N,Cl co-doped fluorescent carbon dots as nanoprobe for detection of tartrazine in beverages

Development of a ratiometric fluorescence sensor based on blue- and orange-emissive carbon dots for the determination of tartrazine in food products

Determination of tartrazine in food products is crucial due to its detrimental impacts on human health if it exceeds the maximum allowed intake limit. It was hypothesized that a ratiometric fluorescence sensor using blue- and orange-emissive carbon dots (B-O-CDs) would outperform single-emission-based sensors in sensitivity and reproducibility. A ratiometric probe was developed by mixing B-CDs and O-CDs, exhibiting emission peaks at 420 and 565 nm, differentially influenced by tartrazine. The fluorescence intensity ratio was used to quantify tartrazine with a detection limit of 64 nM, a linear range of 0.2-60 μM, recovery rates of 97.2-104.4 % and low relative standard deviation values (< 3.5 %) in food samples. The results confirm that the ratiometric approach enhances performance over single-emission-based sensors. The novel use of dual-emissive carbon dots and the inner filter effect offers a rapid, cost-effective, and reliable method for routine tartrazine monitoring in food products.

In Situ Confinement Strategy To Achieve High-Stability Room Temperature Phosphorescent Carbon Dots

Room temperature phosphorescent (RTP) materials show great application potential in fields such as anticounterfeiting, data encryption, sensors, and bioimaging. However, RTP is prone to being quenched by the influence of oxygen atoms due to the particularity of its luminescence mechanism, leading to the difficulty of obtaining RTP materials with long afterglow and high stability. Herein, multicolored carbon dots-RTP composites (CDs-X@BA) were successfully fabricated via a facile in situ confinement strategy using resorcinol as the carbon source. Specifically, resorcinol underwent in situ carbonization and condensation reactions in boric acid (BA) to form CDs, which were then confined in a rigid environment. Interestingly, the synthesized CDs-X@BA exhibit dual emission afterglow of RTP (550 nm) and thermally activated delayed fluorescence (TADF) (470 nm). Of these, RTP is derived from the formed CDs, while TADF is generated from BA. Notably, CDs-X@BA exhibit remarkable stability, even in water and harsh environments. This is attributed to the formed rigid B2O3 matrix, which combines with CDs through physical fixation, hydrogen bonds, and covalent bonds (B-C), fully stabilizing the triplet excitons and suppressing nonradiative transitions. Subsequently, CDs-X@BA exhibit highly promising potential in anticounterfeiting and information security. This work provides new insights for developing high-efficiency RTP materials.

Smartphone-assisted detection of methylene blue using leaf-derived, dual-emissive carbon dots as ratiometric fluorescence probes

Specific assay for methylene blue (MB) in aquaculture is critically required to assess the safety of ecosystems and aquatic products. In this work, a facile method is demonstrated for ratiometric fluorescence determination of MB based on blue/red dual emissive carbon dots (b/r-CDs). b/r-CDs, derived from the leaves of Impatiens balsamina, show weak and strong emission peaks at 432 and 672 nm, respectively, and possess a high photoluminescence quantum yield of 35.7%. The red fluorescence of b/r-CDs at 672 nm, serving as the response signal, can be significantly quenched by MB due to the mechanism of inner filter effect, while the blue fluorescence at 432 nm is insensitive to MB, thus acting as the background reference. With addition of an increased amount of MB, the fluorescence color of b/r-CDs gradually changes from red to blue, which realizes the visual detection. The linear range and limit of detection are measured to be 0.05-10 μM and 15 nM, respectively. Notably, a portable smartphone sensing platform is built for quantitative detection of MB by analyzing the RGB values. Moreover, the practical applications of b/r-CDs for monitoring MB in real water and aquatic products using both fluorescence spectrophotometer and smartphone achieve satisfactory results.

Carbon dots-based dual-emission ratiometric fluorescent sensors for fluorescence and visual detection of hypochlorite and Cu2

Carbon dots (CDs) with blue emission were synthesized by solvothermal method using hydroquinone and 5-aminoisphthalic acid as precursors. The strong oxidation of ClO- caused the fluorescence quenching of CDs at 405 nm, and synchronously generated a new emission peak at 500 nm. Furthermore, upon the addition of Cu2+ to CDs-ClO- system, the green fluorescence at 500 nm was quenched, while the blue emission at 405 nm remained unchanged, due to the complexation between Cu2+ and the amino group on the CDs surface. Meanwhile, the fluorescence color of system changed from blue to bright green and then to dark blue by sequentially increasing the concentrations of ClO- and Cu2+. The fluorescence signal of F500/F405 exhibited a linear relationship with the concentration of ClO- and Cu2+ in a certain range, respectively. Thus, a ratiometric fluorescence sensor based on the obtained CDs were developed to sequentially detect ClO- and Cu2+ with detection limits of 0.40 μM and 0.31 μM, respectively. Additionally, the CDs were mixed with polyvinyl alcohol hydrogel to form test strips, which were successfully used for visual detection of ClO- and Cu2+. Satisfactory results were also obtained in the analysis of ClO- and Cu2+ in actual water samples.

