Functionalized CdS Quantum Dots Research Articles

Elucidating the Size-dependent FRET Efficiency in Interfacially Engineered Quantum Dots Attached to PBSA Sunscreen.

Applying sunscreen on human skin provides photoprotection against the harmful ultraviolet (UV) radiation of the sun. Sunscreen absorbs UV radiations and dissipates the absorbed energy through various radiative and nonradiative pathways. The attachment of functionalized quantum dots (QDs) to the sunscreen component is a novel idea to enhance the absorption cross-section of UV radiations. Therefore, the attachment of the sunscreen component to the ligand functionalized biocompatible QDs and the absorbed energy transfer from sunscreen to the QDs could work as a model system to overall improve the efficiency of the sunscreen. This study elucidates the mechanism of size-dependent Förster resonance energy transfer (FRET) efficiency and its rate between 2-phenylbenzimidazole-5-sulfonic acid (PBSA) and mercaptoacetic acid (MAA) functionalized CdS QDs. In the PBSA-QDs dyad, the PBSA (donor) dissipates UV-absorbed energy to the CdS QDs (acceptor). Following excitation at 306 nm, the steady-state photoluminescence (SSPL) and time-resolved photoluminescence (TRPL) techniques measurements demonstrate that both the nonradiative energy transfer efficiency and rate are QDs size-dependent in addition to donor-acceptor distance, and suggest that bigger sized-QDs result in an increase of the FRET efficiency.

Glutathione Modified Fluorescent CdS QDs Synthesized Using Environmentally Benign Pathway for Detection of Mercury Ions in Aqueous Phase.

An adept, rapid and novel water-soluble glutathione functionalized CdS quantum dots (GSH@CdS QDs) were fabricated using green pathway for sensing of heavy metal contamination prevalent in industrial wastewater. GSH@CdS QDs were facilely synthesized in an aqueous phase reaction and were effectively characterized using FT-IR, XRD, FESEM, HRTEM and EDX techniques. The distinct fluorescence characteristics of GSH@CdS QDs were explored and the QDs showed selective sensitivity towards mercury ions with a low limit of detection of 0.54nM under optimal conditions. The detailed interaction between GSH@CdS QDs and Hg2+ and the probable fluorescence quenching mechanism were established in this study. In comparison to already reported fluorescent probes, GSH@CdS QDs showed high sensitivity, biocompatibility, long fluorescence stability and convenient removal of mercury ions. Graphical Abstract Facile green route for the fabrication of glutathione capped CdS quantum dots for fluorescence-based detection of toxic Hg2+ ions.

A Novel Surface‐Tethered Double‐Signal Electrochemiluminescence Sensor Based on Luminol@Au and CdS Quantum Dots for Mercury Ion Detection

AbstractA novel surface‐tethered double‐signals electrochemiluminescence (ECL) sensor has been developed for the detection of mercury (II) ions (Hg2+). Firstly, cysteamine functionalized CdS quantum dots (CdS QDs‐Cys) as one of ECL nanoprobes were deposited onto the glass carbon electrode. Then electrode was modified with carboxylated thymine via the carboxyl groups of thymine and amino groups of CdS QDs‐Cys. Due to the specific recognition between thymine and Hg2+, the above electrode acted as the substrate to capturing target Hg2+, which could further bind luminol@Au‐Cys‐T multifunctional nanoarchitecture. It was found that the ECL intensity of luminol and CdS QDs both increased with the increasing of mercury ion concentration. Under the optimum condition, the logarithm of the ratio of two signals was linearly proportionally to the logarithmic concentrations of Hg2+ in the range 0.005 ∼ 2.5 nM with a limit of detection of 0.002 nM (S/N=3). The novel sensor displayed good reproducibility and sensitivity and provided an alternative analytical approach for the following research.

Interaction of tetracycline with l-cysteine functionalized CdS quantum dots - Fundamentals and sensing application.

