Surface Of Carbon Quantum Dots Research Articles

Ammonia vapour detection at room temperature via carbon quantum dots based facile system

With widespread industrial use of ammonia and its potential hazards to both human health and the environment, ensuring reliable detection has become paramount. In the present work, we report a study on a novel and highly sensitive gas sensing material, composed of carbon quantum dots (CQDs) for the detection of ammonia vapor at room temperature. The CQDs were synthesized at 200 °C using a hydrothermal single-step process. To investigate the morphology and chemical composition, CQDs were characterized by Fourier transform infrared spectroscopy, Transmission Electron Microscopy, photoluminescence, and UV–Vis spectroscopy. A thin-film of CQDs was then deposited on an ITO-coated glass substrate for the detection and quantification of ammonia vapor (NH3) by monitoring the response under ambient conditions. By corresponding change in conductance, the change in resistance of the film is investigated. The enhanced properties of sensing of the ammonia samples may be due to the combined effect of localized electronic surface states of CQDs and chemical sensitization caused by the catalytic properties of an active functional group on the CQDs surface. Notably, this sensor exhibits higher sensitivity, excellent response time, and greater stability to ammonia vapours compared to previous reports.

Spectrofluorometric determination of calcium in the human nasal secretions investigating the association with olfactory function

Ionic microenvironment of the nasal secretions especially calcium ions play essential role in the olfactory transmission. However, there is a critical need to determine the free calcium levels in healthy people's nasal secretions in contrast to those of patients with olfactory impairment. A selective spectrofluorometric method was created to quantify nasal calcium levels utilizing its quenching ability to the fluorescence of the functionalized carbon quantum dots. The surface of carbon quantum dots was functionalized with calcium ionophore A23187 and ion association complex, calcium phosphotungstate, to improve the selectively to quantify calcium ions. The functionalized carbon quantum dots exhibited a concentration-dependent fluorescence quenching upon interaction with calcium ions. Different factors influencing the quenching process were done to provide efficient analytical process. The new method, demonstrated accurate calcium determination over the concentration range of 200–4000 ng/mL. The suggested technique was used to measure the calcium in the nasal secretions of both healthy people and patients with olfactory impairment. The findings revealed significantly higher calcium levels in the patient with olfactory dysfunction (healthy vs. patient; 735 ± 20 ng/mL vs. 2987 ± 37 ng/mL, p < 0.05).

Fluorescence Cell Imaging by Carbon Quantum Dots Derived from the Medicinal Plant Malva Sylvestris

Carbon quantum dots (CQDs) derived from biological samples exhibit low cytotoxicity and are often used as fluorescent agents for bioimaging cells or bacteria. In this study, fluorescent CQDs derived from Malva sylvestris, a wild edible medicinal plant (common mallow), were used to visualize the human epithelial cells (PNT1A). CQDs with strong blue photoluminescence were synthesized by microwave irradiation of dried M. sylvestris in water. CQDs' structural, morphological, surface features and photoluminescence properties were evaluated. In vitro, cytotoxicity assays revealed that carbon quantum dots from M. sylvestris have no cytotoxic effects on human epithelial cells. Non-cytotoxic and high photoluminescent CQDs from M. sylvestris can be exploited in bioimaging applications as a fluorophore agent

Quantum Yield of the Emission of Carbon Quantum Dots: Tricks Due to Solvent Polarity and Excitation Dynamics