Smartphone-Assisted and Optical Quantification of Copper and Glucose Using Palm Wine-Tailored Carbon Dots and Their Multiple Logic Gate Application

In this work, potassium, sulfur, nitrogen, and chlorine self-doped carbon dots (CDs) were hydrothermally synthesized using palm wine as a carbon source. The palm wine-derived CDs (PW-CDs) are amorphous in nature and displayed an average particle size of 4.19 ± 0.89 nm. The as-synthesized CDs are used to fabricate a photoluminescent sensing probe to simultaneously detect Cu2+ and glucose via the "Turn ON-OFF-ON" mechanism. The PL quenching mechanism of PW-CDs enables the selective and sensitive detection of Cu2+ ions with a detection limit (LOD) of 0.8 ppb (4.7 nM). The sensing probe quantified Cu2+ in tap water, drinking water, and e-waste samples to prove its viability. Using CDs to quantify copper in e-waste leachate samples is a novel approach as no prior instances of such application have been reported. The system's performance is considered to be highly reproducible due to the relative standard deviation being <6.64%, along with excellent recoveries within the range of 93.24-109.86%. The quenched PL can be recovered by introducing glucose into the PW-CD + Cu2+ system; this strategy is employed to quantify glucose with a LOD of 0.11 ppm (0.61 μM). The feasibility of this sensor was confirmed by the determination of glucose in actual human plasma specimens of diabetic patients. It is to be noted that these samples were neither diluted nor spiked with glucose. The developed PW-CD + Cu2+ sensing system yields satisfactory recoveries of 93.45-107.37%. This probe was also incorporated into a smartphone-based sensing platform to detect Cu2+ and glucose with desirable recoveries. The proposed smartphone-based sensing platform is flexible, reliable, and accurate, making it suitable for resource-constrained areas. Furthermore, based on the effect of Cu2+ ions and glucose on the PL response and absorbance spectra of PW-CDs, four logic gates (YES, IMPLICATION, NOT, and OR) were designed, and PW-CDs were also used for cell imaging applications.

Fluorescent multichannel sensor array based on three carbon dots derived from Tibetan medicine waste for the quantification and discrimination of multiple heavy metal ions in water

A fluorescent multichannel sensor array has been established based on three carbon dots derived from Tibetan medicine waste for rapid quantification and discrimination of six heavy metal ions. Due to the chelation between metal ions and carbon dots (CDs), this fluorescence "turn off" mode sensing array can quantify six metal ions as low as "μM" level. Moreover, the six heavy metal ions display varying quenching effects on these three CDs owing to diverse chelating abilities between each other, producing differential fluorescent signals for three sensing channels, which can be plotted as specific fingerprints and converted into intuitive identification profiles via principal component analysis (PCA) and hierarchical cluster analysis (HCA) technologies to accurately distinguish Cu2+, Fe3+, Mn2+, Ag+, Ce4+, and Ni2+ with the minimum differentiated concentration of 5 μM. Valuably, this sensing array unveils good sensitivity, exceptional selectivity, ideal stability, and excellent anti-interference ability for both mixed standards and actual samples. Our contribution provides a novel approach for simultaneous determination of multiple heavy metal ions in environmental samples, and it will inspire the development of other advanced optical sensing array for simultaneous quantification and discrimination of multiple targets.

Carbon dots-based fluorescent probe for the detection of imidacloprid residue in leafy vegetables

Consumption of leafy vegetables with excessive imidacloprid (IMI) can cause serious harm to the human body. To achieve rapid IMI detection, a carbon dots (CDs)-based fluorescent (FL) probe was hydrothermally prepared using O-phenylenediamine as the precursor. The morphology, particle size distribution, crystal structure, optics and chemical bond state of the as-prepared CDs were characterized. The mechanism of the CDs in detecting IMI was investigated by Fourier transform infrared spectroscopy, and the CDs' selectivity, stability, sensitivity, and actual sample recovery were tested. The CDs showed good selectivity, stability, and anti-interference ability. Under optimum conditions, there was a strong linear relationship between the FL intensity of the CDs and the IMI concentration in the range of 0.037-0.2 mg/L. The detection limit was 0.00187 mg/kg. The CDs were successfully applied to detect IMI in lettuce, cole, spinach, and pakchoi with spiked recoveries between 81.026% and 106.803% and a relative standard deviation between 0.001 and 0.027%.

