Fluorescent carbon quantum dots synthesized using phenylalanine and citric acid for selective detection of Fe3+ ions

Synthesis of shape-controlled covalent organic frameworks for light scattering detection of iron and chromium ions

Fabricating covalent organic frameworks with different morphologies based on the same structural motifs is both interesting and challenging. Here, a TTA-TFP-COF was synthesized by both solvothermal and room temperature methods, with 2,4,6-Tris(4-aminophenyl)-1,3,5-triazine (TTA) and 1,3,5-tris(4-formylphenyl)-benzene (TFP) as raw material. Using different synthesis conditions and adding aniline and benzaldehyde as regulators in the synthesis process, we found that these processes could slow down the reaction speed, increase the exchange and metathesis reactions of dynamic reversible reactions, and improve the reversibility of the reaction system. Thus, controllable synthesis of TTA-TFP-COF with different morphologies, including micro-particles, hollow tubes with controllable diameters, and micro-flowers was achieved. Our further study found that metal ions, Fe3+ and Cr3+ ions, could coordinate with N and O in TTA-TFP-COF and partially destroy the structure of TTA-TFP-COF. The particle size of the TTA-TFP-COF became smaller, thus resulting in the decrease of the light scattering intensity of the COF. An excellent linear relationship exists between the light scattering changes (ΔI) and metal ions concentration (c) from 2.0 to 350.0 μM for Fe3+ and 40.0-800.0 μM for Cr3+, respectively. Thus, rapid and selective analytical methods for detecting metal ions were developed by TTA-TFP-COF here.

Progress and obstacles in employing carbon quantum dots for sustainable wastewater treatment

We explored the potential of carbon quantum dots (CQDs) as novel materials for wastewater treatment and their role towards environmental sustainability. The advantages of CQDs over other carbon-based materials, when synthesized using the same precursor material and for the same contaminant are discussed, enabling future researchers to choose the appropriate material. CQDs have demonstrated exceptional adaptability in various wastewater treatment, acting as efficient adsorbents for contaminants, exhibiting excellent photocatalytic properties for degradation of organic pollutants, and functioning as highly sensitive sensors for water quality monitoring. We found that bottom-up approach has better control over particle size (resulting CQDs: 1-4 nm), whereas top-down synthesis approach (resulting CQDs: 2-10 nm) have more potential for large scale applications and tunability. Transmission electron microscopy (TEM) remains the most expensive characterization technique, which provides the best resolution of the CQD's surface. The study emphasizes on the environmental impact and safety considerations pertaining to CQDs by emphasizing the need for thorough toxicity evaluation, and necessary environmental precautions. The study also identifies the lacunae pertaining to critical challenges in practical implementation of CQDs, such as scalability, competition of co-existing contaminants, and stability. Finally, future research directions are proposed, advocating green synthesis approaches, tailored surface functionalization, and, lowering the overall cost for analysis, synthesis and application of CQDs.

Carbon dots as versatile nanomaterials in sensing and imaging: Efficiency and beyond

Carbon dots (CDs) have emerged as a versatile and promising carbon-based nanomaterial with exceptional optical properties, including tunable emission wavelengths, high quantum yield, and photostability. CDs are appropriate for various applications with many benefits, such as biocompatibility, low toxicity, and simplicity of surface modification. Thanks to their tunable optical properties and great sensitivity, CDs have been used in sensing as fluorescent probes for detecting pH, heavy metal ions, and other analytes. In addition, CDs have demonstrated potential as luminescence converters for white organic light-emitting diodes and light emitters in optoelectronic devices due to their superior optical qualities and exciton-independent emission. CDs have been used for drug administration and bioimaging in the biomedical field due to their biocompatibility, low cytotoxicity, and ease of functionalization. Additionally, due to their stability, efficient charge separation, and low recombination rate, CDs have shown interesting uses in energy systems, such as photocatalysis and energy conversion. This article highlights the growing possibilities and potential of CDs as adaptable nanomaterials in a variety of interdisciplinary areas related to sensing and imaging, at the same time addressing the major challenges involved in the current research and proposing scientific solutions to apply CDs in the development of a super smart society.