Carbon quantum dots (CQDs) are recognized as promising fluorescent nanomaterials possessing high thermal stability, tuned photoluminescence, along with the low cost of their production. Quantum yield (QY) of photoluminescence (PL) of CQDs is known to vary largely depending on the synthetic procedures/ chemical composition of CQDs, but there is still no unique approach for explanation of the nature and QY of PL emission of CQDs. Particularly, an accompanying effect of the solvent environment on QY of the PL emission is paid less attention. In this work, we compare photophysical properties of CQDs synthesized by different methods that resulted in the different composition of CQDs. First, fluoralkylated CQDs (Fluocar® Nano) doped with F, N and O heteroatoms, were synthesized via solvothermal method using urea, anhydrous citric acid and 3-(trifluoromethyl) aniline as precursors. Second, hydrophilic CQDs were obtained by liquid-phase synthesis procedure using sucrose (“standard” CQDs). Depending on the synthesis procedure the PL emission properties were tuned according to the polarity of solvent the CQDs were dispersed in. It was found that QY of PL emission of Fluocar® Nano has a much stronger magnitude and absolute dependence on the solvent polarity compared to “standard” CQDs. Fluocar® Nano demonstrated QY of PL emission as high as 93% in dioxane and as low as 30% in aqueous dispersion, whereas QY of the “standard” CQDs varied within 0.7-2.3% when relative solvent polarities ranged from 0.164 to 1.0; however, their relative changes depending on the solvent polarity were similar (Fig.1). Dynamics of the PL emission during first minute of excitation in the form of PL relaxation to some saturated value was also strong for Fluocar® Nano dispersed in less polar solvents, while the emission was stable in a strongly polar aqueous medium. Tentative conclusion was made that the surface of CQDs plays a crucial role in tuning the PL emission, providing different concentration of surface traps that become gradually fed during excitation and different interactions of CQD and polar solvents, respectively. Figure 1

Preparation of MDEA derived nitrogen-doped CQDs nanofluids and their CO2 capturing performance and mechanism investigation

Nanofluids acting as the third-generation absorbents are raising concern. However, the complex preparation method, high material cost, and instability hinder their further promotion. Herein, N-methyldiethanolamine (MDEA) as a classic organic amine solution was first used to prepare nitrogen-doped carbon quantum dots (CQDs) by a mild method, and the effective CQDs yield was determined by TEM, FT-IR, XPS, and fluorescence spectrometry. Generated nitrogen-doped CQDs have abundant surface function groups, a narrow size distribution (1–10 nm), and stable fluorescent properties. Moreover, CQDs nanofluids stability was comprehensively evaluated by Turbiscan stability analyzer, Zeta potential analyzer, and solid content analysis. The results indicated a high stability of CQDs in the amine solution. The CO2 capture performance of CQDs nanofluids was evaluated by a bubble reactor, and the maximum absorption enhancement index reached 1.27 in the mixed amine solution. The desorption process was also improved and nearly 6 % heat duty was saved. Finally, the enhancement mechanism of CQDs nanofluids was discussed. In contrast to other studies focusing on the mass transfer effect of nanofluids on macroscopic kinetics, the microscopic interaction effect between CQDs and CO2 was discussed by in-situ FT-IR and XPS. The results prove that apart from the physical adsorption effect, a chemical reaction also exists to capture CO2 by the nitrogen-doped structure and basic groups on CQDs surface, which endow the unique enhancement effect for CO2 capture system by CQDs. In general, the advantageous performance ensured the potential of CQDs nanofluids as advanced absorbents to achieve a low manufacturing cost and scale application.

Detection of SARS-CoV-2 S protein based on FRET between carbon quantum dots and gold nanoparticles

The COVID-19 pandemic caused by SARS-CoV-2 virus brings nasty crisis for public health in the world. Until now, the virus has caused multiple infections in many people. Detecting antigen to SARS-CoV-2 is a powerful method for the diagnosis of COVID-19 and is helpful for controlling and stopping the pandemic. Herein, a rapid and quantitative detection method of SARS-CoV-2 spike(S) protein was built based on the fluorescence resonance energy transfer (FRET) phenomenon without complicated steps. In the process of detecting, the carbon quantum dots (CQDs) and gold nanoparticles (AuNPs) act as donor and acceptor. By modifying the SARS-CoV-2 antibodies on the surface of CQDs and AuNPs, we achieved S protein specific detection using the distance-based FRET phenomenon. Through the electric charge regulation, the limit of detection (LOD) is 0.05 ng/mL, the linear range is 0.1–100 ng/mL, and the detection process only takes 12 min. The proposed method exhibits several advantages such as be available for variants (B.1.1.529 and B.1.617.2) and be suitable for human serum, which is of significance for detecting viral in time and prevention the viral transmission.