The present paper reports l-cysteine functionalized CdS quantum dots (QDs) as a simple and highly selective turn-off fluorescence sensor for the determination of tetracycline (TET). The unauthorized use of TET may pose serious health hazards in human beings and hence the detection and determination has become very essential. In this regard, we have developed a sensor that enable the quantification of TET in the range 6.00 × 10-4 M to 1.50 × 10-5 M with a limit of detection 7.78 × 10-6 M, under optimized conditions. Steady state and time resolved fluorescence spectroscopic studies were used for investigating the mechanism of quenching and was found to be a combination of static and dynamic processes. The analytical application of the proposed sensor was investigated in pharmaceutical formulation.

Water‐soluble glutathione‐CdS QDs with exceptional antimicrobial properties synthesized via green route for fluorescence sensing of fluoroquinolones

AbstractBACKGROUNDContinual emergence of quinolones in the environment has raised concerns and the repercussions are almost unimaginable. Along with this an increase of antibiotic resistance in microbes has encouraged the pharmaceutical and food industry to create new antimicrobial agents. Nano‐range materials with exceptional antimicrobial properties synthesized via green routes for fluorescence sensing of fluoroquinolones have rarely been reported.RESULTSA facile, eco‐friendly and green approach was utilized for the synthesis of water soluble glutathione (GSH) functionalized CdS quantum dots (QDs) for the selective detection of fluoroquinolones. The prepared QDs exhibited a strong emission peak at 460 nm and the addition of fluoroquinolones caused enhancement and significant blue shift (∼ 50 nm) in the intensity, revealing sensitive and selective detection of fluoroquinolones. The limit of detection was found to be 2.2 µmol L‐1. Also, antimicrobial activities of the QDs were assessed against both Gram positive and Gram negative bacteria and the QDs were found to be effective against the Gram positive bacteria especially Bacillus species in comparison with the Gram negative bacteria.CONCLUSIONSThe current study offers a green route to synthesize water soluble and stable QDs for sensing with exceptional antimicrobial properties. © 2018 Society of Chemical Industry

L- and D-cysteine Functionalized CdS Quantum Dots as Nanosensors for Detection of L-morphine and D-methamphetamine

A new method in differentiation of chiral molecules is reported based on the fluorescence quenching of functionalized CdS quantum dots (CdS-QDs) as nanosensor by differing in the chirality of functionalization species. The chemically functionalized CdS-QDs with strong yellow emission were prepared using chiral L-cysteine (L-Cyst) and D-cysteine (D-Cyst) molecules. Then, the functionalized CdS-QDs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, photoluminescence (PL), ultraviolet-visible (UV-Vis), and Fourier transform infrared (FT-IR) spectroscopies. The prepared L- and D-cysteine functionalized CdS-QDs were exploited as fluorescence probes for detection and determination of L-morphine and D-methamphetamine. It was found that the fluorescence of D- and L-cysteine functionalized CdS-QDs were efficiently quenched by adding D-methamphetamine and L-morphine to them, respectively. The magnitude of fluorescence quenching depended on the concentration of L-morphine and D-methamphetamine solutions according to the Stern-Volmer equation. So, the functionalized CdS-QDs can be used as simple, quick, cheap, and sensitive nanosensor for practical detection of morphine and methamphetamine.

Design of a simple and novel photoelectrochemical aptasensor for detection of 3,3′,4,4′-tetrachlorobiphenyl

In view of the urgent need of determining polychlorinated biphenyls in the environment, we developed a highly sensitive and selective photoelectrochemical (PEC) aptasensor for determination of 3,3′,4,4′-tetrachlorobiphenyl (PCB77) by immobilizing aptamer on N-doped TiO2 nanotubes (N-doped TiO2 NTs). To improve analytical performance of the PEC sensor, the complementary DNA functionalized CdS quantum dots (DNA-CdS QDs) were introduced onto N-doped TiO2 NTs by hybridization. In addition of PCB77, owing to high affinity of aptamer to PCB77, PCB77-aptamer complexes were formed by being bound of PCB77 whilst DNA-CdS QDs were released from the sensing surface. The complexes with poor conductivity hindered the interfacial electron transfer, leading to the photocurrent decrease. The more important is the release of DNA-CdS QDs enhanced the photocurrent decrease, playing the role of signal amplification. The photocurrent change was utilized to detect PCB77 quantitatively. The PEC aptasensor exhibited excellent analytical performance for detection of PCB77 with wide linear range of 0.1–100 ng/L and a low detection limit of 0.1 ng/L. It manifested outstanding selectivity for PCB77 in control experiments by employing six interferents which had similar structure or coexisted with PCB77. Besides, the PEC aptasensor was used to detect the content of PBC77 in the environment.

