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.     

CdTe quantum dots as fluorescence sensor for the determination of aminophylline in aqueous solution

A novel CdTe quantum dots (QDs) based technology platform was established in aqueous solution. It can perform accurate and simple determination of aminophylline concentration in pharmaceutical samples with satisfactory results. Under optimum conditions, the relative fluorescence intensity of CdTe quantum dots is linearly proportional aminophylline concentration from 2.00 to 80.0 μg mL^?1 with a correlation coefficient of 0.9979 for aminophylline determination and a detection limit of 0.531 μg mL^?1.     

Determination of Paracetamol Based on its Quenching Effect on the Photoluminescence of CdTe Fluorescence Probes

L-Cysteine capped CdTe nanoparticles (NPs) were synthesized in aqueous medium, and their application as fluorescence probes in the determination of paracetamol was studied. The L-cysteine capped CdTe NPs were characterized by transmission electron microscopy, X-ray diffraction spectrometry, spectrofluorometry, ultraviolet-visible and Fourier transform infrared spectrometry. Based on the distinct fluorescence quenching of CdTe fluorescence probes in the presence of paracetamol, a simple, rapid and specific method for paracetamol determination was presented. Under optimum conditions, the relative fluorescence intensity of CdTe NPs was linearly proportional to paracetamol concentration from 1.0 × 10⁻⁸ mol/L to 1.6 × 10⁻⁷ mol/L with a detection limit of 4.2 × 10⁻⁹ mol/L. The proposed method was applied to detect paracetamol in commercial tablets with satisfactory results.     

Sensitive Detection of Luteolin Using Thioglycolic Acid–Capped Cadmium Telluride/Cadmium Sulphide Quantum Dots as the Fluorescent Probe

ABSTRACT

A sensitive and simple method for the determination of luteolin (LTL) was developed based on the fluorescence quenching effect of LTL for thioglycolic acid–capped (TGA-capped) CdTe/CdS quantum dots (QDs). Under optimum conditions, a good linear relationship was obtained from 0.3 to 20.0 µg · mL^?1 with a correlation coefficient of 0.9972, and the detection limit was 7.2 ng · mL^?1. The fluorescence quenching mechanism has been proposed on the basis of electron transfer supported by ultraviolet-visible (UV-Vis) absorption, fluorescence (FL) spectroscopy. The proposed method was successfully applied to the determination of LTL in commercial capsules and human urine samples. It manifested several advantages such as high sensitivity, short analysis time, low cost, and ease of operation.     

Fluorescence Turn off Sensor for Brilliant Blue FCF- an Approach Based on Inner Filter Effect

A nanosensor with fluorometric readout based on L-cysteine capped cadmium sulphide quantum dots for discriminative detection and determination of Brilliant blue FCF (BB) (in 0.5 M Tris buffer solution of pH 9.5) over other synthetic food colourants is developed. Mechanism of the nanosensor is based on inner filter effect (IFE). The addition of BB into quantum dot solution might induce the quenching of fluorescence. The nanosensor described in this report reveals its simplicity and flexibility due to less laborious and more cost-effective synthesis. The developed fluorescence sensor showed excellent selectivity towards BB, and allows the detection as low as 3.50 × 10^?7 M. The developed sensor exhibited a linear concentration range of 4.00 × 10^?5 to 4.50 × 10^?6 M. More importantly, the proposed sensor exhibit sensitive responses toward BB in food samples such as sports drink and candies, demonstrating its potential in food analysis, which might be significant in food quality control in the future.     

Determination of Protoporphyrin IX Disodium Salt Based on Fluorescence Quenching of Glutathione-Capped Cadmium/Tellurium Quantum Dots

ABSTRACT

Aqueous glutathione-capped cadmium/tellurium quantum dots with a diameter of about 3 nm were synthesized. The fluorescence was quenched in the presence of protoporphyrin IX disodium salt, with the excitation wavelength at 320 nm. Under the optimal conditions, the quenched fluorescence intensity was linear in the range of 0.096–16 µg · mL^?1 with a concentration of protoporphyrin IX disodium salt, and the detection limit (3σ) was 2.8 × 10^?2 µg · mL^?1. The proposed method has been applied to the determination of protoporphyrin in serum samples with satisfactory results. The interaction mechanism was investigated.     

