On-off-on fluorescent carbon dots from waste tea: Their properties, antioxidant and selective detection of CrO42-, Fe3+, ascorbic acid and L-cysteine in real samples

Carbon dots: An emerging food analysis nanoprobes for detection of contaminants

Carbon dots are the new class of nanomaterials with a size range of 10 nm or less. These are associate with the important material properties such as good biocompatibility, fluorescent nature, small size and easy to synthesize with low toxicity which make them the first choice over the fluorescent inorganic materials and dyes, to be used as biocompatible nanoprobes for the detection of food adulterations. Herein, we have focused on the methods of synthesis of these tiny zero dimensions, fluorescent nanomaterials (CDs), their properties, mechanism of fluorescence, and lastly their wide applications in food analysis which include the detection of additives, heavy metal ions, organic pollutants, foodborne microbes, antibiotic and pesticides. Further, these nanomaterials open the scope to be used as nanoprobes in the food safety concern. Additionally, we discussed the challenges and future scope of CDs as an auspicious and emerging nanomaterial to be used in the food industries.

Carbon dots as new antioxidants: Synthesis, activity, mechanism and application in the food industry

Antioxidants not only prevent food spoilage, but also maintain the nutritional value of food, thereby exerting a crucial protective effect on food industry. Nanomaterials have recently been used as antioxidants because of their remarkable potential to scavenge free radicals. Of them, owing to their relatively high biocompatibility and unique physicochemical properties, carbon dots (CDs) have garnered considerable attention. This paper reviews research progress on CDs as new antioxidants. We here first discuss the methods for synthesizing various antioxidant CDs, followed by the antioxidant activities of different CDs and factors influencing these activities. Then, the possible action mechanisms of antioxidant CDs are discussed. The review particularly focuses on the application of antioxidant CDs, especially in the food industry, including antioxidant coatings, antioxidant packaging materials, and nano-level food additives. Finally, the challenges and prospects for CDs as new antioxidant are described.

Smartphone-driven handheld monitoring of Cr(VI) and living cell imaging using nitrogen-doped yellow fluorescence carbon dots

User-friendly, field-portable, and direct read-out mini-device is indispensable for under-developed countries or resources-insufficient areas. Herein, a field-portable handheld monitoring platform incorporating smartphone, 3D-printed device, and test strip stained with yellow fluorescence (FL) carbon dots (YCDs) proves the efficacy for real-time quantitation of Cr(VI) by a consecutive FL color transformation. YCDs were synthesized with starch, rhodamine 6G, and L-lysine through hydrothermal procedure, manifesting intriguing yellow-emitting behavior locating at 556 nm under 470 nm excitation. With increasing Cr(VI) concentration, FL intensity of YCDs at 556 nm is significantly quenched, accompanying by a continuous FL colour alteration from bright yellow to dark yellow. Inspired by above FL phenomena, YCDs-based test strips are fabricated to realize point-of-care quantifying of Cr(VI). Inspiringly, developed field-portable handheld monitoring platform is further generalized to on-site quantify Cr(VI) concentration in tap water based on wide linear ranges of 0-800 μM, and low limit of detection of 0.349 μM. Furthermore, laser confocal imaging of HeLa cells corroborates that YCDs can be utilized for visual determination of Cr(VI) in living cells, illustrating that YCDs presents powerful biosensing application prospect.

Unlocking the potential of green-engineered carbon quantum dots for sustainable packaging biomedical applications and water purification

Carbon quantum dots (CQDs) with well-defined architectures offer highly fascinating properties such as excellent water-solubility, exceptional luminescence, large specific surface area, non-toxicity, biocompatibility and tuneable morphological, structural, and chemical features. This review comprehensively overviews recent breakthroughs and critical milestones in the green synthesis of CQDs from renewable sources and provides guidance for their sustainable development towards fulfilling the goals of green chemistry. It also discusses the interaction of CQDs with various biopolymers to improve the material performance and functionality. This paper also highlights the latest technological applications of CQDs in numerous fields, including sustainable packaging, biosensing, bioimaging, cancer therapy, drug delivery as well as water purification. Finally, it summarizes the main challenges and provides an outlook on the future directions of CQDs in packaging and biomedical fields. This review can act as a roadmap to guide researchers for tailoring the properties of CQDs for important composite and biomedical fields.

Facile Synthesis of Carbon Dots from Green Resource and Their Application for Selective Determination of Mg2

A simple, fast and sensitive method based on the fluorescence quenching of carbon dots was developed for the determination of Mg2+ in environmental and biological sample. Carbon dots (CDs) were synthesized from arugula seeds by hydrothermal method. The precursor is cheap, easily available and environment friendly. CDs were characterized by selected techniques. They showed a bright blue fluorescent under UV light while under day light the synthesized CDs showed brown colour. The CDs were highly fluorescent. The interaction of CDs with various selected cations such as Ni2+, Sr2+, Cd2+, Mg2+, Cu2+, Al3+, Co2+, K+, Ca2+, Pb2+, Cr3+, Na+, Zn2+, Fe2+, Cu+, Mn2+, Mo6+, Sb3+, Sn4+, Cr6+, Ba2+, Li+ and Fe3+ was studied to check the probable potential application for the studied ions. All the studied ions did not show any effect on the intensity of CDs except Mg2+ which quenched the intensity of the CDs. A linear relation was found between the quenching of CDs intensity and Mg2+ concentration. The quenching was explained with the Stern-Volmer equation that produced the Stern-Volmer constant ([Formula: see text]). [Formula: see text], detection limit (DL) and quantification limit (QL) were observed in the order 2.85 × 105 mol L- 1, 32.6 n mol L- 1 and 108 n mol L- 1 correspondingly. Method based on the fluorescence quenching of CDs is reproducible and useful for the Mg2+ determination in environmental and biological samples.

Poria cocos-derived carbon dots for parallel detection of Cr6+/Fe3+ in complex environments with superior sensitivity

Multifunctional sensor capable of parallel sensing is of great importance thanks to their wide applications and great practicality. In this report, Poria cocos-derived carbon dots (CDs) were adopted for the development of multifunctional sensor for the parallel detection of Cr6+ and Fe3+ with superior sensitivity and applicability. Specifically, extremely low limit of detection (LOD) of 1.07 × 10-3 nM and 1.98 × 10-3 nM were achieved for Cr6+ and Fe3+, respectively. Systematic mechanism explorations revealed that the highly sensitive detection of Cr6+ was attributed to an efficient inner filter effect (IFE), while the sensing of Fe3+ was realized due to a strong static quenching process. Furthermore, the assay was found to be extremely versatile, achieving the reliable detection of Cr6+ and Fe3+ in multiple natural water environments and even biological environment. Utilizing the different reactions of Cr6+ and Fe3+ towards masking reagents, a logic gate that could effectively eliminate the mutual interference of Cr6+ and Fe3+ was successfully designed.

