Design and synthesis of high quantum yield doped carbon nano probe derived from household sources for sensing of the anti-GERD drug pantoprazole

This contribution aims to design and validate a new green, cheap, and fast approach for determining the anti-GERD drug pantoprazole in different matrices. New S and N-doped carbon nanomaterials (S,N-CNMs) have been prepared via microwave irradiation of a mixture of widely available household sources. Remarkably, the utilization of a blend of carbamide and thiocarbamide with table sugar yields S,N-CNMs exhibiting the utmost quantum yield (54 %), hydrophilicity, as well as stable, homogeneous, and diminutive particle size distribution. Fourier transform infrared spectroscopy, transmission electron microscopy, spectrophotometry, and fluorescence spectroscopy were applied to characterize the S,N-CNMs. The S,N-CNMs have been used as a turn-off fluorescence probe to determine pantoprazole via a synergism of the inner filter effect and static quenching mechanisms. The fluorescence quenching is linearly correlated to pantoprazole concentration over the range of 1.0-25.0 µg/mL with a detection limit of 0.16 µg/mL. The developed probe exhibited good selectivity for pantoprazole in the presence of variability of substances. Therefore, it was applied for quality control of pantoprazole in pharmaceutical tablets and vials with an average recovery % of 100.10 ± 0.77 % and 100.33 ± 0.92 %, respectively. Moreover, it was successfully implemented to examine the content uniformity of pantoprazole in tablets. Furthermore, the prepared S,N-CNMs have been successfully used for the analysis of pantoprazole in human plasma after a simple protein precipitation step with a recovery % of 97.88 ± 5.72 %. The greenness and blueness of the developed method have been positively assessed by recent tools showing the eco-friendliness and applicability of the developed method.

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.

Ultrasensitive fluorescent carbon dot sensor for quantification of soluble and insoluble Cr(VI) in particulate matter

This study investigates advanced functional materials to address the need for practical and affordable analytical techniques for monitoring large amounts of insoluble Cr(VI). N,S-doped fluorescent carbon dots (f-CDs) were fabricated through microwave synthesis, with an average diameter of 10 nm. These f-CDs were explored as potential sensors for detecting Cr(VI) in ambient particulate matter (PM). Laboratory experiments yielded positive results, showing average recoveries of 106.0%, 102.3%, 96.4%, and 101.7% for PbCrO4, BaCrO4, CaCrO4, and (NH4)2CrO4, respectively. Applying the fluorescence method to field PM samples, a method detection limit (MDL) of 0.32 ng/m3 for total Cr(VI) quantification was achieved. The fluorescence decay of carbon dots remained stable over time, suggesting that Cr(VI) quenching primarily occurred due to the internal filter effect through a static quenching mechanism. These f-CDs exhibited advantageous properties, including affordability, solubility, luminescence, and sensitivity, positioning them as a promising alternative for Cr(VI) detection in ambient air particulates. This study contributes to further developing carbon-based functional materials for detecting metallic air pollutants.

Green microwave-prepared N and S Co-doped carbon dots as a new fluorescent nano-probe for tilmicosin detection

A straightforward, rapid, and selective fluorescent probe for determination of tilmicosin has been developed based on novel nitrogen and sulfur co-doped CDs (NS-CD). The NS-CDs were synthesized, for the first time, through green, simple one step microwave pyrolysis in only 90 s using glucose as carbon source and l-cysteine as nitrogen and sulfur source. This proposed synthesis method was energy-efficient and resulted in NS-CDs with high production yield (54.27 wt%) and narrow particle size distribution. Greenness of NS-CDs synthesis method was assessed using EcoScale and was proven to be excellent green synthesis. The produced NS-CDs were applied as a nano-probe for determination of tilmicosin in its marketed formulation and milk based on dynamic quenching mechanism. The developed probe showed a good performance for tilmicosin detection in marketed oral solution and pasteurized milk and linearity range of 9-180 μM and 9-120 μM, respectively.