Preparation and characterization of carbon quantum dots grafted Co3O4 nanocomposite for supercapacitors application

A pure Co3O4 nanoparticles and a carbon quantum dots (CQDs) anchored cobalt oxide (Co3O4/CQD) nanocomposite were synthesized by a simple hydrothermal method for supercapacitor application. The powder XRD measurement confirms the formation cubic phase of Co3O4. More HR-TEM measurements. The beneficial surface and electronic properties of CQDs were used for the refinement of the electrochemical accomplishments of Co3O4. The Co3O4/CQD and Co3O4 manifest half-cell specific capacitances of 193.8 F g−1 and 123.6 F g−1 @ current density of 4 A g−1, respectively. The introduction of CQDs into the Co3O4 matrix increased the charge-transfer process, which is primarily responsible for the improved electrochemical capabilities of the nanocomposite. The hybrid asymmetric supercapacitor delivers an energy density of 2.49 W h kg−1 @ a power density of 426 W kg−2 with a capacitance retention of 81.8%.

Carbon Quantum Dots Based on Marine Polysaccharides: Types, Synthesis, and Applications.

The marine environment offers a vast array of resources, including plants, animals, and microorganisms, that can be utilized to extract polysaccharides such as alginate, carrageenan, chitin, chitosan, agarose, ulvan, porphyra, and many more. These polysaccharides found in marine environments can serve as carbon-rich precursors for synthesizing carbon quantum dots (CQDs). Marine polysaccharides have a distinct advantage over other CQD precursors because they contain multiple heteroatoms, including nitrogen (N), sulfur (S), and oxygen (O). The surface of CQDs can be naturally doped, reducing the need for excessive use of chemical reagents and promoting green methods. The present review highlights the processing methods used to synthesize CQDs from marine polysaccharide precursors. These can be classified according to their biological origin as being derived from algae, crustaceans, or fish. CQDs can be synthesized to exhibit exceptional optical properties, including high fluorescence emission, absorbance, quenching, and quantum yield. CQDs' structural, morphological, and optical properties can be adjusted by utilizing multi-heteroatom precursors. Moreover, owing to their biocompatibility and low toxicity, CQDs obtained from marine polysaccharides have potential applications in various fields, including biomedicine (e.g., drug delivery, bioimaging, and biosensing), photocatalysis, water quality monitoring, and the food industry. Using marine polysaccharides to produce carbon quantum dots (CQDs) enables the transformation of renewable sources into a cutting-edge technological product. This review can provide fundamental insights for the development of novel nanomaterials derived from natural marine sources.

Enhanced detection sensitivity of Leptospira DNA using a post-deposition annealed carbon quantum dots integrated tapered optical fiber biosensor

Leptospirosis is an illness caused by a Leptospira bacterial infection, and it can be fatal if not correctly diagnosed and treated. This work explores the development of an optical biosensor that utilizes tapered optical fiber integrated with post-deposition annealed carbon quantum dots (CQDs) to improve Leptospira deoxyribonucleic acid (DNA) detection. A standard optical single-mode fiber was tapered before being deposited with CQDs. The surface properties of CQDs on the tapered optical fiber were then tuned using a simple, one-step annealing process. Leptospira probe DNA was covalently bonded to the annealed CQDs surface using several commercially available linkers. The detection was achieved through probe DNA fragments that were hybridized into different concentrations of complementary target DNA. The biosensor limit of detection remained at 1.0 fM, but a better sensitivity of 2.321 ± 0.048 nm/nM was obtained. The affinity towards Leptospira complementary DNA improved as the equilibrium dissociation constant value was lowered to 0.15 х 10−9 M compared to previous studies. In non-complementary DNA reactions, a minimal wavelength shift is detected, indicating the biosensor's high specificity, whereas studies using genomic DNAs from Leptospira and Clostridium difficile (as a control for genomic DNA) revealed similar observation. The integration of CQDs has achieved these remarkable biosensor traits, which hold great potential for developing a reliable leptospirosis diagnosis.