Green synthesis of carbon dots (CDs) and their use for selective determination of Pb2

Carbon dots were synthesized from fenugreek seeds through a single step hydrothermal method. The method is simple, fast, pleasant to the environment and cheaper. The CDs were characterized by Fourier Transform Infrared (FTIR), UV-visible spectrophotometer, X-ray diffraction (XRD), High Resolution Transmission electron microscopy (HR-TEM), and fluorescence. The CDs obtained were extremely fluorescent. The fluorescent carbon dots exhibited excitation-dependent behavior with the maximum excitation at 372 nm. The interaction of CDs was studied with different selected cations Al3+, Ca2+, Cd2+, Cr3+, Co2+, Cu2+, Cu+, Fe2+, Fe3+, K+, Sn4+, Na+, Ni2+, Pb2+, Mn2+, Zn2+, Sr2+, (NH4)6Mo7O24, 4H2O, Cr6+, Sb3+, Ba2+, Li+, and Mg2+. None of the ions studied showed any effect on its fluorescence intensity except Pb2+ which decreased its intensity. A direct relationship was found between Pb2+ concentrations and quenching of CDs intensity. Detection limit (DL) and quantification limits (QL) were determined as three and ten times of the standard deviation of the blank for ten number of measurements. DL and QL were found in the order 9.345 μM and 31.15 μM respectively. This linear behavior between quenching and Pb2+ concentration is useful for analytical purpose.

Research Progress Towards and Prospects of Carbon Dots Derived from Tea and Chinese Medicinal Materials

This review focuses on the research progress related to carbon dots (CDs) derived from Chinese herbal medicines and tea, covering preparation methods, physicochemical properties, and application fields. It elaborates on preparation approaches like hydrothermal, solvothermal, microwave-assisted, and ultrasonic-assisted methods, and their influence on CDs' structure and properties. It also explores CDs' structural and optical properties. The application fields include antibacterial, sensing, bioimaging, photocatalysis, hemostasis, and energy. Carbon dots show antibacterial activity by destroying bacterial cell membranes, they can detect various substances in sensing, are important for bioimaging, degrade organic pollutants in photocatalysis, have hemostatic and anti-inflammatory effects, and can be used as battery anode materials. Despite progress, challenges remain in improving yield, quantum yield, property control, and understanding their mechanism of action. This review provides a reference for related research and looks ahead to future directions.

Application of Carbon Quantum Dots Derived from Waste Tea for the Detection of Pesticides in Tea: A Novel Biosensor Approach

Chemical pesticide residues have negative consequences for human health and the environment. Prioritizing a detection method that is both reliable and efficient is essential. Our innovative research explored the application of biosensors based on carbon quantum dots (CQDs) derived from waste tea to detect commonly used pesticides in tea. CQDs have been synthesized using a simple one-pot hydrothermal approach and thoroughly characterized using advanced techniques such as high-resolution transmission electron microscopy, ultraviolet-visible spectroscopy, photoluminescence (PL) spectroscopy, Raman spectroscopy, X-ray diffraction, atomic force microscopy, and X-ray photoelectron spectroscopy. The fluorescence resonance energy transfer-based fluorescence "turn on-off" mechanism has been successfully employed to study the detection of four different pesticides, viz., quinalphos 25 EC, thiamethoxam 25 WG, propargite 57 EC, and hexaconazole 5 EC. The detection limits for quinalphos 25 EC, thiamethoxam 25 WG, and propargite 57 EC were determined to be 0.2, 1, and 10 ng/mL, respectively. Notably, these values are significantly lower than the maximum residue level for each pesticide. We achieved a strong linear correlation (R = -0.96) with a detection limit of 0.2 ng/mL for quinalphos 25 EC. The quantum yield was determined to be 40.05%. Our research demonstrates that the developed nanobiosensor reliably and accurately detects pesticides, including those present in experimental samples containing mixtures of pesticides.

Rapid detection of Hg2+ in an ON-OFF-ON process using N doped carbon dots

Contamination of ground water with pollutants released from various anthropogenic activities is a major concern due to its adverse effects on the environment and human health. Rapid and efficient detection of such pollutants is the first step toward remediation of the problem. Herein we report a two-point fluorescence turn OFF-ON detection method for Hg2+ ions using nitrogen doped carbon dots (NCDs). The NCDs obtained through solvothermal treatment of ammonium citrate tribasic in DMF at 190 °C for four hours exhibited a quantum yield of 9.67%. Hg2+ detection is demonstrated in two steps, first the quenching of the fluorescence of NCDs by Hg2+ and second the fluorescence recovery upon addition of ascorbic acid from different sources. A rapid filter paper-based detection device is demonstrated based on the principles developed.

Carbon Dots: A Review with Focus on Sustainability

Carbon dots (CDs) are an emerging class of nanomaterials with attractive optical properties, which promise to enable a variety of applications. An important and timely question is whether CDs can become a functional and sustainable alternative to incumbent optical nanomaterials, notably inorganic quantum dots. Herein, the current CD literature is comprehensively reviewed as regards to their synthesis and function, with a focus on sustainability aspects. The study quantifies why it is attractive that CDs can be synthesized with biomass as the sole starting material and be free from toxic and precious metals and critical raw materials. It further describes and analyzes employed pretreatment, chemical-conversion, purification, and processing procedures, and highlights current issues with the usage of solvents, the energy and material efficiency, and the safety and waste management. It is specially shown that many reported synthesis and processing methods are concerningly wasteful with the utilization of non-sustainable solvents and energy. It is finally recommended that future studies should explicitly consider and discuss the environmental influence of the selected starting material, solvents, and generated byproducts, and that quantitative information on the required amounts of solvents, consumables, and energy should be provided to enable an evaluation of the presented methods in an upscaled sustainability context.

Hydrothermal route upcycling surgical masks into dual-emitting carbon dots as ratiometric fluorescent probe for Cr (VI) and corrosion inhibitor in saline solution

Exploration effective route to convert plastic waste into valuable carbon dots with bifunction of metal fluorescence monitoring and corrosion protection in seawater is promising. Herein, using "white-pollution" polypropylene surgical masks as a single precursor, dual-emitting carbon dots (CDs) with excellent ratiometric fluorescent sensitivity and corrosion inhibitor efficiency were fabricated with high yield (∼100 %) by a one-pot in situ acid oxidation hydrothermal strategy without post-treatment and organic solvents. Chemical, structural, morphological, optical properties and the Cr (VI) detection and Cu inhibition mechanism of the synthesized CDs had been systematically studied. Furthermore, a dual-response-OFF proportional fluorescent probe had been developed for the detection of the analyte Cr (VI) with a low detection limit of 24 nM. Additionally, the corrosion inhibition efficiency of the prepared CDs reached approximately 94.01 % for Cu substrate in 3.5 wt% NaCl electrolyte under a CDs concentration of 200 mg/L, which is higher than that of most previous reports.