A novel method for determination of tinidazole and metronidazole in aqueous solutions based on fluorescence quenching of functionalized CdS quantum dots as luminescent probes

A novel method for determination of tinidazole and metronidazole in aqueous solutions based on fluorescence quenching of functionalized CdS quantum dots as luminescent probes

A selective morphine nanosensor derived from functionalized CdS quantum dots

An optical nanosensor for measurement and detection of morphine using CdS quantum dots (CdS-QDs) functionalized by antimorphine antibody is illustrated. The prepared nanosensor (CdS-QDs-antimorphine) operates based on the selective host-guest interaction between morphine and antimorphine antibody. It was found that modification of CdS-QDs with antimorphine antibody quenches the primary fluorescence of CdS-QDs according to the Forster resonance energy transfer (FRET) mechanism. The next interaction with morphine turns on the fluorescence of CdS-QDs-antimorphine. The modified CdS-QDs can be used as selective nanosensor for rapid determination of morphine.

Sandwich-format electrochemiluminescence assay for PDGF-BB using quantum dots–dendrimer nanocomposites as probe

This work describes a novel electrochemiluminescence aptasensor for highly sensitive detection of platelet-derived growth factor BB (PDGF-BB) using aptamer functionalized CdS quantum dots–polyamidoamine as probe (CdS QDs–PAMAM–Apt). CdS QDs–PAMAM nanocomposites were synthesized by one-pot synthesis in methanol. The prepared nanocomposites were linked with the NH2–aptamer 2 (Apt2) of PDGF-BB to form the CdS QDs–PAMAM–Apt2 probe by glutaraldehyde as coupling reagent. For constructing the aptasensor, MWCNTs–chitosan composites and NH2–aptamer 1 (Apt1) with the same base sequence as Apt2 were immobilized on the electrode by the self-assembled method to recognize the target protein PDGF-BB. In the presence of PDGF-BB, the structure of sandwiched format was formed between the Apt1 and the CdS QDs–PAMAM–Apt2 probe, thereby resulting in a proportional increase of ECL emission. Thanks to the efficient and stable ECL emission of CdS QDs–PAMAM dendrimer and the advantage of MWCNTs for accelerating the electron transfer, the highly sensitive detection of PDGF-BB with a detection limit of 0.13pM was achieved. The linear range is from 0.5pM to 1nM. The present protocol was applied to the analysis of PDGF-BB in human serum samples. The recoveries of PDGF-BB in human serum samples are 87.2–113% and RSD values are less than 3.6%.

Fluorescence detection of Pb2+ based on the DNA sequence functionalized CdS quantum dots

In this paper, we have developed a simple and rapid method for the detection of Pb2+ based on the DNA sequence capped CdS quantum dots (QDs). We utilized the designed guanine (G)-rich DNA sequence (PS2.M) as a coating reagent to synthesize the DNA-capped CdS QDs. The designed G-rich DNA sequence PS2.M can bind with hemin to form G-quadruplex/hemin complex with K+, accompanied by the fluorescence quenching of CdS QDs via the photoinduced electron transfer. Pb2+ can induce conformational changes in the G-quadruplex/hemin complex to release the hemin molecules, so the quenched fluorescence of CdS QDs could be recovered. Therefore, the new fluorescent analysis system could be applied for the detection of Pb2+ based on the label-free DNA sequence capped CdS QDs.

