Metal ions doped carbon quantum dots: Synthesis, physicochemical properties, and their applications

Fast and efficient "on-off-on" fluorescent sensor from N-doped carbon dots for detection of mercury and iodine ions in environmental water

A kind of nitrogen doped carbon dots (N-CDs) was facilely fabricated from polyethyleneimine and anhydrous citric acid, and which was adopted to develop a neoteric "on-off" and "off-on" fluorescent sensor for rapidly and efficiently sensing Hg²⁺ and I^-. The fluorescence of N-CDs was notably quenched (off) in the existence of Hg²⁺ derived from strong interaction and the electron transfer between N-CDs and Hg²⁺, while the quenched fluorescence of the N-CDs and Hg²⁺ system was strikingly regained by addition of I^- (on) resulted from the separation of N-CDs and Hg²⁺ due to the higher binding preference between Hg²⁺ and I^-. Under optimal conditions, the linear detection ranges were 0.01-20 μM for Hg²⁺ and 0.025-7 μM for I^-, respectively. Meanwhile, the detection limits could be down to 3.3 nM for Hg²⁺ and 8.5 nM for I^-, respectively. Satisfied recoveries had also been gained for measuring Hg²⁺ and I^- in practical water samples. The constructed "on-off-on" fluorescent sensor provided a simple, rapid, robust and reliable platform for detecting Hg²⁺ and I^- in environmental applications.

Bi-doped carbon dots for a stable lithium metal anode

Bi-doped carbon dots (Bi-CDs) with rich polar groups and good compatibility were employed as co-deposition electrolyte additives to homogenize Li⁺ flux for dendrite-free Li deposition. High coulombic efficiency (99.0%) and long-term stability (800 h) with reduced overpotential (∼15 mV) were achieved after introducing Bi-CDs in conventional electrolyte for high-performance Li-S batteries.

Thiosemicarbazide functionalized carbon quantum dots as a fluorescent probe for the determination of some oxicams: application to dosage forms and biological fluids

In this study, highly fluorescent water-soluble nitrogen and sulfur doped carbon quantum dots (N, S-CQDs) were synthesized via a one-step hydrothermal process utilizing citric acid as a carbon source and thiosemicarbazide as a sulfur and nitrogen source. The obtained N, S-CQDs exhibited an intense emission band at 415 nm (λ ex = 345 nm). In the presence of either piroxicam, tenoxicam or lornoxicam, the emission band at 415 nm was significantly quenched which might be triggered due to destruction of the surface passivation layer of the N, S-CQDs. A linear correlation was found between the reduction in the fluorescence intensity of N, S-CQDs and the concentration of each drug in the ranges of 2.0-25.0 μM, 10.0-100.0 μM and 20.0-200.0 μM with correlation coefficients of more than 0.999 for all drugs. The detection limits were 0.49 μM, 1.58 μM and 4.63 μM for piroxicam, tenoxicam and lornoxicam, respectively. The effect of experimental parameters affecting the performance of the method was investigated and optimized. The developed sensor has the advantages of simplicity, time-saving, convenience and satisfactory selectivity for determination of the studied drugs in dosage forms with high % recoveries (98.86-101.69%). The method was extended for determination of piroxicam in spiked plasma with % recoveries ranging from 97.95-101.36%. The method was validated in accordance with International Council of Harmonization (ICH) standards, and the results obtained were compared statistically to those given by reported methods, indicating no significant differences in the level of accuracy and precision. The mechanism of the quenching process was studied and elucidated. The structure-activity relationship between the three drugs and the quenching efficiency was also studied and discussed.

A Review on the Catalytic Remediation of Dyes by Tailored Carbon Dots

Water polluted with dyes has become a serious global concern during the twenty-first century, especially for developing countries. Such types of environmental contaminant pose a severe threat to biodiversity, ecosystems, and human health globally; therefore, its treatment is an utmost requirement. Advanced technologies including the use of nanomaterials represent a promising water treatment technology with high efficiencies, low production costs, and green synthesis. Among the nanomaterials, carbon dots, as a new class of carbon-based nanoparticles, have attracted attention due to their unique features and advantages over other nanomaterials, which include high water solubility, easy fabrication and surface functionalisation, excellent electron-donating ability, and low toxicity. Such properties make carbon dots potential nanocatalysts for the Fenton-like degradation of environmental pollutants in water. Although recent studies show that carbon dots can successfully catalyse the degradation of dyes, there are still limited and controversial studies on the ecotoxicity and fate of these nanoparticles in the environment. In this review, the authors aim to summarise the recent research advances in water remediation by technologies using carbon dots, discuss important properties and factors for optimised catalytic remediation, and provide critical analysis of ecotoxicity issues and the environmental fate of these nanoparticles.

Double-signal quantification of amoxicillin based on interaction with 4-aminoantipyrine at copper and nitrogen co-doped carbon quantum dots as an artificial nanozyme

An one-pot hydrothermal method was developed for synthesis of carbon quantum dots co-doped with copper and nitrogen (Cu, N@CQDs). The synthesized Cu, N@CQDs has unique advantages such as high fluorescence quantum yield (39.1%) and high catalytic activity. Oxidative coupling of amoxicillin (AMX) with 4-aminoantipyrine (4-NH₂-APE) in the presence of H₂O₂ as an oxidant to produce pink quinoneimine chromogen was carried out with the aid of Cu, N@CQDs as a peroxidase-like catalyst. This system was used for the colorimetric and fluorometric assays of AMX with reliable results. Colorimetric method is based on the measurement of a pink-colored product at λ_max = 505 nm while the fluorometric assay is based on the quenching of the fluorescence emission of Cu, N@CQDs at 440 nm after excitation at 370 nm. For the colorimetric method, the absorption intensity linearly increased over the concentration range 4.3-110.0 µM with LOD (S/N = 3) of 1.3 µM. For the fluorometric method, the emission intensity of Cu, N@CQDs linearly decreased upon addition of AMX in the concentration range 0.2-120.0 µM with a limit of detection (LOD, S/N = 3) of 0.06 µM. The proposed system was applied to the determination of AMX in different real samples such as pharmaceutical capsules, human serum, milk, and conduit water samples with recoveries in the range 95.8-104.1% and relative standard deviation (RSD %) less than 4.1%.