Fluorescent carbon dots for sensing applications: a review

Luminescent carbon dots (CDs) are important class of nanomaterials with fantastic photoluminescence (PL) properties, great biocompatibility, extraordinary solubility in water, minimal expense, and so on. There are many methods for their preparation and they are mainly classed into two groups, top-down and bottom-up approaches. In order to understand the origin of fluorescence in quantum CDs, three mechanisms have been proposed namely molecular state, surface state, and quantum confinement phenomenon. Fluorescent CDs have significant application in the fields of biochemical sensing, photocatalysis, bioimaging, delivery of drugs, and other related fields. In this review article the application of quantum dots as detecting component, for the sensing of different targets, has been summed up. In fact, the detection of several analytes including, anions, cations, small molecules, polymers, cells, and microscopic organisms has been discoursed. Moreover, the future aspects of CDs as detecting resources have been explored.

Development of an "on-off-on" fluoroprobe utilizing an anthrylimidazole-based fluorescent ionic liquid for sensitive Cr(VI) and ascorbic acid detection

Developing a rapid detection method of Cr(VI) and ascorbic acid (AA) is vital in the food and environmental fields. Herein, an anthrylimidazole-based fluorescent ionic liquid (AI-FIL) with the advantageous fluorescent properties was successfully prepared and used to construct a promising "on-off-on" fluoroprobe for rapid/sensitive Cr(VI) and AA detection. Cr(VI) could effectively quench the fluorescence of AI-FIL owing to the inner-filter effect and photoinduced electron-transfer process. However, the decreased fluorescence could be rapidly recovered by AA owing to the redox reaction between AA and Cr(VI). For Cr(VI) detection, a satisfactorily linear response (0.03-300 μM) was achieved with the corresponding detection limit of 9 nM. For AA detection, a good linearity from 1 to 1000 μM was obtained with the resultant detection limit of 0.3 μM. Moreover, the AI-FIL based fluoroprobe was successfully utilized for Cr(VI) and AA detection in food and water samples with satisfactory accuracy and precision.

Hydrothermal synthesis of modified lignin-based carbon dots derived from biomass waste for fluorescence determination of valsartan

Recently, carbon dots (CDs) have been extensively investigated as potential tools for numerous applications. Modified lignin-based CDs have been synthesized and used in the field of drug detection. They were found to be highly selective and sensitive to valsartan (VAL). Using a simple hydrothermal method, phosphorus and chlorine co-doped CDs were synthesized using lignin extracted from date seeds. The fluorescence properties of the synthesized CDs are influenced by several factors, which were investigated in detail. The optimal synthesis conditions were 1.50 g of lignin, 18 mL of 2 M NaOH, 1 mM H3PO4, 3 mM HCl and the mixture was heated at 220 °C for 16 hours. The synthesized lignin-based CDs have excellent FL properties and are well soluble in water with reasonable stability. Characterization of the prepared CDs revealed that they have various functional groups with a graphene oxide-like structure. The developed CDs show a good quantum yield of 37.7%. The FL of the CDs is quenched by VAL at λ em 313 nm after λ ex at 275 nm by a combination of static and dynamic quenching mechanisms. The response of VAL was linear in the range of 4.0-100.0 μg mL-1. The detection and quantification limits of VAL were 1.23 and 3.71 μg mL-1, respectively. The nanoprobe was successfully used to analyze VAL in drug samples and provided satisfactory results.

Target-Oriented Synthesis of Triphenylphosphine Functionalized Carbon Dots with Negative Charge for ROS Scavenging and Mitochondrial Targeting

Triphenylphosphine functionalized carbon dots (TPP-CDs) showcase robust mitochondria targeting capacity owing to their positive electrical properties. However, TPP-CDs typically involve complicated synthesis steps and time-consuming postmodification procedures. Especially, the one-step target-oriented synthesis of TPP-CDs and the regulation of TPP linkage modes remain challenges. Herein, we propose a free-radical-initiated random copolymerization in combination with hydrothermal carbonation to regulate the TPP backbone linkage for target-oriented synthesis of triphenylphosphine copolymerization carbon dots (TPPcopoly-CDs). The linkage mechanism of random copolymerization reactions is directional, straightforward, and controllable. The TPP content and IC50 of hydroxyl radicals scavenging ability of TPPcopoly-CDs are 53 wt % and 0.52 mg/mL, respectively. TPP serves as a charge control agent to elevate the negatively charged CDs by 20 mV. TPPcopoly-CDs with negative charge can target mitochondria, and in the corresponding mechanism the TPP moiety plays a crucial role in targeting mitochondria. This discovery provides a new perspective on the controlled synthesis, TPP linkage modes, and mitochondrial targeting design of TPP-CDs.

Biomass-derived carbon dots as significant biological tools in the medicinal field: A review

Early disease detection is crucial since it raises the likelihood of treatment and considerably lowers the cost of therapy. Therefore, the improvement of human life and health depends on the development of quick, efficient, and credible biosensing methods. For improving the quality of biosensors, distinct nanostructures have been investigated; among these, carbon dots have gained much interest because of their great performance. Carbon dots, the essential component of fluorescence nanoparticles, having outstanding chemical characteristics, superb biocompatibility, chemical inertness, low toxicity and potential optical characteristics have attracted the researchers from every corner of the globe. Several carbon dots applications have been thoroughly investigated in recent decade, from optoelectronics to biomedical investigations. This review study primarily emphasizes the recent advancements in the field of biomass-derived carbon dots-based drug delivery, gene delivery and bioimaging, and highlights achievements in two major areas: in vivo applications that involve carbon dots absorption in zebrafish and mice, tumour therapeutics, and imaging-guided drug delivery. Additionally, the possible advantages, difficulties, and future possibilities of using carbon dots for biological applications are also explored.

A sensitive sensor based on carbon dots for the determination of Fe3+ and ascorbic acid in foods

To develop a feasible, sensitive, and essential sensor is important for the identification of Fe3+ ions and ascorbic acid (AA). Herein, highly fluorescent heteroatom co-doped carbon dots (N,S-CDs) with a quantum yield (QY) of 24.6% were synthesized, using hydrothermal treatment of L-cysteine (Cys) and 1-amino-2-naphthol-4-sulfonic acid (ANSA). The fluorescence emission of the as-prepared N,S-CDs was quenched strongly by Fe3+ ions, and this was further recovered by the reduction effect of AA on Fe3+. Based on this, continuous fluorescence sensing of Fe3+ and AA with an "on-off-on" style was developed. The detection of Fe3+ and AA were in relatively wider linear ranges of 5.00-105 μmol L-1 and 4.97-54.8 μmol L-1, with a detection limit of 0.10 μmol L-1 and 2.4 nmol L-1 (S/N = 3), respectively. Then, the N,S-CDs were successfully used to measure Fe3+ ions and AA in some daily food samples, and this method exhibited some advantages over most other reported techniques in the term of response speed, quantum yield, and detection limit.