High-performance photocatalytic peroxymonosulfate activation by carbon quantum dots via precise surface chemistry regulation: Insight into the structure–function relations

Carbon quantum dots (CQDs) are considered promising metal-free green catalysts for the activation of persulfates, but direct experimental evidence to identify the true active sites on the surface of CQDs is still lacking. We prepared CQDs with different oxygen contents by controlling the carbonisation temperature, using a simple pyrolysis method. Photocatalytic activity experiments show that CQDs200 exhibits the best PMS activation performance. By investigating the relationship between the oxygen functional groups on CQDs surface and photocatalytic activity, it was postulated that the C=O groups might be the predominant active site, which was confirmed by selective chemical titrations of the C=O, C-OH and COOH groups. Furthermore, limited to the weak photocatalytic properties of the pristine CQDs, ammonia and phenylhydrazine were used to precisely nitrogen-modify the o-CQD surface. We found that phenylhydrazine-modified o-CQDs-PH promoted the absorption of visible light and the separation of photocarriers, thus enhancing the activation of PMS. Theoretical calculations provide more insights from different levels of the pollutant, fine-tuned CQDs, and their interactions.

A sensitive electrochemical genosensor for measuring gastric cancer biomarker, microRNA-106b, based on asparagine polymerization on carbon quantum dots modified electrode

The aim of this work is to develop an electrochemical genosensor to measure microRNA 106b (miR-106b) as a gastric cancer biomarker. To construct the miR-106b genosensor, asparagine (As) was electropolymerized on the surface of carbon quantum dots modified glassy carbon electrode (CQDs/GCE). In the next step, ssDNA was immobilized on the modified electrode surface (As/CQDs/GCE) and then hybridized with miR-106b. Finally, differential pulse voltammograms of the accumulated chlorogenic acid (CGA), as an electroactive label, on the surface of immobilized ssDNA was recorded before (ssDNA/As/CQDs/GCE) and after hybridization with miR-106b (miR-106b/BSA/ssDNA/As/CQDs/GCE). The difference in the peak current of these two voltammograms was used as an analytical signal to measure of miR-106b. Using this genosensor, a linear concentration range from 1.0 fM to 1.0 µM and a detection limit of 0.39 fM were obtained for the measurement of miR-106b. The obtained data indicate that it is possible to recognize miR-106 from a non-complementary and a single-base mismatch sequence using the genosensor. In addition, the measurement of miR-106b in a human serum sample was successfully performed using the genosensor.

On the role of UV-generated ROS in the desorption of cephalexin from CQDs-based drug-loadable platform

Since the emergence of carbon quantum dots (CQDs), they have attracted much considerations because of their potential applicability in myriad industries. Innumerable efforts have been made to demystify the mysterious world of CQDs from physicochemical view point. In the present work, CQDs were synthesized via a thermal decomposition method following by post-treatment of the sample using ethylenediaminetetraacetic acid (EDTA) as the surface modifier to prepare EDx-CQDs sample where x represents the weight of the utilized EDTA in the study. Then, cephalexin (Cp) with various concentarations were loaded onto the EDx-CQDs to investigate the possibility of Cp adsorption. Cp desorption process was initiated by a 365 nm UV light source. Noteworthily, structural changes of EDx-CQDs before and after UV exposure of drug-loaded sample were assessed by conducting a series of spectroscopic analyses. Transmission electron microscopy (TEM), energy-dispersive x-ray mapping (EDX), ultra-violet-visible (UV–Vis), photoluminescence (PL) spectroscopy, x-ray diffraction (XRD), Raman scattering spectroscopy, and Fourier transform-infrared (FT-IR) analyses were employed to scrutinize physical, chemical, and structural alterations. A combined reactive oxygen species (ROS) mechanism was found to be responsible for the desorption of Cp molecules from CQDs surface. The entanglement of both mechanisms initiates a chain ROS reaction leading to complete detachment of Cp molecules.