Biomass-derived carbon dots as emerging visual platforms for fluorescent sensing

Biomass-derived carbon dots (CDs) are non-toxic and fluorescently stable, making them suitable for extensive application in fluorescence sensing. The use of cheap and renewable materials not only improves the utilization rate of waste resources, but it is also drawing increasing attention to and interest in the production of biomass-derived CDs. Visual fluorescence detection based on CDs is the focus of current research. This method offers high sensitivity and accuracy and can be used for rapid and accurate determination under complex conditions. This paper describes the biomass precursors of CDs, including plants, animal remains and microorganisms. The factors affecting the use of CDs as fluorescent probes are also discussed, and a brief overview of enhancements made to the preparation process of CDs is provided. In addition, the application prospects and challenges related to biomass-derived CDs are demonstrated.

Environmentally sustainable synthesis of whey-based carbon dots for ferric ion detection in human serum and water samples: evaluating the greenness of the method

Carbon dots (CDs) are valued for their biocompatibility, easy fabrication, and distinct optical characteristics. The current study examines using whey to fabricate CDs using the hydrothermal method. When stimulated at 350 nm, the synthetic CDs emitted blue light at 423 nm and revealed a selective response to ferric ion (Fe3+) in actual samples with great sensitivity, making them a suitable probe for assessing Fe3+ ions. The produced carbon dots demonstrated great photostability, high sensitivity, and outstanding biocompatibility. The findings showed that Fe3+ ions could be quickly, sensitively, and extremely selectively detected in an aqueous solution of carbon dots, with a revealing limit of 0.409 μM in the linear range of 0-180 μM. Interestingly, this recognition boundary is far inferior to the WHO-recommended threshold of 0.77 μM. Two metric tools which were AGREE and the ComplexGAPI were also used to evaluate the method's greenness. The evaluation confirmed its superior environmental friendliness.

Microwave-Assisted Synthesis of Functionalized Carbon Nanospheres Using Banana Peels: pH-Dependent Synthesis, Characterization, and Selective Sensing Applications

This work presents a microwave-based green synthesis method for producing carbon nanospheres (CNSs) and investigates the impact of presynthesis pH on their size and assembly. The resulting CNSs are monodispersed, averaging 35 nm in size, and exhibit notable characteristics including high water solubility, photostability, and a narrow size distribution, achieved within a synthesis time of 15 min. The synthesized CNS features functional groups such as -OH, -COOH, -NH, -C-O-C, =C-H, and -CH. This diversity empowers the CNS for various applications including sensing. The CNS exhibits a distinct UV peak at 282 nm and emits intense fluorescence at 430 nm upon excitation at 350 nm. These functionalized CNSs enable selective and specific sensing of Cu2+ ions and the amino acid tryptophan (Trp) in aqueous solutions. In the presence of Cu2+ ions, static-based quenching of CNS fluorescence was observed due to the chelation-enhanced quenching (CHEQ) effect. Notably, Cu2+ ions induce a substantial change in UV spectra alongside a red-shift in the peak position. The limits of detection and quantification for Cu2+ ions with CNS are determined as 0.73 and 2.45 μg/mL, respectively. Additionally, on interaction with tryptophan, the UV spectra of CNS display a marked increase in the peak at 282 nm, accompanied by a red-shift phenomenon. The limits of detection and quantification for l-tryptophan are 4.510 × 10-3 and 1.50 × 10-2 μg/mL, respectively, indicating its significant potential for biological applications. Furthermore, the practical applicability of CNSs is demonstrated by their successful implementation in analyzing real water samples and filter paper-based examination, showcasing their effectiveness for on-site sensing.

Sustainable synthesis of lignin-derived carbon dots with visible pH response for Fe3+ detection and bioimaging

Synthesis of lignin-based carbon dots (LCDs) with high quantum yield (QY), stable fluorescence properties and biocompatibility has been a challenge. Here, we propose an improved two-step strategy for producing high-quality LCDs from enzymatic hydrolysis lignin (EHL). The p-aminobenzenesulfonic acid used in the strategy not only provides nitrogen and sulfur elements, but also tailors the disordered three-dimensional structure of EHL. The successful co-doping of N and S elements favors the reduction of the optical energy bandgap (Eg), resulting in a high QY of 45.05% for LCDs. The LCDs exhibited superior selectivity and sensitivity for Fe3+ with a limit of detection (LOD) of 0.15 μM when Fe3+ concentration was 50-500 μM. In addition, LCDs demonstrated significant fluorescence in HepG2 cells and HepG2 cells loaded with LCDs at a concentration of 80 μg/mL showed good viability, suggesting that they are suitable for in vivo applications. The luminescent centers of LCDs change during pH regulation and thus show a special visual response to pH changes, making them have great potential for detecting metabolism in living cells. This work provides a novel and low-cost method for fabricating sustainable fluorescent probes for chemical sensing and bioimaging.