N, S-Codoped Carbon Dots-Based Reusable Solvatochromic Organogel Sensors for Detecting Organic Solvents

The visualization and analysis of organic solvents using fluorescent sensors are crucial, given their association with environmental safety and human health. Conventional fluorescent sensors are typically single-use sensors and they often require sophisticated measurement instruments, which limits their practical and diverse applications. Herein, we develop solvatochromic nitrogen and sulfur codoped carbon dots (NS-CDs)-based organogel sensors that display color changes in response to different solvents. NS-CDs are synthesized using a solvothermal method to produce monodispersed particles with exceptional solubility in various organic solvents. NS-CDs exhibit distinct photoluminescent emission spectra that correlate with the solvent polarity, and the solvent-dependent photoluminescent mechanism is investigated in detail. To highlight the potential application of solvatochromic NS-CDs, portable and low-cost NS-CDs-embedded organogel sensors are fabricated. These sensors exhibit highly robust solvatochromic performance despite repeated solvent switches, thus ensuring consistent and reliable measurements in practical applications. This study provides valuable insights into the solvatochromism of carbon dots and opens up new avenues for designing real-time organic solvent sensing platforms.

Orange peel-derived carbon dots/Cu-MOF nanohybrid for fluorescence determination of l-ascorbic acid and Fe3. Anal Chim Acta 2024;1287:342066. [PMID: 38182373 DOI: 10.1016/j.aca.2023.342066]

Recycling and reuse of biomass waste in synthesis of nanomaterials have recently received much attention as an effective solution for environmental protection and sustainable development. Herein, nitrogen-doped carbon dots (N-CDs) with blue emission were synthesized from the orange peels as a precursor through a simple hydrothermal method and then, modified with ethylenediamine tetraacetic acid (N-CD@EDTA). The N-CD@EDTA was embedded as a fluorophore in Cu-based metal-organic framework (MOF-199) structure (N-CD@EDTA/MOF-199) to construct fluorescence sensor toward l-ascorbic acid (L-AA) determination. The N-CD@EDTA/MOF-199 nanohybrid significantly and selectively turned on toward L-AA determination during the fluorimetric experiments. Under optimal conditions, the probe showed a suitable linear response in the concentration range of 10 nM-100 μM with a low limit of detection (LOD) of 8.6 nM and high sensitivity of 0.201 μM-1. The possible mechanism of recognition and adsorption, including the reduction of Cu 2+ nodes in the MOF-199 structure in the presence of L-AA and the release of trapped N-CD@EDTA into the solution, was explored. Moreover, the N-CD@EDTA/MOF-199/L-AA (100 μM) system was further applied as a fluorescent "on-off" sensor for Fe3+ determination with a LOD of 1.15 μM. The proposed probe was successfully used in orange juice and water samples to determine L-AA and Fe3+ with satisfactory recovery, which displays the promising capability of sensor in real samples. The recoveries obtained by suggested method are consistent with that obtained from high performance liquid chromatography (HPLC) and atomic absorption spectroscopy which confirm the favorable characteristic of the sensor for accurate determination of L-AA and Fe3+ in practical applications.

Green, facial zinc doped hydrothermal synthesis of cinnamon derived fluorescent carbon dots (Zn-Cn-CDs) for highly selective and sensitive Cr6+ and Mn7+ metal ion sensing application

Carbon dots have demonstrated a great potential as luminescent nanoparticles in energy, drug delivery, sensors, and various biomedical applications as well as environmental pollutants and water analysis. Although, such nanoparticles appear to exhibit low toxicity compared to other semiconductor and metal based luminescent nanomaterials. Today, we know that toxicity of carbon dots (CDs) strongly depends on the protocol of fabrication. The various dopants or heteroatoms have been used to enhance the optical and physicochemical properties. In this work, zinc doped aqueous fluorescent Zn-Cn-CDs have been synthesized from cinnamon by hydrothermal synthesis method. The synthesized Zn-Cn-CDs were confirmed for their physicochemical properties by using various characterization techniques viz. UV-Vis. and spectrofluorometer for optical properties, Fourier transform infrared spectroscopy (FTIR) and XRD, as well as TEM and XPS, was done for morphological and chemical analysis. The successfully synthesized Zn-Cn-CDs showed outstanding optical performance for metal ion sensing applications. The developed heteroatom doped Zn-Cn-CDs as a fluorescent probe exhibited higher selectivity and sensitivity for Cr6+ and Mn7+ metal ions. The obtained results showed a better linear range with excellent limit of detection (LOD) 3.97 µg/mL and 2.05 µg/mL for Cr6+ and Mn7+ metal ions respectively. The low cost, simple and highly fluorescent probe can be effectively applicable for development of environmental pollutants sensing purposes.

Carbon nanoprobe derived from Nyctanthes arbor-tristis flower: Unveiling the surface defect-derived fluorescence

Dual Emissive (green and blue) Carbon dots (C-Dots) aka g-CD and b-CD were synthesized using flowers of Nyctanthes arbortristis as the sole precursor via hydrothermal method without the aid of any external passivating agent. In the present report, the effect of time and temperature on the hydrothermal reaction was evaluated in order to modulate the surface defects that could lead to dual emissions. To gauge the nature, size, morphology, and optoelectronic characteristics, the C-Dots were characterized using high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), UV-Vis spectroscopy and Fluorescence spectroscopy. The fluorescence studies of both the Carbon Dots revealed their excitation-dependent emission characteristics with the bathochromic shift. Furthermore, both g-CD and b-CD could effectively be utilized as efficient fluorescent probes for the selective and sensitive detection of Fe3+. These fluorescent nanoprobes could selectively detect Fe3+ over a wide range of concentrations (3 µM to 100 µM) with limit of detection (LOD) as low as 0.06 µM and 0.70 µM respectively. These tuneable Carbon Dots having wider solubilities would open a new avenue as Nanosensors for real-time applications.

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.

