One-pot synthesis of carbon dots co-doped with N and S: high quantum yield governed by molecular state and fluorescence detection of Ag+

Fluorescent carbon-based nanoparticles, called chronically as carbon dots (CDs), were synthesised from citric acid (CA) and 2-Aminothiophenol (2AT) via an N and S co-doped hydrothermal method. After a series of micro-structural characterisation, N and S elements could be sufficiently doped by means of the heteroatom in the CDs solution. The as-prepared CDs solution showed blue colour fluorescence with the highest QY of 78.6%, and study on the UV–visible and PL spectra further revealed that the outstanding fluorescence of as-prepared CDs mainly originates from the generated molecular fluorophores instead of the surface state. Owing to the strong fluorescence, the as-prepared CDs can be used as a sensing probe for the detection of Ag⁺ with high sensitivity and selectivity. However, the changes of fluorescence intensity exhibited the complex nature of the quenching mechanism due to the –SH and –NH₂ groups on the fringes of carbonaceous cores or molecular fluorophores to aggregate into another fluorescent cores with the assistance of Ag⁺ ions, which promises a new approach for efficient detection of Ag⁺ for the application in industrial pollutants.

This figure shows citric acid (CA) and 2-Aminothiophenol (2AT) via an N and S co-doped hydrothermal method to prepare CDs with blue colour fluorescence and the highest QY of 78.6%. Owing to the excellent fluorescence, the as-prepared CDs can be used as a sensing probe for the detection of Ag⁺ with high sensitivity and selectivity, and the changes of fluorescence intensity exhibited the complex nature of the quenching mechanism due to the –SH and –NH₂ groups on the fringes of carbonaceous cores or molecular fluorophores to aggregate into another fluorescent cores with the assistance of Ag⁺ ions, which promises a new approach for efficient detection of Ag⁺ for the application in industrial pollutants.     

One step synthesis of ultra-high quantum yield fluorescent carbon dots for “on-off-on” detection of Hg2+ and biothiols

In this paper, the carbon dots (CDs) with strong blue fluorescence were synthesized through hydrothermal method, which using folic acid, ammonium citrate and ethylenediamine as precursors. The prepared CDs with a high absolute quantum yield of 81.94% and showed excellent stability in high concentration salt solution and different pH conditions. With the addition of Hg²⁺, the signal of CDs was selectively quenched. At the same time, the CDs-Hg²⁺ system could be recovered after the introduction of biothiols. Moreover, the fluorescence of CDs showed a good linear relationship with Hg²⁺ (1–15 µM), and the detection limit as low as 0.08 µM. In addition, the prepared CDs with low toxicity could be used to detect Hg²⁺ in living cells and actual water samples.

     

Rapid and Direct Spectrofluorometric and Chemometrics Methods for the Simultaneous Determination of Two Dansyl Derivatives

ABSTRACT

In this study the simultaneous molecular spectrofluorometric determination of ultratrace amounts of two dansyl chloride derivatives, DMNPS (5-(dimethylamino)naphthalene-1-sulfonyl 4-phenylsemicarbazide) and DMNPH (2-(5-(dimethylamino)naphthalen-1-ylsulfonyl)-N-phenylhydrazinecarbothioamide), was accomplished using a genetic algorithm joint partial least squares (GA-PLS) technique that leads to very low detection limits (lower than 10^?6 mol/L) The linear dynamic ranges of the compounds were 1–6 µ mol L^?1 and 1–7 µ mol L^?1 for DMNPS and DMNPH, respectively. Quantification was performed using the emission wavelength range from 360 to 600 nm with an optimum calibration sample number of 25 and prediction sample number of 7. The technique was proved to be beneficial.     

