Fluorescence “Switch on” of Conjugates of CdTe@ZnS Quantum Dots with Al, Ni and Zn Tetraamino-Phthalocyanines by Hydrogen Peroxide: Characterization and Applications as Luminescent Nanosensors

In this study, we have developed a novel nanoprobe for H₂O₂ based on the conjugation of CdTe@ZnS quantum dots (QDs) to different metal tetraamino-phthalocyanine (MTAPc): (M?=?(OAc)Al, {OAc?=?acetate}, Ni and Zn). Chemical coordination of the QDs to the MTAPc resulted in the fluorescence “switch off” of the linked QDs which was associated with Förster resonance energy transfer (FRET). In the presence of varying concentration of H₂O₂, the fluorescence of the linked QDs was progressively “switched on” and the FRET mechanism between the QDs and the MTAPc was disrupted. The sensitivity/limit of detection of the nanoprobe followed the order: QDs-ZnTAPc (2.2 μM)?>?QDs-NiTAPc (4.4 μM)?>?QDs-AlTAPc (9.8 μM) while the selectivity followed the order: QDs-NiTAPc?>?QDs-AlTAPc?>?QDs-ZnTAPc. The varying degree of sensitivity/selectivity and mechanism of detection is discussed in detail.     

基于CdTe量子点荧光猝灭-恢复方法测定依诺沙星的研究

水相合成了巯基丙酸保护的CdTe量子点。根据在Cu2+存在的情况下,CdTe量子点荧光恢复程度与依诺沙星浓度成正比的现象,建立了基于CdTe量子点荧光猝灭-恢复测定依诺沙星的新方法。考察了溶液pH值以及Cu2+浓度等对检测体系的影响。在p H=10的硼砂缓冲溶液中,在Cu2+浓度为2.3×10-5mol/L的条件下,依诺沙星浓度在8.0×10-7~3.0×10-5mol/L范围内与量子点荧光恢复程度呈良好的线性关系,检出限为7.2×10-8mol/L。该方法用于实际样品中依诺沙星的检测,回收率为95.5%~105.0%。     

Novel Fluorometric Assay for Detection of Cysteine as a Reducing Agent and Template in Formation of Copper Nanoclusters

This study was designed to develop a highly selective and sensitive method towards fluorimetric sensing of cysteine (Cys) in water and human serum by using copper nanocluster. The Cys-CuNCs were characterized by scanning electron microscopy (SEM), FTIR, fluorescence and UV–Vis analysis. Spectroscopic evidences showed different intensities that were attributed to the different size of Cys-CuNCs. Enhancement in fluorescence intensity of copper nanoclusters with an increase in concentration of cysteine may enable them to be good candidates in detection systems. Selective recognition of cysteine in aqueous and serum samples was achieved during the formation of various copper nanoclusters (Cys-CuNCs) with different size. Under the optimized conditions, two linear range of the nanobiosensor for cysteine were between the 5 μM to 50 μM with detection limit of 2.4 μM and between 60 μM to 500 μM with detection limit of 55 μM. Fluorescence intensity increased with addition of cysteine concentration from 5 to 50 μM. The proposed low-cost nanobiosensor exhibited high reproducibility and good selectivity. It has been used also for the determination of cysteine in human serum samples with recoveries of 97–103 % and RSDs of 1.8–3.6 %     

壳聚糖包覆CdTe量子点传感器测定痕量汞

研究了在水相中合成了高质量的巯基乙酸包被的CdTe,通过1-(3-二甲氨基丙基)-3-乙基碳二亚胺(EDC)连接了壳聚糖。在pH6.4的PBS缓冲溶液中十六烷基三甲基溴化铵(CTMAB)存在下,汞离子对壳聚糖包覆的CdTe量子点具有荧光猝灭作用,实现了对水溶液中汞的定量检测。在最优条件下,壳聚糖包覆的量子点荧光猝灭与汞呈良好的线性关系,线性范围为0.3—15.0μg/L,检出限为9.5×10-8g/L。对5.0μg/L Hg2+平行测定11次,相对标准偏差为4.8%。该法用于水样品测定,相对标准偏差在5.0%以下,回收率为95.7%—102.6%,并且与ICP-AES相比,结果基本一致。该法用于实际样品测定误差较小,精密度与准确度均令人满意。     