A comprehensive exploration of tartrazine detection in food products: Leveraging fluorescence nanomaterials and electrochemical sensors: Recent progress and future trends

Azo dyes are widely used as food coloring agents because of their affordability and stability. Examples include brilliant blue, carmoisine, sunset yellow, allura red, and tartrazine (Tar), etc. Notably, Tar is often utilized in hazardous food goods. They are frequently flavoured and combined with food items, raising the likelihood and danger of exposure. Therefore, detecting Tar in food is crucial to prevent health risks. Fluorescence nanomaterials and electrochemical sensors, known for their high sensitivity, affordability, simplicity, and speed, have been widely adopted by researchers for Tar detection. This comprehensive paper delves into the detection of Tar in food products. It extensively covers the utilization of advanced carbon-based nanomaterials, including CDs, doped CDs, and functionalized CDs, for sensitive Tar detection. Additionally, the paper explores the application of electrochemical sensors. The paper concludes by addressing current challenges and prospects, emphasizing efforts to enhance sensitivity, and selectivity for improved food safety.

Chiral CDs-based fluorescence sensor for rapid and specific sensing K4[Fe(CN)6] in table salt and salted food

Potassium ferricyanide (K4[Fe(CN)6]) as anti-caking agent plays an important role in avoiding the formation of chunks for fine particulate solids. However, inappropriate and excessive addition and decomposition of K4[Fe(CN)6] are detrimental to physical health. At present, appropriate strategies for convenient and accurate analysis of K4[Fe(CN)6] in table salt and pickled food are desirable. Herein, an efficient "ON-OFF-ON" fluorescent sensor based on chiral carbon dots was prepared by a simple one-step hydrothermal method. The chiral CDs with L-Tryptophan and D-Tryptophan as chiral source were named as L-CDs and D-CDs. Notably, the bright fluorescence of L/D-CDs could be effectively quenched by K4[Fe(CN)6] through dynamic quenching mechanism. This fluorescent sensor achieved excellent sensitive and selective detection of K4[Fe(CN)6] with a limit of detection (LOD) of 25.0 ng·mL-1. In addition, the L/D-CDs could be applied not only for selective fluorescent recognition of K4[Fe(CN)6] by the methods of portable filter paper and hydrogels, but also as fluorescent dye for repeated message encryption and decryption.

Recent advancements in nanomaterial based optical detection of food additives: a review

Food additives have become a critical component in the food industry. They are employed as preservatives to decelerate the negative effects of environmental and microbial factors on food quality. Currently, food additives are used for a variety of purposes, including colorants, flavor enhancers, nutritional supplements, etc., owing to improvements in the food industry. Since the usage of food additives has increased dramatically, the efficient monitoring of their acceptable levels in food products is quite necessary to mitigate the problems associated with their inappropriate use. The traditional methods used for detecting food additives are generally based on standard spectroscopic and chromatographic techniques. However, these analytical techniques are limited by their high instrumentation cost and time-consuming procedures. The emerging field of nanotechnology has enabled the development of highly sensitive and specific sensors to analyze food additives in a rapid manner. The current article emphasizes the need to detect various food additives owing to their potential negative effects on humans, animals, and the environment. In this article, the role of nanomaterials in the optical sensing of food additives has been discussed owing to their high accuracy, ease-of-use, and excellent sensitivity. The applications of nanosensors for the detection of various food additives have been elaborated with examples. The current article will assist policymakers in developing new rules and regulations to mitigate the adverse effects of toxic food additives on humans and the environment. In addition, the prospects of nanosensors for the optical detection of food additives at a commercial scale have been discussed to combat their irrational use in the food industry.

Recent Advancements in Metal and Non-Metal Mixed-Doped Carbon Quantum Dots: Synthesis and Emerging Potential Applications

In nanotechnology, the synthesis of carbon quantum dots (CQDs) by mixed doping with metals and non-metals has emerged as an appealing path of investigation. This review offers comprehensive insights into the synthesis, properties, and emerging applications of mixed-doped CQDs, underlining their potential for revolutionary advancements in chemical sensing, biosensing, bioimaging, and, thereby, contributing to advancements in diagnostics, therapeutics, and the under standing of complex biological processes. This synergistic combination enhances their sensitivity and selectivity towards specific chemical analytes. The resulting CQDs exhibit remarkable fluorescence properties that can be involved in precise chemical sensing applications. These metal-modified CQDs show their ability in the selective and sensitive detection from Hg to Fe and Mn ions. By influencing their exceptional fluorescence properties, they enable precise detection and monitoring of biomolecules, such as uric acid, cholesterol, and many antibiotics. Moreover, when it comes to bioimaging, these doped CQDs show unique behavior towards detecting cell lines. Their ability to emit light across a wide spectrum enables high-resolution imaging with minimal background noise. We uncover their potential in visualizing different cancer cell lines, offering valuable insights into cancer research and diagnostics. In conclusion, the synthesis of mixed-doped CQDs opens the way for revolutionary advancements in chemical sensing, biosensing, and bioimaging. As we investigate deeper into this field, we unlock new possibilities for diagnostics, therapeutics, and understanding complex biological processes.

