Photoluminescent Carbon Dots Research Articles

Influence of synthesis parameters on the optical properties of carbon dots

Photoluminescent carbon dots were synthesized by hydrothermal treatment from agricultural waste. Considering that the composition of the dots’ surface depends on the precursor source and that this composition influences the optical properties, this study focused on analyzing the effect of synthesis parameters on the formation of functional groups, on the core structure, on the morphology, and their influence on the absorption, excitation, emission, and quantum performance properties. It was obtained that by increasing the synthesis temperature, functional groups C = O, C = N, and CO were formed in the carbon dots obtained from the three precursors, and an additional group C = C in dots obtained from plantain peels, which are the only one that showed a degradation of the cellulose band. The absorption response indicated the formation of graphitic nuclei with oxygenated groups responsible for the red shift of the absorption maximum moving from 266 to 283 nm. The Raman response indicates that there are graphitic domains in the nucleus, where the defects band has a high intensity for the three precursors. The higher quantum yield value presented by the plantain dots is due to the surface, not the graphitic core. The spherical shape and size of around 2 nm were observed by TEM.

One-step hydrothermal synthesis of F,N,S-doped photoluminescent carbon dots with yellowish-orange emission for sensitive Cu2+ ion detection: Environmental and biomedical applications

Herein, fluorine-, nitrogen-, and sulfur-doped carbon dots (FNS-CDs) were prepared via a one-step hydrothermal synthesis using flufenamic acid and thiourea as precursors, which showed yellowish-orange fluorescence both in aqueous solution and in the solid state. The as-prepared FNS-CDs were monodisperse and had an average diameter of 4 nm, good water solubility, a fluorescence quantum yield of 18.63 %, and excellent pH and ionic strength stability. The optimal excitation/emission wavelengths of the FNS-CDs were 406/570 nm, with an excitation-dependent wavelength range of 365–435 nm. The surface states, morphologies, and elemental compositions of the FNS-CDs were characterized using FTIR, XRD, TEM, and XPS. In addition, the FNS-CDs without any further modification exhibited high selectivity and sensitivity as nanosensors for Cu2+ over other metal ions. The PL quenching phenomenon can be used to detect Cu2+ ions within a linear range of 1–25 μM with a detection limit of 83.10 nM and an association constant of 1.29 × 104 M−1. The PL of the FNS-CDs was significantly quenched by Cu2+ ions through static quenching and was restored upon the subsequent addition of EDTA. The practical application was demonstrated through the detection of Cu2+ ions in real water samples, yielding recovery rates ranging from 97.8 % to 103.9 % with an RSD below 2.5 %. The FNS-CDs/Cu2+ complex exhibits potent antibacterial activity against S. aureus (85.27 %±2.1 %) and E. coli (91.31 %±1.6 %), whereas the FNS-CDs/Cu2+ has a higher inhibitory effect on the growth of E. coli. Furthermore, the FNS-CDs (100 μg/mL) were used for cell imaging, showing low toxicity to HCT-116 cells exhibited yellowish-orange fluorescence under a confocal microscope.

Polyvinylalcohol Composite Filled with Carbon Dots Produced by Laser Ablation in Liquids.

Carbon dots (CDs), owing to their excellent photoluminescent features, have been extensively studied for physics preparation methods and for biomedical and optoelectronic device applications. The assessment of the applicability of CDs in the production of luminescent polymeric composites used in LEDs, displays, sensors, and wearable devices is being pursued. The present study reports on an original, environmentally friendly, and low-cost route for the production of carbon dots with an average size of 4 nm by laser ablation in liquid. Jointly, to prove the significance of the study for a wide range of applications, a free-standing flexible polyvinyl alcohol (PVA) composite containing photoluminescent carbon dots was manufactured. CDs were prepared using targets of porose charcoal with a density of 0.271 g/cm3 placed in phosphate-buffered saline (PBS) liquid solution and irradiated for 30 min by pulsed IR diode laser. The optical properties of the obtained suspension containing carbon dots were studied with UV-ViS and FTIR spectroscopies. The photoluminescence of the produced carbon dots was confirmed by the emission peak at 480 nm in the luminescence spectrum. A narrow luminescence band with a full width at half-maximum (FWHM) of less than 40 nm could be an asset in spectral emission analysis in different applications. Atomic force microscopy confirms the feasibility of manufacturing CDs in clean and biocompatible environments, paving the way for an easier and faster production route, crucial for their wider applicability.