Spectrofluorometric quantitative analysis of aripiprazole based on quenching of natural derived carbon quantum dots in spiked human plasma

Autism spectrum disorder is a significant concern worldwide, particularly in Middle Eastern countries. Aripiprazole, a psychiatric medicine that works as a partial agonist at D2 receptors, is often used for autism-related behavior issues in children. Monitoring the therapy of aripiprazole could enhance the safety and effectiveness of treatment for autistic individuals. The purpose of this study was to develop a highly sensitive and environmentally friendly method for analysis of aripiprazole in plasma matrix. To achieve this, water-soluble N-carbon quantum dots were produced from a natural green precursor, guava fruit, and used in fluorescence quenching spectroscopy to determine the presence of aripiprazole. The synthesized dots were analyzed and characterized using transmission electron microscopy and Fourier transform infrared spectroscopy, and they showed a strong fluorescence emission peak at 475 nm. The proposed method was validated according to ICH M10 guidelines and was shown to be highly sensitive, allowing for nanoscale determination of aripiprazole in plasma matrix. Additionally, the method was compared to a previously reported spectrophotometric method, and it was found to be more sensitive and consistent with the principles of green analytical chemistry.

Paper test strip for fluorescence detection of iron ion based on nitrogen, zinc and copper codoped carbon dots

In this study, a test strip for fluorometric analysis of iron ion (Fe3+) was constructed based on nitrogen, zinc and copper codoped carbon dots (NZC-CDs) as fluorescence probes. NZC-CDs were synthesized by hydrothermal method. The morphology, size, components, crystal state and optical properties of NZC-CDs were characterized by transmission electron microscope (TEM), Fourier-transform infrared (FT-IR), x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), UV-vis absorption and fluorescence spectroscopy techniques, respectively. NZC-CDs exhibited bright blue fluorescence under UV lamp with a quantum yield at 17.76%. The fluorescence of NZC-CDs was quenched by Fe3+possibly due to the static quenching. The possible fluorescence quenching mechanism was also discussed. The quenching fluorescence was linear with the concentration of Fe3+in the range of 2.5-400μM with a low detection limit of 0.5μM. For the convenient detection, the test strips based on filter paper were employed for Fe3+assay. Moreover, the present approach was successfully applied in the determination of Fe3+in real samples including black fungus, duck blood and pork liver. The sensing method had the potential application in more food analysis.

Fluorescence Turns on-off-on Sensing of Ferric Ion and L-Ascorbic Acid by Carbon Quantum Dots

This study used a hydrothermal approach to create a sensitive and focused nanoprobe. Using an “on-off-on” sensing mechanism, the nanoprobe was employed to detect and quantify ferric ions and L-ascorbic acid. Synthesis of the carbon quantum dots was achieved with a single hydrothermal step at 180°C for 24 hours using hot pepper as the starting material. The prepared CQDs showed high fluorescence with a quantum yield of 30% when excited at 350 nm, exhibiting excitation-dependent fluorescence. The emission of the CQDs can be quenched by adding ferric ions, which can be attributed to complex formation leading to nonradiative photoinduced electron transfer (PET). Adding L-ascorbic acid, which can convert ferric ions into ferrous ions, break the complex, and restore the fluorescence of CQD. The linear range and LOD were (10–90) μM and 1 μM for ferric ions, respectively, and L-ascorbic acid’s linear range was (5–100) μM while LOD was 0.1 μM quantification of both substances was accomplished. In addition, orange fruit was used as an actual sample source for ascorbic acid analysis, yielding up to 99% recovery.

Implementing neural network approach to create carbon-based optical nanosensor of heavy metal ions in liquid media

