Capped CdS Quantum Dots Research Articles

Probing the interactions of chitosan capped CdS quantum dots with pathogenic bacteria and their biosensing application.

Chitosan modified CdS quantum dots (CdS@CTS) can be used as an effective bacterial biosensor due to their good bioaffinity among chitosan molecules and bacterial membranes. CdS@CTS is an ultrafast, sensitive, direct and biocompatible biosensor for pathogenic bacteria (Pseudomonas aeruginosa and Staphylococcus aureus). Chitosan biopolymer of CdS@CTS provides bioaffinity sites that can be employed for the assembly on pathogen bacteria cells due to the chemical similarity of the chitosan and the bacteria membranes. Thus, S. aureus and P. aeruginosa cells were detected at low concentrations of 150 and 200 cfu mL-1, respectively, in an extremely short time (1 min). The CdS@CTS-bacteria interaction is noncovalent. From the thermodynamic results, the van der Waals force and hydrogen bonding formation are characterized by negative enthalpy (ΔH), while positive entropy (ΔS) is considered as the evidence for typical hydrophobic interactions. Moreover, negative ΔH and positive ΔS might play a role in the electrostatic interactions. The negative free energy (ΔG) shows that the binding events were spontaneous processes. Matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS) and transmission electron microscopy (TEM) were performed to evaluate the interactions and the biocompatibility of CdS@CTS toward bacteria cells. Their biocompatibility, together with the high sensitivity and the presence of multifunctional forces, making these quantum dots (CdS@CTS) an excellent and novel biosensor which can be widely applied in the near future.

Cu2+-modulated cysteamine-capped CdS quantum dots as a turn-on fluorescence sensor for cyanide recognition

A new fluorescence sensor for detection of cyanide ions (CN−) in aqueous media based on the recovered fluorescence of cysteamine capped CdS quantum dots [Cys-CdS QDs]-Cu2+ system was proposed. The fluorescence intensity of Cys-CdS QDs was quenched by Cu2+ due to the binding of Cu2+ to cysteamine on the surface of the QDs. The degree of fluorescence quenching was proportional to the concentration of Cu2+. However, in the presence of CN−, the fluorescence intensity of Cys-CdS QDs was found to be efficiently recovered. Experimental results showed that the pH of the buffer solution and the concentration of Cu2+ affected the fluorescence intensity upon adding CN−. Under the optimal condition, the recovered fluorescence intensity was linearly proportional to the increasing CN− concentration in the range 2.5–20μM. The limit of detection and the limit of quantification were found to be 1.13μM and 3.23μM, respectively. In addition, among the tested ions, only CN− could turn on the fluorescence intensity suggesting that the [Cys-CdS QDs]-Cu2+ system was a highly selective sensor for CN−. Moreover, this proposed sensor was demonstrated to detect CN− in drinking water with satisfactory results.

Photoelectrochemical Immunosensor Array Based on Thioglycolic Acid Capped CdS Quantum Dots for Multiplexed Detection of Veterinary Drug Residues

AbstractA photoelectrochemical immunosensor based on multi‐electrode array was developed for simultaneous and sensitive determination of veterinary drug residues. In this system, poly(dimethyldiallylammonium chloride) (PDDA), Au nanoparticles (Au NPs) and thioglycolic acid (TGA)‐capped CdS quantum dots (QDs) were layer‐by‐layer assembled onto the home‐made Au electrode array. The assembling process of the (CdS/PDDA/Au NPs/PDDA)n multilayer was characterized by electrochemical impedance spectroscopy. And then the antibodies for clenbuterol (CB), ractopamine (RAC) and chloramphenicol (CAP) were covalently immobilized onto the Au electrode array by 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide (EDC) coupling reaction, respectively. The concentrations of CB, RAC and CAP were measured based on the photoelectrochemical effects of CdS QDs. Under the optimal conditions, the limits of detection (LOD) for CB, RAC and CAP were 25, 50 and 2.2 pg/mL (3Δ), respectively, with acceptable recovery over the range of 95.40%–105.5% in pig liver samples. All results indicate that the immunosensor array system has potential application for practical, effective and high throughput analysis of veterinary drugs residues.