Biomass derived green carbon dots for sensing applications of effective detection of metallic contaminants in the environment

The rapid consumption of metals and unorganized disposal have led to unprecedented increases in heavy metal ion concentrations in the ecosystem, which disrupts environmental homeostasis and results in agricultural biodiversity loss. Mitigation and remediation plans for heavy metal pollution are largely dependent on the discovery of cost-effective, biocompatible, specific, and robust detectors because conventional methods involve sophisticated electronics and sample preparation procedures. Carbon dots (CDs) have gained significant importance in sensing applications related to environmental sustainability. Fluorescence sensor applications have been enhanced by their distinctive spectral properties and the potential for developing efficient photonic devices. With the recent development of biomass-functionalized carbon dots, a wide spectrum of multivalent and bivalent transition metal ions responsible for water quality degradation can be detected with high efficiency and minimal toxicity. This review explores the various methods of manufacturing carbon dots and the biochemical mechanisms involved in metal detection using green carbon dots for sensing applications involving Cu (II), Fe (III), Hg (II), and Cr (VI) ions in aqueous systems. A detailed discussion of practical challenges and future recommendations is presented to identify feasible design routes.

Turning food waste into value-added carbon dots for sustainable food packaging application: A review

Carbon dots (CDs) are a recent addition to the nanocarbon family, encompassing both crystalline and amorphous phases. They have sparked significant research interest due to their unique electrical and optical properties, remarkable biocompatibility, outstanding mechanical characteristics, customizable surface chemistry, and negligible cytotoxicity. Their current applications are mainly limited to flexible photonic and biomedical devices, but they have also garnered attention for their potential use in intelligent packaging. The conversion of food waste into CDs further contributes to the concept of the circular economy. It provides a comprehensive overview of emerging green technologies, energy-saving reactions, and cost-effective starting materials involved in the synthesis of CDs. It also highlights the unique properties of biomass-derived CDs, focusing on their structural performance, cellular toxicity, and functional characteristics. The application of CDs in the food industry, including food packaging, is summarized in a concise manner. This paper sheds light on the current challenges and prospects of utilizing CDs in the packaging industry. It aims to provide researchers with a roadmap to tailor the properties of CDs to suit specific applications in the food industry, particularly in food packaging.

Assessment of biomass-derived carbon dots as highly sensitive and selective templates for the sensing of hazardous ions

Access to safe drinking water and a hygienic living environment are the basic necessities that encourage healthy living. However, the presence of various pollutants (especially toxic heavy metal ions) at high concentrations in water renders water unfit for drinking and domestic use. The presence of high concentrations of heavy-metal ions (e.g., Pb2+, Hg2+, Cr6+, Cd2+, or Cu2+) greater than their permissible limits adversely affects human health, and increases the risk of cancer of the kidneys, liver, skin, and central nervous system. Therefore, their detection in water is crucial. Due to the various benefits of "green"-synthesized carbon-dots (C-dots) over other materials, these materials are potential candidates for sensing of toxic heavy-metal ions in water sources. C-dots are very small carbon-based nanomaterials that show chemical stability, magnificent biocompatibility, excitation wavelength-dependent photoluminescence (PL), water solubility, simple preparation strategies, photoinduced electron transfer, and the opportunity for functionalization. A new family of C-dots called "carbon quantum dots" (CQDs) are fluorescent zero-dimensional carbon nanoparticles of size < 10 nm. The green synthesis of C-dots has numerous advantages over conventional chemical routes, such as utilization of inexpensive and non-poisonous materials, straightforward operations, rapid reactions, and renewable precursors. Natural sources, such as biomass and biomass wastes, are broadly accepted as green precursors for fabricating C-dots because these sources are economical, ecological, and readily/extensively accessible. Two main methods are available for C-dots production: top-down and bottom-up. Herein, this review article discusses the recent advancements in the green fabrication of C-dots: photostability; surface structure and functionalization; potential applications for the sensing of hazardous anions and toxic heavy-metal ions; binding of toxic ions with C-dots; probable mechanistic routes of PL-based sensing of toxic heavy-metal ions. The green production of C-dots and their promising applications in the sensing of hazardous ions discussed herein provides deep insights into the safety of human health and the environment. Nonetheless, this review article provides a resource for the conversion of low-value biomass and biomass waste into valuable materials (i.e., C-dots) for promising sensing applications.

Carbon Dots-Types, Obtaining and Application in Biotechnology and Food Technology

Materials with a "nano" structure are increasingly used in medicine and biotechnology as drug delivery systems, bioimaging agents or biosensors in the monitoring of toxic substances, heavy metals and environmental variations. Furthermore, in the food industry, they have found applications as detectors of food adulteration, microbial contamination and even in packaging for monitoring product freshness. Carbon dots (CDs) as materials with broad as well as unprecedented possibilities could revolutionize the economy, if only their synthesis was based on low-cost natural sources. So far, a number of studies point to the positive possibilities of obtaining CDs from natural sources. This review describes the types of carbon dots and the most important methods of obtaining them. It also focuses on presenting the potential application of carbon dots in biotechnology and food technology.

Aggregation-caused dual-signal response of gold nanoclusters for ratiometric optical detection of cysteine

Designing ratiometric sensors for cysteine (Cys) monitoring with high accuracy is of great significance for disease diagnosis and biomedical studies. The current ratiometric methods mainly rely on multiplex probes, which not only complicates the operation but also increases the cost, making it difficult for quantitative Cys detection in resource-limited areas. Herein, one-pot prepared gold nanoclusters (Au NCs) that glow red fluorescent were synthesized by employing glutathione as the stabilizer and reducing agent. When Fe3+ is present with Au NCs, the fluorescence is quenched and the scattering is strong because of the aggregation of Au NCs. With introduction of Cys, Cys can efficiently compete with glutathione-modified Au NCs for Fe3+, which leads to increase of fluorescence and decrease of scattering. The ratiometric determination of Cys can be thereby realized by collecting the fluorescence and SRS spectrum simultaneously. The linear range for Cys was 5-30 µM with a detection limit of 1.5 µM. In addition, the sensing system exhibits good selectivity for Cys and shows potential application in biological samples.

Two-Pronged Approach: Synergistic Tuning of the Surface and Carbon Core to Achieve Yellow Emission in Lignin-Based Carbon Dots

In this study, yellow emissive lignin-based carbon dots (Y-CDs) were successfully prepared through a synergistic approach to adjust its surface and carbon core states. The lignin was initially effectively oxidized and carboxymethylated to impart abundant -COOH onto the precursor, which eventually adjusts the surface state of the CDs. Subsequently, α-naphthol was employed during the solvothermal treatment of lignin with the aim of elevating the sp2 domain content in the CDs and, thus, adjusting its carbon core state. The obtained Y-CDs possessed abundant carboxyl groups and nanoscale spherical shape with an average diameter of 5.21 nm. Meanwhile, the energy gap of Y-CDs was 2.46 eV and the optimal emission wavelength was 561 nm under the excitation wavelength of 410 nm. Synergistic adjusting carbon core and surface of the Y-CDs would alter the surface charge distribution and promote the delocalization of π electrons, and thus lead to a red shifting with the emission wavelength of 154 nm. Furthermore, a shape memory film with excellent recovery performance and fluorescent properties was designed by embedding the Y-CDs into polyvinyl alcohol (PVA) polymer. The incorporation of Y-CDs could impart the film with considerable high-value applications in the fields of intelligent sensing, biomedicine, and tissue engineering.