Exploring the potential of eco-friendly carbon dots in monitoring and remediation of environmental pollutants.

Photoluminescent carbon dots (CDs) have garnered significant interest owing to their distinctive optical and electronic properties. In contrast to semiconductor quantum dots, which incorporated toxic elements in their composition, CDs have emerged as a promising alternative, rendering them suitable for both environmental and biological applications. CDs exhibit astonishing features, including photoluminescence, charge transfer, quantum confinement effect, and biocompatibility. Recently, CDs derived from green sources have drawn a lot of attention due to their strong photostability, reduced toxicity, better biocompatibility, enhanced fluorescence, and simplicity. These attributes have shown great promise in the areas of LED technology, bioimaging, photocatalysis, drug delivery, biosensing, and antibacterial activity. In contrast, this review offers a comprehensive overview of various green sources utilized to produce CDs and methodologies, along with their merits and demerits, with a notable emphasis on physiochemical properties. Additionally, the paper provides insight into the bibliometric analysis and recent advancements of CDs in sensing, photocatalysis, and antibacterial activity. In this field, extensive research is underway, and a total of 7,438 articles have been identified. Among these, 4242 articles are dedicated to sensing applications, while 1518 and 1678 focus on adsorption and degradation. Carbon dots demonstrate exceptional sensing capabilities within the nanomolar range with a selectivity of up to 95% for pollutants. They exhibit excellent degradation efficiency exceeding 90% within 10-130 min and possess an adsorption capacity from 100 to 800 mg/g. These fascinating qualities render them suitable for diverse applications.

A facile green synthesis of photoluminescent carbon dots using Pumpkin seeds for ultra-sensitive Cu2+ and Fe3+ ions detection in living cells

A facile and efficient green synthesis of photoluminescent carbon dots (CDs) was achieved using pumpkin seeds (PS) through the hydrothermal-carbonization method. Pumpkin seeds, well-known for their nutrient-rich composition, offer potential health benefits, including heightened fertility, enhanced heart health, and improved blood sugar regulation. The as-synthesized PS-CDs characterization through UV–vis, photoluminescence (PL), FTIR, XRD, and HR(TEM) analysis. The PL PS-CDs exhibited an excitation-dependent behavior, with the peak shifting from 410 nm to 475 nm under excitation wavelengths ranging from 270 nm to 400 nm. Notably, the synthesized PS-CDs displayed outstanding advantages, such as a high fluorescent quantum yield of 12.7 % with bright blue emissions when exposed to UV light at 365 nm. High-resolution TEM images revealed an average size of approximately 4.0 ± 0.2 nm for the synthesized PS-CDs, ranging from 2 to 7 nm with interlayer distance of 0.21 nm. PL spectra of PS-CDs solution, with an excitation wavelength of 338 nm and emission wavelength of 420 nm, were examined in the presence of various metal ions (50 μM). The fluorescence lifetime of the PS-CDs showed an exponential curve, with an average lifetime (τav) of 8.47 ns for Cu2+and 3.61 ns for Fe3+ ions, respectively, which is strongly indicates that quenching occurs through a static mechanism. The PS-CDs exhibited high sensitivity and selectivity towards Cu2+ and Fe3+ ions, with a linear relationship observed up to a concentration of 50 μM and detection limits of 0.43 and 0.11 μM (S/N = 3), respectively. Moreover, the low-toxicity and strongly fluorescent PS-CDs were successfully applied for cell imaging. The practical utility of the developed sensor was determined through the analysis of Cu2+ and Fe3+ ions in spiked water samples, highlighting its considerable analytical and bioanalytical applications.