Novel Fluorometric Turn On Detection of Aluminum by Chalcone-Based Chemosensor in Aqueous Phase

A novel, 100% water-soluble chalcone based chemosensing receptor {1-[3-(2-Hydroxy-phenyl)-3-oxo-propenyl]-naphthalen-2-yloxy}-acetic acid, L was synthesized and characterized. The receptor L is designed based on the chelation enhanced fluorescence (CHEF) mechanism. The chemosensing properties of L were evaluated by UV–vis and fluorescence spectrometric methods. It exhibits highly selective recognition ability towards aluminum ions in water over other metal ions. The binding stoichiometry of L? Al³⁺ complex is 2:1 by means of Job’s plot and the detection limit is 5.66?×?10^??8 M.     

Coal Pitch Derived Yellow-Emissive Carbon Dots and Their Application in Luminescent Solar Concentrators

Using coal pitch as the carbon source to synthesize carbon dots (CDs), one of the most promising photoluminescence (PL) materials, can play an important role in the global demand for carbon neutralization. However, the reported CDs derived from coal pitch are mainly limited blue emission. Here, a new route to synthesize yellow-emissive CDs from coal pitch is developed by extracting the lightweight aromatic compounds from coal pitch and solvothermally treating the extracts in dichloromethane in the presence of a small amount of nitric acid and sulfuric acid. Notably, the obtained CDs exhibit excitation independent yellow emission, large Stokes shift and good photostability. The application of the CDs for luminescent solar concentrators (LSCs) is evaluated. It is found that the CDs can be well dispersed in polymethyl methacrylate (PMMA) matrix and fabricated transparent LSCs. The synthesized LSC (4 × 4 × 0.2 cm³) with the optimal CDs concentration exhibits an optical conversion efficiency (η_opt) of 3.31% and power conversion efficiency (η_PCE) of 1.95% under simulated sun light illumination (100 mW cm⁻²). This research offers a new strategy to synthesize new kind of CDs with desired performance by exploiting the native chemistries of coal pitch.     

Dual Fluorometric Detection of Fe3+ and Hg2+ Ions in an Aqueous Medium Using Carbon Quantum Dots as a “Turn-off” Fluorescence Sensor

The present study aimed to develop a carbon dots-based fluorescence (FL) sensor that can detect more than one pollutant simultaneously in the same aqueous solution. The carbon dots-based FL sensor has been prepared by employing a facile hydrothermal method using citric acid and ethylenediamine as precursors. The as-synthesized CDs displayed excellent hydrophilicity, good photostability and blue fluorescence under UV light. They have been used as an efficient “turn-off” FL sensor for dual sensing of Fe³⁺ and Hg²⁺ ions in an aqueous medium with high sensitivity and selectivity through a static quenching mechanism. The lowest limit of detection (LOD) for Fe³⁺ and Hg²⁺ ions was found to be 0.406 µM and 0.934 µM, respectively over the concentration range of 0-50 µM. Therefore, the present work provides an effective strategy to monitor the concentration of Fe³⁺ and Hg²⁺ ions simultaneously in an aqueous medium using environment-friendly CDs.

Graphical Abstract

     

Study on the Interaction of the CpG Alternating DNA with CdTe Quantum Dots

A novel sensitive method for detection of DNA methylation was developed with thioglycollic acid (TGA)-capped CdTe quantum dots (QDs) as fluorescence probes. Recognition of methylated DNA sites would be useful strategy due to the important roles of methylation in disease occurrence and developmental processes. DNA methylation occurs most often at cytosine-guanine sites (CpG dinucleotides) of gene promoters. The QDs significantly interacted with hybridized unmethylated and methylated DNA. The interaction of CpG rich methylated and unmethylated DNA hybrid with quantum dots as an optical probe has been investigated by fluorescence spectroscopy and electrophoresis assay. The fluorescence intensity of QDs was highly dependent to unmethylated and methylated DNA. Specific site of CpG islands of Adenomatous polyposis coli (APC), a well-studied tumor suppressor gene, was used as the detection target. Under optimum conditions, upon the addition of unmethylated dsDNA, the fluorescence intensity increased in linear range from 1.0?×?10^??10 to 1.0?×?10^??6M with detection limit of 6.2?×?10^??11 M and on the other hand, the intensity of QDs showed no changes with addition of methylated dsDNA. We also demonstrated that the unmethylated and methylated DNA and QDs complexes showed different mobility in electrophoresis assay. This easy and reliable method could distinguish between methylated and unmethylated DNA sequences.     