High luminescent N,S,P co-doped carbon dots for the fluorescence sensing of extreme acidity and folic acid

Carbon dots are popular luminescent materials because of their excellent fluorescence properties, but the low quantum yield limits their application. Heteroatom doping is a more convenient and popular approach to increase the quantum yield of carbon dots. Here, novel N,S,P heteroatom co-doped carbon dots (N,S,P-CDs) were synthesized by a simple one-step hydrothermal method using m-phenylenediamine, L-cysteine and phosphoric acid as raw materials. The as-prepared N,S,P-CDs showed excellent photoluminescence properties with a fluorescence quantum yield of up to 41%, which greatly encourages their application in fluorescence sensing. The N,S,P-CDs exhibited good fluorescence stability under salt solution, xenon lamp irradiation and ultraviolet lamp irradiation except for a high sensitivity to extreme acidity. The fluorescence intensity of the N,S,P-CDs can be decreased by as much as 85% when the pH of the solution changes from 2.50 to 4.75, that is, a small fluctuation in pH can cause an intense response of the fluorescence of the N,S,P-CDs. Therefore, an excellent fluorescence sensing platform for accurately monitoring the pH of extreme acidity has been constructed. In addition, the N,S,P-CDs can be applied for quantitative detection of folic acid based on the strong quenching effect of folic acid on the fluorescence of the N,S,P-CDs. Good linearity was obtained in the concentration range of 4.85-82.45 μM, with a detection limit of 0.148 μM. The constructed sensing platform was used for the determination of folic acid in actual samples of orange juice, oatmeal and tablets with satisfactory results.

Green-derived carbon dots: A potent tool for biosensing in food safety

The impact of food contaminants on ecosystems and human health has attracted widespread global attention, and there is an urgent need to develop reliable food safety detection methods. Recently, carbon dots (CDs) have been considered as a powerful material to construct sensors for chemical analysis. Based on the concept of resource conversion and sustainable development, the use of natural, harmless, and renewable materials for the preparation of CDs without the involvement of chemical hazards is a current hot topic. This paper reviews the research progress of green-derived CDs and their application in food safety biosensing. The fabrications of green-derived CDs using various biomasses are described in detail, and the application of CDs especially the sensing mechanisms of photoluminescence, colorimetric, electrochemiluminescence and other sensors are provided. Finally, existing shortcomings and current challenges as well as prospects for food safety monitoring are discussed. We believe that this work provides strong insight into the application of CDs in the sensing of various contaminants.

Current trends in carbon-based quantum dots development from solid wastes and their applications

Urbanization and a massive population boom have immensely increased the solid wastes (SWs) generation and are expected to reach 3.40 billion tons by 2050. In many developed and emerging nations, SWs are prevalent in both major and small cities. As a result, in the current context, the reusability of SWs through various applications has taken on added importance. Carbon-based quantum dots (Cb-QDs) and their many variants are synthesized from SWs in a straightforward and practical method. Cb-QDs are a new type of semiconductor that has attracted the interest of researchers due to their wide range of applications, which include everything from energy storage, chemical sensing, to drug delivery. This review is primarily focused on the conversion of SWs into useful materials, which is an essential aspect of waste management for pollution reduction. In this context, the goal of the current review is to investigate the sustainable synthesis routes of carbon quantum dots (CQDs), graphene quantum dots (GQDs), and graphene oxide quantum dots (GOQDs) from various types SWs. The applications of CQDs, GQDs, and GOQDs in the different areas are also been discussed. Finally, the challenges in implementing the existing synthesis methods and future research directions are highlighted.

A facile fluorescence platform for chromium and ascorbic acid detection based on "on-off-on" strategy

In this paper, a facile and rapid fluorescence "on-off-on" strategy for the detection of chromium (Cr(VI)) and ascorbic acid (AA) was developed, which was based on the water-soluble carbon dots (CDs). The CDs was synthesized by a microwave-assisted treatment of L-tartaric acid, citric acid, and urea. The CDs have many advantages, such as high fluorescence quantum yield (20.5%) and good fluorescence stability. Based on inner filter effect (IFE) and static quenching, the fluorescence of the CDs can be quenched by Cr(VI) quickly; while the reduction of IFE and reducing action can make the fluorescence of the CDs recover by AA efficiently. Moreover, under the optimal experimental conditions, the CDs had a good detection performance for Cr(VI) in the range of 0.8 ∼ 189 µM with the limit of detection (LOD) of 0.16 µM. The linear detection for AA was ranged from 0.43 to 25.7 µM with a LOD of 0.1 µM. More importantly, the as-constructed fluorescence detecting platform was successfully applied for Cr(VI) and AA detection in the environmental samples and fruit samples, respectively. In addition, the application potential of the CDs in fluorescent films and anti-counterfeiting materials was further discussed in detail. This work will provide a novel idea for designing a portable sensor based on the CDs to quickly and sensitively detect Cr(VI) and AA.

Biobased carbon dots production via hydrothermal conversion of microalgae Chlorella pyrenoidosa

A promising green hydrothermal process was used to produce biobased nanomaterials carbon dots (CDs) by using microalgae Chlorella pyrenoidosa (CP) and its main model compounds (i.e., glucose, glycine, and octadecanoic acid). The possible reaction pathway including hydrolysis, Amadori rearrangement, cyclization/aromatization, and polymerization was first proposed for the hydrothermal process to produce microalgae-based CDs. Interactions among carbohydrates and proteins in microalgae were vital intermediate reactions in the generation of CDs. The mass yield of CDs reached 7.2% when the CP was hydrothermally treated with 20:1 of liquid-to-solid ratio at 230 °C for 6 h. It was confirmed that nitrogen, sulfur, phosphorous, and potassium were doped onto CP-based CDs (CD-CP) successfully without additional reagents or treatments. The CD-CP yield was 4.0-24.3 times higher than that of model compound-based CDs. Regarding morphology, CD-CP was constituted by many spherical nanoparticles smaller than 20 nm. These CDs emitted blue fluorescence under ultraviolet light, and the fluorescence quantum yield of CD-CP was 4.7-9.4 times higher than that of CP model compound-based CDs. Last, CD-CP displayed broad application prospects as a sensor for Fe³⁺ detection in wastewater with high sensitivity.

