Capped Cadmium Sulfide Quantum Dots Research Articles

Speciation of arsenic (III) and arsenic (V) based on quenching of CdS quantum dots fluorescence using hybrid sequential injection–stopped flow injection gas–diffusion system

A hybrid sequential injection–stopped flow injection system was developed for the speciation of arsenic based on the quenching of mercaptoacetic acid capped cadmium sulfide quantum dots (CdS–MAA QDs) fluorescence intensity. The analytical procedure involves the generation of arsine from As(III) by sodium borohydride in acetate buffer medium pH 6.0. The generated arsine (donor stream) diffuses across the PTFE membrane of the gas–diffusion unit into an acceptor stream and then interacts with CdS–MAA QDs. Total arsenic was determined after pre-reduction of As(V) to As(III) with 1% (m/v) mercaptoacetic acid. Concentration of As(V) in the sample solutions can be deduced from the difference of total arsenic and As(III). Optimization of the experimental conditions and instrumental parameters were investigated. Under optimal conditions, limits of detection were 20μgL−1 for As(III) and 40μgL−1 for As(V). Recoveries in the range 84–103% were obtained from sediment sample.

Electrophoretically deposited CdS quantum dots based electrode for biosensor application

A platform comprising of electrophoretically prepared thioglycolic acid (TGA) capped cadmium sulfide (CdS) quantum dots (QDs) deposited onto an indium tin oxide (ITO) coated glass plate has been utilized for covalent immobilization of cholesterol oxidase for application to a cholesterol sensor. The presence of TGA capped CdS in the nano regime has been confirmed through a UV-visible study. The electrophoretically deposited Nano-CdS/ITO electrode characterized using transmission electron microscopy (TEM), X-ray diffraction, scanning electron microscopy (SEM) and Fourier transform infra-red (FT-IR) techniques indicates the presence of a hexagonal nanocrystalline homogeneous structure on the ITO surface. The results of electrochemical response studies conducted using this CdS QDs based cholesterol sensor reveal a low detection limit (1.87 mg dl−1) and high sensitivity (2.87 μA/mg dl−1/cm2), a low value of Michaelis–Menten constant (Km) (0.22 mM) reveals high enzyme affinity. This novel quantum dot based cholesterol biosensing electrode has implications for the development of other important biosensor applications.

Determination of arsenic based on quenching of CdS quantum dots fluorescence using the gas-diffusion flow injection method

A sequential injection analysis system for determination of arsenic based on hydride generation and fluorescence quenching of mercaptoacetic acid capped cadmium sulfide quantum dots (CdS–MAA QDs) is described. The generated arsine diffused across the PTFE membrane in a gas-diffusion unit and subsequently interacted with CdS–MAA QDs. The parameters affecting the arsine generation and the fluorescence quenching of QDs were studied. Under the optimum conditions, it was observed that a increase in the concentration of As(III) corresponded well to a decrease in fluorescence intensity according to the Stern–Volmer relationship. The extent of quenching was dependent on the concentration of arsenic in the range of 0.08–3.20 mmol L −1, with the detection limit of 0.07 mg L −1. The precision (%RSD) from eight replicates of the determination of As(III) 1.0 mg L −1 was found to be 1.4%. The proposed method was applied to the determination of arsenic in ground water samples with satisfactory recoveries.

External Electric Field Effects on Optical Property and Excitation Dynamics of Capped CdS Quantum Dots Embedded in a Polymer Film

Nanocomposites of benzyl mercaptan (BM)-capped cadmium sulfide (CdS) quantum dots (QDs) have been prepared and investigated by using electric field modulation spectroscopy. Applied electric fields on absorption and photoluminescence (PL) spectra as well as PL decays of BM-capped CdS QDs embedded in a poly(methyl methacrylate) (PMMA) film have revealed a field-induced alteration. Electro-photoluminescence (E-PL) exhibits field-induced quenching of photoluminescence in the presence of electric fields. The observed E-PL spectra and field-induced change in decay profile suggest that the PL intensity alternation originates from the electric field effect on emitting state population rather than PL quantum yield, probably as a result of the presence of field-assisted dissociation into hole and electron at the photoexcited state having a charge-separated character. Field-induced change in absorption spectra showed the spectral broadening caused by the stark shifts, indicating a large electric dipole moment in the...

Optical characterization of CdS semiconductor nanoparticles capped with starch

Starch capped cadmium sulfide (CdS) nanoparticles were synthesized by aqueous solution precipitation. Starch added during the synthesis of nanoparticles resulted in cadmium-rich nanoparticles forming a stable complex with starch. The size of the CdS quantum dots was measured using high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The average diameter (d) of nanoparticles spanned the range 4.8±0.4 to 5.7±0.2nm when the pH of the solution was varied within the range 10–14. The main Raman phonon of CdS, the longitudinal optical mode located around 300cm−1, softens as diameter decreases, in accordance with theoretical predictions. In addition, the largest Raman response of starch, near 478cm−1, related with the important skeletal vibration modes of the starch pyranose ring, dominates the spectra of the CdS capped nanoparticles and also softens as the size decreases. This fact indicates a strain variation on CdS as a function of d which increases as the pH increases.

Langmuir–Blodgett manipulation of capped cadmium sulfide quantum dots

Cadmium sulfide quantum dots, as prepared by the single source approach, have been used as the starting materials for Langmuir–Blodgett deposition on several types of substrates. Conventional procedures, such as isotherms and Brewster angle measurements, were used to investigate the manipulation of organically capped Q-CdS. The optical properties of the films obtained were studied and compared to solutions containing the original dots.