Selective Determination of Atropine Using poly Dopamine-Coated Molecularly Imprinted Mn-Doped ZnS Quantum Dots

In this study, a selective method for the determination of atropine in pharmaceutical formulations was proposed. L-cysteine capped Mn-doped ZnS quantum dots (QDs) were prepared in an in-situ method using sodium thiosulfate precursor and characterized by spectrofluorometer, Fourier transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM) and X-ray diffractometer (XRD). Dopamine hydrochloride was used as a precursor for preparation of poly dopamine-coated molecularly imprinted Mn-doped ZnS quantum dots. Finally, these prepared molecularly imprinted Mn-doped ZnS quantum dots were used for determination of atropine in pharmaceutical formulations. The obtained linear range for determination of atropine was in the range of 2 × 10^?8 – 7 × 10^?6 M, with a correlation coefficient (R²) of 0.9889; and the detection limit (S/N = 3) was 3.2 nM.     

Synthesis of 2-Mercaptonicotinic Acid-Capped CdSe Quantum Dots and its Application to Spectrofluorometric Determination of Cr(VI) in Water Samples

The CdSe quantum dots (QDs) capped with 2-mercaptonicotinic acid (H₂MN) were prepared through a controllable process at 80 °C. The prepared QDs were characterized by XRD, TEM, IR, UV–Vis and fluorescence (FL) techniques. It was found that the QDs were nearly mono-disperse with the diameters in the range of 8–10 nm. These QDs are capable to exhibit strong FL even in concentrated acidic media. They exhibit an enhanced fluorescence in the presence of Cr(VI), which was used for the determination of Cr(VI) in water samples. The linear range was found to be 1?×?10^?7–6.0?×?10^?6 M with the RSD and DL of 0.92 % and 5?×?10^?8 M, respectively. Except that Ca²⁺ and Fe³⁺ which can be eliminated through a simple precipitation process, the other co-existent ions present in natural water were not interfered. The recoveries obtained for the added amounts of Cr(VI) were in the range of 96.9–103.2 %, which denote on application of the method, satisfactorily.     

Hydrothermal synthesis of functionalized CdS nanoparticles and their application as fluorescence probes in the determination of uracil and thymine

A novel, sensitive, and convenient method for the determination of uracil and thymine by functionalized CdS nanoparticles (NPs) was proposed. CdS NPs were prepared by hydrothermal process and modified with thioglycollic acid (TGA) in aqueous solution. The fluorescence intensity of functionalized CdS NPs was quenched in the presence of uracil or thymine. Under optimal conditions, the relative fluorescence intensity (F₀/F) was proportional to the concentration in the range of 9.0×10^?6–1.0×10^?4 mol/L for uracil (r=0.9985) and 8.8×10^?7–1.5×10^?4 mol/L for thymine (r=0.9960). The corresponding detection limits were 9.6×10^?7 mol/L and 3.2×10^?7 mol/L, respectively. In addition, the possible quenching mechanism was also discussed.     

Quantum Dots (QDs) Based Fluorescent Sensor for the Selective Determination of Nimesulide

Fluorescent PET (Photoinduced Electron Transfer) has been of particular growth in recent times. A novel PET based fluorescent sensor using unmodified CdSe quantum dots (QDs) has been developed for the trace determination of Nimesulide (NIM). The sensor is based on the selective fluorescence quenching of quantum dots by NIM in presence of other NSAIDs and is found that intensity of quenching is linearly related to NIM concentration in the range 8.2?×?10^?7 – 4.01?×?10^?5?M. The mechanism of interaction is discussed. Finally, the potential application of the proposed method for the trace determination of NIM in pharmaceutical formulation is demonstrated.     

Determination of l-proline based on anodic electrochemiluminescence of CdTe quantum dots

A novel flow injection method for detection of l-proline was proposed in the presence of CdTe quantum dots (QDs). This method is based on the enhanced anodic electrochemiluminescence (ECL) emission of CdTe QDs l-proline in aqueous system. CdTe QDs were modified with thioglycolic acid to obtain stable water-soluble QDs and intensive anodic ECL emission in Na₂CO₃–NaHCO₃ buffer solution at an indium tin oxide (ITO) electrode, which was used for the sensitive detection of ECL enhancement using our homemade flow cell. Under the optimal conditions, the ECL intensity was correlated linearly with the concentration of l-proline over the range of 1.0×10^?8?1.0×10^?4 g mL^?1 (r=0.9996) and the detection limit was 5.0×10^?9 g mL^?1. The relative standard deviation was 1.12% for 6.0×10^?5 g mL^?1 l-proline (n=11). The possible mechanism was discussed. This method put forward a new efficient ECL methodology for enhancement-related determination of l-proline successfully.     

