains, which we demonstrate as active targeting groups to recognize cancer cells. The CDs-PEG-BT are designed to efficiently incorporate a high amount of anticancer drugs such as irinotecan (16-28%) and to act as NIR-activated nanoheaters capable of triggering local hyperthermia and massive drug release inside tumors, thus provoking sudden and efficient tumor death. The potential of the irinotecan-loaded CDs-PEG-BT (CDs-PEG-BT@IT) in fluorescence imaging was studied on 2D cultures and on complex 3D spheroids mimicking in vivo tumor architectures, showing their capability of selectively entering cancer cells through biotin receptors overexpressed in cell membranes. The efficient anticancer effect of these CDs was thoroughly assessed on multicellular 3D spheroids and patient organoids (tumor-on-a-dish preclinical models) to predict the drug response in humans in view of personalized medicine applications. CDs-PEG-BT@IT have a smart combination of properties, which pave the way to their real-world use as anticancer theranostic agents for image-guided photothermal applications.

Controllable acidophilic dual-emission fluorescent carbonized polymer dots for selective imaging of bacteria

Fluorescent materials can be powerful contrast agents in photoelectric devices and for bioimaging. As emerging fluorescent materials, carbonized polymer dots (CPDs) with high quantum yields (QYs), long-wavelength emission and multiple functions are highly desired. Despite great progress in the synthetic methods and QYs of CPDs, multiple emission of CPDs is challenging. Therefore, we developed CPDs with dual-emission fluorescence in terms of inherent blue and red emission. In addition, CPDs with sole blue emission (B-CPDs) and red emission (R-CPDs) were synthesized, respectively, by regulating the reaction conditions to control the quantitative structure and emission centers. The absolute QY of R-CPDs in water was 24.33%. These three types of CPDs with dual/sole emission could be used in optoelectronic and bioimaging applications. With different CPDs coated on a commercially available gallium nitride light-emitting diode chip as a color-conversion layer, LEDs with blue, yellow, and red emission were achieved. Benefiting from the different emission intensities and emission peaks of R/B-CPDs in different pH conditions, they were used (without further modification) to distinguish between Porphyromonas gingivalis, Streptococcus mutans, Escherichia coli and Staphylococcus aureus in dental plaque biofilms (the first time this has been demonstrated). These findings could enable a new development direction of CPDs based on the design of multi-emission centers.

Carbon dots: Applications in bioimaging and theranostics

Carbon dots are a carbonaceous nanomaterial that were discovered accidentally and are now drawing significant attention as a new quantum-sized fluorescent nanoparticle. Carbon dots are biocompatible, non-toxic, photostable, and easily functionalized with good photoluminescence and water solubility. Due to these unique properties, they are used broadly in live cell imaging, catalysis, electronics, biosensing, power, targeted drug delivery, and other biomedical applications. Here, we review the recent development of carbon dots in nanomedicine from their use in drug carriers to imaging agents to multifunctional theranostic systems. Finally, we discuss the challenges and views on next-generation carbon dot-based theranostics for clinical applications.

Hydrophobic carbon dots with blue dispersed emission and red aggregation-induced emission

Carbon dots (CDs) have been studied for years as one of the most promising fluorescent nanomaterials. However, CDs with red or solid-state fluorescence are rarely reported. Herein, through a one-pot solvothermal treatment, hydrophobic CDs (H-CDs) with blue dispersed emission and red aggregation-induced emission are obtained. When water is introduced, the hydrophobic interaction leads to aggregation of the H-CDs. The formation of H-CD clusters induces the turning off of the blue emission, as the carbonized cores suffer from π-π stacking interactions, and the turning on of the red fluorescence, due to restriction of the surfaces' intramolecular rotation around disulfide bonds, which conforms to the aggregation-induced-emission phenomenon. This on-off fluorescence of the H-CDs is reversible when the H-CD powder is completely dissolved. Moreover, the H-CD solution dispersed in filter paper is nearly colorless. Finally, we develop a reversible two switch-mode luminescence ink for advanced anti-counterfeiting and dual-encryption.