Carbon Dot Therapeutic Platforms: Administration, Distribution, Metabolism, Excretion, Toxicity, and Therapeutic Potential

Ultrasmall nanoparticles are often grouped under the broad umbrella term of "nanoparticles" when reported in the literature. However, for biomedical applications, their small sizes give them intimate interactions with biological species and endow them with unique functional physiochemical properties. Carbon quantum dots (CQDs) are an emerging class of ultrasmall nanoparticles which have demonstrated considerable biocompatibility and have been employed as potent theragnostic platforms. These particles find application for increasing drug solubility and targeting, along with facilitating the passage of drugs across impermeable membranes (i.e., blood brain barrier). Further functionality can be triggered by various environmental conditions or external stimuli (i.e., pH, temperature, near Infrared (NIR) light, ultrasound), and their intrinsic fluorescence is valuable for diagnostic applications. The focus of this review is to shed light on the therapeutic potential of CQDs and identify how they travel through the body, reach their site of action, administer therapeutic effect, and are excreted. Investigation into their toxicity and compatibility with larger nanoparticle carriers is also examined. The future of CQDs for theragnostic applications is promising due to their multifunctional attributes and documented biocompatibility. As nanomaterial platforms become more commonplace in clinical treatments, the commercialization of CQD therapeutics is anticipated.

Synthesis of Doped/Hybrid Carbon Dots and Their Biomedical Application

Carbon dots (CDs) are a novel type of carbon-based nanomaterial that has gained considerable attention for their unique optical properties, including tunable fluorescence, stability against photobleaching and photoblinking, and strong fluorescence, which is attributed to a large number of organic functional groups (amino groups, hydroxyl, ketonic, ester, and carboxyl groups, etc.). In addition, they also demonstrate high stability and electron mobility. This article reviews the topic of doped CDs with organic and inorganic atoms and molecules. Such doping leads to their functionalization to obtain desired physical and chemical properties for biomedical applications. We have mainly highlighted modification techniques, including doping, polymer capping, surface functionalization, nanocomposite and core-shell structures, which are aimed at their applications to the biomedical field, such as bioimaging, bio-sensor applications, neuron tissue engineering, drug delivery and cancer therapy. Finally, we discuss the key challenges to be addressed, the future directions of research, and the possibilities of a complete hybrid format of CD-based materials.

Synthesis and Properties of Nitrogen-Doped Carbon Quantum Dots Using Lactic Acid as Carbon Source

Nitrogen-doped carbon quantum dots (N-CQDs) were synthesized in a one-step hydrothermal technique utilizing L-lactic acid as that of the source of carbon and ethylenediamine as that of the source of nitrogen, and were characterized using dynamic light scattering, X-ray photoelectron spectroscopy ultraviolet-visible spectrum, Fourier-transformed infrared spectrum, high-resolution transmission electron microscopy, and fluorescence spectrum. The generated N-CQDs have a spherical structure and overall diameters ranging from 1-4 nm, and their surface comprises specific functional groups such as amino, carboxyl, and hydroxyl, resulting in greater water solubility and fluorescence. The quantum yield of N-CQDs (being 46%) is significantly higher than that of the CQDs synthesized from other biomass in literatures. Its fluorescence intensity is dependent on the excitation wavelength, and N-CQDs release blue light at 365 nm under ultraviolet light. The pH values may impact the protonation of N-CQDs surface functional groups and lead to significant fluorescence quenching of N-CQDs. Therefore, the fluorescence intensity of N-CQDs is the highest at pH 7.0, but it decreases with pH as pH values being either more than or less than pH 7.0. The N-CQDs exhibit high sensitivity to Fe³⁺ ions, for Fe³⁺ ions would decrease the fluorescence intensity of N-CQDs by 99.6%, and the influence of Fe³⁺ ions on N-CQDs fluorescence quenching is slightly affected by other metal ions. Moreover, the fluorescence quenching efficiency of Fe³⁺ ions displays an obvious linear relationship to Fe³⁺ concentrations in a wide range of concentrations (up to 200 µM) and with a detection limit of 1.89 µM. Therefore, the generated N-CQDs may be utilized as a robust fluorescence sensor for detecting pH and Fe³⁺ ions.

Catalytic degradation of methylene blue using iron and nitrogen-containing carbon dots as Fenton-like catalysts

Carbon dots were modified with iron and nitrogen groups to produce specific surface groups and charge which demonstrated high efficiency for the Fenton-like degradation of methylene blue whilst markedly minimising its effluent toxicity.

Carbon-dot doped, transfer-free, low-temperature, high mobility graphene using microwave plasma CVD

Microwave plasma chemical vapor deposition is a well-known method for low-temperature, large-area direct graphene growth on any insulating substrate without any catalysts.