Solubility tuning of alkyl amine functionalized carbon quantum dots for selective detection of nitroexplosive

The major issue of luminescent carbon quantum dots (CQDs) is the solubility in wide range of solvent and disappearance of luminescence behavior in its solid state due to aggregation caused quenching. To resolve this issue, in the present work, we have tuned the solubility of carbon quantum dots in different kinds of solvents through surface functionalization technique. Here, we have synthesized three sets of alkyl amine functionalized carbon quantum dots from citric acid and alkyl amine by solvothermal method. We have observed that the solubility of CQDs increases from aqueous medium to organic medium with increasing length of hydrophobic alkyl chains attached at the surface of CQDs. It is seen that n-butyl amine functionalized CQDs (C4-CQD) are soluble in any type of solvents. Here we have also observed that the C4-CQD shows aggregation induced emission instead of aggregation caused quenching in solid state and shows bright yellow luminescence color upon excitation. Besides this, we also report selective detection of both dinitroaniline (DNA) and dinitrophenol (DNP) using this C4-CQD via fluorescence quenching and colorimetric methods. In organic medium both shows significant quenching with emission peak of carbon quantum dots is red shifted (∼30 nm) in presence of DNP whereas no significant peak shift is observed for DNA. CQDs containing paper strip shows yellow spot in presence of DNP but no such characteristic color is appeared after addition of DNA. Using these two techniques, we have selectively identified both DNA and DNP among other nitro compounds by our as-synthesized carbon dots.

Surface passivated p-phenylenediamine carbon quantum dots (p-CQDs) as fluorescent turn-on probes for the detection of Li+ and L-arginine by two different mechanisms

Surface modification technique is currently acknowledged as a practical, efficient, and acceptable tool for producing large quantities of high-quality carbon quantum dots (CQDs), however the research on the quenching and recovery mechanism of the fluorescence of CQDs should receive more attention. Herein, the p-phenylenediamine carbon quantum dots (p-CQDs) exhibiting outstanding characteristics has been synthesized from erbium nitrate (Er(NO3)3) ethanol solution. It shows as a highly efficient “on-off-on” fluorescent probe for the detection of Fe3+, Li+ and l-arginine (L-Arg). The fluorescence of p-CQDs can be quenched by the appearance of Fe3+ (p-CQDs-Fe3+), then can be restored by adding either Li+ or L-Arg (p-CQDs-Fe3+-Li+ or p-CQDs-Fe3+-L-Arg). The zeta potentials were measured for the four fluorescent systems p-CQDs, p-CQDs-Fe3+, p-CQDs-Fe3+-Li+ and p-CQDs-Fe3+-L-Arg. The results show that the loss of charges on the surface of CQDs is the key point which can determine this probe to remain “on” or “off” mode. In addition, we found that the mechanism of fluorescence “turn-on” is different in p-CQDs-Fe3+-Li+ and p-CQDs-Fe3+-L-Arg system, the former is trying to open the transmission channel of intramolecular photons, which manifests as fluorescence recovery. The latter may strip Fe3+ from the surface of p-CQDs.