Shining light on carbon dots: Toward enhanced antibacterial activity for biofilm disruption.

In spite of tremendous efforts dedicated to addressing bacterial infections and biofilm formation, the post-antibiotic ear continues to witness a gap between the established materials and an easily accessible yet biocompatible antibacterial reagent. Here we show carbon dots (CDs) synthesized via a single hydrothermal process can afford promising antibacterial activity that can be further enhanced by exposure to light. By using citric acid and polyethyleneimine as the precursors, the photoluminescence CDs can be produced within a one-pot, one-step hydrothermal reaction in only 2 h. The CDs demonstrate robust antibacterial properties against both Gram-positive and Gram-negative bacteria and, notably, a considerable enhancement of antibacterial effect can be observed upon photo-irradiation. Mechanistic insights reveal that the CDs generate singlet oxygen (1O2) when exposed to light, leading to an augmented reactive oxygen species level. The approach for disruption of biofilms and inhibition of biofilm formation by using the CDs has also been established. Our findings present a potential solution to combat antibacterial resistance and offer a path to reduce dependence on traditional antibiotics.

Synthesis of nitrogen-doped fluorescent carbon dots for determination of nickel ions and morin from aqueous solution simultaneously

Considering the significant impact of heavy metals on environment and food safety inspection in trace determination, the orange photoluminescent carbon dots (O-CDs) was innovative designed by promoting the co-hydrothermal reaction of polyethyleneimine and resazurin. The produced O-CDs exhibit exceptional optical performance, advantageous water solubility and outstanding photostability. It is worth emphasizing that the proposed O-CDs has significant advantages in constructing sequential sensing platform for sensitive determination of Ni2+ and morin. Simultaneous taking Ni2+ for analytes and fluorescence quenching agents on the O-CDs sensing platforms, a good linear relationship can be received in the range of 5–50 μM with satisfactory sensitivity. Subsequently, morin can effectively promote the fluorescence recovery of O-CDs@Ni2+ on account of stronger binding force between morin and Ni2+. Based on the above results, effective recovery of 97.26 %-100.90 % and 98.24 %-101.99 % is observed towards nickel ion and morin in real food samples. These findings provide an original strategy for the construction of long-wavelength emission carbon dots, which provides a pathway for the determination of typical pollutants based on efficient and robust nanosensors in the field of food safety.

“Turn ON-OFF-ON” photoluminescence detection of EDTA using Moringa oleifera gum-derived carbon dots

This study offers a simplistic approach to hydrothermally synthesizing photoluminescent carbon dots (CDs) using Moringa oleifera Gum (MOG) to detect and quantify EDTA. The as-synthesized Moringa oleifera Gum-derived CDs (MOG-CDs) exhibited an average size of 3.41±0.44 nm and are amorphous. They are naturally doped with calcium and sulphur. Functional groups linked with these heteroatoms and oxygenated linkers are responsible for excellent water dispersibility, good stability, and remarkable optical properties of MOG-CDs. The MOG-CDs demonstrated a high quantum yield of 27.53%. The PL intensity of MOG-CDs was selectively quenched by the introduction of Pb2+ ions, which were further used as a passivating agent for EDTA detection, i.e., the quenched PL can be restored by the addition of EDTA into MOG-CD+Pb2+ system. This Turn “ON-OFF-ON” strategy was used to quantify EDTA with a LOD of 2.6 ppb (8.9 nM). The practicality and viability of the proposed photoluminescent probe were validated by quantifying EDTA in actual samples. The results demonstrated favourable spiked recoveries ranging from 92.59% to 108.69%, indicating a high level of accuracy. Additionally, it displayed excellent reproducibility, as suggested by relative standard deviation (RSD) <5.51%. In parallel, an "IMPLICATION" Boolean logic gate was constructed by employing the PL restoration of the MOG-CD+Pb2+ sensing probe in the presence of EDTA.