Recent advances on fluorescent biomarkers of near-infrared quantum dots for in vitro and in vivo imaging

Luminescence probe has been broadly used for bio-imaging applications. Among them, near-infrared (NIR) quantum dots (QDs) are more attractive due to minimal tissue absorbance and larger penetration depth. Above said reasons allowed whole animal imaging without slice scan or dissection. This review describes in vitro and in vivo imaging of NIR QDs in the regions of 650-900 nm (NIR-I) and 1000-1450 nm (NIR-II). Also, we summarize the recent progress in bio-imaging and discuss the future trends of NIR QDs including group II-VI, IV-VI, I-VI, I-III-VI, III-V, and IV semiconductors.

Carbon dot-sensitized MoS2 nanosheet heterojunctions as highly efficient NIR photothermal agents for complete tumor ablation at an ultralow laser exposure

Currently, one of the major hurdles hindering the clinical applications of photothermal therapy (PTT) and photothermal-chemo combination therapy (PCT) is the lack of highly efficient, readily derived, and irradiation-safe photothermal agents in the biologically transparent window. Herein, we report the first design and rational construction of 0D/2D/0D sandwich heterojunctions for greatly enhanced PTT and PCT performances using 0D N-doped carbon dots and 2D MoS2 nanosheets as the assembly units. The well-matching heterojunctions enabled an additional enhancement in NIR absorbance owing to the carrier injection from carbon dots to MoS2 nanosheets, and achieved a much higher photothermal conversion efficiency (78.2%) than that of single NIR-CDs (37.6%) and MoS2 (38.3%) only. In virtue of the heterojunction-based PTT, complete tumor recession without recurrence or pulmonary metastasis was realized at an ultralow and safe laser exposure (0.2 W cm-2) below the skin tolerance irradiation threshold. Furthermore, by taking advantage of the strong X-ray attenuation and effective drug loading capacity of MoS2 nanosheets, the CT imaging-guided PCT was achieved at 0.1 W cm-2, without inducing noticeable toxic side effects. Our findings can substantiate the potential of a novel 0D/2D heterojunction for cancer theranostics.

Highly luminescent N-doped carbon dots from black soya beans for free radical scavenging, Fe3+ sensing and cellular imaging

The novel N doped carbon dots (N-CDs) were readily fabricated through one-step pyrolysis method from black soya beans. The obtained N-CDs possessed excellent photoluminescence properties with quantum yield of 38.7 ± 0.64% and dual responsive properties towards free radical and Fe3+. The N-CDs exhibited favorable radical scavenging activity (RSA) against 1,1-diphenyl-2-picrylhydrazyl (DPPH) and superoxide anion radicals. Fe3+ could induce photoluminescence quenching of N-CDs through static quenching characteristics. The possible quenching mechanism was presented. Combining with negligible toxicity and preferable biocompatibility, the N-CDs were extended to imaging intracellular Fe3+. As an attractive candidate, the N-CDs demonstrated a great potential in free radical scavenging, sensing and cellular imaging.

Green Synthesis of Fluorescent Carbon Dots from Gynostemma for Bioimaging and Antioxidant in Zebrafish

Fluorescent carbon dots (CDs) have been synthesized via the calcination method using natural gynostemma as the precursor, without any toxic ingredients or surface passivation chemicals. CDs have a narrow size distribution, and the mean particle size is about 2.5 nm. CDs exhibit good water dispersibility and can emit intense blue fluorescence under 365 nm UV light in an aqueous solution, which can be stable in different conditions. The biotoxicity of CDs on the embryonic development of zebrafish is evaluated, the hatch rate and survival rate of embryos are around 90%, and the malformation rate is less than 10%. Because of the excellent fluorescence stability and biocompatibility, CDs can be used in zebrafish for bioimaging. In addition, the antioxidative stress property of CDs is investigated both in vitro and in vivo, and the presence of CDs can promote the mRNA expression of related genes to encode more antioxidant proteins in zebrafish. Therefore, fluorescent CDs would be a potential candidate for bioimaging and treating diseases caused by excessive oxidation damage, such as cancer, senility, and other diseases associated with aging.