Photostable and printable fluorescence carbon quantum dots for advanced message encryption and specific reversible multiple sensing of Cu2+ and cysteine

The ability to manipulate carbon quantum dots (CQDs) fluorescence with specific substances has been of primary importance for applications in advanced dynamic information encryption. The development of CQDs with specific functionalization, high selectivity and excellent fluorescence stability for information security and sensing remains a challenge. In this paper, we present an N-doped and tryptophan functionalized CQDs that can be applied not only as a fluorescent ink for multiple message encryption but also for fluorescent sensitive and selective recognition of Cu2+ and cysteine (Cys) by multi-method, including aqueous solutions, filter paper, hydrogels and in human DU-145 Prostate cancer cells. Theoretical calculations and mechanistic studies suggested that this on–off-on mechanism was attributed to the transfer of electrons between Cu2+ and functionalized groups on the surface of CQDs and stronger coordination capability with Cys. The above results showed that these newly designed CQDs will greatly enrich the fundamental understanding of CQDs by explaining the recognition mechanism between Cu2+ and Cys, and provide an opportunity for anti-counterfeiting, solid-state fluorescent materials, cellular imaging and environmental.

High quantum yield carbon quantum dots as selective fluorescent turn-off probes for dual detection of Fe2+/Fe3+ ions

Carbon quantum dots (CQDs) are fluorescent nanoparticles that have great potential for use as nontoxic fluorescent probes. However, synthesizing CQDs with high photoluminescence quantum yield (QY) in a rapid and facile way from commonly available and low-cost reagents is still challenging. In this work, Tween®80 was used as a surface passivation agent along with citric acid/urea in a one-step microwave procedure to make extremely blue luminous nitrogen doped CQDs. When excited at 350 nm, these CQDs had a fluorescent quantum yield of 75.5 %. The significant high quantum yield and stability of these CQDs are attributed to the high aromatic sp2 domain size within the CQD core and improved carbon and oxygen functional groups at the CQDs surface. We employed the CQDs as a fluorescent probe to detect Fe2+ and Fe3+ ions and could establish a linear relationship between photoluminescence quenching efficiency (F0-F/F0) and ion concentration with a detection limit of 6.5 µM and 2.5 µM for Fe2+ and Fe3+, respectively. Our studies suggest that the highly selective detection of iron ions is a result of partial transfers of excited electrons from the CQDs to the d orbital of the iron ions, instead of contributing to radiative relaxation that induces photoluminescence quenching of the CQDs. Other reported carbon dots for this application have a substantially lower quantum yield and only detect Fe3+ ions. Therefore, our CQDs have considerable benefits over similar probes. Subsequent research may adapt them to other areas due to the high quantum yield and stability.

The effect of microwave power level and post-synthesis annealing treatment on oxygen-based functional groups present on carbon quantum dots

Despite widespread interest in understanding the properties of carbon quantum dots (CDOTs), there appear to be fewer studies systamaticaly investigating CDOTs' luminescent mechanisms. The primary objective of this study is to prepare CDOTs with desirable optical properties and to understand the photoluminescence (PL) mechanisms involved in order to control the emission charectersitcs. The optical properties of CDOTs are strongly influenced by the functional groups (-OH, –CHO, –COOH, –CO, –COO) formed on the surface of the dots. The key factors affecting the nature and number of functional groups are the preparation method, post synthesis treatment, and the precursor materials. Ascorbic acid was used as the starting material in this study to synthesize CDOTs via microwave-assisted synthesis techniques. Then, the effect of microwave power level and post synthesis annealing temperature on the oxygen-based functional groups present on the surface of the dots was evaluated systematically. It was found that the increasing microwave power level increases the density of functional groups present on the surface of CDOTs, which positively affects the PL. However, annealing at high temperatures decreases the concentration of functional groups and reduces the PL intensity. The PL emission peaks were deconvoluted and the emission wavelength corresponding to each functional group was identified. This work underlines the role of oxygen based functional groups on the PL emission and the ways to control them by physical means.