The present study is devoted to the creation of multifunctional optical carbon dots-based nanosensor to simultaneously measure concentrations of metal ions (Cu²⁺, Ni²⁺, Cr³⁺) and NO₃^- anion in liquid media. Such nanosensor operates on the basis of its fluorescence (FL) change under the influence of ions in the medium. However, the absence of analytical model, describing CD FL mechanism, the superposition of various luminescence quenching mechanisms during the interaction of carbon dots (CD) with cations, hampers the usage of classical approaches to solve this inverse multiparametric spectroscopic problem. To solve it neural networks were used that analyzed complex fluorescence signal from CD aqueous suspensions comprising Cu²⁺, Ni²⁺, Cr³⁺, NO₃^- ions in the concentration range from 0 to 4.95 mM. The following neural network architectures ensured optical spectroscopy inverse problem solution: multilayer perceptrons, 1D and 2D convolutional neural networks. The developed sensor enables simultaneous determination of the concentrations of heavy metal ions Cu²⁺, Ni²⁺, Cr³⁺ with a root mean squared error of 0.28 mM, 0.79 mM, 0.24 mM respectively. Based on the data given in the literature we can assert that the accuracy of the studied nanosensor satisfies the needs of monitoring the composition of waste and technological water. The developed nanosensor has a unique multimodality: with the simplicity of the synthesis protocol the sensor enables simultaneous determination of three heavy metal ions concentrations, while analogues are being developed mainly to measure the concentration of one (in rare cases two) heavy metal ions.

Fabrication of P and N Co-Doped Carbon Dots for Fe3+ Detection in Serum and Lysosomal Tracking in Living Cells

Doping with heteroatoms allows the retention of the general characteristics of carbon dots while allowing their physicochemical and photochemical properties to be effectively modulated. In this work, we report the preparation of ultrastable P and N co-doped carbon dots (PNCDs) that can be used for the highly selective detection of Fe³⁺ and the tracking of lysosomes in living cells. Fluorescent PNCDs were facilely prepared via a hydrothermal treatment of ethylenediamine and phytic acid, and they exhibited a high quantum yield of 22.0%. The strong coordination interaction between the phosphorus groups of PNCDs and Fe³⁺ rendered them efficient probes for use in selective Fe³⁺ detection, with a detection limit of 0.39 μM, and we demonstrated their practicability by accurately detecting the Fe³⁺ contents in bio-samples. At the same time, PNCDs exhibited high lysosomal location specificity in different cell lines due to surface lipophilic amino groups, and real-time tracking of the lysosome morphology in HeLa cells was achieved. The present work suggests that the fabrication of heteroatom-doped CDs might be an effective strategy to provide promising tools for cytology, such as organelle tracking.

A paper-based microfluidic sensor array combining molecular imprinting technology and carbon quantum dots for the discrimination of nitrophenol isomers

Paper-based microfluidic analytical devices (μPADs) have recently attracted attention as a rapid test kit owing to their low cost and nonrequirement for external driving pump. However, low accuracy and poor anti-interference ability of μPADs under complex detection condition limit their practical applications. Here, we present a facile way to prepare a novel fluorescence sensor-array μPAD for multi-analyte discrimination based on molecular imprinting technology, and its sensing behavior was studied by using three nitrophenol (NP) isomers (2-, 3-, and 4-NP) as the testing models. Carbon quantum dots (CQDs) emitting blue light were grafted on glass-fiber paper, followed by in-situ modification of three types of molecularly imprinted polymers (MIPs) with 2-, 3-, and 4-NP as template. Each sensing unit on the array showed differential yet cross-reactive binding affinity to NP isomers, resulting in distinct fluorescence quenching efficiency. Thus, precise distinguishment of the three NPs was realized with the MIPs/CQDs/paper-based sensor array. Furthermore, the discrimination ability of the platform was evaluated in mixtures of the NP isomers. Practicability of this apparatus was validated by identification of blind samples and 100% accuracy was achieved. The μPAD has proven to be highly sensitive and accurate, which will serve as an ideal analytical tool in the fields of environment monitoring, disease prognosis, food safety and so on.

Carbon dots-based nanomaterials for fluorescent sensing of toxic elements in environmental samples: Strategies for enhanced performance

Rapid industrialization and manufacturing expansion have caused heavy metal pollution, which is a critical environmental issue faced by global population. In addition, the disadvantages presented by conventional detection methods such as the requirement of sophisticated instruments and qualified personnel have led to the development of novel nanosensors. Recently, carbon dots (CDs) have been presented as a multifunctional nanomaterial alternative for the accurate detection of heavy metal ions in water systems. The capacity of CDs to detect contaminants in wastewater -including heavy metals- can be found in the literature; however, to the best of our knowledge, none of them discusses the most recent strategies to enhance their performance. Therefore, in this review, beyond presenting successful examples of the use of CDs for the detection of metal ions, we further discuss the strategies to enhance their photoluminescence properties and their performance for environmental monitoring. In this manner, strategies such as heteroatom-doping and surface passivation are reviewed in detail, as well as describing the mechanisms and the effect of precursors and synthesis methods. Finally, the current challenges are described in detail to propose some recommendations for further research.