Sensor Heavy Metal from Natural Resources for a Green Environment: A Review Relation Between Synthesis Method and Luminescence Properties of Carbon Dots

Carbon dots are 10-nm nanomaterial classes as excellent candidates in various applications: physics, biology, chemistry, and food science due to high stable biocompatibility and high surface expansive. Carbon dots (CDs) produced from natural materials have received wide attention due to their unique benefits, easy availabilities, sufficient costs, and harmless to the ecosystem. The various properties of CDs can be obtained from various synthesis methods: hydrothermal, microwave-assisted, and pyrolysis. The CDs have shown enormous potential in metal particle detection, colorimetric sensors, electrochemical sensors, and pesticide sensor. This review provides systematic information on a synthesis method based on natural resources and the application to the environmental sensors for supporting the clean environment. We hopefully this review, useful as a reference source in providing the guidance or roadmap of new researchers to develop new strategy in increasing luminescence properties CDs for multi detection of heavy metal in the environment.

Reuse of waste Myrica rubra for green synthesis of nitrogen-doped carbon dots as an "on-off-on" fluorescent probe for Fe3+ and ascorbic acid detection

As one kind of high nutrition fruits, abandoned Myrica rubra causes great waste due to short storage period. For resource utilization, we herein fabricated the Myrica rubra-based N-doped carbon dots (MN-CDs) by a facile/green hydrothermal method. MN-CDs, fabricated from four regions of China, displayed significant differences in their corresponding fluorescence intensities (FIs). Interestingly, different batches of waxberry samples from the same region (Wenzhou, China) exhibited slight differences in their FIs, and also an excellent anti-photobleaching and anti-salt capacity. Based on Fe³⁺-triggered quenching effect and fluorescent recovery by redox reaction of AA and Fe³⁺, MN-CDs were employed to construct an "on-off-on" switch probe for sequential detection of Fe³⁺ and ascorbic acid (AA). Through Zeta potential, UV spectrum, Stern-Volmer equation, and valence-conduction band theory, the Fe³⁺-triggered quenching belonged to a static quenching process, which resulted from the synergistic contribution of inner filtering effect and photo-induced electron transfer mechanisms. The linear ranges for Fe³⁺ and AA detections were 1-1000 and 0.1-1000 mM. The limits of detection were 0.3 μM for Fe³⁺ in environmental waters, and 0.03 μM for AA in pharmaceutical tablets and fruit juice samples. Under 365-nm UV lamp, the color changes of test papers were easily observed from dark blue and bright blue in the presence of Fe³⁺ and AA, and thus the MN-CDs-based switch probe could be satisfactorily used for visually qualitative detection of Fe³⁺ and AA outdoor with our naked eyes. To sum up, MN-CDs not only realize resource reutilization of abandoned Myrica rubra, but also offer an convenient outdoor approach for qualitative detection of Fe³⁺ and AA in complex matrices.

A Continuously Tunable Full-Color Emission Nitrogen-Doped Carbon Dots and for Ultrasensitive and Highly Selective Detection of Ascorbic Acid

Nitrogen-doped carbon dots exhibiting excitation-dependent full-color emissions (F-NCDs) were prepared via the one-step hydrothermal method with citric acid and phenylenediamine. Specifically, the emission wavelength of the F-NCDs tuned from 452 nm to 602 nm due to the introduction of new energy levels by C=O and C=N functional groups. We exploited its stability in illumination, ionic strength, and pH, as well as its specificity, sensitivity, especially in ascorbic acid (AA) detection. F-NCDs could measure the AA concentration in the linear ranges of 0~0.1 and 0.1~1 mmol/L with the detection limit (LOD, S/N = 3) as low as 2.6 nmol/L. Additionally, we successfully detected AA in bovine serum with our F-NCDs and obtained the result within 1 min. Because of full-color emission features, we believe our F-NCDs have a great potential in fluorescent sensor detection.

Application of carbon dots in food preservation: a critical review for packaging enhancers and food preservatives

Carbon dots (CDs) have two unique advantages: one is ease of synthesis at low price, the other is desirable physical and chemical properties, such as ultra-small size, abundant surface functional groups, nontoxic/low-toxicity, good biocompatibility, excellent antibacterial and antioxidant activities etc. These advantages provide opportunities for the development of new food packaging enhancers and food preservatives. This paper systematically reviews the studies of CDs used to strengthen the physical properties of food packaging, including strengthen mechanical strength, ultraviolet (UV) barrier properties and water barrier properties. It also reviews the researches of CDs used to fabricate active packaging with antioxidant and/or antibacterial properties and intelligent packaging with the capacity of sensing the freshness of food. In addition, it analyzes the antioxidant and antibacterial properties of CDs as preservatives, and discusses the effect of CDs applied as coating agents and nano-level food additives for extension the shelf life of food samples. It also provides a brief review on the security and the release behavior of CDs.

Sustainable and Green Synthesis of Waste-Biomass-Derived Carbon Dots for Parallel and Semi-Quantitative Visual Detection of Cr(VI) and Fe3

Carbon dot (CD)-based multi-mode sensing has drawn much attention owing to its wider application range and higher availability compared with single-mode sensing. Herein, a simple and green methodology to construct a CD-based dual-mode fluorescent sensor from the waste biomass of flowers of wintersweet (FW-CDs) for parallel and semi-quantitative visual detection of Cr(VI) and Fe3+ was firstly reported. The FW-CD fluorescent probe had a high sensitivity to Cr(VI) and Fe3+ with wide ranges of linearity from 0.1 to 60 µM and 0.05 to 100 µM along with low detection limits (LOD) of 0.07 µM and 0.15 µM, respectively. Accordingly, the FW-CD-based dual-mode sensor had an excellent parallel sensing capacity toward Cr(VI) and Fe3+ with high selectivity and strong anti-interference capability by co-using dual-functional integration and dual-masking strategies. The developed parallel sensing platform was successfully applied to Cr(VI) and Fe3+ quantitative detection in real samples with high precision and good recovery. More importantly, a novel FW-CD-based fluorescent hydrogel sensor was fabricated and first applied in the parallel and semi-quantitative visual detection of Cr(VI) and ferrous ions in industrial effluent and iron supplements, further demonstrating the significant advantage of parallel and visual sensing strategies.

Preparation of boronic acid-modified polymer dots under mild conditions and their applications in pH and glucose detection

For the first time, boronic acid-modified polymer dots (B-PDs) were fabricated by a "synthesis-modification integration" route using polyethylenimine (PEI) and phenylboronic acid as precursors. Under optimized preparation conditions, the B-PDs exhibited an average size of 2.2 nm, good water solubility, and high fluorescence quantum yield of 8.69%. The B-PDs showed reversible fluorescence response in acid solutions (blue emissions) and alkaline solutions (green emissions). The fluorescence emissions of B-PDs demonstrated an obvious red shift with varying the pH value from 1 - 13. Moreover, glucose could assemble on the surface of B-PDs due to the reversible reaction between boronic acid and cis-diols, which resulted in a blue shift of emission wavelength and an obvious increase of FL intensity at λ_ex = 380 nm based on the aggregation-induced enhancement effect. The glucose sensing method was thus developed in the range 0.0001 - 1.0 mol L^-1. Applications to real human blood and glucose injection samples demonstrated satisfactory results. The B-PDs based on the analytical method display good selectivity, wide detection range, and simplicity in preparation and detection, implying promising applications as a practical platform for biosensing.