Fluorescent Carbon Dot as Nanosensor for Sensitive and Selective Detection of Cefixime Based on Inner Filter Effect

Here a simple and sensitive fluorescent assay for detecting Cefixime based on inner filter effect (IFE) has been proven, which is conceptually different from the previously reported CEF fluorescent assays. In this sensing platform, fluorescent carbon dots (CDs) were prepared by one-pot synthesis and was directly used as fluorophore in IFE. The method is based on the complexation reaction between cefixime and palladium ion in the presence of acidic buffer solution (pH 4). The Pd(II)-CEFcomplex was capable of functioning as a powerful absorber in IFE to influence the excitation of fluorophore (CDs). Production Pd(II)-CEFcomplex induced the absorption band transition from 310 to 400 nm, which resulted in the complementary overlap with the excitation spectra of CDs. Due to the competitive absorption, the excitation of CDs was significantly weakened, resulting in the quenching of CDs. The present IFE-based sensing strategy showed a good linear relationship from 0.2 × 10^?6 M to 8 × 10^?6 M (R² = 0.987) and provided an exciting detection limit of 0.5 × 10^?7 (3δ/slope). The proposed method has been successfully applied for the determination of cefixime in raw milk and human urine samples.     

Determination of Microamounts of Proteins by Resonance Light Scattering with Copper Phthalocyanine Tetrasulfonic Acid

Abstract

Based on the strong enhancement effect of proteins on the resonance light scattering of copper phthalocyanine tetrasulfonic acid, a method for the determination of microamounts of proteins has been developed. Under the experimental conditions (2.0×10^?6 mol/L copper phthalocyanine tetrasulfonic acid, pH 2.60, ionic strength 0.001 mol/L NaCl), the linear range of this assay is 0.06–4.0 µg/mL for bovine serum albumin (BSA), 0.1–2.0 µg/mL for human serum albumin (HSA), 0.0–2.0 µg/mL for human γ‐IgG, and 0.2–6.0 µg/mL for ovalbumin. The detection limits (3δ) are 16.8 ng/mL for BSA, 23.4 ng/mL for HSA, 37.6 ng/mL for human γ‐IgG, and 48.3 ng/mL for ovalbumin, respectively. This method has been applied to the analysis of total proteins in human serum samples collected from the hospital, and the results were in good agreement with those reported by the hospital.     

Ultrasensitive fluorescent probe for copper ion based on cadmium selenide/cadmium sulfide quantum dots capped with dimercaprol

A new ultrasensitive copper ion fluorescent probe based on cadmium selenide/cadmium sulfide quantum dots capped with dimercaprol is described. Dimercaprol was bonded to the quantum dots through a surface ligand exchange to form dimercaprol-capped quantum dots whose fluorescence could be quenched by the coordination of dimercaprol on quantum dots’ surface with copper ion. The fluorescent probe based on dimercaprol-capped quantum dots showed a very good linear response range to copper ion from 0.1 to 50?µg?L^?1 with the detection limit of 0.087?µg?L^?1. The proposed method exhibited excellent sensitivity and selectivity due to the specific and strong affinity of dimercaprol with copper ion and the unique photoluminescence properties of quantum dots. The possible quenching mechanism was discussed and the probe was successfully applied to the determination of ultratrace copper in real samples.     