Carbon dot composites for bioapplications: a review

Recent advancements in the synthesis of carbon dot composites and their applications in biomedical fields (bioimaging, drug delivery and biosensing) have been carefully summarized. The current challenges and future trends of CD composites in this field have also been discussed.

Green and facile synthesis of iron-doped biomass carbon dots as a dual-signal colorimetric and fluorometric probe for the detection of ascorbic acid

A new method based on biomass Fe-CDs with fluorescence properties and simulated oxidase activity colorimetric and fluorometric dual-readout assay for highly effective detection of AA was established.

Photothermal-enhanced peroxidase-like activity of CDs/PBNPs for the detection of Fe3+ and cholesterol in serum samples

Carbon dots/Prussian blue nanoparticles (CDs/PBNPs) with fluorescence (FL) performance and peroxidase-like activity are synthesized by a simple two-step method. The FL of CDs/PBNPs can be effectively quenched by Fe³⁺. Fe³⁺ can accelerate the peroxidase-like activity of CDs/PBNPs. More excitingly, the peroxidase-like activity of CDs/PBNPs could be further enhanced due to the influence of the photothermal effect. Based on the FL property and enhanced peroxidase-like activity, a cascade strategy is proposed for detection of Fe³⁺ and free cholesterol. CD/PBNPs act as FL probe for detection of Fe³⁺. The enhanced peroxidase-like activity of CDs/PBNPs can also be used as colorimetric probe for the detection of free cholesterol. The detection ranges of Fe³⁺ and free cholesterol are 4-128 μM and 2-39 μM, and the corresponding limit of detections are 2.0 μM and 1.63 μM, respectively. The proposed strategy has been verified by the feasibility determination of Fe³⁺ and free cholesterol, suggesting its potential in the prediction of disease.

Development of Ag nanoparticle-carbon quantum dot nanocomplex as fluorescence sensor for determination of gemcitabine

Gemcitabine hydrochloride is an established chemotherapeutic agent in several solid tumors. In spite of outstanding therapeutic efficacy, there are some serious fetal side effects with gemcitabine in higher concentrations which necessitate developing a sensitive sensor for its quantification. Herein, a fluorescent metal-nanoparticles conjugated carbon quantum dot (MN-CQD) was prepared by a mixture of citric acid/ammonia sulfate and different metals using hydrothermal method. Based on the primary experiments, the efficiency of Ag nanoparticle-CQDs for gemcitabine determination was found to be much better than others. The AgNp-CQDs fluorescence was quenched by gemcitabine anticancer drug via photo-induced charge transfer which renders the system into fluorescence "OFF" status. Under the experimental conditions, the linear range of detection was 0.003-0.1 μM in an aqueous solution with a correlation coefficient of 0.96 and a limit of detection equal to 0.002 µM. The relative standard deviation (RSD) for gemcitabine determination was 3.4% (n = 3). Finally, after optimizing the conditions, the concentration of analyte was determined in real samples including human plasma and urine. These results confirm that the as prepared fluorescence based nanosensor can be used for sensitive quantification of gemcitabine in real samples.

A Facile Approach for Elemental-Doped Carbon Quantum Dots and Their Application for Efficient Photodetectors

The present work demonstrates a facile hydrothermal approach to synthesize lanthanide-doped carbon quantum dots (CQDs) with europium and/or gadolinium elements. Taking the advantage of broadband adsorption in the ultraviolet-visible region, the doped QDs are directly used as building blocks for photo-electrochemical (PEC)-type photodetectors (PDs) and their performance is systematically investigated under various conditions. The europium (Eu) and gadolinium (Gd) co-doped (C:EuGd) QDs exhibit better photo-response than the single-elemental doped ones and also show outstanding long-term stability. According to the apparent response to light from 350 to 400 nm, the C:EuGd QDs are demonstrated to hold great potential for narrow-band PDs. This work highlights the practical applications of lanthanide-doped CQDs for PDs, and the results are beneficial for the development of elemental-doped CQDs in general.

A bifunctional nanozyme of carbon dots-mediated Co9S8 formation

Controlling the size of nanocrystals and inhibiting their agglomeration are of paramount importance for achieving ideal catalytic performance. Here we discovered that carbon dots (CDs) are not only able to serve as reductants but also as stabilizers of ultrasmall Co₉S₈ nanocrystals by means of their surface terminal groups. As a result, ultrasmall Co₉S₈ nanocrystals are incorporated into porous carbon nanosheets formed by splicing CDs. The resultant nanocomposites display a rich pore structure accompanying with large specific surface area and outstanding bifunctional performances to mimic the catalytic activity of peroxidase and oxidase without exerting any external energy. More importantly, the unique architecture endows Co₉S₈ nanocrystals with high stability and good durability. The nanocomposites have been demonstrated as a colorimetric sensor for detection of ascorbic acid with a superior anti-interference ability as well as a detection limit of 0.2 μM. Our findings open new synthetic opportunities by tuning the interaction of CDs with the surrounding environment and enable advanced applications such as biomedicine and catalytic transformations.