Agglomeration behavior of lipid-capped gold nanoparticles

The current investigation deciphers aggregation pattern of gold nanoparticles (AuNPs) and lipid-treated AuNPs when subjected to aqueous sodium chloride solution with increasing ionic strengths (100–400 nM). AuNPs were synthesized using 0.29 mM chloroauric acid and by varying the concentrations of trisodium citrate (AuNP1 1.55 mM, AuNP2 3.1 mM) and silver nitrate (AuNP3 5.3 μM, AuNP4 10.6 μM) with characteristic LSPR peaks in the range of 525–533 nm. TEM analysis revealed AuNPs to be predominantly faceted nanocrystals with the average size of AuNP1 to be 35?±?5 nm, AuNP2 15?±?5 nm, AuNP3 30?±?5 nm, and AuNP4 30?±?5 nm and the zeta-average for AuNPs were calculated to be 31.23, 63.80, 26.08, and 28 nm respectively. Induced aggregation was observed within 10 s in all synthesized AuNPs while lipid-treated AuNP2 (AuNP2-L) was found to withstand ionic interferences at all concentration levels. However, lipid-treated AuNPs synthesized using silver nitrate and 1.55 mM trisodium citrate (AuNP3, AuNP4) showed much lower stability. The zeta potential values of lipid-treated AuNPs (AuNP1-L-1x/200, ??17.93?±?1.02 mV; AuNP2-L-1x/200, ??21.63?±?0.70; AuNP3-L-1x/200, ??14.54?±?0.90; AuNP3-L-1x/200 ??13.77?±?0.83) justified these observations. To summarize, AuNP1 and AuNP2 treated with lipid mixture 1 equals or above 1x/200 or 1x/1000 respectively showed strong resistance against ionic interferences (up to 400 mM NaCl). Use of lipid mixture 1 for obtaining highly stable AuNPs also provided functional arms of various lengths which can be used for covalent coupling.

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Graphical abstract Agglomeration behavior of gold nanoparticles before and after lipid capping

     

A simple fluorescence quenching method for roxithromycin determination using CdTe quantum dots as probes

A new method for the determination of roxithromycin based on the fluorescence quenching of 3-mercaptopropionic acid-capped CdTe quantum dots (MPA-CdTe QDs) was developed. In ethanol medium, the fluorescence of CdTe quantum dots at 552 nm was quenched in the presence of roxithromycin. Based on this a simple, sensitive, and selective method for rapid determination of roxithromycin was described. Reaction time, interfering substances on the fluorescence quenching, and mechanism of the interaction of CdTe QDs with roxithromycin were investigated. After optimization, the proposed method allows the determination of roxithromycin over the range 25.0-350.0 μg ml⁻¹. The detection limit is 4.6 μg ml⁻¹. The proposed method was successfully applied to commercial capsules and tablets with satisfactory results. The recovery of the method was in the range of 96.8-102.5%.     

Fluorescent Detection of Phosphate in Aqueous Solution Based on Near Infrared Emission Ag<Subscript>2</Subscript>S QDs/Metal − Organic Shell Composite

A novel fluorescence method for sensitive and selective detection of phosphate was developed based on near infrared emission Ag₂S QDs/ Metal ? Organic Shell Composite via the deposition of metal-organic (zinc-nitrogen) coordination shell around Ag₂S QDs . Under optimal conditions described, the fluorescence intensity of the composite was decreased at 685 nm in the presence of phosphate, which was linearly related to the concentration of phosphate in the range of 0. 7 to 4.2 μM and 11.2 to 88.2 μM with the relative correlation coefficient of R² = 0.998 and 0.987 respectively and detection limit as low as 6 nM. In addition, the proposed method was successfully utilized in serum samples, tap water and Yangtze River water samples with the recoveries ranged from 94.76 to 100.86 %, which presaged more opportunities for application in related bioassay and water sample researches.     