Green synthesis of N,S-doped carbon dots for tartrazine detection and their antibacterial activities

A simple, green and low-cost method was developed for the synthesis of highly fluorescent N,S-doped carbon dots (N,S-CDs) via the hydrothermal treatment of Gandha Prasarini (GP) leaves as a natural source of carbon, nitrogen and sulfur. The as-prepared N,S-CDs exhibited excitation-dependent green fluorescence emission (λex = 450 nm, λem = 525 nm) with excellent stability, and were used as a fluorescent probe for the selective detection of tartrazine with a limit of detection of 0.18 μM. The fluorescence quenching of N,S-CDs was due to the inner filter effect. The developed method has been employed for the determination of tartrazine in honey and soft drinks with satisfactory recovery ranging from 92 to 110.2%. In addition, the antibacterial activity of the N,S-CDs was explored against both Gram-negative bacteria, Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa), and Gram-positive bacteria, Staphylococcus aureus (S. aureus). The antibacterial mechanism of the N,S-CDs was investigated. The results indicated that the antibacterial activity was due to the membrane damage of the bacteria by the N,S-CDs. Besides, the N,S-CDs showed negligible lytic effects on human erythrocytes. These findings will inspire further exploitation of CD-based nano-bactericides in biomedical applications.

Carbon dots with aggregation-induced emission enhancement (AIEE) for detection of Zr4+/ Hf4+ and PTP1B activity

The frequent use of Zirconium (Zr) and Hafnium (Hf) in modern industries may result in serious environment issues, and thus developing analytical methods to facilitate the control of these two resembled metal elements is urgently needed. However, up to now, rapidly and conveniently detecting Zr⁴⁺ and Hf⁴⁺ is still full of challenge. In this study, nitrogen and sulfur co-doped carbon dots (N, S-Cdots) with aggregation-induced emission enhancement (AIEE) were prepared and used for turn-on detection of Zr⁴⁺ and Hf⁴⁺ within 10 min. The photoluminescent intensity of N, S-Cdots showed a good linear correlation with Zr⁴⁺ and Hf⁴⁺concentrations ranging from 0 to 30 μM with the limit of detection (LOD) of 0.47 and 0.53 μM, respectively. Furthermore, this fluorometric assay was successfully used for quantitative analysis of Zr⁴⁺ and Hf⁴⁺ in real water samples with satisfactory recoveries in the range of 91.16-108.50% and 90.28-106.49%, respectively. Finally, the developed N, S-Cdots sensing system was used for assay PTP1B activity and screening its inhibitor with Zr⁴⁺ as the medium. Our work demonstrated that the as-prepared N, S-Cdots with AIEE can offer a simple and reliable alternative for rapid detection of Zr⁴⁺ and Hf⁴⁺ in water samples, in addition to being potential useful in phosphatase analysis and drug discovery.

The Role of Surface Groups in Dictating the Chiral-Solvent-Induced Assembly of Carbon Dots into Structures Exhibiting Circularly Polarized Luminescence

Here, the use of achiral nanoparticles and solvent-induced chirality transfer is combined for the making of large structures exhibiting chiroptical properties in the form of circularly polarized luminescence (CPL). The nanoparticles that the authors use are carbon dots (C-Dots) that are known for their bright luminescence and the ability to tune their surface moieties by using different precursors in their synthesis. Here, the result of adding the chiral solvent limonene into an aqueous solution of various C-Dots is explored, differentiated by their surface group. It is shown that only nitrogen-containing C-Dots with amine functional groups see the emergence of a CPL signal and the formation of a large fibrillar assembled structure. The various forces happening in the interface between the C-Dots and the limonene phase and the role of the amine groups in both the chirality transfer interactions and the interactions between C-Dots in the assembly process are discussed, whereas these two processes intertwine with each other. The ability to form fluorescent chiral structures exhibiting CPL from achiral nanoparticles and the understanding of the various interactions in this process are both important to the rationale design of any supramolecular chiral assemblies.