Carbon Quantum Dots Conjugated Rhodium Nanoparticles as Hybrid Multimodal Contrast Agents

Nanoparticle (NP)-based contrast agents enabling different imaging modalities are sought for non-invasive bio-diagnostics. A hybrid material, combining optical and X-ray fluorescence is presented as a bioimaging contrast agent. Core NPs based on metallic rhodium (Rh) have been demonstrated to be potential X-ray Fluorescence Computed Tomography (XFCT) contrast agents. Microwave-assisted hydrothermal method is used for NP synthesis, yielding large-scale NPs within a significantly short reaction time. Rh NP synthesis is performed by using a custom designed sugar ligand (LODAN), constituting a strong reducing agent in aqueous solution, which yields NPs with primary amines as surface functional groups. The amino groups on Rh NPs are used to directly conjugate excitation-independent nitrogen-doped carbon quantum dots (CQDs), which are synthesized through citrate pyrolysis in ammonia solution. CQDs provided the Rh NPs with optical fluorescence properties and improved their biocompatibility, as demonstrated in vitro by Real-Time Cell Analysis (RTCA) on a macrophage cell line (RAW 264.7). The multimodal characteristics of the hybrid NPs are confirmed with confocal microscopy, and X-ray Fluorescence (XRF) phantom experiments.

A chemiluminescence probe enhanced by cobalt and nitrogen-doped carbon dots for the determination of a nitrosative stress biomarker

A chemiluminometric method is introduced for the determination of the stress biomarker, 3-nitrotyrosine (3-NT) based on the H₂O₂-NaIO₄ reaction enhanced by cobalt and nitrogen-doped carbon dots (Co,N-CDs). In this chemiluminescence (CL) system, the emission proved to be originated from the excited-state Co,N-CDs (λ_max = 504 nm). Comparing the effect of Co,N-CDs with that of some other metal ion-doped CDs and undoped CDs indicated the high efficiency of Co,N-CDs in the CL amplification (about 1980-fold). This was attributed to the fact that Co,N-CDs, in addition to other functions, could act as catalytic center, to accelerate the decomposition of H₂O₂ and to increase the number of hydroxyl radicals. It was found that 3-NT inhibits the action of Co,N-CDs by an electron transfer process, leading to a decline in the CL intensity of the system. Therefore, a new CL sensing platform was introduced for the assay of 3-NT in the range 5.0 to 300 nM with a detection limit of 1.5 nM. The probe was utilized for the analysis of biological samples.

Fe-Coordinated Carbon Nanozyme Dots as Peroxidase-Like Nanozymes and Magnetic Resonance Imaging Contrast Agents

The catalytic activities of currently developed peroxidase-mimic nanozymes are generally limited. Therefore, further efforts are still needed to improve the catalytic performance of peroxidase nanozymes. Herein, we synthesized Fe-coordinated carbon nanozyme dots (Fe-CDs) that can serve as both efficient peroxidase nanozymes and T₂-magnetic resonance imaging (MRI) contrast agents. The intrinsic peroxidase-like activity of the Fe-CDs was explored by catalytic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) with hydrogen peroxide (H₂O₂). The product showed better performance over natural horseradish peroxidase (HRP) and other mimetic peroxidases. Quantification of glucose and ascorbic acid detection showed that this nanozyme could be used to detect a minimum limit as low as 5 μM glucose. Moreover, the colorimetric detection technique was used to detect serum glucose in mice, and the detection result was comparable with autobiochemistry analyzer results using a glucose assay kit. Furthermore, the Fe-CDs showed good magnetism properties and provided promising MR imaging of tumors with excellent biocompatibility.

Green sonochemistry assisted synthesis of hollow magnetic and photoluminescent MgFe2O4-carbon dot nanocomposite as a sensor for toxic Ni(ii), Cd(ii) and Hg(ii) ions and bacteria

The purpose of this study was synthesis of photoluminescent nanoparticles for detection of toxic metal ions. Also, these controllable magnetic nanocomposites were used for detection of Pseudomonas aeruginosa bacteria. Carbon nano-templates were formed by calcination and sonication of lemon extract as a bio-compatible precursor. Then MgFe₂O₄ nanoparticles were incorporated on the carbon nano-templates. The composite was calcinated to decompose carbon and obtain hollow structures. Finally, photoluminescent carbon dots were deposited on the porous magnesium ferrite core. Because of the hollow structure, carbon dots can diffuse to the Mg-ferrite core so magnetic and photoluminescence properties are available simultaneously. Photoluminescence intensity decreases with increasing Ni(ii), Cd(ii), Hg(ii) metal ions and Pseudomonas aeruginosa. Results show an effective nanostructure for identification of toxic metal ions and also bacteria.

The purpose of this study is synthesis of magnetic and photoluminescence nanoparticles at the same time for finding of bacteria that could be fatal and its detection are crucial for some illness prohibition.

Dopamine Functionalized S,N Co-doped Carbon Dots as a Fluorescent Sensor for the Selective Detection of Fe3+ and Fe2+ in Water

In current work, novel functionalized carbon dots have been designed and synthesized by covalently linking dopamine to the surface of S,N co-doped carbon dots (DA-S,N-CDs) for the selective detection of Fe³⁺ and Fe²⁺ in water. The as-synthesized DA-S,N-CDs emit blue fluorescence peaked at 470 nm and exhibit excitation-dependent tunable emissions. The tolerance towards pH, salt, and UV irradiation of synthesized carbon dots reveals excellent stability. Upon exposure to Fe³⁺ or Fe²⁺, the fluorescence of DA-S,N-CDs was selectively quenched, while other competitive cations did not change significantly. Under the optimal experimental conditions, the fluorescence intensity of DA-S,N-CDs showed a good linear relationship with the concentrations of Fe³⁺ and Fe²⁺ (5 - 200 μM for Fe³⁺ and 5 - 300 μM for Fe²⁺), and the limit of detection was 2.86 and 2.06 μM, respectively. Furthermore, considering the excellent stability and anti-interference, DA-S,N-CDs have been successfully used for the detection of Fe³⁺ and Fe²⁺ in environmental water.