A novel method for ranitidine hydrochloride determination in aqueous solution based on fluorescence quenching of functionalised CdS QDs through photoinduced charge transfer process: Spectroscopic approach

A novel method for the quantitative determination of ranitidine hydrochloride (RNH) based on the fluorescence quenching of functionalised CdS quantum dots (QDs) by RNH in aqueous solution was proposed. The method is simple, rapid, specific and highly sensitive with good precision. The thioglycolic acid (TGA)-capped CdS QDs were synthesized from cadmium nitrate and sodium sulfide in alkaline solution. Under the optimal conditions, the Stern-Volmer calibration plot of F(0)/F against concentration of RNH was linear in the range of 0.50-15.0 μg mL(-1) with a correlation coefficient of 0.996. The limit of detection (LOD) was 0.38 μg mL(-1). The method was satisfactorily applied to the direct determination of RNH in pharmaceutical formulations with no significant interference from excipients. The results were found to be in good agreement with those obtained by the reference method and the claimed value. The accuracy and reliability of the method were further ascertained by recovery studies via the standard-addition method, with percentage recoveries in the range of 98.47 to 102.30%. The possible fluorescence quenching mechanism for the reaction was also discussed.

Thioglycolic Acid Capped CdS Quantum Dots as Fluorescence Probe for Ultrasensitive Determination of Tetracycline and Oxytetracycline

AbstractWater soluble CdS quantum dots (QDs) have been synthesized using thioglycolic acid (TGA) as surface modifying agent through a one step process by using safe and low cost materials. These TGA capped CdS QDs are highly stable in aqueous solution and applied for ultrasensitive tetracycline (TC) and oxytetracycline (OTC) sensing. The approach was based on the fluorescence of the QDs selectively quenched in the presence of TC and OTC, respectively. Under optimal conditions, the relative fluorescence intensities of CdS QDs were decreased linearly with increasing TC and OTC in the range of 0.05 to 10.0 μM and 0.1 to 10.0 μM, respectively. The limit of detection (S/N = 3) was 5.0 nM for TC and 10.0 nM for OTC, respectively. The RSD for eleven determinations of 5.0 μM TC was 1.26% and 5.0 μM OTC was 0.8%, respectively. There was no significant wavelength shift on the fluorescence‐quenched signals in the presence of the drugs. The effect of common foreign substances on the fluorescence of the QDs was examined to evaluate the selectivity and the results showed a high selectivity of the TGA capped CdS QDs towards TC and OTC. The method presented here is simple, rapid, inexpensive, sensitive and suitable for practical application.

Ultrasensitive cysteine sensing using citrate-capped CdS quantum dots

The importance of cysteine (Cys) in biological systems has stimulated a great deal of efforts in the development of analytical methods for the determination of this amino acid. In this work, a novel fluorescent probe for Cys based on citrate (Cit)-capped CdS quantum dots (QDs) is reported. The Cit-capped CdS QDs fluorescent probe offers good sensitivity and selectivity for detecting Cys. A good linear relationship was obtained from 1.0 × 10 −8 mol L −1 to 5.0 × 10 −5 mol L −1 for Cys. The detection limit was calculated as 5.4 × 10 −9 mol L −1. The proposed method was applied to detect Cys in human urine samples, which showed satisfactory results. This assay is based on both the lability of Cit and the strong affinity of thiols to the surface of CdS QDs. The addition of Cys improved the passivation of the surface traps of CdS QDs and enhanced the fluorescence intensity.

Synthesis, characterization, photo and physicochemical properties of 11-mercaptoundecanoic acid and tetraaniline capped CdS quantum dots

Surface modification of quantum dots (QDs) for improved photo and physicochemical properties is a topic of potential technological interest. Herein, we report on the synthesis of aggregation free 11-mercaptoundecanoic acid and tetraaniline (TA) capped CdS QDs with narrow size distribution (∼2.3 nm diameter), which are further characterized using UV–visible spectroscopy, photoluminescence spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The TA capped CdS QDs show improved photoluminescence and photostability, which is attributed to the effective grafting of TA on CdS QDs through N-atoms, changing the surface chemical environment and facilitating charge transfer.