Rapid Quantitative Detection for Nitrofurantoin Based on Nitrogen-Doped Highly Photoluminescent Carbon Dots.

Nitrogen-doped carbon dots (NCD) with high fluorescence retention and good stability were successfully fabricated using citric acid and urea via a facile and eco-friendly one-step microwave method, which exhibited superior specificity for detection of nitrofurantoin (NFT). Upon the addition of NFT, the fluorescence intensity of NCD at 450 nm was significantly decreased. Besides, a satisfactory linear relationship between the fluorescence quenching efficiency and concentrations of NFT was obtained. Especially, NCD was qualitatively and quantitatively applied for detection NFT in milk and meat extract samples with a high recovery rate. Consequently, it was suggested that the detection method had potential application in the specific detection of NFT, offering a novel approach for veterinary drug residue detection.

Synthesis of Green Photoluminescence Carbon Dots Using Edible Seafood Mushroom and Their Anti‐Counterfeiting Applications

AbstractCarbon dots (CDs) have emerged as versatile fluorescent nanomaterials for diverse applications. The synthesis of CDs from natural products offers a sustainable alternative to chemical methods. This study presents the preparation of green fluorescent CDs (G‐CDs) using seafood mushrooms as the carbon source and 5‐amino‐2‐methylphenol as the nitrogen source through a hydrothermal approach. The G‐CDs exhibit maximum excitation/emission peaks at 467/519 nm and a high quantum yield of up to 17.2% in ethanol. Additionally, the G‐CDs demonstrate excellent photostability, salt tolerance, and chemical stability. The excitation‐independent emissions suggest the presence of unique surface‐state luminescent centers. The application of the G‐CDs as an anti‐counterfeiting fluorescent ink is demonstrated. This work highlights the promise of converting natural food sources into high‐performance CDs, expanding their utility across various domains including biomedicine, sensing, and security.

Highly selective fluorometric detection of streptokinase via fibrinolytic release of photoluminescent carbon dots integrated into fibrin clot network

This work pioneers a selective fluorometric assay for the fibrinolytic agent streptokinase by strategically coupling its thrombolytic action to fluorescence signaling using carbon dots integrated into fibrin clot network. Streptokinase triggers clot lysis and caused release of photoluminescent carbon dots integrated within the fibrin network in a concentration-dependent manner. Transmission electron microscope (TEM) imaging verifies distinct aggregation of the carbon dots upon addition to fibrin. The carbon dots are derived via an eco-friendly hydrothermal approach using cucumber peel as the source of carbon. Structural and optical characterization of the carbon dots were performed using different techniques including X-ray diffraction, TEM, Fourier-transform infrared spectroscopy, and ultraviolet–visible absorption and fluorescence spectroscopies. All experimental parameters influencing the formation of the fibrin clot and factors governing the release of carbon dots upon the addition of streptokinase have been fully optimized. This fluorescence assay offers high selectivity for streptokinase over potential interferences in addition to excellent sensitivity with a 0.017 μg/mL limit of detection and a wide linear range (0.05–500 μg/mL). Successful application to pharmaceutical formulations is demonstrated with excellent recovery and precision. By ingeniously linking streptokinase activity to carbon dot fluorescence, this novel assay provides a rapid, simple and eco-friendly method for selective streptokinase detection.

Simple and green approach for photoluminescent carbon dots prepared via Faba bean seeds as a luminescent probe for determination of Hg+ ions and cell imaging.