Direct Z-scheme SiNWs@Co3O4 photocathode with a cocatalyst of sludge-derived carbon quantum dots for efficient photoelectrochemical hydrogen production

Solar driven photoelectrochemical (PEC) hydrogen production has attracted considerable attention, but the design of highly efficient, robust and low-cost photocathode still remains a significant challenge. Herein, we report a novel SiNWs@Co₃O₄Z-scheme heterojunction photocathode with carbon quantum dots eco-friendly derived from sludge (SCQDs) as the co-catalyst. The photocathode not only leads to effective separation of electron-hole pair, lower transmission resistance, and longer lifetime of charge carriers, but also elevates the stability by preventing direct contact between the SiNWs and the electrolyte as well as the self-oxidation. Simultaneously, the excellent electron transport properties of the SCQDs further improved the PEC performance. Correspondingly, a maximum current density of 14.88 mA·cm^-2 was obtained at -0.67 V with the applied bias photon-to-current efficiency (ABPE) achieving 8.4% under visible light irradiations at pH = 7. This work provides a promising scheme for Si-based photocathodes for PEC hydrogen production with a high performance, reliable stability, and low-cost.

Highly fluorescent carbon dots from coix seed for the determination of furazolidone and temperature

In this work, blue emission fluorescent carbon dots (CDs) were fabricated by using the hydrothermal strategy from coix seed for the first time. We found that the prepared CDs possessed many excellent characteristics including excitation-dependent properties, good solubility and strong photostability. The optimal excitation and emission wavelength of CDs were 363 and 435 nm, respectively. Unbelievably, the fluorescence of CDs was selectively and effectively quenched with the addition of furazolidone (Fu). The quenching mechanisms might be assumed to the static quenching and inner filter effect (IFE). Based on this principle, a novel fluorescence probe was developed for the determination of Fu. At the same time, the proposed probe showed excellent sensitivity and selectivity towards Fu with a wide linear range from 0.5 to 100 μM, and the corresponding detection limit was 0.096 μM. Moreover, the CDs also could be applied for the sensing of temperature. The practical application of the CDs for Fu detection in real samples was also confirmed with the satisfactory recoveries changing from 96.6% to 108.5%, which provided huge possibility in the field of medical analysis.

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.

Environmental footprint of voltammetric sensors based on screen-printed electrodes: An assessment towards "green" sensor manufacturing

Voltammetric sensors based on screen-printed electrodes (SPEs) await diverse applications in environmental monitoring, food, agricultural and biomedical analysis. However, due to the single-use and disposable characteristics of SPEs and the scale of measurements performed, their environmental impacts should be considered. A life cycle assessment was conducted to evaluate the environmental footprint of SPEs manufactured using various substrate materials (SMs: cotton textile, HDPE plastic, Kraft paper, graphic paper, glass, and ceramic) and electrode materials (EMs: platinum, gold, silver, copper, carbon black, and carbon nanotubes (CNTs)). The greatest environmental impact was observed when cotton textile was used as SM. HDPE plastic demonstrated the least impact (13 out of 19 categories), followed by ceramic, glass and paper. However, considering the end-of-life scenarios and release of microplastics into the environment, ceramic, glass or paper could be the most suitable options for SMs. Amongst the EMs, the replacement of metals, especially noble metals, by carbon-based EMs greatly reduces the environmental footprint of SPEs. Compared with other materials, carbon black was the least impactful on the environment. On the other hand, copper and waste-derived CNTs (WCNTs) showed low impacts except for terrestrial ecotoxicity and human toxicity (non-cancer) potentials. In comparison to commercial CNTs (CCNTs), WCNTs demonstrated lower environmental footprint and comparable voltammetric performance in heavy metal detections, justifying the substitution of CCNTs with WCNTs in commercial applications. In conclusion, a combination of carbon black or WCNTs EMs with ceramic, glass or paper SMs represents the most environmentally friendly SPE configurations for voltammetric sensor arrangement.

Simple and Sensitive Multi-components Detection Using Synthetic Nitrogen-doped Carbon Dots Based on Soluble Starch

Although carbon dots (CDs) as fluorescent sensors have been widely exploited, multi-component detection using CDs without tedious surface modification is always a challenging task. Here, two kinds of nitrogen-doped CDs (NCD-m and NCD-o) based on soluble starch (SS) as carbon source were prepared through one-pot hydrothermal process using m-phenylenediamine and o-phenylenediamine as nitrogenous dopant respectively. Through fluorescence "on-off" mechanism of CDs, NCD-m and NCD-o could be used as a fluorescence sensor for detection of Fe 3+ and Ag + with LOD of 0.25 and 0.51 μM, respectively. Additionally, NCD-m could be used for indirect detection of ascorbic acid (AA) with LOD of 5.02 μM. Moreover, fluorescence intensity of NCD-m also exhibited the sensitivity to pH change from 2 to 13. More importantly, Both NCD-m and NCD-o had potential application for analysis of complicated real samples such as tap water, Vitamin C tablets and orange juice. Ultimately, the small size of NCD-m could contribute to reinforcing intracellular endocytosis, which allowed them to be used for bacteria imaging. Obviously, these easily obtainable nitrogen-doped CDs were able to be used for multi-components detection. Strategy for synthesis of nitrogen-doped carbon dots (NCDs) and a schematic for fabrication of as-prepared NCDs for detection of Fe 3+, Ag + and ascorbic acid (AA).

Lysosome targeting, Cr(vi) and l-AA sensing, and cell imaging based on N-doped blue-fluorescence carbon dots

N-doped blue-fluorescence carbon dots (N-CDs) were fabricated via a one-pot hydrothermal method using folic acid and p-phenylenediamine. The obtained N-CDs exhibited strong fluorescence (FL) with a considerable quantum yield (QY) of 21.8% and exceptional optical stability under different conditions. Upon introducing Cr(vi), blue FL of N-CDs was distinctly quenched. On subsequent addition of l-AA, the FL of N-CDs could be partially recovered. The fluorescence changes of N-CDs have been utilized to detect Cr(vi) and l-AA in aqueous solutions with linear ranges of 0.10-150 μM and 0.75-2.25 mM, respectively, as well as limit of detection values of 9.4 nM and 25 μM, respectively. Furthermore, as-obtained N-CDs can be extended to monitor the fluctuation of intracellular Cr(vi) and l-AA. More intriguingly, N-CDs can target lysosomes with a satisfactory Pearson correction coefficient of 0.87, which indicates a promising application prospect in the biomedical field.