Vancomycin-modified nitrogen and chloride doped carbon dots and their application as a Staphylococcus aureus probe

In this research, N, Cl-doped carbon dots (N, Cl-CDs) were prepared in choline chloride-glycerol deep eutectic solvent (DES) by microwave method. N, Cl-CDs surface was modified with vancomycin for detection of Staphylococcus aureus (S. aureus) bacteria in the range of 10²-10⁷ colony-forming unit per milliliter (CFU/mL). The detection limit was 10¹ CFU/mL. Morphology and structure of N, Cl-CDs were characterized by transmission electron microscopy (TEM), X-ray photon spectroscopy (XPS), photoluminescence spectroscopy, FT-IR spectroscopy, energy dispersive X-ray spectroscopy (EDXS) and zeta potential. The prepared N, Cl-CDs had excellent dispersion in water, particle size range of 2-3 nm, and quantum yield of 38.75%. Speed, wide linear range and more convenient were advantages of new probe with respect to other methods.

Fluorescent detection of tartrazine based on the supramolecular self-assembly of cationic perylene diimide

A cationic perylene probe was designed and synthesized for sensitive determination of tartrazine. In the presence of tartrazine, the fluorescence of the perylene probe was quenched by efficient supramolecular self-assembly of the perylene derivate. The quenching is caused by the synergistic effect of noncovalent interactions including static electricity, π-π stacking, and hydrophobic interaction. Benefiting from these advantages, the probe exhibited excellent sensing performance to tartrazine within 2 min. The detection and quantification limit of tartrazine are as low as 2.42 and 8.07 nmol L-1, respectively, with a wide linear operation range from 15 to 500 nmol L-1. Most importantly, due to the high binding affinity (3.22 × 107 mol L-1) between the perylene probe and tartrazine, the sensing system shows great anti-interference capacity. Subsequently, the visualization application of the approach was evaluated by portable device, and the limits of detection for visual detection for test strip, membrane, and hydrogel were 0.5, 0.5, and 5 μmol L-1, respectively. The approach has been applied to monitor tartrazine in various food condiments with recoveries in the range 91.29-108.83%. As far as we know, this is the first report of using perylene-based probe for tartrazine determination, offering a promising strategy for the construction of perylene-based detection system in the field of food safety.

Dual emission N-doped carbon dots as a ratiometric fluorescent and colorimetric dual-signal probe for indigo carmine detection

Novel dual-emission fluorescent nitrogen-doped carbon dots (N-CDs) were synthesized by a facile one-pot hydrothermal method using ascorbic acid and rhodamine B as precursors and melamine as nitrogen source. The obtained N-CDs exhibited dual-emitting peaks at 435 nm and 578 nm under the single excitation of 350 nm. The fluorescence at 578 nm was more effectively quenched by indigo carmine (IC) based on the internal filtration effect and aggregation-induced emission quenching. Meanwhile, the apparent color change of N-CDs from pink to blue-purple after adding various concentrations of IC could be clearly observed with the naked eye. Therefore, a ratiometric fluorescent and colorimetric dual-signal probe based on N-CDs was developed for IC detection with high selectivity and sensitivity. The addition of IC caused the ratiometric fluorescent value (F₄₃₅/F₅₇₈) to increase linearly within the range from 0 to100 µM with a detection limit (LOD) of 0.18 µM and the colorimetric signal presented a linear response in the range of 0-133 µM with a LOD of 57.4 nM. Furthermore, the IC in juice drink, candy, and water was successfully detected. Besides, the N-CDs were also designed as a ratiometric temperature probe, and the ratiometric fluorescence signal (F₄₃₅/F₅₇₈) was linearly and reversibly responsive to temperature in the range of 20-75 °C.

Advances in Fluorescent Sensing Carbon Dots: An Account of Food Analysis

Illuminating the use of nanomaterials, carbon quantum dots (CQDs) have transfigured the food safety arena because of their bright luminescence, optical properties, low toxicity, and enhanced biocompatibility. Therefore, fluorescent resonance energy transfer, photoinduced electron transfer, and an internal filtering effect mechanism allow precise detection of food additives, heavy metal ions, pathogenic bacteria, veterinary drug residues, and food nutrients. In this review, we describe the primal mechanism of CQD-based fluorescence sensors for food safety inspection. This is an abridged description of the nanodesign and future perspectives of more advanced CQD-based sensors for food safety analysis.

Multiple Stimuli-Response Polychromatic Carbon Dots for Advanced Information Encryption and Safety

Optical information encryption and safety have aroused great attention since they are closely correlated to data protection and information safety. The development of multiple stimuli-response optical materials for constructing large-capacity information encryption and safety is very important for practical applications. Carbon dots (CDs) have many gratifying merits, such as polychromatic emission, diverse luminous categories, and stable physicochemical properties, and are considered as one of the most ideal candidates for information protection. Herein, carbon core, functional groups, solvents, and other crucial factors are reviewed for outputting polychromatic emission of multiple luminous categories. In particular, substrate engineering strategies have been emphasized for their critical role in yielding excellent optical features of multiple luminous categories. High-capacity information encryption and safety strategies are reviewed by relying on the rich optical properties of CDs, such as polychromatic emission, multiple luminous categories of fluorescence, afterglow, and upconversion, as well as external-stimuli-assisted optical changes. Some perspectives for preparing excellent CDs and further developing information security strategies are proposed. This review provides a good reference for the manipulation of polychromatic CDs and the development of next-generation information encryption and safety.