Sensitive and Selective Detection of Antibiotic D-Penicillamine Based on a Dual-Mode Probe of Fluorescent Carbon Dots and Gold Nanoparticles

This paper reported a dual-mode probe for D-penicillamine on the basis of pH-mediated gold nanoparticles aggregation and fluorescence resonance energy transfer (FRET) from carbon dots. D-penicillamine is a zwitterionic compound and has different forms depending on specific pH ranges. The thiol group of D-penicillamine has high affinity towards the surface of gold nanoparticles and can replace other surface ligands. When pH values were close to its isoelectrical point (pH(I)), the D-penicillamine capped gold nanoparticles aggregated through hydrogen bonding or electrostatic interactions, resulting in the releasing of carbon dots from gold nanoparticles. The dual-mode probe consisted of fluorescent carbon dots and gold nanoparticles, and the fluorescence of carbon dots was quenched by the attached gold nanoparticles due to the FRET. Then, the fluorescence can be recovered in presence of D-penicillamine due to the gold nanoparticles aggregation in specific pH range. Under the optimum conditions, the probe has linear response for D-penicillamine in the 0.25–1.5 μM concentration range with a detection limit of 0.085 μM. This method provides a potential application in sensitive detection of D-penicillamine.     

水溶性量子点荧光探针用于帕珠沙星的含量测定

文章采用荧光光谱和紫外光谱研究了CdTe量子点(CdTe QDs)与广谱抗菌药物帕珠沙星的相互作用。结果表明,随着帕珠沙星浓度的增加,CdTe QDs荧光强度有规律的降低,但通过透射电镜图对QDs及加入帕珠沙星后的QDs进行比较,发现QDs仍然均一单分散,表明反应的作用机理可能是帕珠沙星促使QDs表面键合的有机分子发生变化,在Cd空位表现出的表面缺损上形成了碲氧复合物,致使荧光猝灭。因此该反应可作为一种新颖的快速检测帕珠沙星含量的方法。在一定条件下,帕珠沙星溶液的浓度与量子点荧光强度成线性关系,线性范围为10.0～850 μg·mL-1,相关系数r为0.995 4,检测限(S/N=3)为3.254×10-3 μg·mL-1。药物对量子点的猝灭常数为2.188×104 L·mol-1。应用到冻干粉针剂和氯化钠注射液中帕珠沙星的含量测定,所得结果与标示量一致。该方法较常用检测方法具有简便、快捷、灵敏、线性范围宽的优点,并有望进一步开展发药物体内显像及作用机理的研究。     

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.     

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.     

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.     

A selective and sensitive tert-butylhydroquinone sensor based on synergy of CTAB and AuNPs–PVP–graphene nanohybrids

Gold nanoparticles (AuNPs)–polyvinylpyrrolidone (PVP)–graphene (Gr) nanohybrids were prepared by a facile one-pot green strategy. The obtained Au–PVP–Gr composites were characterized by scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. Then, a novel electrochemical sensor for highly sensitive and selective detection of tert-butylhydroquinone (TBHQ) is proposed based on cetyltrimethyl-ammonium bromide (CTAB) and Au–PVP–Gr modified glassy carbon electrode (GCE). Due to the synergistic effect of CTAB and Au–PVP–Gr, the developed sensor displays a wide linear range from 0.02 to 0.1 and 0.1 to 100.0 μM. A low detection limit of 0.009 μM was observed. Further, the sensitivity and selectivity of PVP–CTAB/Au–PVP–Gr/GCE was demonstrated by its practical application in the determination of TBHQ in real samples.     

Mechanistic Aspects of Quantum Dot Based Probing of Cu (II) Ions: Role of Dendrimer in Sensor Efficiency

Selective quenching of luminescence of quantum dots (QDs) by Cu²⁺ ions vis-à-vis other physiologically relevant cations has been reexamined. In view of the contradiction regarding the mechanism, we have attempted to show why Cu²⁺ ions quench QD-luminescence by taking CdS and CdTe QDs with varying surface groups. A detailed study of the solvent effect and also size dependence on the observed luminescence has been carried out. For a 13% decrease in particle diameter (4.3 nm →3.7 nm), the quenching constant increased by a factor of 20. It is established that instead of surface ligands of QDs, conduction band potential of the core facilitates the photo-induced reduction of Cu (II) to Cu (I) thereby quenching the photoluminescence. Taking the advantage of biocompatibility of dendrimer and its high affinity towards Cu²⁺ ions, we have followed interaction of Cu²⁺-PAMAM and also dendrimer with the CdTe QDs. Nanomolar concentration of PAMAM dendrimer was found to quench the luminescence of CdTe QDs. In contrast, Cu²⁺-PAMAM enhanced the fluorescence of CdTe QDs and the effect has been attributed to the binding of Cu²⁺-PAMAM complex to the CdTe particle surface. The linear portion of the enhancement plot due to Cu²⁺-PAMAM can be used for determination of Cu²⁺ ions with detection limit of 70 nM.     