Biocompatible sulfur nitrogen co-doped carbon quantum dots for highly sensitive and selective detection of dopamine

In this work, sulfur and nitrogen co-doped carbon quantum dots (S,N-CQDs) were prepared via one-pot hydrothermal treatment of EDTA disodium and sodium sulfide. The prepared S,N-CQDs were characterized by TEM, XRD, FT-IR, XPS, UV-vis absorption and fluorescence spectra to characterize their morphology, crystal structure, functional groups, elemental composition, and optical properties. It was found that S and N elements were successfully doped into the CQDs and the morphology was approximately spherical with an average particle size of 2.16 nm, in which the excitation/emission wavelengths were 350 and 420 nm, respectively. Compared with single element doped CQDs, double element doped CQDs have a higher quantum yield and excellent optical stability. Cell experiments showed that S,N-CQDs had good biocompatibility because they had no obvious toxicity on both normal cell lines and cancer cell lines. More importantly, based on the synergy of static quenching and dynamic quenching, the S,N-CQDs were used as effective fluorescent probes for sensitive detection of DA, with high anti-interference and low limit of detection. Based on the good biocompatibility of S,N-CQDs, the detection of dopamine in actual serum samples were carried out and the results showed an excellent recovery rate. Therefore, this work provides a dopamine sensor with a practical application prospect.

Doped-carbon dots: Recent advances in their biosensing, bioimaging and therapy applications

As a fascinating class of fluorescent carbon dots (CDs), doped-CDs are now sparked intense research interest, particularly in the diverse fields of biomedical applications due to their unique advantages, including low toxicity, physicochemical, photostability, excellent biocompatibility, and so on. In this review, we have summarized the most recent developments in the literature regarding the employment of doped-CDs for pharmaceutical and medical applications, which are published over approximately the past five years. Accordingly, we discuss the toxicity and optical properties of these nanomaterials. Beyond the presentation of successful examples of the application of these multifunctional nanoparticles in photothermal therapy, photodynamic therapy, and antibacterial activity, we further highlight their application in the cellular labeling, dual imaging, and in vitro and in vivo bioimaging by use of fluorescent-, photoacoustic-, magnetic-, and computed tomography (CT)-imaging. The potency of doped-CDs was also described in the biosensing of ions, small molecules, and drugs in biological samples or inside the cells. Finally, the advantages, disadvantages, and common limitations of doped-CD technologies are reviewed, along with the future prospects in biomedical research. Therefore, this review provides a concise insight into the current developments and challenges in the field of doped-CDs, especially for biological and biomedical researchers.

Carbon Dot-NaCl Crystals for White-Light Generation and Fabry-Perot Lasing

Phosphor materials with broad spectral range and an average emission lifetime (20 μs) have been achieved from carbon dots (CDs)-NaCl crystals. A one-pot synthesis pathway has been developed for CDs-NaCl crystals formation at room temperature. Precursor for CDs materials was screened at room temperature by oxidation methodology from different simple sugar molecules. CDs (size less than 10 nm) prepared from the fructose sugar exhibit most intense emission. Utilizing ripe banana peel (contains ∼27% of fructose) as a precursor for the carbon dot formation, white-light emission with a CIE index of (0.29, 0.34) has been achieved from the single source with CDs-NaCl crystals upon excitation at 430 nm. The crystals also function as Fabry-Perot (F-P) mode resonator for lasing, with a laser threshold value of 0.9 mW and a resonating Q-factor of 207. These results outline a new approach for realizing F-P lasing and white light emission from a non-toxic green source with a quick, facile and low-cost synthesis procedure.

Leonardos I, Stalikas CD. Metabolomic Profiling Unveils the Impact of Non-Doped and Heteroatom-Doped Carbon Nanodots on Zebrafish (Danio rerio) Embryos

Recently, concern has been raised over the transport, transformation, and fate of carbon nanodots (CNDs) after their release into the environment. Their toxicity towards organisms and humans has recently been addressed as an important issue. In this study, a metabolomic approach was employed to obtain an insight into the effect of CNDs (either pristine or doped with nitrogen and nitrogen/sulfur) on zebrafish. Embryos were exposed to concentrations corresponding to lethal concentration (LC) LC₅₀ (550, 400, and 150 μg mL⁻¹), LC_50/2 (275, 200, and 75 μg mL⁻¹), and LC_50/4 (138, 100, and 38 μg mL⁻¹) of the three CNDs (non-doped, N-doped, and N,S-codoped, respectively) to scrutinize the interactions of the CNDs with the larvae. Numerous differences in the metabolic pathways were recorded in all cases. Seven metabolic pathways were detected in the control larvae. When the larvae were exposed to concentrations equal to LC₅₀, LC_50/2, and LC_50/4 of non-doped CNDs, 12, 12, and 3 metabolic pathways were detected, respectively. In the case of N-doped CNDs, 4, 7, and 4 pathways were detected, while in the case of N,S-codoped CNDs, 8, 5, and 5 pathways were detected when exposed to concentrations of LC₅₀, LC_50/2, and LC_50/4, respectively. In all cases, certain metabolic pathways were altered while others were either down-regulated or up-regulated. Some of these changes include the activation of alanine, aspartate, and glutamate metabolism, aminoacyl-tRNA biosynthesis, butanoate metabolism, D-glutamine, and D-glutamate metabolism, glutathione metabolism, selenoamino acid metabolism, valine, leucine, and isoleucine degradation pathways. Moreover, the deactivation of starch and sucrose metabolism, the glycine, serine, and threonine metabolism, among others, were recorded. Our findings underline the importance to further study the impact of CNDs on marine organisms. As zebrafish has been shown to share many similarities with humans in bioprocesses and genome, it can be assumed that CNDs may also pose a threat to human health.