A novel FRET probe for selective and sensitive determination of vitamin B12by functionalized CdS QDs in aqueous media: applications to pharmaceutical and biomedical analysis

Vitamin B12 (VB12) is one of the essential B complex vitamins, it is a water soluble nutrient and a medicine. Herein we developed, a novel but straightforward method for the selective and sensitive quantitative determination of VB12 based upon measuring the fluorescence quenching of functionalized CdS quantum dots (QDs) in aqueous media. The mercaptopropionic acid (MPA) functionalized CdS QDs were directly synthesized from cadmium chloride and sodium sulfide in aqueous media by a chemical method. The detection mechanism involves photoinduced charge transfer from CdS QDs towards VB12 at the surface of the CdS QDs resulting in the fluorescence quenching of CdS QDs followed by nonradiative fluorescence resonance energy transfer. Under the optimized conditions, the relationship between the fluorescence intensity of the CdS QDs and VB12 concentration was linear in the range of 5.0–100 μg mL−1 with a limit of detection of 6.91 μg mL−1. The selectivity experiment indicated excellent selectivity for VB12 over a number of interfering species. Moreover the method was successfully applied in the determination of VB12 in complex matrices, namely blood serum, urine and pharmaceutical formulations (multivitamin injection), without sample pretreatment. The accuracy and reliability of the method was further ascertained by recovery studies via the standard addition method with percentage recoveries in the range of 97.15%–99.49% being obtained. In addition, the probable fluorescence quenching mechanism of the CdS QDs induced by VB12 is also discussed.

Synthesis Of Mercaptopropionic Acid Stabilized CdS Quantum Dots for Bioimaging In Breast Cancer

Semiconductor inorganic nanocrystals or quantum dots (QDs) are nowadays extensively used for imaging and analysis of bio-molecules owing to their superior optical properties over conventional organic fluorophores. They have excellent potential for synthesizing molecular probes against various biological markers such as free antigens, cell surface markers/antigens, bacteria, viruses and tissues. Traditional synthesis protocols of the QDs generally lead to the formation of hydrophobic nanocrystals. For biological applications, post-synthesis modifications need to be introduced to render required hydrophilicity. However, such additional steps make the tiny QDs structures bulky, which is unwanted in subsequent in-vivo executions. The present work reports a simple method for the direct synthesis of hydrophilic carboxyl (–COOH) functionalized CdS QDs using mercaptopropionic acid as a sulfur source and stabilizer. This aqueous synthesis route avoids the requirement of extra surface modification steps. The size and surface morphology of the synthesized CdS QDs were studied by electron microscopy. The average diameter of the QDs has been found to be in the range of 2-3.5nm. Spectral studies confirmed the grafting of –COOH terminal on the synthesized nanocrystals. Band gap energy and the theoretical size of the particles were calculated and found in good agreement with the experimental analysis. Due to the size quantization effect, the estimated band gap energy (2.6eV) of the QDs was on a higher side than that reported (2.4eV) for the bulk material. The synthesized nanocrystals can be further conjugated with bio-molecules for high-throughput drug screening, clinical immunological assays and protein-protein interaction studies.

Surface-modified CdS quantum dots as luminescent probes for sulfadiazine determination

A novel, sensitive and convenient determine technology based on the quenching of the fluorescence intensity of functionalized CdS quantum dots by sulfadiazine was proposed. Luminescent CdS semiconductor quantum dots (QDs) modified by thioglycollic acid (TGA) were synthesized with the microwave method. The modified CdS QDs are water-soluble, stable and highly luminescent. The possible mechanism for the reaction was also discussed. When sulfadiazine was added into the CdS QDs colloid solution, the surface of CdS QDs generates the electrostatic interaction in aqueous medium, which induces the quenching of fluorescence emission at 489 nm. Under optimum condition, the fluorescence intensity versus sulfadiazine concentration gave a linear response according Stern–Volmer equation with an excellent 0.9981 correlation coefficient. The linearity range of the calibration curve was 1.2 × 10 −5 to 2.13 × 10 −3 mol L −1. The limit of detection (3 δ) is 8.0 μmol L −1. The relative standard deviation for five determinations of 0.13 × 10 −3 mol L −1 sulfadiazine is 1.4%. The concentrations of sulfadiazine injections were determined by the proposed method with a satisfactory result.