Dispersive liquid–liquid microextraction based on solidification of floating organic drop for separation and preconcentration of malachite green before its determination by flow injection spectrophotometry

ABSTRACT

A simple and fast dispersive liquid–liquid microextraction based on solidification of floating organic drop has been developed for the separation and preconcentration of malachite green in water samples prior to its determination by flow injection spectrophotometry. Sodium lauryl sulfate, an anionic surfactant, was used for the ion-pair formation with malachite green. The factors affecting the ion-pair formation and extraction were optimized. Under the optimized conditions (volume of 1-undecanol as the extraction solvent, 40 μL; the volume of ethanol as the disperser solvent, 100 μL; sodium lauryl sulfate concentration, 7.5 × 10^?7 mol L^?1, and the pH of the sample, ～3.0), the calibration graph was linear over the range of 0.8–25 µg L^?1 with the detection limit of 0.3 µg L^?1 and the preconcentration factor of 750. The relative standard deviation at 7 µg L^?1 (n = 6) was found to be 2.1%. The developed method was successfully applied to the determination of malachite green in river water and fish farming water samples.     

Preconcentration and Separation of Gold(III) from Ore Samples by Solid-Phase Extraction Prior to Its Catalytic Fluorescent Determination

ABSTRACT

A new catalytic kinetic fluorescent quenching method for the determination of trace gold(III) was investigated. The method was based on the catalytic effect of gold on oxidation of 3-(3′-methylphenyl)-5- (2′-arsenoxylphenylazo) rhodanine by hydrogen peroxide in potassium hydrogen phthalate–hydrochloric acid (pH = 3.4). Under the optimum conditions, the great decrease of fluorescence intensity has a linear relationship against the concentration of gold in the range of 0 to 12.0 µg·L^?1 with a detection limit of 6.0 × 10^?10g·L^?1. The coexistent metal ions can be separated, and gold can be enriched by TBP resin of solid-phase extraction, which greatly improves the selectivity and sensitivity of the system. The method can be used to determine trace amounts of gold in ore samples successfully with satisfactory results.     

Negative curvature dependent plasmonic coupling and local field enhancement of crescent silver nanostructure

In this contribution, novel luminescent gold nanoclusters were synthesized by utilizing bovine serum albumin as templates with a simple, rapid, and one-pot procedure. The as-prepared gold nanoclusters were highly dispersed in aqueous solution and emitted an intense red fluorescence under UV light (365?nm). They exhibited strong fluorescence and the maximum excitation and emission wavelengths were 480 and 613.5?nm. In addition, the bovine serum albumin-stabilized gold nanoclusters were successfully utilized as novel fluorescent probes for the detection of quercetin for the first time. It was found that the addition of quercetin induced the strong fluorescence intensity of the gold nanoclusters to decrease. The decrease in fluorescence intensity of the gold nanoclusters caused by quercetin allowed the sensitive detection of quercetin in the range of 8.9?×?10^?8?C1.8?×?10^?4?mol?L^?1. The detection limit for quercetin is 1.8?×?10^?8?mol?L^?1 at a signal-to-noise ratio of 3. The present sensor for quercetin detection possessed a low detection limit and wide linear range. In addition, the real samples were analyzed with satisfactory results.     

基于石墨烯量子点的荧光探针应用于抗坏血酸检测的研究

基于石墨烯量子点(GQDs)的荧光性能建立了一种非标记荧光方法,用于灵敏和选择性测定抗坏血酸(AA)。GQDs溶液在紫外光激发下发出很强的蓝色荧光,当向溶液中加入AA后,GQDs溶液的荧光被猝灭。猝灭机理可能为在弱酸性介质中,AA与GQDs发生氧化还原反应,AA转移电子给GQDs。荧光猝灭强度与AA浓度在5.0×10~(-6)~7.5×10~(-5)mol/L范围内呈良好的线性关系,检出限低至1.0×10~(-6)mol/L。该体系成本低、操作简单,并且在多种可能干扰的物质存在下对AA表现出很高的选择性。本方法应用于生物样品中AA的检测,回收率在95.2%~115.3%之间。     

Bis-Benzimidazolyl Diamide Based Fluorescent Probe for Copper(II): Synthesis, Structural and Fluorescence Studies