In this research, for the first time, a dedicated sensor was designed to detect Hg+ ions using photoluminescent carbon dots (CDs). Due to preferred green synthesis of CDs from bio-resources, carbohydrate-rich faba bean seeds as a potential carbon precursors were applied to the synthesis of CDs. In the absence of substances such as acid or base and any other additives, the CDs were prepared from the faba bean seeds by the hydrothermal method in aqueous solution. The synthesized CDs exhibited maximum emission intensity at 387 nm, when excited at 310 nm and their luminescence quantum yield was calculated about 5.94%. Then, the fluorescence emission of CDs was examined at the presence of the different metal ions. Results reveled that the CDs have good selectivity toward the Hg+ ions, so that the fluorescence emission is significantly changed in the presence of this ions with the detection limit (LOD) as low as 0.35 μM. Furthermore, since of very low cytotoxicity, these CDs can be applied for cell imaging.

Synthesis of Photoluminescent Carbon Dots Using Hibiscus Tea Waste and Heteroatom Doping for Multi-Metal Ion Sensing: Applications in Cell imaging and Environmental Samples

Novel photoluminescent carbon dots (CDs) were synthesized through a facile hydrothermal method using Hibiscus tea extract as a natural carbon source and boric acid as a boron source. The optical and physicochemical properties of the as-synthesized nitrogen- and boron-doped CDs (NB-CDs) were characterized using UV–Visible (UV–Vis), photoluminescence (PL) spectroscopy, Fourier-transform infrared (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The as-synthesized NB-CDs showed spherical morphology of approximately 6.2 ± 0.5 nm with quantum yield (9.2%), high aqueous solubility, strong photo-stability, and excitation-dependent PL behavior. The obtained NB-CDs exhibited high stability over a wide pH range and high ionic strength. Additionally, NB-CDs exhibited PL enhancement response with excellent sensitivity toward multi-metal ions, including Ag+, Cd2+, and Cr3+ ions, with very low detection limits of 44.5, 164.4, and 54.6 nM, respectively, with a wide concentration range of 0–10 μM. Upon testing the cytotoxicity of the NB-CDs at a concentration of 20 μg/mL for 24 h, we found no obvious inhibition of cell viability. Therefore, the proposed sensor method can be successfully applied to detect Ag+, Cd2+, and Cr3+ ions in cell imaging as well as in real water environmental samples.

Machine Learning-Mediated Ultrasensitive Detection of Citrinin and Associated Mycotoxins in Real Food Samples Discerned from a Photoluminescent Carbon Dot Barcode Array.

Economically viable remote sensing of foodborne contaminants using minimalistic chemical reagents and simultaneous automation calls for a concrete integration of a chemical detection strategy with artificial intelligence. In a first of its kind, we report the ultrasensitive detection of citrinin and associated mycotoxins like aflatoxin B1 and ochratoxin A using an Alizarin Red S (ARS) and cystamine-derived carbon dot (CD) that aptly amalgamate with machine learning algorithms for automation. The photoluminescence response of the CD as a function of various solvents and pH is used to generate array channels that are further modulated in the presence of the mycotoxins whose digital images were acquired to determine pixelation, essentially creating a barcode. The barcode was fed to machine learning algorithms that actualize and intertwine convoluted databases, demonstrating Extreme Gradient Boosting (XGBoost) as the optimized model out of eight algorithms tested. Spiked samples of wheat, rice, gram, maize, coffee, and milk were used to evaluate the testing model where an exemplary accuracy of 100% even at 10 pmol of mycotoxin concentration was achieved. Most importantly, the coexistence of mycotoxins could also be detected through the CD array and XGBoost synergy hinting toward a broader scope of the developed methodology for smart detection of foodborne contaminants.

Synthesis of photoluminescence carbon dots from red beetroot and utilizing its extract as blue-emitted fluorescence probes for spectrofluorimetric determination of tenoxicam in varied pharmaceutical samples