Solid-Phase Pyrolysis Synthesis of Highly Fluorescent Nitrogen/Sulfur Codoped Graphene Quantum Dots for Selective and Sensitive Diversity Detection of Cr(VI)

In this study, a simple one-step solid-phase pyrolysis synthesis procedure was employed to prepare N and S codoped highly fluorescent graphene quantum dots (N/S-GQDs). The as-synthesized quantum dot showed λ_excitation-dependent blue fluorescence (FL) emission with a relative quantum yield of about 22% and displayed good biocompatibility, high water dispersibility, and excellent stability under extreme conditions (i.e., ionic strength, pH, and temperature). The potential applicability of the as-synthesized quantum dot was tested by employing solution- and paper-based FL detection modes for Cr(VI) detection. The proposed solution- and paper-based FL sensors showed lower limit of detection (LOD) values of 0.01 and 0.4 μM, respectively. The as-constructed paper- and solution-based FL sensors proved the feasibility of sensitive, cost-effective, and on-site detection of Cr(VI).

Innovative spectrofluorimetric determination of vildagliptin based on a "switch off/on" NS-doped carbon dot nanosensor

A simple, fast, and green one-step microwave pyrolysis approach was proposed for the synthesis of highly fluorescent nitrogen/sulfur-doped carbon dots (NS-CDs). The proposed NS-CDs were prepared in only one minute from citric acid and thiosemicarbazide. In the presence of Cu2+, the fluorescence of NS-CDs was significantly quenched ("turn off") through the formation of a non-fluorescent NS-CDs/Cu2+ complex. This designed sensor could be applied for label-free determination of vildagliptin based on the competition between vildagliptin and the functional groups on NS-CDs for Cu2+ complexation, and hence NS-CD fluorescence recovery ("turn on"). Under the optimized conditions, the developed probe (NS-CDs/Cu2+) demonstrated a good sensing performance for vildagliptin with linearity in the range of 45-240 μM and a detection limit of 13.411 μM. Owing to its sensitivity, this sensor was successfully applied for vildagliptin determination in human urine samples.

Valorisation of bio-derived fluorescent carbon dots for metal sensing, DNA binding and bioimaging

Carbon dots are quasi-spherical and zero dimensional nanomaterials with unique optical and electronic properties. In this work, a facile and sustainable strategy was employed to synthesise nitrogen doped carbon dots from Terminalia chebula via hydrothermal treatment with a quantum yield of 19.9%. The structural and optical properties of nitrogen doped carbon dots (N-CDs) were studied by UV-Visible absorption and fluorescence spectroscopy. The surface functional groups, average particle size and elemental analysis were assessed with the help of Fourier Transform Infra Red spectroscopy, High Resolution Transmission Electron Microscopy and Energy Dispersive X-ray analysis respectively. The N-CDs exhibited excitation dependent emission upon irradiation with UV light, pH stability over neutral range and excellent photostability. The average particle size of the synthesised N-CDs was found to be 3.56 nm. The fluorescence intensity of the N-CDs quenched linearly with increase in concentration of Fe³⁺ ions. The limit of detection (LOD) of N-CDs with Fe³⁺ ions was calculated to be 4.5 nM using Stern-Volmer plot. The fluorescence was restored by addition of EDTA to Fe³⁺ coordinated N-CD system. Further, the synthesised N-CDs interacted with ct-DNA through intercalative mode and the binding constant calculated using the Benesi Hildebrand plot was 1.78 × 10⁸ mg/mL. The cytotoxicity of N-CDs was evaluated using MTT assay. The excellent biocompatible and less toxic nature of N-CDs was extrapolated to serve as fluorescent probes for imaging E.coli and SKMEL cells. From the results of this work, it is evident that the synthesised N-CDs can be used to develop efficient fluorescent metal sensors. The fluorescent property of N-CDs enables it to find extension as a potential curative drug, an efficient patterning agent and an effective biomarker to image biological cells causing no damage to normal cells.

Morphology Effect of One-Dimensional MnO2 Nanostructures on Heteroatom-Doped Carbon Dot-Based Biosensors for Selective Detection of Glutathione