Recent advances in the construction and analytical applications of carbon dots-based optical nanoassembly

Recently, more and more attention has been focused on the construction and analytical applications of optical nanoassembly through combining carbon dots (CDs) with various other functional nanomaterials. The rational design and manufacture of CDs-based optical nanoassembly will be critical to meeting the needs of analytical science. The last decade has witnessed the immense potential of CDs-based optical nanoassembly in multiple sensing applications owing to their controlled optical properties, adjustable surface chemistry and microscopic morphology. This feature article collects the recent advances in the research and development of CDs-based optical nanoassembly and their applications in analytical sensors, aiming to provide vital insights and suggestions to inspire their broad sensing applications.

Metal-doped and hybrid carbon dots: A comprehensive review on their synthesis and biomedical applications

Carbon dots (CDs) are the most promising candidates of the carbon family with superior properties like ultra-small size, high aqueous solubility, low cytotoxicity, and inherent photoluminescence which makes them suitable for diverse biomedical applications. Methods have been developed to enhance their applications. Doping/surface passivation of CDs improves their physicochemical properties, visible light absorption probability, and quantum yield by controlling their size, morphology, structure, and band-gap energy. Recently, metal-doped CDs have emerged as an important class of nanomaterials with numerous biomedical applications. Additionally, the conjugation of CDs with semiconductor metal-oxide nanoparticles (NPs) enhances their free radical production rates under visible light irradiation. Conjugation of fluorescent CDs with magnetic NPs leads to the development of multimodal imaging platforms. Similarly, ternary conjugates composed of fluorescent CDs, near-infrared (NIR) responsive, and magnetic NPs are useful for multi-modal imaging-guided, and NIR-responsive synergistic chemo-phototherapy. However, no comprehensive review is published yet which covers metal-doped and hybrid CDs. Therefore, herein we provide detailed information about their synthesis and important biomedical applications. Firstly, we have covered various synthesis methods for CD conjugation including the critical analysis of the effects of the reaction conditions and doping/conjugation on the structure and properties of the CDs. Then we have extensively reviewed their biomedical applications as antimicrobial, antioxidant, and bioimaging agents, and in the field of cancer phototherapy with special emphasis on their mechanisms of actions. Finally, the future directions of research and the applications of the metal-doped and hybrid CDs have been discussed. We believe that this review article will enrich the understanding of different synthetic routes of CD-nanocomposites and their biomedical applications.

Natural carbon-based quantum dots and their applications in drug delivery: A review

Natural carbon based quantum dots (NCDs) are an emerging class of nanomaterials in the carbon family. NCDs have gained immense acclamation among researchers because of their abundance, eco-friendly nature, aqueous solubility, the diverse functionality and biocompatibility when compared to other conventional carbon quantum dots (CDs).The presence of different functional groups on the surface of NCDs such as thiol, carboxyl, hydroxyl, etc., provides improved quantum yield, physicochemical and optical properties which promote bioimaging, sensing, and drug delivery. This review provides comprehensive knowledge about NCDs for drug delivery applications by outlining the source and rationale behind NCDs, different routes of synthesis of NCDs and the merits of adopting each method. Detailed information regarding the mechanism behind the optical properties, toxicological profile including biosafety and biodistribution of NCDs that are favourable for drug delivery are discussed. The drug delivery applications of NCDs particularly as sensing and real-time tracing probe, antimicrobial, anticancer, neurodegenerative agents are reviewed. The clinical aspects of NCDs are also reviewed as an initiative to strengthen the case of NCDs as potent drug delivery agents.

A "Polymer Template" Strategy for Carbonized Polymer Dots with Controllable Properties

Limited avenues are available for property control of carbonized polymer dots (PDs) owing to the unsatisfactory understanding of PDs" formation. Herein, a de novo "polymer template" strategy is presented for PDs with customizable functional surface groups (FSG), size, and underlying fluorescence, with a detailed mechanism. The strategy relies on novel di-active site polymers (DASPs) prepared from alkenyl azides via [3+2] cycloaddition and guanidino hydrolysis. Benefiting from these specific reactions, the DASPs were convenient for mass production and stable for storage, and could be transformed to PDs upon addition of nucleophilic agents through nucleophilic addition and substitution at 70 °C. By regulating the types of alkenyl azides, nucleophilic agents, and reaction conditions, the as-prepare PDs could be tailored with controlled types of core, FSG, and particle size, as well as fluorescence properties of quantum yield from 8.2-55.6 %, and emission maximum from 380-500 nm. These specialties make this "polymer template" strategy a promising start for building PDs-based sensor platforms. Moreover, the strategy could further our understanding towards PDs' formation, and open up a new way to customize PDs for specific needs in the fields of analysis, catalysis, images, etc.