Facile hydrothermal synthesis and purification of fluorescent carbon dots for food colorant tartrazine detection based on a dual-mode nanosensor

Colorant tartrazine is widely used in the food industry, but its long-term and excessive consumption is harmful to human health. Therefore, it is necessary to establish a sensitive detection method for tartrazine. Blue fluorescent carbon dots with L-arginine and o-phenylenediamine as precursors, namely L-Arg/oPD-CDs, were prepared via the hydrothermal method. Then, L-Arg/oPD-CDs were further purified by dialysis, thin layer chromatography and column chromatography. A dual-mode nanosensor based on fluorescent and UV absorption was successfully developed. Excellent linear ranges of 0-5 μM and 10-50 μM were obtained with a low detection limit of 42.3 nM based on fluorescence. A good linear range of 0-50 μM was obtained with a low detection limit of 130.15 nM based on UV absorption. The quenching mechanism of tartrazine towards L-Arg/oPD-CDs fluorescence was the inner filter effect. In addition, a dual-mode nanosensor was used for tartrazine determination in millet, maize flour, carbonated drink, and sugar samples. This study provides new insight into the detection of tartrazine by applying a dual-mode nanosensor.

Selective and sensitive detection of tartrazine in beverages by sulfur quantum dots with high fluorescence quantum yield

In this work, sulfur quantum dots (TPA-SQDs) protected by terephthalic acid as a stabilizer were synthesized using a one-pot method. When excited at 310 nm, the synthesized TPA-SQDs solution emitted strong blue fluorescence at 428 nm, and the absolute quantum yield was as high as 85.99%. The proposed SQDs can be used as a fluorescent probe to specifically quench tartrazine (TZ), showing a good linear relationship (R² = 0.996) at TZ concentrations of 0.1-20 μM, with a detection limit of 39 nM. By analysing the fluorescence lifetime, UV-Vis absorption spectrum and zeta potential of the assay system, it can be speculated that the fluorescence quenching mechanism of TZ on TPA-SQDs is the inner filter effect (IFE). The proposed method was applied to the detection of TZ in vitamin water and orange juice, and the results were consistent with the determination results by high-performance liquid chromatography. The recoveries and relative standard deviations were 93.2-102.6% and 1.34-2.88%, respectively, which provided an alternative method for the determination of TZ in beverages or other food samples.

An Electrochemical Sensor for Sunset Yellow Detection Based on Cu@Cu2O-BNPC Formed by Modified Porous Carbon

Control and detection of sunset yellow (SY) are an utmost demanding issue due to its high risk of detrimental effects on living systems caused by excessive ingestion. In this study, we reported the synthesis of Cu@Cu₂O nanoparticle-decorated B and N codoped porous carbon (BNPC) and its use in developing a novel electrochemical sensor for SY. The Cu@Cu₂O-BNPC catalyst was fabricated through single-step polymerization, followed by carbonization. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy characterization results showed that Cu@Cu₂O anchored on the porous BNPC successfully. Compared with the BNPC-modified electrode, it was found that the Cu@Cu₂O-BNPC-modified electrode showed superior electrocatalytic activity in both electrochemical impedance spectroscopy and cyclic voltammetry tests. The as-prepared Cu@Cu₂O-BNPC catalyst directly acted as a sensor for amperometric detection of SY without further assembling, which exhibited an ultrahigh sensitivity of 0.09 μA nM^-1 cm^-2, a low limit of detection (2.4 nM), and a wide linear detection ranging from 10 nM to 8 μM. To further validate its possible application, the proposed method was successfully used for the determination of SY in Fanta drinks with satisfactory results.

Halogen-Doped Carbon Dots: Synthesis, Application, and Prospects

Carbon dots (CDs) have many advantages, such as tunable photoluminescence, large two-photon absorption cross-sections, easy functionalization, low toxicity, chemical inertness, good dispersion, and biocompatibility. Halogen doping further improves the optical and physicochemical properties of CDs, extending their applications in fluorescence sensors, biomedicine, photocatalysis, anti-counterfeiting encryption, and light-emitting diodes. This review briefly describes the preparation of CDs via the "top-down" and "bottom-up" approaches and discusses the preparation methods and applications of halogen (fluorine, chlorine, bromine, and iodine)-doped CDs. The main challenges of CDs in the future are the elucidation of the luminescence mechanism, fine doping with elements (proportion, position, etc.), and their incorporation in practical devices.