Selective Detection of Fe3+ by Nitrogen–Sulfur-Doped Carbon Dots Using Thiourea and Citric Acid

The quantum yield and fluorescence properties of carbon dots are key issues for environmental detection. In this study, nitrogen–sulfur-doped carbon dots (N,S-CDs) were prepared hydrothermally by adding thiourea to provide the N source. By adjusting the ratio of citric acid (CA) to thiourea (N,S) and adding anhydrous ethanol, blue fluorescent doped carbon dots with a quantum yield of up to 53.80% were obtained. The particle morphology and crystalline organization of the N,S-CDs were analyzed using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Fourier transform infrared (FTIR) spectroscopy was used to illuminate distinct functional units through the recording of typical vibration bands. The luminescence properties of the N,S-CDs were investigated using ultraviolet–visible (UV-vis) absorption spectroscopy and steady-state fluorescence spectroscopy (PL). In addition, the fluorescence stability of the N,S-CDs was studied in detail. The results showed that the functional groups of the N,S-CDs chelate Fe3+ ions to quench the fluorescence of carbon dots. This shows that the N,S-CDs exhibit high selectivity for Fe3+ ions. With the addition of Fe3+ in the concentration of 0–100 µM, the fluorescence intensity of the N,S-CDs exhibited distinct and linear dependence upon the Fe3+ concentration (R2 = 0.9965), and the detection limit (D = 3ơ/m) was measured as 0.2 µM. The excellent optical properties and Fe3+ selectivity of the N,S-CDs provide a huge boost for application in the field of environmental monitoring.

A Review on Carbon Dots: Synthesis, Characterization and Its Application in Optical Sensor for Environmental Monitoring

The development of carbon dots (CDs), either using green or chemical precursors, has inevitably led to their wide range application, from bioimaging to optoelectronic devices. The reported precursors and properties of these CDs have opened new opportunities for the future development of high-quality CDs and applications. Green precursors were classified into fruits, vegetables, flowers, leaves, seeds, stem, crop residues, fungi/bacteria species, and waste products, while the chemical precursors were classified into acid reagents and non-acid reagents. This paper quickly reviews ten years of the synthesis of CDs using green and chemical precursors. The application of CDs as sensing materials in optical sensor techniques for environmental monitoring, including the detection of heavy metal ions, phenol, pesticides, and nitroaromatic explosives, was also discussed in this review. This profound review will offer knowledge for the upcoming community of researchers interested in synthesizing high-quality CDs for various applications.

Recent Progress in Fluorescent Probes For Metal Ion Detection

All forms of life have absolute request for metal elements, because metal elements are instrumental in various fundamental processes. Fluorescent probes have been widely used due to their ease of operation, good selectivity, high spatial and temporal resolution, and high sensitivity. In this paper, the research progress of various metal ion (Fe3+,Fe2+,Cu2+,Zn2+,Hg2+,Pb2+,Cd2+) fluorescent probes in recent years has been reviewed, and the fluorescence probes prepared with different structures and materials in different environments are introduced. It is of great significance to improve the sensing performance on metal ions. This research has a wide prospect in the application fields of fluorescence sensing, quantitative analysis, biomedicine and so on. This paper discusses about the development and applications of metal fluorescent probes in future.

Water stable, red emitting, carbon nanoparticles stimulate 3D cell invasion via clathrin-mediated endocytic uptake

Bright fluorescent nanoparticles with excitation and emission towards the red end of the spectrum are highly desirable in the field of bioimaging. We present here a new class of organic carbon-based nanoparticles (CNPs) with a robust quantum yield and fluorescence towards the red region of the spectrum. Using organic substrates such as para-phenylenediamine (PPDA) dispersed in diphenyl ether under reflux conditions, we achieved scalable amounts of CNPs with an average size of 27 nm. These CNPs were readily taken up by different mammalian cells, and we show that they prefer clathrin-mediated endocytosis for their cellular entry route. Not only can these CNPs be specifically taken up by cells, but they also stimulate cellular processes such as cell invasion from 3D spheroid models. This new class of CNPs, which have sizes similar to those of proteinaceous ligands, hold immense potential for their surface functionalization. These could be explored as promising bioimaging agents for biomedical imaging and intracellular drug delivery.