Functionalized CdS quantum dots-based luminescence probe for detection of heavy and transition metal ions in aqueous solution

Strong luminescence CdS quantum dots (QDs) have been prepared and modified with l-cysteine by a facile seeds-assistant technique in water. They are water-soluble and highly stable in aqueous solution. CdS QDs evaluated as a luminescence probe for heavy and transition metal (HTM) ions in aqueous solution was systematically studied. Five HTM ions such as silver(I) ion, copper(II) ion, mercury(II) ion, cobalt(II) ion, and nickel(II) ion significantly influence the photophysics of the emission from the functionalized CdS QDs. Experiment results showed that the fluorescence emission from CdS QDs was enhanced significantly by silver ion without any spectral shift, while several other bivalent HTM ions, such as Hg 2+, Cu 2+, Co 2+, and Ni 2+, exhibited effective optical quenching effect on QDs. Moreover, an obvious red-shift of emission band was observed in the quenching of CdS QDs for Hg 2+ and Cu 2+ ions. Under the optimal conditions, the response was linearly proportional to the concentration of Ag + ion ranging from 1.25 × 10 −7 to 5.0 × 10 −6 mol L −1 with a detection limit of 2.0 × 10 −8 mol L −1. The concentration dependence of the quenching effect on functionalized QDs for the other four HTM ions could be well described by typical Stern–Volmer equation, with the linear response of CdS QDs emission proportional to the concentration ranging from 1.50 × 10 −8 to 7.50 × 10 −7 mol L −1 for Hg 2+ ion, 3.0 × 10 −7 to 1.0 × 10 −5 mol L −1 for Ni 2+ ion, 4.59 × 10 −8 to 2.295 × 10 −6 mol L −1 for Cu 2+ ion, and 1.20 × 10 −7 to 6.0 × 10 −6 mol L −1 Co 2+ ion, respectively. Based on the distinct optical properties of CdS QDs system with the five HTM ions, and the relatively wide linear range and rapid response to HTM ions, CdS QDs can be developed as a potential identified luminescence probe for familiar HTM ions detection in aqueous solution.

Determination of Silver Ion with Cadmium Sulfide Quantum Dots Modified by Bismuthiol II as Fluorescence Probe

CdS quantum dots (QDs) modified with bismuthiol II potassium salt is prepared in one step. Based on the characteristic fluorescence enhancement of CdS QDs at 480 nm by silver ions, simultaneously, a red shift of fluorescence emission bands of CdS QDs from 460 to 480 nm is observed. A simple, rapid, sensitive and specific detection method for silver ion is proposed. Under optimum conditions, the fluorescence intensity of CdS QDs was linearly proportional to silver ion concentration from 0.01 to 5.0 micromol L(-1) with a detection limit of 1.6 nmol L(-1). In comparison with single organic fluorophores, functionalized CdS quantum dots are brighter, more stable against photobleaching and do not suffer from blinking. Furthermore, the proposed method shows higher sensitivity and selectivity. A possible fluorescence enhancement mechanism is also studied.

Functionalized cadmium sulfide quantum dots as fluorescence probe for silver ion determination

CdS quantum dots (QDs) modified with l-cysteine has been prepared by one step. They are water-soluble and biocompatible. To improve CdS QDs stability and interaction between silver ion and functionalized CdS QDs in aqueous solution, some amounts of fresh l-cysteine were added to functionalized CdS solution. Based on the characteristic fluorescence enhancement of CdS QDs at 545 nm by silver ions in the presence of some amounts of fresh l-cysteine, simultaneously, a gradual red shift of fluorescence emission bands of CdS QDs from 545 to 558 nm was observed. A simple, rapid, sensitive and specific detection method for silver ion was proposed. Under optimum conditions, the fluorescence intensity of CdS QDs is linearly proportional to silver concentration from 2.0 × 10 −8 to 1.0 × 10 −6 mol/L with a detection limit of 5.0 × 10 −9 mol/L. In comparison with single organic fluorophores, functionalized CdS quantum dots are brighter, more stable against photobleaching, and don’t suffer from blinking. Furthermore, owing to the fluorescence enhancement effect of CdS QDs by silver ion, the proposed method showed lower detection blank and higher sensitivity. Possible fluorescence enhancement mechanism was also studied.