A new fluorescent probe based on a bis-benzimidazole diamide N ²,N ^2′-bis[(1-ethyl-benzimidazol-2-yl)methyl]biphenyl-2,2′-dicarboxamide ligand L ₁ with a biphenyl spacer group and a Copper(II) trinuclear metallacycle has been synthesized and characterized by X-ray single crystallography, elemental and spectral (FT-IR, ¹H & ¹³C NMR, UV-Visible) analysis. The fluorescence spectra of L ₁ in MeOH show an emission band centered at 300 nm. This band arises due to benzimidazolyl moiety in the ligating system. The diamide L ₁ in the presence of Cu²⁺ show the simultaneous ‘quenching’ of (300 nm) and ‘enhancement’ of (375 nm) emission band. Similar fluorescence behavior was found in water–methanol mixture (9:1). The new emission band at 375 nm is attributed to intra ligand π–π* transition of the biphenyl moiety. L ₁ exhibited high selectivity and sensitivity towards Cu²⁺ in both the medium over other common metal ions like Ni²⁺, Co²⁺, Mn²⁺, Mg²⁺, Zn²⁺, Pb²⁺ and Hg²⁺. The binding constant with Cu²⁺ was calculated by the Benesi-Hildebrand equation. Selective “off-on-off” behavior of L ₁ in methanol has also been studied. The fluorescent intensity of 375 nm bands in L ₁ enhances (turns-on) upon addition of Cu²⁺ and quenches (turn-off) upon addition of Na₂-EDTA.     

壳聚糖碳点的水热法制备及其对金属离子的选择性研究

以壳聚糖为碳源通过水热法合成碳点,对影响碳点荧光强度的水热温度、水热时间和壳聚糖质量分数进行考察。通过紫外分光光度计、荧光分光光度计、原子力显微、Fourier红外光谱仪、X-ray光电子能谱、X射线衍射仪对壳聚糖碳点的光学性质、化学结构、晶体结构、形貌结构等进行表征分析。结果表明,在水热温度200℃、水热时间9 h、壳聚糖质量分数2%的条件下制备得到的壳聚糖碳点量子产率为32.86%。碳点呈现出主要尺寸为3～10 nm的球形颗粒状,且在波长335 nm激发下,发射峰位于410 nm(蓝)。对金属离子的选择性研究分析表明,Fe~(3+)对碳点溶液的荧光猝灭效应最显著,说明碳点对Fe~(3+)具有较好敏感性和高选择性,且荧光猝灭效率对Fe~(3+)浓度在0～100μmol/L范围内呈现线性响应,因此有望将碳点作为荧光探针应用于Fe~(3+)的检测表征。     

Online Copper Removal for Selenium Determination by Hydride Generation–Inductively Coupled Plasma Optical Emission Spectrometry

Abstract

Selenium determination in samples with a high copper content by hydride generation–inductively coupled plasma optical emission spectrometry (HG‐ICP‐OES) after online copper removal and selenium (VI) reduction is described. An activated carbon minicolumn was used for the retention of copper and its subsequent separation of Se. Se(VI) was then online reduced by heating into a PTFE coiled reactor with 12 M HCl. The analyte was introduced into a water stream containing sodium tetrahydroborate (NaBH₄) in order to generate selenium hydride (H₂Se). The detection limit (DL) obtained was 0.8 µg L^?1, and the precision, expressed by the relative standard deviation (RSD), was 2.5% (n=10; 10 µg L^?1 selenium level). The current method was applied to the Se determination in two copper reference materials, MBH‐39DK 3601 (with a Se content of 90 mg kg^?1) and MBH‐39 DK 3604 (with a Se content of 15 mg kg^?1).     