Tenoxicam (TNX) belongs to non-steroidal drugs that effectively treat many inflammatory disorders. In this study, luminescent carbon dots were synthesized from red beetroot as a green fluorescence probe. The synthesized carbon dots' morphology, size, and spectroscopic features were investigated and characterized by spectrophotometric, FTIR, SEM, spectrofluorimetric, and TEM techniques. The synthesized carbon dots possessed an emission at 430 nm and an excitation at 366.5 nm. Meanwhile, TNX is a yellow-colored compound with a spectrophotometric absorbance peak at 370 nm. Based on the inner filter effect mechanism, the emission fluorescence intensity of the synthesized carbon dots has been markedly quenched upon the addition of TNX. In addition, the quenching in the fluorescence intensity was quantitively related to the concentration of TNX at the linear range of 0.25 - 2.5 µg/mL (r2 = 0.9989) with a LOD of 0.08 µg/mL and LOQ of 0.24 µg/mL. The second side of this study is based on enhancing the fluorescence intensity of the acetonitrile extract of red beetroot upon the addition of TNX solution. This enhancement was recorded at a fluorescence emission of 357 nm with a fluorescence excitation of 305.5 nm. In addition, the enhancement in the fluorescence intensity was quantitively related to the concentration of TNX at the linear range of 0.5 - 8.0 µg/mL (r2 = 0.9995) with a LOD of 0.16 µg/mL and LOQ of 0.49 µg/mL. The analytical conditions were well-optimized, and the developed method was validated according to ICH guidelines. Finally, the proposed spectrofluorimetric approaches were applied to determine TNX in vials, tablets, and capsules with good recovery and accepted statistical results.

Multicolor emission-based nitrogen, sulfur and boron co-doped photoluminescent carbon dots for sequential sensing of Fe3+ and cysteine: RGB color sensor and live cell imaging

Herein, a simple hydrothermal synthesis is used to prepare multiple heteroatom-doped photoluminescent carbon dots (CDs) from thiourea (N and S source) and boric acid (B source) as precursors. The optical and physicochemical properties of the as-synthesized NSB-CDs were studied using UV–Vis, photoluminescence, TEM, FT-IR, XRD, Raman, and XPS analyses. The NSB-CDs exhibited excellent stability, high photostability, pH, and ionic strength tolerance; they retained their excellent stability independent of excitation. The NSB-CDs featured small sizes of approximately 3.2 ± 0.4 nm (range: 2.0–5.0 nm) as evidenced using TEM measurements. The NSB-CDs were used as a photoluminescent sensing platform to detect Fe3+ as well as cysteine (Cys) molecules. The competitive binding of Cys to Fe3+ resulted in NSB-CDs that retained their photoluminescence. For the rapid identification and quantification of Fe3+ and Cys, NSB-CDs were developed as a “switch-on” dual-function sensing platform. The linear detection range of Fe3+ was 0–20 μM (limit of detection [LOD]: 54.4 nM) and that of Cys was 0–50 μM (LOD: 4.9 nM). We also introduced a smartphone RGB analysis method for detecting low-concentration solutions based on digital images. The NSB-CDs showed no toxicity at 100 μg/mL. Photoluminescent probes for multicolor live-cell imaging can be used with NSB-CDs at this concentration, suggesting that NSB-CDs may be promising photoluminescent probes.

Detection of trace ascorbic acid in urine by “inhibition” fluorescent sensor based on periodate and highly luminescent N, B co-doped carbon dots

Herein, we presented an ingenious method for the detection of trace ascorbic acid (AA) using fluorescent sensing system, which was composed of periodate (IO4−) and nitrogen-boron co-doped carbon dots (N, B-CDs). Highly photoluminescent carbon dots with a quantum yield of 84.5% were synthesized by a one-step hydrothermal method using citric acid, ethylenediamine and boric acid as raw materials. The fluorescence of N, B-CDs could be statically quenched by IO4−, and non-fluorescent complexes were formed on the surface of carbon dots at the same time. With the pre-addition of ascorbic acid, the process of fluorescence quenching by IO4− was inhibited due to the preferential redox reaction between AA and IO4−. Based on the principle mentioned above, we designed the “inhibition” fluorescent sensor that can easily realize the detection of AA, and an extremely low limit of detection of 0.035 nM with a linear interval of 0–1600 pM was obtained. In addition, the sensing system has been applied to the detection of AA in human urine and obtained satisfactory results. The developed “inhibition” fluorescent sensor with high sensitivity and selectivity, has shown great potential and application prospects in the field of biosensing.