A Label-Free Fluorescent Sensor Based on Si,N-Codoped Carbon Quantum Dots with Enhanced Sensitivity for the Determination of Cr(VI)

A signal shut-off probe of Si, N-codoped carbon quantum dots (Si, N-CQDs) was exploited to detect Cr(VI) by fluorescence quenching without the aid of any biomolecules or labeling materials. The sensing system prepared the precursor of diacetone acrylamide and the silane coupling agent 3-aminopropyltriethoxysilane (KH-550) by a simple hydrothermal method, and the quantum yield is as high as 75% Si, N-CQDs. The fluorescence stability and microstructure of the Si, N-CQDs were studied. The Si, N-CQDs has a high sensitivity for detecting Cr(VI) with the linear range of 0–200 μM and the detection limit of 0.995 μM. The quenching mechanism of Si, N-CQDs is attributed to FRET.

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

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

Orange-emissive N,S-co-doped carbon dots for label-free and sensitive fluorescence assay of vitamin B12

N,S-CDs with orange fluorescent emission were synthesized via a hydrothermal method using o-phenylenediamine and thiourea. A novel fluorometric method for the determination of VB12 based on the IFE was established.

Recent developments on carbon dots-based green analytical methods: New opportunities in fluorescence assay of pesticides, drugs and biomolecules

Fluorescent carbon dots (CDs) grabs huge attention in analytical and bioanalytical applications due to their high selectivity towards target analyte, specificity, photostability, and quantum yield. Cost-effective and biocompatible properties of...

Utilization of waste biomass of Poa pratensis for green synthesis of n-doped carbon dots and its application in detection of Mn2+ and Fe3

In this study, a novel and sustainable approach was used to synthesize nitrogen-doped carbon dots (NCDs) from the waste biomass of Poa Pratensis (Kentucky bluegrass (KB)) by a facile hydrothermal method. The prepared KBNCDs were subjected to various characterization techniques, including X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy to verify the formation of carbon dots and their surface functional groups. The KBNCDs exhibited good hydrophilic fluorescence (FLU) properties with an acceptable quantum yield (7%). The synthesized KBNCDs showed excitation wavelength-dependent FLU emission behavior with strong cyan-blue FLU upon irradiation with 365 nm UV-light. The hydrophilic optical properties of the as-synthesized KBNCDs were used to detect Fe³⁺ and Mn²⁺ ions in an aqueous medium with good selectivity and sensitivity. It was found that the FLU of the KBNCDs is quenched in the presence of Fe³⁺ and Mn²⁺ ions, and the quenching rate was linear with the concentration of Fe³⁺ and Mn²⁺ ions. The limit of detection (LOD) of KBNCDs with metal ions was calculated using the Stern-Volmer relationship. The LOD values for Fe³⁺ or Mn²⁺ ions were calculated as 1.4 and 1.2 μM, respectively with the detection range from 5.0 to 25 μM. Based on these results, this study provides an underpinning for the development of KBNCD as FLU sensors that can be used in aqueous media.

Synthetic Approaches, Modification Strategies and the Application of Quantum Dots in the Sensing of Priority Pollutants

Polycyclic aromatic hydrocarbons (PAHs) and nitro-aromatic compounds (NACs) are two classifications of environmental pollutants that have become a source of health concerns. As a result, there have been several efforts towards the development of analytical methods that are efficient and affordable that can sense these pollutants. In recent decades, a wide range of techniques has been developed for the detection of pollutants present in the environment. Among these different techniques, the use of semiconductor nanomaterials, also known as quantum dots, has continued to gain more attention in sensing because of the optical properties that make them useful in the identification and differentiation of pollutants in water bodies. Reported studies have shown great improvement in the sensing of these pollutants. This review article starts with an introduction on two types of organic pollutants, namely polycyclic aromatic hydrocarbons and nitro-aromatic explosives. This is then followed by different quantum dots used in sensing applications. Then, a detailed discussion on different groups of quantum dots, such as carbon-based quantum dots, binary and ternary quantum dots and quantum dot composites, and their application in the sensing of organic pollutants is presented. Different studies on the comparison of water-soluble quantum dots and organic-soluble quantum dots of a fluorescence sensing mechanism are reviewed. Then, different approaches on the improvement of their sensitivity and selectivity in addition to challenges associated with some of these approaches are also discussed. The review is concluded by looking at different mechanisms in the sensing of polycyclic aromatic hydrocarbons and nitro-aromatic compounds.