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.     

Highly sensitive electrochemical detection of dopamine and uric acid on a novel carbon nanotube-modified ionic liquid-nanozeolite paste electrode

A novel biosensor has been constructed by incorporating modified nanosized natural zeolite and 3-hydroxypropanaminium acetate (HPAA) as a novel room temperature ionic liquid, supported on multiwalled carbon nanotube (MWCNTs) and employed for the simultaneous determination of dopamine (DA) and uric acid (UA). A detailed investigation by transmission electron microscopy and electrochemistry is performed in order to elucidate the preparation process and properties of the composites. The voltammetric studies using the modified carbon paste electrode show two well-resolved anodic peaks for DA and UA with a potential difference of 160 mV, revealing the possibility of the simultaneous electrochemical detection of these compounds. The modified carbon paste electrode shows good conductivity, stability, and extraction effect due to the synergic action of HPAA, MWCNTs, and iron ion-doped natrolite zeolite. Under optimized conditions, the peak currents are linear from 8.12?×?10^?7 to 3.01?×?10^?4?mol?L^?1 and from 9.31?×?10^?7 to 3.36?×?10^?4?mol?L^?1 with detection limits of 1.16?×?10^?7 and 1.33?×?10^?7?mol?L^?1 for DA and UA using the differential pulse voltammetric method, respectively. Finally, the modified carbon paste electrode proved to have good sensitivity and stability and is successfully applied for the simultaneous determination of DA and UA in human blood serum and urine samples.     

Novel Glutathione-Capped Cadmium Telluride Quantum Dots-Based Off–On Fluorescence Sensor for Highly Sensitive and Selective Monitoring of Histidine

A novel glutathione-capped cadmium telluride quantum dots-based fluorescence “off–on” sensor was designed and applied for highly sensitive and selective monitoring of histidine in aqueous solution. To provide a platform for histidine detection, manganese ion was first employed as an effective quencher to decrease the fluorescence of glutathione-capped cadmium telluride quantum dots because of the binding of manganese ion to glutathione on the surface of quantum dots and the electron transfer from the photoexcited glutathione-capped cadmium telluride quantum dots to manganese ion. Due to its high binding affinity with manganese ion, histidine can make the manganese ion to be dissociated from the surface of glutathione-capped cadmium telluride quantum dots to form more stable complex with histidine in solution, and set free the luminescent glutathione-capped cadmium telluride quantum dots, thereby recovering the fluorescence of glutathione-capped cadmium telluride quantum dots. Experimental results showed that the recovered fluorescence intensity was directly proportional to the concentration of histidine in the range of 0.006 to 465.0 µg mL^?1 with a correlation coefficient (R) of 0.9977, and the detection limit (3σ/K) was 1.82 ng mL^?1. Relevant experiments also revealed that the fluorescence sensor gives excellent selectivity for histidine over other common amino acids. To further investigate perfect analysis performance, this sensor was utilized to determine histidine in synthetic samples with satisfactory results.     

A Novel Fluorimetric Bulk Optode Membrane Based on NOS Tridentate Schiff Base for Selective Optical Sensing of Al<Superscript>3+</Superscript> Ions

A novel fluorimetric optode has been developed for the highly selective and sensitive for the determination of ultra trace amounts of Al³⁺ ions. The proposed fluorescent optode is based on the incorporation of a simple and effective fluorescent sensor tridentate NOS Schiff base N-(2-hydroxynaphthylidene)-2-aminothiophenol (H₂L) in a plasticized PVC containing KTpClPB as a lipophilic anionic additive. H₂L was synthesized by a facile one-step Schiff base reaction. The plasticized PVC-membrane displays a calibration response for Al³⁺ ions over a wide concentration range from 1.0 × 10^?9 to 4.4 × 10^?3 mol/L. The fluorescence signal of the optode membrane can be easily recovered by immersion in 0.01 M EDTA. In addition to high stability and reproducibility, the sensor shows a unique selectivity towards Al³⁺ ion with respect to common co-existing cations, particularly Ga³⁺and In³⁺. The proposed optode was applied successfully for determination of Al³⁺ in some real samples, including bottled drinking waters, bottled mineral waters and soft drinks.     

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。     

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.     