Reply to the comment on the paper “Ultrasonication induced nano-emulsification of thyme essential oil: Optimization and antibacterial mechanism against Escherichia coli”

Carbon dots (CDs) are the emerging class of carbon-based nanomaterials with immense applications in various fields. In this work, CDs were synthesized using a simple microwave method using citric acid and tris base as precursors. The highly photoluminescent CDs were well characterized for examining the structural and optical properties. It was found successful for triple mode applications in food, metal ion sensing and fluorescent ink. As an inner filter-based fluorescent sensor, CDs detected tartrazine with an LOD (limit of detection) of 54 nM in the linear range 2–12 μM. The practicability of the probe was confirmed using its analysis in food samples. It also worked well as an electrochemical sensor for detecting Mn(II) ions in real water samples with a very low LOD of 0.37 nM. Finally, CDs were employed as a fluorescent ink for drawing and writing applications. High fluorescence of the as prepared CDs thus proved its potential for anticounterfeiting applications. This work not only adds new knowledge and data on material properties through thorough characterization of a new CD but also introduces a new sensor that is capable of triple mode application with excellent selectivity, sensitivity and practical viability.

Green Synthesis of Blue Light-Emitting Carbon Dots Using Tridax procumbens Leaves: Optical and Electrochemical Studies

We report the preparation of biocompatible blue emitting carbon dots (CDs) using Tridax procumbens (T. procumbens) leaf extract as a bio-source. A one-step hydrothermal method was employed to prepare highly effective photoluminescent CDs. As-synthesized CDs were characterized using Ultraviolet-visible spectroscopy (UV-visible), Photoluminescence (PL), Fourier transform infrared (FT-IR), transmission electron microscopy (TEM) and Confocal Raman spectroscopy techniques. In addition, the third-order optical nonlinearity of the prepared CDs was carried out using Z-scan technique with the help of continuous wave diode pumped Nd:YAG laser (532 nm). The nonlinear optical (NLO) susceptibility, nonlinear absorption coefficient and nonlinear refractive index were calculated. The synthesized CDs exhibited good excitation dependent properties. The CDs/Nafion modified glassy carbon electrode (CDs/Nf/GCE) was prepared and its electrochemical and catalytic properties were evaluated by using cyclic voltammetry (CV). The CDs/Nf/GCE exhibited high electrocatalytic activity for dopamine oxidation in physiological condition. This new CDs/Nf/GCE showed a linear range of Dopamine (DA) detection from 40 to 220 μM with the limit of detection (LOD) of 2.7 μM. The stability and reproducibility of the electrode were also investigated which indicated that this green synthesized CDs could be used for the development of electrochemical sensor to determine DA concentration in biological samples.

Microwave abetted synthesis of carbon dots and its triple mode applications in tartrazine detection, manganese ion sensing and fluorescent ink

Carbon dots (CDs) are the emerging class of carbon-based nanomaterials with immense applications in various fields. In this work, CDs were synthesized using a simple microwave method using citric acid and tris base as precursors. The highly photoluminescent CDs were well characterized for examining the structural and optical properties. It was found successful for triple mode applications in food, metal ion sensing and fluorescent ink. As an inner filter-based fluorescent sensor, CDs detected tartrazine with an LOD (limit of detection) of 54 nM in the linear range 2–12 μM. The practicability of the probe was confirmed using its analysis in food samples. It also worked well as an electrochemical sensor for detecting Mn(II) ions in real water samples with a very low LOD of 0.37 nM. Finally, CDs were employed as a fluorescent ink for drawing and writing applications. High fluorescence of the as prepared CDs thus proved its potential for anticounterfeiting applications. This work not only adds new knowledge and data on material properties through thorough characterization of a new CD but also introduces a new sensor that is capable of triple mode application with excellent selectivity, sensitivity and practical viability.