Highly Fluorescent Carbon Dots as a Potential Fluorescence Probe for Selective Sensing of Ferric Ions in Aqueous Solution

This paper’s emphasis is on the development of a fluorescent chemosensor for Fe3+ ions in an aqueous solution, using hydrophilic carbon dots (O-CDs). A simple, cost-effective, and environmentally friendly one-step hydrothermal synthesis method was used to synthesize fluorescent hydrophilic O-CDs from Oxalis corniculata (Family; Oxalidaceae). The graphitic structure and size distribution of the O-CDs was verified by X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy studies. The resulting O-CDs had a near-spherical shape and an adequate degree of graphitization at the core, with an average diameter of 4.5 nm. X-ray photoelectron and Fourier transform infrared spectroscopy methods revealed the presence of several hydrophilic groups (carbonyl, amine, carboxyl, and hydroxyl, along with nitrogen and oxygen-rich molecules) on the surface of O-CDs. The synthesized hydrophilic O-CDs with excitation wavelength-dependent emission fluorescence characteristics showed a high quantum yield of about 20%. Besides this, the hydrophilic O-CDs exhibited a bright and controllable fluorescence with prolonged stability and photo-stability. These fluorescent hydrophilic O-CDs were used as a nanoprobe for the fluorometric identification of Fe3+ ions in an aqueous solution, with high sensitivity and selectivity. By quenching the blue emission fluorescence of this nanosensor, a highly sensitive Fe3+ ion in the range of 10–50 µM with a minimum detection limit of 0.73 µM was achieved. In addition, the developed nanosensor can be used to sense intracellular Fe3+ ions with high biocompatibility and cellular imaging capacity, and it has a lot of potential in biomedical applications.

Carbon dots: synthesis, properties and biomedical applications

Carbon dots (CDs) are a new type of carbon nanomaterial that have unique physical and chemical properties, good biocompatibility, low toxicity, and easy surface functionalization, making them widely used in biological imaging, environmental monitoring, chemical analysis, targeted drug delivery, disease diagnosis, therapy, etc. In this review, our content is mainly divided into four parts. In the first part, we focused on the preparation methods of CDs, including arc discharge, laser ablation, electrochemical oxidation, chemical oxidation, combustion, hydrothermal/solvent thermal, microwave, template, method etc. Next, we summarized methods of CD modification, including heteroatom doping and surface functionalization. Then, we discussed the optical properties of CDs (ultraviolet absorption, photoluminescence, up-conversion fluorescence, etc.). Lastly, we reviewed the common applications of CDs in biomedicine from the aspects of in vivo and in vitro imaging, sensors, drug delivery, cancer theranostics, etc. Furthermore, we also discussed the existing problems and the future development direction of CDs.

Measurement of mercury with highly selective fluorescent chemoprobe by carbon dots and silver nanoparticles

This work describes a novel fluorescent chemoprobe that uses carbon dots and silver nanoparticles (AgNPs) to monitor mercury ions in aqueous samples attributed to the principle of inner filter effect. The fluorescent response signal of the carbon dots is diminished by AgNPs, attributed to inner filter effect, and is restored with the addition of Hg²⁺. The fluorescent chemoprobe was specific over the range from 0.01 to 2.5 μM and a high sensitivity of 3.6 nM. The chemoprobe was validated using real local aqueous samples, and the spike recoveries of 97.4%-103% were excellent and satisfied. The data indicated that the developed fluorescent chemoprobe was sensitive, selective, stable and reliable. This fluorescent chemoprobe provides a sensitive tool with broad prospects for mercury detection in aqueous samples and the work will offer ideas for designing and constructing novel fluorescent probes.

An Overview of the Recent Developments in Carbon Quantum Dots—Promising Nanomaterials for Metal Ion Detection and (Bio)Molecule Sensing

The fluorescent carbon quantum dots (CQDs) represent an emerging subset of carbonaceous nanomaterials, recently becoming a powerful tool for biosensing, bioimaging, and drug and gene delivery. In general, carbon dots are defined as zero-dimensional (0D), spherical-like nanoparticles with <10 nm in size. Their unique chemical, optical, and electronic properties make CQDs versatile materials for a wide spectrum of applications, mainly for the sensing and biomedical purposes. Due to their good biocompatibility, water solubility, and relatively facile modification, these novel materials have attracted tremendous interest in recent years, which is especially important for nanotechnology and nanoscience expertise. The preparation of the biomass-derived CQDs has attracted growing interest recently due to their low-cost, renewable, and green biomass resources, presenting also the variability of possible modification for the enhancement of CQDs’ properties. This review is primarily focused on the recent developments in carbon dots and their application in the sensing of different chemical species within the last five years. Furthermore, special emphasis has been made regarding the green approaches for obtaining CQDs and nanomaterial characterization toward better understanding the mechanisms of photoluminescent behavior and sensing performance. In addition, some of the challenges and future outlooks in CQDs research have been briefly outlined.