An ultrasensitive chemiluminescence assay for 4-nitrophenol by using luminol-NaIO4 reaction catalyzed by copper, nitrogen co-doped carbon dots

A chemiluminescence (CL) assay on the basis of the tremendous enhancing effect of copper and nitrogen co-doped carbon dots (Cu,N-CDs) on the luminol-NaIO₄ reaction was introduced for the determination of nanomolar levels of 4-nitrophenol (4-NP). Cu,N-CDs were synthesized by a hydrothermal approach and characterized by TEM, XRD, EDX, and FTIR analysis. The potential CL mechanism was elucidated by recording the CL spectrum and by evaluating the influence of reactive oxygen species. It was found that 4-NP remarkably inhibited the luminol-NaIO₄-Cu,N-CDs reaction and reduced the CL signal of the reaction. This fact was applied for developing a CL assay for 4-NP. Under the optimized conditions, 4-NP could be determined in the concentration range of 0.25 to 150 nM, with a detection limit as low as 0.06 nM. This assay was successfully exploited for the analysis of 4-NP in real environmental samples.

Fluorescent Carbon Quantum Dots-Synthesis,Functionalization and Sensing Application in FoodAnalysis

Carbon quantum dots (CQDs) with stable physicochemical properties are one of theemerging carbon nanomaterials that have been studied in recent years. In addition to the excellentoptical properties such as photoluminescence, photobleaching resistance and light stability, thismaterial also has favorable advantages of good biocompatibility and easy functionalization, whichmake it an ideal raw material for constructing sensing equipment. In addition, CQDs can combinedwith other kinds of materials to form the nanostructured composites with unique properties, whichprovides new insights and ideas for the research of many fields. In the field of food analysis,emerging CQDs have been deeply studied in food composition analysis, detection and monitoringtrace harmful substances and made remarkable research progress. This article introduces andcompares the various methods for CQDs preparation and reviews its related sensing applicationsas a new material in food components analysis and food safety inspection in recent years. It isexpected to provide a significant guidance for the further study of CQDs in the field of foodanalysis and detection. CQDs; synthesis; fluorescent sensing; food analysis.

Platinum ions mediate the interactions between DNA and carbon quantum dots: diagnosis of MRSA infections

In this study, we have developed a rapid and cost-effective method employing platinum ion (Pt4+)-capped fluorescent carbon quantum dots (CQDs) coupled with loop-mediated isothermal amplification (LAMP) to detect dual MRSA genes. We synthesized nitrogen- and chlorine-co-doped fluorescent CQDs (CQDSPDs) from spermidine trihydrochloride via a simple one-step pyrolysis. The CQDSPDs capped with Pt4+ ions through the cooperative coordination of the amine and chlorine groups on the surface of CQDs facilitated the double-stranded DNA (dsDNA)-induced fluorescence quenching of CQDs, and enabled the construction of the CQDSPDs/Pt4+ probe for the detection of as few as 10 copies of the MRSA gene (mecA and femA). The sensitivity and specificity of the CQDSPDs/Pt4+ probe for MRSA detection in clinical specimens (n = 24) were 94% and 86%, respectively. Our results reveal that the CQDSPDs/Pt4+ probe has great potential for the diagnosis of antibiotic-resistant superbugs with high sensitivity, specificity, and agreement.

Facile Fluorescence Dopamine Detection Strategy Based on Acid Phosphatase (ACP) Enzymatic Oxidation Dopamine to Polydopamine

Facile and effective detection of dopamine (DA) plays a significant role in current clinical applications. Substantially, special optical nanomaterials are important for fabricating easy-to-control, cheap, selective, and portable fluorescence DA sensors with superior performance. Herein, carbon dots (CDs) prepared from melting method were applied as signal to establish a simple but effective fluorescence strategy for DA determination based on the enzymatic activity of acid phosphatase (ACP), which induces DA to form polydopamine (pDA). The formed pDA caused by the enzymatic oxidization of ACP toward DA can interact with CDs through the inner filter effect. Such behavior effectively quenched the CDs' fluorescence. The degree of fluorescence quenching of CDs was positively correlated with the DA content. Under the optimized reaction conditions, the proposed fluorescence method exhibited a comparable analytical performance with other DA sensors with good selectivity. Furthermore, this method has been successfully applied to detect DA in DA hydrochloride injection and human serum samples. It shows that this method features potential practical application value and is expected to be used in clinical research.

N,Fe-Doped Carbon Dot Decorated Gear-Shaped WO3 for Highly Efficient UV-Vis-NIR-Driven Photocatalytic Performance

The development of efficient and non-toxic photocatalysts with a full spectrum response is a primary strategy in the area of photocatalytically mediated pollutant elimination. Herein, we report the preparation of novel nitrogen and iron co-doped carbon dots/gear-shaped WO3 (N,Fe-CDs/G-WO3) with significantly improved broad-spectrum utilization. Characterization results demonstrated that the gear-shaped G-WO3, decorated by N,Fe-CDs with excellent electron transfer/reservoir properties, possessed abundant oxygen vacancies, had large specific surface areas, had multiple light-reflections and had a narrow band gap. As a result, the N,Fe-CDs/G-WO3 composite exhibited excellent photocatalytic activity towards the degradation of water contaminants under full spectrum irradiation. For example, the photodegradative efficiencies of rhodamine B (RhB) reached 81.4%, 97.1%, and 75% in 2 h, under ultraviolet, visible, and near-infrared (UV, vis, and NIR) light irradiation, respectively. Moreover, the N,Fe-CDs/G-WO3 composite also exhibited an outstanding photocatalytic degradation efficiency for other dyes, pharmaceuticals, and personal care products (PPCPs) like methylene blue (MB), ciprofloxacin (CIP), tetracycline hydrochloride (TCH), and oxytetracycline (OTC) (91.1%, 70.5%, 54.5%, and 47.8% in 3 h, respectively). The radical trapping experiments indicated that h+ and ·OH were the main reactive oxidative species (ROS), and the conversion between Fe (III) and Fe (II) played a key role in the photocatalytic reactions. Such a N,Fe-CD decorated material with brilliant photocatalytic activity has tremendous potential for application in environmental remediation.