Structural versatility of MnO₂ nanostructures plays a significant role in biosensing applications. So, we have prepared simple and selective "turn-off-on" sensing probes for the detection of glutathione (GSH), based on nitrogen, sulfur codoped carbon dots (N, S-Cdots) and different morphologies of one-dimensional (1-D) MnO₂ nanostructures. N, S-Cdots with a high fluorescence quantum yield (73.42%) were prepared by a green approach through high-temperature pyrolysis in just 5 min. The different morphologies of 1-D MnO₂ nanostructures (nanowires with varying aspect ratios and nanorods) were synthesized through a hydrothermal method by varying the reaction period (8, 10, and 12 h). MnO₂ nanowires prepared at 8 h showed a high specific surface area (34 m² g^-1) with a large aspect ratio. They showed significant fluorescence quenching, Stern-Volmer constants, and binding constants in the presence of N, S-Cdots. Further, ultraviolet-visible absorption, zeta potential, and time decay studies showed that the quenching mechanism of the developed sensing system was the inner filter effect, which was further confirmed by using the Parker equation. The N, S-Cdots-MnO₂ nanowire (with a high aspect ratio) sensing system showed the best limit of detection, i.e., 28.5 μM for GSH. This fast, simple, eco-friendly, and cost-effective sensing system can be further used for real-time biosensing and bioimaging application.

Fluorescent Carbon Dot-Supported Imaging-Based Biomedicine: A Comprehensive Review

Carbon dots (CDs) provide distinctive advantages of strong fluorescence, good photostability, high water solubility, and outstanding biocompatibility, and thus are widely exploited as potential imaging agents for in vitro and in vivo bioimaging. Imaging is absolutely necessary when discovering the structure and function of cells, detecting biomarkers in diagnosis, tracking the progress of ongoing disease, treating various tumors, and monitoring therapeutic efficacy, making it an important approach in modern biomedicine. Numerous investigations of CDs have been intensively studied for utilization in bioimaging-supported medical sciences. However, there is still no article highlighting the potential importance of CD-based bioimaging to support various biomedical applications. Herein, we summarize the development of CDs as fluorescence (FL) nanoprobes with different FL colors for potential bioimaging-based applications in living cells, tissue, and organisms, including the bioimaging of various cell types and targets, bioimaging-supported sensing of metal ions and biomolecules, and FL imaging-guided tumor therapy. Current CD-based microscopic techniques and their advantages are also highlighted. This review discusses the significance of advanced CD-supported imaging-based in vitro and in vivo investigations, suggests the potential of CD-based imaging for biomedicine, and encourages the effective selection and development of superior probes and platforms for further biomedical applications.

Design, synthesis and biological evaluation of novel dual-targeting fluorescent probes for detection of Fe3+ in the lysosomes of hepatocytes mediated by galactose-morpholine moieties

In this work, novel dual-targeting probes composed of galactose and morpholine were designed and synthesized for monitoring Fe³⁺ levels in the lysosome of hepatocyte. MP-Gal-1, MP-Gal-2 and MP-Gal-3 showed good selectivity and sensitivities toward Fe³⁺ with the detection limits of 9.40 × 10^-8 M, 7.68 × 10^-8 M and 7.10 × 10^-8 M, respectively. 1:2 stoichiometry is the most likely recognition mode between probe and Fe³⁺. Low toxic MP-Gal-1, MP-Gal-2 and MP-Gal-3 exhibited favorable hepatic targeting effect in both cell and tissue levels, which was because the galactose group of probe could be recognized by ASGPR overexpressed on the hepatocytes. The hepatocyte-targeting capacity followed MP-Gal-1 < MP-Gal-2 < MP-Gal-3 trend, which was attributed to the galactose cluster effect. MP-Gal-1, MP-Gal-2 and MP-Gal-3 also displayed good lysosomes-targeting capacities, because the basic morpholine moiety of probes could be easily attracted by the acidic lysosome. Therefore, MP-Gal-1, MP-Gal-2 and MP-Gal-3 have good dual targeting capacities (liver and lysosome) and could be used to detect lysosomal Fe³⁺ in the liver, which is great significant for precise diagnosis and treatment of liver lysosomal iron-related diseases.

Synthesis of multicolor-emitting nitrogen–sulfur co-doped carbon dots and their photochemical studies for sensing applications

Photoluminescent carbon dots (CDs) possess several advantages, which include high stability and a non-toxicity that are essential in different applications such as catalysis, drug delivery, and sensors. The presence of heteroatoms modifies their physicochemical characteristics. In this work, a combination of CDs is manufactured utilizing a solvothermal technique using citric acid and thiourea. After separating each section using column chromatography, green and yellow CDs with average diameters of 8.3 and 7.0 nm, respectively, are generated. Next, optical and structural characterizations indicated that the variation in the emission color was caused by differences in surface functional groups rather than particle size. The photoelectrochemical properties are explored by including quinone derivatives and metal ions, which are quenchers for the CDs. The photoluminescence quenching results showed the presence of anionic functional groups on the surface of the CDs. Furthermore, these functional groups interacted strongly with particular types of metal ions, indicating that they may be employed as metal ion sensors.