Tagetes erecta as an organic precursor: synthesis of highly fluorescent CQDs for the micromolar tracing of ferric ions in human blood serum

The present article illustrates the green synthesis of novel carbon quantum dots (CQDs) from biomass viz. Tagetes erecta (TE), and subsequently fabrication of a metal ion probe for the sensing of Fe³⁺ in real samples. TE-derived CQDs (TE-CQDs) have been synthesized by a facile, eco-friendly, bottom-up hydrothermal approach using TE as a carbon source. The successful synthesis and proper phase formation of the envisaged material has been confirmed by various characterization techniques (Raman, XRD, XPS, TEM, and EDS). Notably, the green synthesized TE-CQDs show biocompatibility, good solubility in aqueous media, and non-toxicity. The as-synthesized TE-CQDs show an intense photoluminescence peak at 425 nm and exhibit excitation dependent photoluminescence behavior. The proposed TE-CQD-based probe offers a remarkable fluorescence (FL) quenching for Fe³⁺ with high selectivity (K_q ∼ 10.022 × 10¹³ M⁻¹ s⁻¹) and a sensitive/rapid response in a linear concentration range 0–90 μM (regression coefficient R² ∼ 0.99) for the detection of Fe³⁺. The limit of detection (LOD) of the probe for Fe³⁺ has been found as 0.37 μM in the standard solution. It has further been applied for the detection of Fe³⁺ in real samples (human blood serum) and displays good performance with LOD ∼ 0.36 μM. The proposed TE-CQD-based ion sensing probe has potential prospects to be used effectively in biological studies and clinical diagnosis.

TE-CQDs synthesized via the hydrothermal method for the detection of Fe³⁺ in HBS.

Preparation of boron nitrogen co-doped carbon quantum dots for rapid detection of Cr(VI)

A novel fluorescent probe based on the static quenching and the inner filter effect between boron nitrogen co-doped carbon quantum dots (B, N-CDs) and Cr(VI) was developed for the quantitative determination of Cr(VI) in real water samples. B, N-CDs were prepared using the hydrothermal method with ammonium citrate and bis(pinacolato) diboron as raw materials. Compared with undoped CDs, the fluorescence properties of the B, N-CDs were improved. The fluorescence quantum yield of the B, N-CDs was as high as 59.01%. After optimization of the experimental parameters, the B, N-CDs could be used as a fluorescence probe to detect Cr(VI). Strong linear correlation (R² = 0.9986) was established in the Cr(VI) concentration range 0.3-500 μM, and a detection limit of 0.24 μM was achieved. Moreover, the B, N-CDs successfully detected Cr(VI) in real water samples, indicating that they have broad application prospects in the sensitive detection of Cr(VI).

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.

Utilization of Carbon Dots Derived from Volvariella volvacea Mushroom for a Highly Sensitive Detection of Fe3+ and Pb2+ Ions in Aqueous Solutions

In this study, Volvariella volvacea (VV) mushroom was utilized as a green carbon precursor to synthesize carbon dots (CDs) and applied as a fluorescent (FL) sensor to detect Fe3+ and Pb2+ ions. The VV-CDs showed a high photostability and FL properties with a quantum yield of about 11.5%. The VV-CDs exhibited an excitation-dependent emission manner, with an optimum emission wavelength at 440 nm excited at 360 nm. The VV-CDs were evaluated and shown to be facile and effective FL sensors for detecting Pb2+ and Fe3+ ions based on the FL quenching efficiency, demonstrating the special complex chelate between the metal ions and effective surface functional groups of VV-CDs. VV-CDs displayed high responses to Fe3+ and Pb2+ ions, with the linear relationship of 1-100 μM and limits of detection (LODs) of 12 and 16 nM for Pb2+ and Fe3+ ions, respectively. Furthermore, the FL sensor was validated with real water samples, showing very good spike recoveries.

Synthesis, crystal structures, and luminescent properties of Zn(ii), Cd(ii), Eu(iii) complexes and detection of Fe(iii) ions based on a diacylhydrazone Schiff base

Acylhydrazone Schiff bases are rich in N and O atoms to coordinate with metal ions to form multidentate complexes.