One-step high-yield preparation of nitrogen- and sulfur-codoped carbon dots with applications in chromium(vi) and ascorbic acid detection

In this research, a nitrogen- (N) and sulfur- (S) codoped carbon dot (CDs-IPM)-based sensor was synthesized using a single-step hydrothermal method. Specifically, microcrystalline cellulose (MCC) was the main raw material, which was extracted from banana pseudo-stem-based waste, while autonomous sulfonic acid-functionalized ionic liquid (SO3H-IL) and polyethylene glycol 400 (PEG 400) acted as the N, S dopant, and surface modifier, respectively. Comprehensive spectroscopic characterization of the synthesized CDs-IPM revealed the introduction of S, N atoms in the matrix with existence of surface oxygenic functional groups. The CDs-IPM possessed enhanced photoluminescence (PL) intensity, synthetic yield, and PL quantum yield (PLQY). Additionally, electron transfer between the CDs-IPM, hexavalent chromium (Cr(vi)), and subsequent ascorbic acid (AA) succeeded in turning the fluorescence on and off. The detection limit was 17 nM for Cr(vi), while it was 103 nM for AA. Our study data can simplify the process of synthesis of CDs utilizing biodegradable starting materials. The probe reported in this study may serve as a valuable addition to the field of environment monitoring by virtue of its enhanced detection sensitivity, high selectivity, and stability.

Visual Monitoring of Nucleic Acid Dynamic Structures during Cellular Ferroptosis Using Rationally Designed Carbon Dots with Robust Anti-Interference Ability to Reactive Oxygen Species

Ferroptosis triggered by an iron-dependent accumulation of lipid reactive oxygen species (ROS) has drawn widespread attention. Directly visualizing the dynamic structures of nucleic acids during the ferroptosis of cells is of great importance considering their vital roles in numerous biological functions. However, direct imaging remains challenging, largely due to the extremely high concentrations of ROS generated during ferroptosis, which can affect the imaging of nucleic acid targeted fluorescent probes. To overcome this challenge, nucleic acid-responsive carbon dots (CDs) providing favorable optical properties together with high chemical stability were synthesized. Furthermore, the CDs penetrated the cell membrane quickly and accumulated in the nuclei of cells. The robust anti-interference ability to ROS allows the CDs to visualize the dynamic structures of nucleic acids during ferroptosis. Moreover, the CDs were successfully employed in the imaging of nucleic acids during cell division. The nuclei-targeting CDs show great potential as a powerful tool for imaging nuclei in ferroptosis-related biological and clinical research.

Moxifloxacin detection based on fluorescence resonance energy transfer from carbon quantum dots to moxifloxacin using a ratiometric fluorescence probe

With an increase in the MOX concentration, the fluorescence intensity of CQDs decreases, whereas the fluorescence intensity of MOX increases gradually.

Fluorescent sensing platform based on green luminescence carbon dots and AuNPs for clenbuterol detection in pork liver

In this paper, water-soluble green fluorescent carbon dots (G-CDs) were prepared using p-phenylenediamine and glutathione (GSH) as the precursors. The G-CDs exhibit excellent optical properties, and the maximum emission wavelength is located at 522 nm (under 410 nm excitation), which greatly overlaps with the absorption spectrum of AuNPs. Consequently, an effective “off–on” fluorescent sensing platform involved in G-CDs and AuNPs for detection of clenbuterol (CLB) was constructed. The fluorescence of G-CDs was strongly quenched by AuNPs due to the inner filter effect (IFE). As CLB was introduced, the quenched fluorescence intensity was recovered due to the specific interaction between the AuNPs and CLB. The recovered fluorescence intensity is linear to CLB concentration in the range of 13–270 ng mL⁻¹ with a low detection limit of 3.75 ng mL⁻¹. The prepared sensor has been successfully applied for CLB detection in pork liver and could be utilized in food analysis.

Carbon dots (G-CDs) with bright green fluorescence are synthesized by hydrothermal treatment of p-phenylenediamine and glutathione. Employing the G-CDs and AuNPs as sensing platform, a simple fluorescence sensor to detect clenbuterol was established.

A Label-Free Immunosensor Based on Gold Nanoparticles/Thionine for Sensitive Detection of PAT Protein in Genetically Modified Crops

Genetically modified (GM) crops containing phosphinothricin acetyltransferase (PAT) protein has been widely planted worldwide. The development of a rapid method for detecting PAT protein is of great importance to food supervision. In this study, a simple label-free electrochemical immunosensor for the ultrasensitive detection of PAT protein was constructed using thionine (Thi)/gold nanoparticles (AuNPs) as signal amplification molecules and electrochemically active substances. Under optimum conditions, the limits of detection of the sensor for soybean A2704-12 and maize BT-176 were 0.02% and 0.03%, respectively. The sensor could detect crops containing PAT protein and had no cross-reaction with other proteins. After storage at 4°C for 33 days, the sensor still retained 82.5% of the original signal, with a relative standard deviation (RSD) of 0.92%. The recoveries of the sensor for soybean A2704-12 and maize BT-176 were 85%-108% and 98%-113%, respectively. The developed PAT-target immunosensor with high sensitivity, specificity, and satisfactory reproducibility and accuracy will be a useful tool in the trace screening of GM crops. Moreover, this design concept can be extended to other proteins by simply changing the antibody.