Luminescent carbon dots (CDs) have been synthesized by a solvothermal approach and their photochemical properties are evaluated. Responses to specific metal ions are observed, and the relationship with surface functional groups is discussed.

Organic/Inorganic Self-Assembled Hybrid Nano-Architectures for Cancer Therapy Applications

Since the conceptualization of nanomedicine, numerous nanostructure-mediated drug formulations have progressed into clinical trials for treating cancer. However, recent clinical trial results indicate such kind of drug formulations has a limited improvement on the antitumor efficacy. This is due to the biological barriers associated with those formulations, for example, circulation stability, extravasation efficiency in tumor, tumor penetration ability, and developed multi-drug resistance. When employing for nanomedicine formulations, pristine organic-based and inorganic-based nanostructures have their own limitations. Accordingly, organic/inorganic (O/I) hybrids have been developed to integrate the merits of both, and to minimize their intrinsic drawbacks. In this context, the recent development in O/I hybrids resulting from a self-assembly strategy will be introduced. Through such a strategy, organic and inorganic building blocks can be self-assembled via either chemical covalent bonds or physical interactions. Based on the self-assemble procedure, the hybridization of four organic building blocks including liposomes, micelles, dendrimers, and polymeric nanocapsules with five functional inorganic nanoparticles comprising gold nanostructures, magnetic nanoparticles, carbon-based materials, quantum dots, and silica nanoparticles will be highlighted. The recent progress of these O/I hybrids in advanced modalities for combating cancer, such as, therapeutic agent delivery, photothermal therapy, photodynamic therapy, and immunotherapy will be systematically reviewed.

Biomass-derived carbon quantum dots: a novel and sustainable fluorescent "ON-OFF-ON" sensor for ferric ions

Fluorescent carbon dot sensing probes have attracted much attention in recent times due to their amazing properties regarding chemical inertness, solubility, non-toxicity, optoelectronic behavior, and charge transport functionality. Herein, we report the green synthesis of lotus stem-derived carbon dots (LS-CQDs) from the naturally available lotus stem by a simple and economical hydrothermal method without the use of an oxidizing agent. HR-TEM and DLS measurements confirm the quasi-spherical shaped LS-CQDs, with a 2.5 nm average diameter. The LS-CQDs possess better aqueous dispersibility and stability due to the presence of hydrophilic hydroxyl, carboxyl, and amine surface functional groups, as manifested by FT-IR analysis. The LS-CQDs demonstrate excellent fluorescence properties that are sensitive to conditions of pH, time, and temperature. Furthermore, the prepared LS-CQDs display an interesting fluorescence "ON-OFF-ON" property. The LS-CQDs depict a selective and sensitive fluorescence quenching response in the presence of ferric ions. Moreover, the prepared LS-CQDs exhibit a quantum yield of about 0.44%. The LS-CQDs show an excellent sensing response with the limit of detection (LOD) equal to 0.212 ppm. The promising sensitivity and selectivity of LS-CQDs were utilized for the detection of ferric ions in the water samples collected from three polluted sources viz. lake water (Dal lake), underground water (tube well), and stream water. For all the collected water samples the results were reasonably good with the achievement of recovery factor above 1. Therefore, we strongly believe that the present study will serve as a good guiding star for the selective and sensitive detection of ferric ions from various polluted water bodies.

Electrochemiluminescence of water-dispersed nitrogen and sulfur doped carbon dots synthesized from amino acids

A facile one-pot hydrothermal approach for synthesizing water-dispersed nitrogen and sulfur doped carbon dots (NS-CDs) with high luminescence quantum yield was explored, using cysteine and tryptophan as precursors. The NS-CDs were characterized by means of FT-IR spectroscopy, XRD, TEM, etc. It was found that the absolute photoluminescence quantum yield (QY) of the NS-CDs determined with an integrating sphere can reach up to 73%, with an average decay time of 17.06 ns. Electrochemiluminescence (ECL) behaviors and mechanisms of the NS-CDs/K₂S₂O₈ coreactant system were investigated. When the working electrode was modified with the prepared NS-CDs, the ECL efficiency of the NS-CDs with K₂S₂O₈ was 24%, relative to Ru(bpy)₃Cl₂/K₂S₂O₈. This work shows great potential for the NS-CDs to be used in bioanalytical applications.