Recent Advances in Carbon Nanomaterials for Cancer Phototherapy

Carbon nanomaterials have received great attention from the scientific community over the past few decades because of their unique physical and chemical properties. In this minireview, we will summarize the recent progress of the use of various carbon nanomaterials in the field of cancer phototherapy. The structural characteristics of each category and the surface functionalization strategies of these nanomaterials will be briefly introduced before focusing on their therapeutic applications. Recent advances on their use in photothermal therapy, photodynamic therapy, and combined phototherapies are presented. Moreover, a few challenges and perspectives on the development of carbon nanomaterials for future theranostics are also discussed.

Recent insights into near-infrared light-responsive carbon dots for bioimaging and cancer phototherapy

The current developments of NIR-responsive CDs and their applications in bioimaging and phototherapy are highlighted in this review.

Self-assembly of nanoparticles by human serum albumin and photosensitizer for targeted near-infrared emission fluorescence imaging and effective phototherapy of cancer

A self-assembly nanoplatform of HSA@Cy-HPT for targeted near-infrared emission fluorescence imaging and effective phototherapy of cancer.

An eco-friendly imprinted polymer based on graphene quantum dots for fluorescent detection of p-nitroaniline

An eco-friendly fluorescent molecularly imprinted polymer anchored on the surface of graphene quantum dots (GQDs@MIP) was developed with an efficient sol–gel polymerization for highly sensitive and selective determination of p-nitroaniline (p-NA).

In Vivo Tumor Photoacoustic Imaging and Photothermal Therapy Based on Supra-(Carbon Nanodots)

Carbon nanodots (CNDs) with high photothermal conversion efficiency are considered as emerging nanomaterials for advanced biomedical applications attributing to their high biocompatibility, low-cost, and unique photophysical properties. In previous work, supra-CNDs are synthesized exhibiting high absorption in the near-infrared (NIR) region and good NIR photothermal conversion performance. In this work, supra-CNDs are explored as a photothermal agent for photothermal therapy (PTT) and a contrast agent for photoacoustic (PA) imaging, respectively. As a result, in vivo tumor PTT is realized under 655 nm laser irradiation via intratumor injecting supra-CNDs. In vivo PA imaging reveals that supra-CNDs can accumulate in the tumor tissue via the blood circulation after intravenous injection. Moreover, in vivo PTT is conducted after intravenous injection and subsequent tumor accumulation of supra-CNDs, and the lives of mice are prolonged due to the tumor growth inhibition after PTT. These attractive properties indicate that the supra-CNDs can be used as biomedical agents for PA imaging and tumor therapy.

A postmodification strategy to modulate the photoluminescence of carbon dots from blue to green and red: synthesis and applications

Green and red fluorescent carbon dots were successfully prepared by the conjugation of CD-B with VC and acetaldehyde, respectively.

Simultaneous ultraviolet and first near-infrared window absorption of luminescent carbon dots/PVA composite film

Liquid Carbon Dots (CDs) were successfully synthesized by hydrothermal method using urea and citric acid as raw materials. TEM images confirmed that the CDs have a spherical shape with a homogeneous distribution. The as-prepared liquid CDs could absorb ultraviolet (UV) and first near infra-red (NIR) window simultaneously. However, the photoluminescence (PL) of the liquid CDs was damaged by their quenching effect. To overcome this issue, the liquid CDs were dispersed in poly(vinyl) alcohol (PVA) to fabricate the composite film. Herein, the dual-peak absorption properties of the CDs/PVA composite films were investigated for the first time. The composite films could maintain the simultaneous UV and first NIR window absorption property even after being preheated up to 200 °C, implying that the structure of CDs was well retained during the transition from the liquid to films. Daylight treatment for seven days produced minimum changes in the UV-vis and PL spectra, which indicates that the CDs/PVA film has more stable optical properties than the liquid CDs.

The simultaneous UV and first NIR absorption of the CDs/PVA composite could be maintained up to 200 °C, with minimum PL changes.

Robust organic nanoparticles for noninvasive long-term fluorescence imaging

Organic nanoparticles obtained from fluorophores with aggregation-caused quenching and aggregation-induced emission features for noninvasive long-term bioimaging are summarized and highlighted.