Development of sulfur doped carbon quantum dots for highly selective and sensitive fluorescent detection of Fe2+ and Fe3+ ions in oral ferrous gluconate samples

Sulfur-doped carbon quantum dots (S-CQDs) with stable blue fluorescence were synthesized through a facile one-step hydrothermal method by using ascorbic acid and thioglycolic acid as carbon and sulfur sources. The prepared S-CQDs exhibited a sensitive and selective response to Fe³⁺ ions in comparison with Fe²⁺ and other metal ions, In the presence of adequate H₂O₂, Fe²⁺ was completely transformed to Fe³⁺ that is the determinable form of iron ions, and the difference in the change of the fluorescence intensity of S-CQDs before and after adding H₂O₂ was used for detection of Fe²⁺ and Fe³⁺ ions, respectively. Under the optimum experimental conditions, the fluorescence intensity of S-CQDs gradually decreased with increasing of Fe³⁺ concentration ranging from 0 to 200 μM. Good linearity was achieved over the range of 0-200 μM. The detection limit of the developed method was 0.050 μM for Fe³⁺. The recoveries of Fe²⁺ and Fe³⁺ spiked in real samples ranged from 98.2% to 112.4%. Finally, the proposed S-CQDs integrated with Fenton system was applied to the detection of Fe²⁺ and Fe³⁺ ions in oral ferrous gluconate samples, which presents potential applications in the speciation and determination of Fe²⁺ and Fe³⁺ ions in complex samples.

Simultaneous quantification of peroxidase and ascorbic acid in biosamples with an automatic system based on a Fe(iii)/methylthymol blue-carbon dot simulative enzyme

Simultaneous and automatic quantification of peroxidase and ascorbic acid based on one reaction system and application of a carbon dot simulative enzyme.

Fluorescent N/Al Co-Doped Carbon Dots from Cellulose Biomass for Sensitive Detection of Manganese (VII)

Development of metallic and nonmetallic heteroatom doped carbon dots have gained attention due to their enhanced physicochemical and photoluminescence properties. In this study, a facile one pot hydrothermal carbonisation approach was taken to synthesise nitrogen, aluminum co-doped carbon dots (N/Al-CDs) with a photoluminescence quantum yield of 28.7%. Durian shell, a cellulose biomass waste, was used as the primary carbon source and compared to previously reported cellulose based carbon dots, this study presents one of the highest quantum yields. The structural and fluorescent properties of the synthesised N/Al-CDs were characterized through X-ray photoelectron spectroscopy (XPS), fluorescence spectra, and Fourier transform infrared spectroscopy (FTIR). The maximum emission was at 415 nm upon excitation at 345 nm. The synthesised N/Al-CDs were resistant to photobleaching and highly photostable within the pH, ionic strength and temperature variations investigated. The transmission electron microscopy (TEM) images showed particles were quasi-spherical and well dispersed with an average diameter of 10.0 nm. Further, the N/Al-CDs was developed as a fluorescence sensor for highly selective and sensitive detection of Mn (VII) ions. A linear relationship was developed over a concentration range of 0-100 μM while the limit of detection was 46.8 nM. Application of the sensor for detection of Manganese (VII) to two real water samples showed relative standard deviation was less than 3.9% and 1.3%, respectively.

A highly sensitive and accurate SERS/RRS dual-spectroscopic immunosensor for clenbuterol based on nitrogen/silver-codoped carbon dots catalytic amplification

Preparation of multifunctional codoped carbon dots, and their new analytical applications in surface-enhanced Raman scattering (SERS) quantitative analytical method are still challenge. To overcome these problems, the nitrogen/silver-codoped carbon dots (CD_N/Ag) with highly catalytic amplification are prepared by microwave method, and characterized by spectrophotometry and electron microscopy. The results show that CD_N/Ag can strongly catalyze trisodium citrate-HAuCl₄ reaction to generate red nanogold with resonance Rayleigh scattering (RRS) effect and SERS effect using Victoria blue B (VBB) as molecular probes. The CD_N/Ag catalytic amplification and specific immunoreaction of clenbuterol (Clen) are coupled with highly sensitive SERS and accurate RRS to fabricate a new dual-spectroscopic strategy with a detection limit of 0.68 pg mL^-1 Clen.

Copper-Doped Carbon Dots for Optical Bioimaging and Photodynamic Therapy

Carbon dots (CDs), as an effective bioimaging agent, have aroused widespread interest. With the increasing number of CDs used in photodynamic therapy (PDT), developing efficient CDs with multiple functions such as imaging and phototherapy has become a new challenge. Herein, a new type of copper-doped CDs (Cu-CDs) with a high fluorescence quantum yield of 24.4% was synthesized from a copper complex of poly(acrylic acid) through coordination between the carboxyl group and copper ions. Owing to their good solubility, bright fluorescence, and low cytotoxicity, the Cu-CDs can be used for fluorescence imaging in both the HeLa (human cervical cancer) cell line and SH-SY5Y (human neuroblastoma cells) multicellular spheroids (3D MCs). More importantly, the Cu-CDs show a high quantum yield of singlet oxygen (¹O₂; 36%), good photoinduced cytotoxicity, and effective inhibition of 3D MC growth. Therefore, the Cu-CDs can be used as a promising imaging-guided PDT agent. This study provides a new carbon-based nanomaterial for multifunctional photodiagnostic and therapeutic agents for biological applications.