Fluorescent recognition of Fe3+ in acidic environment by enhanced-quantum yield N-doped carbon dots: optimization of variables using central composite design

A versatile synthetic approach for development of highly fluorescent nitrogen-doped carbon dots (N-CDs) from carboxymethylcellulose in the presence of linear polyethyleneimine (LPEI) has been developed. According to single factor method, central composite design incorporated with response surface methodology matrix was applied to find and model optimal conditions for the temperature (220-260 °C), duration (1-3 h) and LPEI weight (0.5-1.5%). The statistical results show that duration was the most significant parameter for efficient carbonization conversion rate in comparison with temperature and LPEI weight. The reduced cubic model (R2 = 0.9993) shows a good correlation between the experimental data and predicted values. The optimal variables were temperature of 260 °C, duration of 2 h and LPEI weight of 1%. Under these conditions, quantum yield of up to 44% was obtained. The numerically optimized N-CDs have an average size of 3.4 nm with graphitic nature owing to the abundant amino species incorporated into the carbon core framework. The blue-green N-CDs possess emission dependent upon the solvent polarity, wide pH stability with enhanced emission in an acidic environment. Impressively, the N-CDs show long-shelf-life for up to 1 year with no noticeable precipitation. The N-CDs were able to recognize a high concentration of Fe3+ ions with a detection limit of 0.14 μM in acidic solution owing to the special coordination for Fe3+ to be captured by electron-donating oxygen/ amino groups around N-CDs. Moreover, the N-CDs can also be used as a new kind of fluorescent ink for imaging applications.

A simple and ubiquitous device for picric acid detection in latent fingerprints using carbon dots

This work addresses the synthetic optimization of carbon dots (CDs) and their application in sensing picric acid from latent fingerprints by exploiting a smartphone-based RGB tool. The optimization of the synthesis of CDs is investigated towards achieving shorter reaction time, better product yield and fluorescence quantum efficiency. Precursors such as citric acid and thiourea were chosen for the synthesis of CDs. Among the various synthetic methodologies, it is found that the pyrolysis method offers ∼50% product yield within 15 min. The morphology and optical properties of the prepared CDs are characterized using the typical microscopic and spectroscopic techniques, respectively. The synthesized CDs exhibit quasi-spherical shape with an average particle size of 1.7 nm. The excitation dependent emissive properties of CDs are investigated by time resolved fluorescence spectroscopy. Furthermore, the excellent fluorescence properties (φ = 11%) of CDs are explored as a fluorescent fingerprint powder for the identification of latent fingerprints on various substrates. In addition, the presence of picric acid in latent fingerprints was detected. Furthermore, this study is extended to perform real time detection of fingerprints and harmful contaminants in fingerprints by utilizing a smartphone-based RGB color analysis tool. Based on these investigations, the prepared CDs could be a prospective fluorescent material in the field of forensics.

Detecting Ferric Iron by Microalgal Residue-Derived Fluorescent Nanosensor with an Advanced Kinetic Model

Biomass-derived carbon quantum dots (CQDs) are attractive to serve as fluorescent nanosensors owing to their superior environmental compatibility and biocompatibility. However, the detection range has been limited, only in partial agreement with the experimental data. Thus, an advanced kinetic model for quantifying the fluorescence quenching over a wide range is on demand. Here, we describe a nanosensor for Fe(Ⅲ) detection in real waters, which is developed via microalgal residue-derived CQDs with an advanced kinetic model. The multiple-order kinetic model is established to resolve the incoherence of previous models and unveil the entire quenching kinetics. The results show that the detection range of Fe(Ⅲ) can reach up to 10 mM in the high detection end. The newly obtained kinetic model exhibits satisfactory fittings, clearly elucidating a dynamic quenching mechanism. This work provides a new insight into CQDs-based detection of heavy metals in real water samples by establishing an innovative multiple-order kinetic model.