CdTe量子点荧光猝灭法测定钴

以CdTe量子点作为荧光探针,基于荧光猝灭法对钴(Ⅱ)进行了定量检测,考察了缓冲溶液体系、量子点浓度、反应时间等多种因素的影响。实验结果表明,在pH8.0的0.2mol/LNa2HPO4-NaH2PO4缓冲液中,反应时间为10min,钴(Ⅱ)浓度为1.6×10-5—20×10-5mol/L范围时,其线性回归方程为F0/F=1.45+0.096Q(10-5mol/L),检出限为3×10-7mol/L。该方法检测范围宽,灵敏度高,为钴的测定提供了新的方法。     

巯基乙胺稳定的CdTe量子点荧光猝灭法测定间苯二酚

以CdTe量子点作为荧光探针,基于荧光猝灭法对间苯二酚进行了定量检测,考察了缓冲溶液体系、量子点浓度、反应时间等多种因素的影响.实验结果表明,在pH 6.5的0.2mol/LNa<,2>HPO<,2>-NaH<,2>PO<,4>缓冲液中,反应时间为15min.间苯二酚浓度为1.6×10<'-6>-2.0×10<'-5>...     

Copper- or manganese-doped ZnS quantum dots as fluorescent probes for detecting folic acid in aqueous media

3-Mercaptopropionic acid-capped core/shell ZnS:Cu/ZnS and ZnS:Mn/ZnS doped quantum dots (QDs) prepared through hydrothermal methods exhibit high photoluminescence intensity as well as good photostability. These water-dispersible nanoparticles exhibit high fluorescence sensitivity to folic acid due to the high affinity of the carboxylate groups and nitrogen atoms of folic acid towards the Zn surface atoms of the doped dots. Quenching of the fluorescence intensity of the QDs allows the detection of folic acid concentrations as low as 11 μM, thus affording a very sensitive system for the sensing of this biologically active molecule in aqueous solution. The possible quenching mechanism is discussed.     

以巯基丙酸为稳定剂的水溶性CdTe量子点的水热合成及表征

以巯基丙酸(MPA)为稳定剂,采用水热合成方法在160 ℃下合成水溶性CdTe量子点。研究了不同反应时间及反应前驱体溶液的不同pH值对合成的CdTe量子点光学性质的影响。结果表明:所制得的CdTe量子点的荧光发射波长在510~661 nm范围内连续可调,并且CdTe量子点的光学性质强烈地依赖于反应前驱体溶液的pH值,最佳pH值为9。透射电子显微镜和X射线衍射分析表明所制备的CdTe量子点的形状接近于球形,粒径分布较均匀。与回流方法制备的水溶性量子点相比,高温条件下的水热合成方法简单,反应时间短,CdTe量子点生长速度快,100 min就可生长到3.5 nm,并且所制得的CdTe量子点荧光强度高,稳定性好,荧光量子产率也较高,最高可达44.6%。     

Surface Molecular Imprinting on Silica-Coated CdTe Quantum Dots for Selective and Sensitive Fluorescence Detection of p-aminophenol in Water

In this paper, a selective and sensitive sensor for the determination of p-aminophenol (PAP) was developed by grafting molecularly imprinted polymers (MIPs) on the surface of silica-coated CdTe quantum dots (CdTe@SiO₂@MIPs). The obtained CdTe@SiO₂@MIPs were characterized by X-ray powder diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and fluorescence spectroscopy. The fluorescence intensity of CdTe@SiO₂@MIPs was more strongly quenched by PAP than that of the structural analogues of PAP. Under the optimal conditions, the fluorescence intensity of the CdTe@SiO₂@MIPs decreased sensitively with the increase of PAP concentration in the range of 0.05–50 μM. The limit of detection was 0.02 μM (3σ/K _sv). The sensor was successfully used to determine PAP in tap and lake water samples, and the average recoveries of PAP at various spiking levels ranged from 97.33 % to 103.3 % with relative standard deviations below 20 %.     

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.