N,Cl-Codoped Carbon Dots from Impatiens balsamina L. Stems and a Deep Eutectic Solvent and Their Applications for Gram-Positive Bacteria Identification, Antibacterial Activity, Cell Imaging, and ClO- Sensing

In this study, we first synthesized metal-free N,Cl-doped carbon dots (N,Cl-CDs) using Impatiens balsamina L. stems as green precursors in a deep eutectic solvent (DES). The obtained N,Cl-CDs were characterized through transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, fluorescence (FL) spectroscopy, and ultraviolet (UV) spectroscopy. In addition to the common features of carbon dots (CDs), such as high light stability, small size, low toxicity, good aqueous solubility, and favorable biocompatibility, these N,Cl-CDs exhibited excellent recognition and selectivity for Gram-positive bacteria by doping with N and Cl elements using DES. The N,Cl-CDs with positive charge cannot only differentiate Gram-positive bacteria by selective fluorescence imaging but also have antibacterial effects on Gram-positive bacteria. Through potential, ROS, and morphological analyses of bacteria before and after treatment with N,Cl-CDs, the antibacterial mechanisms of bacteriostasis, Enterococcus faecium, Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, and Salmonella were explored. In addition, N,Cl-CDs demonstrated low cytotoxicity and good cell imaging ability in cancer and normal cells. Moreover, they can be used as a fluorescence sensor for the detection of ClO- with a detection range from 100 nM to 40 μM and a limit of detection (LOD) of 30 nM. In summary, the prepared N,Cl-CDs could be applied as environmentally friendly Gram-positive bacterial identification and antibacterial agents. Additionally, their cell imaging and ClO- detection abilities were outstanding.

Fluorescent carbon dots from Indian Bael patra as effective sensing tool to detect perilous food colorant

Herein a simple strategy has been demonstrated for the synthesis of environmentally amiable and highly fluorescent carbon dots from the most useful plant of Indian classical Ayurveda i.e. Bael patra fruit. The morphological features and chemical composition of the prepared carbon dots were characterized through High resolution transmission electron microscopy, Field emission scanning electron microscopy and X-ray photoelectron spectroscopy. Owing to their highly emission nature, the applicability of carbon dots was tested against various food colorant i.e. Allura red. Under the optimized conditions, the decreased fluorescence intensity exhibited a good linear relationship with increasing concentration of Allura red. Additionally, an extensive research was carried out to determine the adsorption efficiency of carbon dots for Allura red and heavy metals. Based on the context, here we report the novelty of this work, demonstrating the decontamination of various samples from Allura red and heavy metals with the application of carbon dots.

Naked-Eye Detection of Hepatitis B Surface Antigen Using Gold Nanoparticles Aggregation and Catalase-Functionalized Polystyrene Nanospheres

Developing rapid, efficient, highly sensitive, simple, stable, and low-cost virus marker detection products that are appropriate for basic facilities is of great importance in the early diagnosis and treatment of viruses. Naked-eye detection methods are especially important when medical testing facilities are limited. Polystyrene nanospheres (PSs) with catalytic and specific recognition functions were successfully developed by simultaneously modifying catalase and goat anti-hepatitis B surface antibodies on nanospheres. The modified PSs contributed significantly to the amplification of the signal. Via the specific antigen-antibody reaction, the bifunctional nanospheres could be captured on microplate and then catalyzed the decomposition of hydrogen peroxide to reduce chloroauric acid and synthesize gold nanoparticles (AuNPs). Due to the surface plasmon resonance of AuNPs, the solution color change could be observed with the naked eye and the limit of detection (LOD) was 0.1 ng/mL. Furthermore, the LOD observed with instrumentation was 0.01 ng/mL, which meant that a rapid, efficient, and highly sensitive method for the detection of hepatitis B surface antigens was successfully developed, and neither complex sample pretreatment nor expensive equipment was needed.

Detection of tartrazine in fake saffron containing products by a sensitive optical nanosensor

A fluorescent assay for the selective analysis of tartrazine was developed. Tartrazine is a health-threatening food additive commonly used as fake saffron. An optical nanosensor was fabricated based on molecular imprinting technique in which carbon dots (CDs) as fluorophores and tartrazine as a template molecule were embedded in molecularly imprinted polymer (MIP) matrix. The synthesized CDs embedded in MIP (CDs-MIP) was characterized by various methods. The fluorescence intensity of (CDs-MIP) was selectively quenched in the presence of tartrazine in comparison with other similar food color additives. The correlation between the quenching of CD-MIP and the concentration of tartrazine was used as an optical sensing for rapid detection of tartrazine in the range of 3.3-20.0 nM (1.8-10.7 μg L^-1) with detection limit of 1.3 nM (0.70 μg L^-1). Eventually, the designed nanosensor was successfully applied for tartrazine detection in foodstuffs such as fake saffron, saffron tea and saffron ice cream samples.