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Microalgal residue-derived carbon dots synthesized by hydrothermal method are introduced

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An advanced kinetic model with wide concentration applicability is developed

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Waste biomass-derived Fe(Ⅲ) nanosensor is applied in accurate detection of actual water

Carbon Allotrope-Based Optical Fibers for Environmental and Biological Sensing: A Review

Recently, carbon allotropes have received tremendous research interest and paved a new avenue for optical fiber sensing technology. Carbon allotropes exhibit unique sensing properties such as large surface to volume ratios, biocompatibility, and they can serve as molecule enrichers. Meanwhile, optical fibers possess a high degree of surface modification versatility that enables the incorporation of carbon allotropes as the functional coating for a wide range of detection tasks. Moreover, the combination of carbon allotropes and optical fibers also yields high sensitivity and specificity to monitor target molecules in the vicinity of the nanocoating surface. In this review, the development of carbon allotropes-based optical fiber sensors is studied. The first section provides an overview of four different types of carbon allotropes, including carbon nanotubes, carbon dots, graphene, and nanodiamonds. The second section discusses the synthesis approaches used to prepare these carbon allotropes, followed by some deposition techniques to functionalize the surface of the optical fiber, and the associated sensing mechanisms. Numerous applications that have benefitted from carbon allotrope-based optical fiber sensors such as temperature, strain, volatile organic compounds and biosensing applications are reviewed and summarized. Finally, a concluding section highlighting the technological deficiencies, challenges, and suggestions to overcome them is presented.

Boron and nitrogen codoped carbon dots as fluorescence sensor for Fe3+ with improved selectivity

Carbon dots (CDs) are popular as fluorescence sensors, and metal ions are typical analytes. However, CDs used as fluorescent sensors for Fe³⁺ have some interferences coming from co-existed ions. In this study, we suspect that sp³ boron atom in phenylboronic acid group will be more compatible with Fe³⁺ to form coordination bonds, thereby increasing the selectivity to Fe³⁺. Hence, we designed and synthesized boron and nitrogen codoped carbon dots (BN-CDs) for detection of Fe³⁺ via a hydrothermal method using o-phenylenediamine (OPA) and 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzylchloroformate as precursors. From the results, we found that BN-CDs had superior selectivity to Fe³⁺ in the presence of the other common interfering metal ions like Cu²⁺, Fe²⁺ and Pb²⁺. Besides, the obtained BN-CDs exhibited good water solubility, favorable photostability, excellent pH stability between pH 2-11, and strong fluorescence intensity with quantum yield up to 31.5 %. These excellent properties of carbon dots validate that our idea is feasible, and can be used for design CDs for Fe³⁺ detection. Quenching mechanism study showed the fluorescence intensity of BN-CDs could be dramatically quenched by Fe³⁺ through dynamic and static synergy process. Finally, the as prepared BN-CDs were successfully applied to the determination of Fe³⁺ in fetal bovine serum and lake water.

Carbon Dot-functionalized Interferometric Optical Fiber Sensor for Detection of Ferric Ions in Biological Samples

This work reports an interferometric optical microfiber sensor functionalized with nitrogen- and sulfur-codoped carbon dots (CDs) for the detection of ferric ions (Fe³⁺). Compared to other CD-based ferric ion sensors, the sensing mechanism of this presented sensor is dependent on the refractive index modulations due to selective Fe³⁺ adsorption onto the CD binding sites at the tapered region. This is the first study in which CD-based sensing was performed at the solid phase as a chelator, which does not rely on its fluorescence properties. The detection performance of the proposed sensor is not only comparable to a conventional fluorescence-based CD nanoprobe sensor but also capable of delivering quantitative analysis results and ease of translation to a sensor device for on-site detection. The presented sensor exhibits Fe³⁺ detection sensitivity of 0.0061 nm/(μg/L) in the linear detection range between 0 and 300 μg/L and a detection limit of 0.77 μg/L based on the Langmuir isotherm model. Finally, the potential use of the CD-functionalized optical microfiber sensor in the real environmental and biological Fe³⁺ monitoring applications has also been validated in this work.