Facile synthesis of fluorescent quantum dot‐polymer nanocomposites via frontal polymerization

AbstractWe report an available approach for quickly fabricating CdS QD‐polymer nanocomposites via frontal polymerization (FP). First, we synthesized (3‐mercaptopropyl)‐1‐trimethoxysilane (MPS)‐capped CdS quantum dots (QDs). With these MPS‐capped CdS QDs containing mercapto groups, MPS‐capped CdS QDs can be easily incorporated into a poly(N‐methylolacrylamide) (PNMA) matrix via FP. A variety of features for preparing QD‐polymer nanocomposites, such as initiator concentration and CdS concentration, were thoroughly investigated. The fluorescence properties of QD‐polymer nanocomposites prepared via FP are comparatively investigated on the basis of ultraviolet–visible (UV–vis) spectra and photoluminescence (PL) spectra. Results show that the PL intensity of QD‐polymer nanocomposites prepared via the FP method is superior to that obtained by the traditional batch polymerization (BP) method. In addition, by measuring the changes of PL intensity of the samples immersed in different concentrations of copper acetate solution, we found the QD‐polymer nanocomposites can be ultrasensitive to copper ions. This FP process can be exploited as a facile and rapid way for synthesis QD‐polymer nanocomposites on a large scale, avoiding the fluorescence quenching of nanocrystals during incorporation nanocrystals into polymer matrices. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2170–2177, 2010

Quantum dots – electrospray ionization mass spectrometry: 3‐mercaptopropanic acid capped CdS quantum dots as accelerating and enrichment probes for microwave tryptic digestion of proteins

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RETRACTED: Mercaptoacetic acid capped CdS quantum dots as fluorescence single shot probe for mercury(II)

Water soluble CdS quantum dots (QDs) have been synthesised using mercaptoacetic acid (MAA) as surface modifying agent through a one step process by using safe and low cost materials. These MAA capped CdS QDs are highly stable in aqueous solution and have strong affinity for mercury ion as a result of interaction with the functional group present in the capping agent. This probe is based on the characteristic of fluorescence quenching of functionalised CdS QDs. Under the optimum conditions, the fluorescence intensity of CdS QDs is linearly proportional to the mercury ion concentration in the range 0.05 x 10(-7) to 4.0 x 10(-7) M with a detection limit of 4.2 x 10(-9) M. There is no significant wavelength shift on the fluorescence-quenched signals in the presence of mercury ion at the pH 7.4. Compare to the organic dyes, these nanoparticles are brighter and more stable against photobleaching. The effect of common foreign cations oil the fluorescence of the QDs was examined to evaluate the selectivity and the results showed a high selectivity of the MAA capped CdS QDs towards Hg(II) ions, The method presented here is simple, rapid, inexpensive, sensitive and suitable for practical application. (C) 2008 Published by Elsevier B.V.

Unambiguous evidence for wurtzite phase in capped CdS quantum dots

The problem of identification of the correct crystalline structure of CdS nanoclusters below 2.5 nm in size is outlined. Structure of thiophenol capped CdS nanoclusters in the size range 1.2–4.3 nm, synthesized using cadmium acetate solution in methanol, is discussed using powder XRD and electron diffraction data. Unambiguous confirmation of the wurtzite phase in CdS nanoclusters below 2.5 nm size is reported. The observation of 102 wurtzite peak in the XRD patterns of such nanoclusters indicates low stacking fault concentration.