Carbon dots: The next generation platform for biomedical applications

Among the wide range of carbon family nanomaterials, carbon dots (CDs) one of the promising candidate which has attracted tremendous attention due to its unique advantages such as facile synthesis procedure, easy surface functionalization, outstanding water solubility, low toxicity and excellent photo-physical properties. Due to these unique advantages, CDs are extensively used in catalysis, electronics, sensing, power as well as in biological sectors. In this review we will discuss recent progress in synthesis, structure and fluorescence properties of CDs with special highlight on its biomedical applications, more precisely we will highlight on CDs, for drug/gene delivery, bioimaging and photothermal and photodynamic therapy applications. Furthermore, we discuss the current challenges and future perspective of CDs in the field of biomedical sector.

Tuning Carbon Dots' Optoelectronic Properties with Polymers

Due to their unique properties of photoluminescence, biocompatibility, photostability, ease of preparing, and low cost, carbon dots have been studied extensively over the last decade. Soon after their discovery, it was realized that their main optical attributes may be protected, enhanced, and tuned upon proper surface passivation or functionalization. Therefore, up to date, numerous polymers have been used for these purposes, resulting to higher-quality carbon dots regarding their quantum yield or further emission-related aspects and compared to the primitive, bare ones. Hence, this review aims to clarify the polymers' role and effect on carbon dots and their features focusing on the quality characteristics of their photoluminescence upon passivation or functionalization. Given in fact the numbers of relevant publications, emphasis is given on recent articles capturing the latest advances for polymers in carbon dots for expanding emission lifetimes, advancing quantum yields, tuning emission wavelengths, enhancing specific spectral range absorption, and tailoring optoelectronic properties in general.

Near-infrared fluorescent carbon dots encapsulated liposomes as multifunctional nano-carrier and tracer of the anticancer agent cinobufagin in vivo and in vitro

Integrating the optical properties of near-infrared fluorescent carbon dots into liposomes may construct a multifunctional nano-system with the potential as a drug carrier, tracer and efficacy intensifier of the anticancer agent. In this study, the liposomes loaded with hydrophilic near-infrared carbon dots as a nano-carrier and tracer of lipophilic anticancer agent cinobufagin were developed. Prepared liposomes were characterized by particle size, morphology and entrapment efficiency. The drug release behavior, the tracer function, the anticancer effect and the side effect were investigated in vitro and in vivo. It was observed that the photoluminescence emission of carbon dots could be strongly enhanced up to 5 times by nano-liposomes. Due to this property, the bio-imaging of CDs + CB liposomes in vitro and in vivo could be clearly obtained. Our results also showed that the CDs + CB liposomes could be uptaken by cells (the lysosomes targeted) and delivered to the tumor site, and undoubtedly, the CDs + CB liposomes demonstrated sustained drug release, enhanced anticancer efficacy and low side effects in vivo. With the assistance of imaging function of CDs, the CDs + CB liposomes can easily display the distribution of drugs, which is very helpful for drug development and may open a novel avenue for drug delivery.

Multifunctional hyaluronic acid-derived carbon dots for self-targeted imaging-guided photodynamic therapy

It is of vital importance to engineer the surface structures of carbon dots (CDs) to satisfy their practical biomedical applications, including imaging and treatment. In this work, one type of hyaluronic acid-derived CD (HA-CD) was synthesized via a facile one-step hydrothermal method using cancer cell-targeted HA as a precursor. The as-prepared HA-CDs were targeted actively toward CD44 receptor-overexpressing cancer cells because a partial HA structure remained on the HA-CD surface. Beyond this, HA-CDs can act as a novel photosensitizer, because they can generate O₂˙^- under 650 nm laser irradiation, and they also exhibit excellent blue photoluminescence emission. The in vitro results revealed that HA-CDs imaged selectively CD44-overexpressing cancer cells and inhibited their growth under 650 nm laser irradiation. Thus, HA-CDs can serve as a promising self-targeted imaging-guided photodynamic therapy (PDT) agent for cancer. The present research provides a promising new method to simply construct multifunctional CD-based targeted phototheranostic systems.