Sensitive Synchronous Spectrofluorimetric Study of Certain Sunscreens Using Fluorescence Enhancers in Cosmeceutical Formulations

Synchronous spectrofluorimetric methods could be successfully adopted for simultaneous determination of Octinoxate (OMC), Avobenzone (AVO), Octyltriazone (OT), and Phenyl benzimidazole sulfonic acid (PBSA) in moisturizing sunscreen lotion, utilizing β-CD as fluorescence enhancer, and determination of Avobenzone (AVO), Homosalate, Tinosorb M and Phenyl benzimidazole sulfonic acid (PBSA) in presence of Octocrylene (OCR) in whitening sunscreen cream, using micellar medium of Sodium Dodecyl Sulfate (SDS) to enhance fluorescence intensity. For first product, zero order synchronous spectrofluorimetric method was used for determination of OMC and AVO, and derivative synchronous spectrofluorimetric technique was utilized for OT and PBSA in quaternary mixture. Linear calibration curves were obtained in a concentration range of 0.5–8 μg mL^??1 for OMC and AVO, and in range of 0.05–3 μg mL^??1 for OT and 0.001–5 μg mL^??1 for PBSA, by measuring the fluorescence at 370, 405, 333.2 and 340.6 nm, respectively. For second product, first derivative synchronous fluorescence method was used for each UV-filter. A linear calibration curves were obtained in a concentration range of 0.5–8 μg mL^??1 for AVO, in range of 0.1–8 μg mL^??1 for Homosalate, 2–10 μg mL^??1 for Tinosorb M and 0.001–5 μg mL^??1 for PBSA, by measuring the fluorescence at 409.8, 373, 307.2 and 316.8 nm, respectively. The detection limits are well below the maximum admissible concentration. The proposed methods were validated according to ICH guidelines and successfully applied to determine sunscreens in pure form and in Cosmeceutical formulations. All the results obtained were compared with those of published methods, where no significant difference was observed.     

A Novel Pyrene Fluorescent Sensor Based on the π–π Interaction Between Pyrene and Graphene of Graphene–Cadmium Telluride Quantum Dot Nanocomposites

In this article, water-soluble graphene–cadmium telluride quantum dot nanocomposites were fabricated through the synthesis of cadmium telluride quantum dots in the presence of graphene aqueous dispersion. It was found that pyrene could remarkably quench fluorescence of graphene–cadmium telluride quantum dot nanocomposites. On this basis, a novel method for the determination of pyrene was developed. Factors affecting the pyrene detection were investigated, and the optimum conditions were determined. Under the optimum conditions, a linear relationship could be established between the quenching of fluorescence intensity of graphene–cadmium telluride quantum dot nanocomposites and the pyrene concentration in the range of 6.00 × 10^?8–2.00 × 10^?6 mol L^?1 with a correlation coefficient of 0.9959. The detection limit was 4.02 × 10^?8 mol L^?1. Furthermore, the nanocomposites were applied to practical determination of pyrene in different water samples with satisfactory results.     

Synthesis and Characterization of New Light Emitter Symmetrical Phenoxazinium Salt and Its Potential Application as Sensor for Assessment of Hg2+

The sensitization of the excited triplet state of a novel symmetrical Bis(dialkylamino)phenoxazinium salt was developed in the presence of Hg²⁺. This effect was used to determine the concentration of Hg²⁺ in different water samples. The phenoxazinium salt sensor was characterized by different spectroscopic tools such as: UV, FTIR, NMR and fluorescence spectra. The sensor has an emission band at 347 nm in DMSO. Hg²⁺ in DMSO at pH 5.6 can remarkably quench the fluorescence intensity of the sensor at 347 nm and a new band was appeared at 436 nm due to the strong complex formation between Hg²⁺ and sensor. The quenching of the band intensity at 347 and the enhancement of the intensity of the new band at 436 were used to determine the Hg²⁺ in different waste water samples. The dynamic range found for the determination of Hg²⁺ concentration is 8.7?×?10^-10 – 1.4?×?10^-6 mol L^?1 with a detection limit of 5.8?×?10^?10 mol L^?1 and quantification detection limit of 1.8?×?10^-9 mol L^-1.