Characterization of N‐doped carbon quantum dots synthesized by DBD‐based cold atmospheric pressure plasma jet

AbstractThis study develops a new approach for the synthesis of fluorescent N‐doped carbon quantum dots (CQDs), using cold atmospheric pressure plasma jet. Herein, the CQDs were synthesized with two plasma exposure times of 30 and 60 min. The UV‐Vis absorption spectrum confirms the existence of carbonic core and surface functional groups. The Fourier transform infrared spectrum shows that carbonyl groups and amide groups exist on the surface of CQDs. Depending on the plasma exposure time, the mean average sizes of CQDs are 3.63 and 5.45 nm with strong photoluminescence emission. Generally, our results indicated that using different mechanisms for plasma discharge, lead to different physical and chemical properties of produced plasma and consequently of synthesized CQDs. The synthesized N‐doped CQDs exhibited strong fluorescence and higher quantum yield compared to previous reports.

Efficient Reduction of Cr(VI) with Carbon Quantum Dots.

Hexavalent chromium (Cr(VI)) pollution is a global problem, and the reduction of highly toxic Cr(VI) to less toxic Cr(III) is considered to be an effective method to address Cr(VI) pollution. In this study, low-toxicity carbon quantum dots (CQDs) were used to reduce Cr(VI) in wastewater. The results show that CQDs can directly reduce Cr(VI) at pH 2 and can achieve a reduction efficiency of 94% within 120 min. It is observed that under pH higher than 2, CQDs can activate peroxymonosulfate (PMS) to produce reactive oxygen species (ROS) for the reduction of Cr(VI) and the reduction efficiency can reach 99% within 120 min even under neutral conditions. The investigation of the mechanism shows that the hydroxyl groups on the surface of CQDs can be directly oxidized by Cr(VI) because of the higher redox potential of Cr(VI) at pH 2. As the pH increases, the carbonyl groups on the surface of CQDs can activate PMS to generate ROS, O2•–, and 1O2, which result in Cr(VI) being reduced. To facilitate the practical application of CQDs, the treatment of Cr(VI) in real water samples by CQDs was simulated and the method reduced Cr(VI) from an initial concentration of 5 mg/L to only 8 μg/L in 150 min, which is below the California water quality standard of 10 μg/L. The study provides a new method for the removal of Cr(VI) from wastewater and a theoretical basis for practical application.

Sustainable fabrication of N-doped carbon quantum dots and their applications in fluorescent inks, Fe (III) detection and fluorescent films

N-doped CQDs are efficiently fabricated with a green synthesis avenue, and exhibit huge potential in anticounterfeit application as the fluorescent ink, a smart fluorescent sensor towards ionic detection, and fluorescent polymer films. • One-step hydrothermal strategy is devised for synthesizing N-doped CQDs from garlic skins. • The obtained water-soluble N-doped CQDs exhibit a strong cyan luminescence with a quantum yield of ∼9%. • The CQDs present huge potential in anticounterfeit application as the fluorescent ink. • The CQDs show highly sensitive and selective determination of cations as a smart fluorescent sensor. • The PVA/CQDs film gives high visible transparency and nearly 100% UV-blocking ratio. In this work, the highly fluorescent N-doped carbon quantum dots (CQDs) were successfully synthesized via a simple hydrothermal method by using garlic skins (GSs) as the sole carbon source. The resultant N-doped CQDs with excitation-dependent emission demonstrates remarkable quantum yield of ∼9% and superior fluorescence stability. Their strong cyan-emission character upon irradiation with UV light (365 nm) reveals their huge potential in anticounterfeit field as the fluorescent ink. Owing to the fluorescence quenching resulted from the tightly chelating of Fe 3+ to the surface of N-doped CQDs, the CQDs can be applied a functional sensor for the detection of Fe 3+ , and the limit of detection is estimated as 4.44 μM. Furthermore, the CQDs is dispersed into poly (vinyl alcohol) (PVA) matrix to make PVA/CQDs composite film. The unique optical properties of CQDs are inherited by the PVA/CQDs film, giving intensive cyan fluorescence and high visible transparency, as well as nearly 100% UV-blocking ratio in the UV region.