Ultrasonic preparation of tetraoxalyl ethylenediamine melamine resin-coated multiwalled carbon nanotubes for trace Ni(II) sensing

Under an aid of ultrasonic, tetraoxalyl ethylenediamine melamine resin-coated multiwalled carbon nanotubes were prepared for Ni(II) sensing in aqueous solution. The processes involved the fabrication of tetraoxalyl ethylenediamine melamine resin by one pot way, the coating of tetraoxalyl ethylenediamine melamine resin at multiwalled carbon nanotubes (MWCNTs), and the determination of Ni(II). The present materials were carefully examined by Fourier transform infrared spectroscopy, field emission scanning electron microscope, and electrochemistry techniques. A great deal of amorphous microsphere could be observed for tetraoxalyl ethylenediamine melamine resin with an average diameter of 1.2 μm, and MTE could evenly adhere at the surface of MWCNTs by the ultrasonic. Tetraoxalyl ethylenediamine melamine resin-coated multiwalled carbon nanotube-modified paraffin-impregnated graphite electrode was successfully used for the determination of Ni(II) by differential pulse adsorptive anodic stripping voltammetry. The current responses (?0.3 V) were linearly increased depending on the concentration from 1?×?10^?11 to 3?×?10^?10 M (i (μA)?=?11.1?+?7.9 c (1?×?10^?12 M); R?=?0.9901, 3σ?=?7?×?10^?12 M).     

Development of an Optode for Detection of Trace Amounts of Hg2+ in Different Real Samples Based on Immobilization of Novel Tetradentate Schiff Bases Bearing Two Thiol Groups in PVC Membrane

A very sensitive and reversible optical chemical sensor based on a novel tetradentate Schiff base namely N.N^/bis(2-aminothiophenol)benzene-1,2-dicarboxaldehyde (ATBD) immobilized within a plasticized PVC film for Hg²⁺ determination is described. At optimum conditions (i.e. pH 6.0), the proposed sensor displayed a linear response to Hg²⁺ over 1.0?×?10^?10 ? 1.0?×?10^?2 mol L^?1 with a limit of detection of 7.23?×?10^?11 mol L^?1 (0.0145 μgL^?1). Moreover, the results revealed that, under batch condition, the sensor is fully reversible within a response time?~?35 s. In addition to its high stability and reproducibility, the sensor showed good selectivity towards Hg²⁺ ion with respect to common metal cations. The sensor was successfully applied for determination of Hg²⁺ ion in some real samples, including hair, urine and well water samples. The results were in good correlation with the data obtained using cold vapor atomic absorption spectrometry.     

Spectrophotometric Studies of the Reaction of Zinc(II) with Some Azo‐Triazol Compounds and Its Application to the Spectrophotometric Determination of Microamounts of Zinc(II)

Abstract

A new, simple, and sensitive quantitative spectrophotometric method for the rapid determination of zinc(II) using six azo compounds based on 3‐amino‐1,2,4‐triazole, namely {3‐(2,4‐dihydroxy‐1‐phenylazo)‐1,2,4‐triazole) (I), 3‐(2‐hydroxy‐5‐methyl‐1‐phenylazo)‐1,2,4‐triazole) (II), 3‐(2‐hydroxy‐5‐acetyl‐1‐phenylazo)‐1,2,4‐triazole) (III), 3‐(2‐hydroxy‐5‐ethylcarboxylate‐1‐phenylazo)‐1,2,4‐triazole) (IV), 3‐(2‐hydroxy‐5‐formyl‐1‐phenylazo)‐1,2,4‐triazole) (V), and 3‐(2‐hydroxy‐5‐bromo‐1‐phenylazo)‐1,2,4‐triazole) (VI), has been developed for use in aqueous media containing 40% (v/v) methanol. Linear calibration graphs are obtained up to 2.6, 5.9, 5.2, 5.2, 8.2 and 9.0 µg mL^?1 using ligands I, II, III, IV, V, and VI, respectively. Absorption maxima, molar absorptivities, and Sandell's sensitivities of 1:2 (M:L) complexes were found to be 490, 530, 505, 520, 550, and 510 nm, 4.86×10⁴, 2.10×10⁴, 1.26×10⁴, 0.10×10⁴, 0.19×10⁴, and 0.29×10⁴ L mol^?1 cm^?1, and 0.0014, 0.0031, 0.0052, 0.0662, 0.0348, and 0.0225 µg cm^?1 for ligands I, II, III, IV, V, and VI, respectively. Using the masking agents, the color reactions are free from interference by more than 30 ions investigated. The method has been applied to the spectrophotometric determination of trace amounts of zinc in pharmaceutical formulations and human hair samples. A study of some zinc solid complexes showed that chelation takes place through one nitrogen atom of the azo group and proton displacement from the hydroxyl group.