Development of a highly sensitive fluorescence method for tartrazine determination in food matrices based on carbon dots

In this work, an ultrasensitive sensing system based on fluorescent carbon dots (CDs) was developed for the tartrazine (Tar) determination. The CDs were prepared via a simple one-pot hydrothermal method with m-phenylenediamine as the only precursor. The physical and chemical properties were in detail characterized by transmission electron microscopy (TEM), MALDI-TOF MS, UV-vis absorption and photoluminescence (PL) spectroscopy, elemental analysis, and Fourier transform infrared spectroscopy (FTIR). Upon exposure to Tar, the fluorescence of CDs was efficiently quenched via the dynamic interaction between CDs and Tar as well as the inner filter effect (IFE). With this information, the CDs were proposed as a fluorescence probe for Tar detection. It was found that CDs had high sensitivity and selectivity for Tar sensing, and the linear relationship was observed in the range of 0.01-25.0 μM with the corresponding detection limit (3σ/k) of 12.4 nM, which is much more sensitive than any of the existed CD-based sensing platform. The investigated sensing system was finally utilized for Tar sensing in various food matrices with a high degree of accuracy. The spiked recoveries were in a range of 96.4-105.2%, and the relative standard deviations (RSDs) were lower than 4.13%. This work highlights the great application prospects of CDs for Tar sensing in a rapid, simple, and sensitive way.

Selective Determination of Dopamine in Pharmaceuticals and Human Urine Using Carbon Quantum Dots as a Fluorescent Probe

A cost-effective and environmentally friendly method was formulated for rapid dopamine (DA) detection that was based on the fluorescence (FL) quenching of carbon quantum dots (C-dots). Upon adding DA to the C-dots’ solution, we noticed a regular reduction in their fluorescence intensity. The effects of pH, amount of C-dots, reaction temperature and time on the determination of DA were investigated. Under the optimized experimental conditions, trace amounts of DA could be analyzed. Furthermore, dopamine hydrochloride injection and human urine samples with and without spiked DA were analyzed using the developed sensing system. The procedure was validated following the guidelines of the European Medicines Agency (EMA) in terms of the following: calibration range (0.3–100 μM), linearity (R2 = 0.9991), limit of detection (LOD) (93 nM). Recoveries of dopamine with spiked samples at three different levels were between 95.0 and 105.9%, and the relative standard deviations (RSDs) were within 2.68% (n = 6). This method is simple and suitable for the determination of dopamine in pharmaceuticals and human urine for clinical application. Compared with previous reports, the proposed method offers great advantages including ease of C-dot sensor preparation (one-pot synthesis), environmentally friendly sample preparation by using either water or phosphate buffer solution only, a short response time and selectivity.

Green Synthesis of Fluorescent Carbon Dots from Elaeagnus angustifolia and its Application as Tartrazine Sensor

This article has introduced and examined a novel and green approach for the very first time, which had been developed for the synthesis of carbon dots (CDs) and performed through the utilization of Elaeagnus angustifolia (E. A) as a natural carbon source. This straightforward procedure has been based upon a hydrothermal treatment with a quantum yield of 16.8% that had been designed to synthesize water-soluble CDs in one step and result in a satisfying fluorescence. Additionally, we have attempted to assess the sensing system that had been exerted through the usage of CDs for the detection of food colorant tartrazine, since they can function as a fluorescent sensor due to the interplay that occurs among tartrazine and CDs leading to the quenching of their fluorescence. The detection limit has been measured to be equaled to 0.086 μM (86 nM) and the linear range has been observed to be 0.47-234 μM. The proposed highly sensitive and simple method has exhibited an excellent selectivity and proved to be effectively applicable for distinguishing the tartrazine of real samples.

Green synthesis of fluorescent N,S-carbon dots from bamboo leaf and the interaction with nitrophenol compounds

A simple and green approach for the synthesis of photoluminescent N,S-carbon dots (N,S-CDs) has been proposed using a single natural source precursor (bamboo leaf) as raw materials. The as-synthesized N,S-CDs exhibited a highly stable, excitation wavelength-dependent emission, excellent photobleaching, alkali, and salt tolerance. Here, the mechanism of N,S-CDs luminescence was studied via the UV-vis absorption spectrum and photoluminescence spectroscopy. Based on the quenching properties of nitrophenol compounds on the fluorescence of N,S-CDs, the interaction between N,S-CDs and nitrophenol compounds was investigated on detail in aqueous solution. More importantly, the study on photophysical properties of the N,S-CDs may provide the basis for the development of the N,S-CDs for the fluorescent probe of nitrophenol compounds.

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.

Hg2+ detection, pH sensing and cell imaging based on bright blue-fluorescent N-doped carbon dots

A multifunctional sensing platform based on bright blue-fluorescent nitrogen-doped carbon dots (N-CDs) has been ingeniously designed for the sensitive determination of Hg²⁺ and pH.