Attenuated Total Reflection Infrared Studies of Oleate and Trioctylphosphine Oxide Ligand Adsorption and Exchange Reactions on CdS Quantum Dot Films

Ligand exchange reactions at the surface of oleate- and trioctylphosphine oxide (TOPO)-capped CdS quantum dots have been studied with attenuated total reflection infrared (ATR-IR) spectroscopy, using thin films deposited from organic solvent suspensions. The oleate and trioctylphosphine capping ligands were found to form highly ordered and densely packed monolayers on the CdS surface. Adsorbed oleate is coordinated to CdS in a chelating bidentate manner through the carboxylate functional group, while adsorbed trioctylphosphine oxide is coordinated though the P=O functional group and appears to have numerous adsorption environments on the CdS surface. Exposure of such films to aqueous solution was found to cause partial delamination of the films from the ATR prism interface which was reversible upon redrying. Ligand exchange reactions on the oleate- and trioctylphosphine-capped CdS films were studied in situ at room temperature by allowing the films to be exposed to dilute aqueous solutions of thiol-containing ligands. Oleate and trioctylphosphine oxide are both strongly adsorbed to the CdS surface, and ligand exchange with monothiol-containing ligands has been found to be highly dependent upon experimental conditions, in particular pH, where exchange is only observed at solution pH where the exchanging ligand is uncharged. This is attributed to the inability of a charged ligand to penetrate the hydrophobic polymethylene layer on the CdS surface.

Development of Quantum Dots Modified Acetylcholinesterase Biosensor for the Detection of Trichlorfon

AbstractPoly (N‐vinyl‐2‐pyrrolidone) (PVP)‐capped CdS quantum dots (QCdS‐PVP) was synthesized with CdCl2 and Na2S in the presence of PVP. QCdS‐PVP has been used for the immobilization and stabilization of the acetylcholinesterase (AChE). The electrocatalytic activity of QCdS‐PVP leads to a greatly improved electrochemical detection of the enzymatically generated thiocholine product, and higher sensitivity and stability. The GCE/QCdS‐PVP/AChE biosensor was used for the detection of organophosphate pesticides (OPs), such as trichlorfon. The sensor performance, including pH and inhibition time, was optimized with respect to operating conditions. Under the optimal conditions, the biosensor was used to measure as low as 12 ppb trichlorfon with a 5‐min inhibition time.

Quantum dots modified electrode and its application in electroanalysis of hemoglobin

In this work, quantum dots (QDs) have been successfully applied in the preparation of chemically modified electrode (CME) in the electrochemical determination (ECD) of proteins. Poly ( N-vinyl-2-pyrrolidone) (PVP)-capped CdS quantum dots (PCQDs) were synthesized from CdCl 2 and Na 2S in the presence of PVP. Characteristics of the PCQDs were studied by TEM, UV–Vis spectrum and FT-IR spectrum. Results showed that the PCQDs were small size, 2–4 nm, with homogenous distributions. The PCQDs were also proved to have good biocompatibility by UV–Vis spectrometry. To our best knowledge, it is the first time to modify the PCQDs onto the surface of glassy carbon electrode to fabricate a PCQDs CME. The PCQDs CME possessed rather good electron transport characteristic that was consistent with the higher charge detaching efficiency of CdS quantum dot resulting from its quantum size effect. The electrochemical behaviors of hemoglobin on this PCQDs CME have been investigated by cyclic voltammetry (CV). Novel reduction responses were observed for hemoglobin on the PCQDs CME in aqueous solutions, which could not be obtained on bare GCE. In addition, the results of flow injection analysis (FIA) showed the high stability and reproducibility of the PCQDs CME. The peak current was a linear function of concentrations in the range 1.0 × 10 −8 to 2.0 × 10 −5 M for Hb, with detection limit of 5.0 × 10 −9 M. The FIA–ECD system has been successfully applied to assess the Hb content of clinic blood samples with advantages of sensitiveness, speediness, easy control and small sample-consumption.

The electronic and optical properties of dendrimer-capped CdS quantum dots: a UV-vis and x-ray spectroscopy study

The electronic and optical properties of a series of PAMAM-dendrimer capped CdS quantum dots (QDs) have been investigated with UV-vis absorption (UV-abs), photoluminescence (PL), x-ray absorption near-edge structure (XANES) and x-ray excited optical luminescence (XEOL) techniques. The size-dependent electronic behavior of the QDs was observed in both the UV-abs and XANES (S K-edge) spectroscopy. Findings from the PL and XEOL studies provide complementary information to the UV- and x-ray absorption results and shed further light on the stability of the CdS QDs upon aging.