Synthesis and characterizations of polycrystalline walnut-like CdS nanoparticle by solvothermal method with PVP as stabilizer

https://doi.org/10.1016/j.matchemphys.2008.03.020Get rights and content

Abstract

A wide range of cadmium sulfide (CdS) 3D polycrystalline walnut-like nanocrystals were prepared by solvothermal method with polyvinylpyrrolidone (PVP) as stabilizer. The morphology, structure, and phase composition of the as-prepared CdS nanoparticles were examined by using various techniques (X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED)). The optical properties of CdS were characterized by photoluminescence (PL) spectra. The paper showed that when the proper dosage of PVP (0.12 g 50 mL−1) and the temperature of reaction (120 °C) were taken, continuous polycrystalline nanoparticles with regular morphology were obtained. The mechanism for the PVP-assisted synthesis of CdS 3D nanostructures and the growth process of CdS nanoparticles via Ostwald Ripening process under different temperatures with different dosages of PVP were also investigated. A sensitive electrochemical detection device of DNA hybridization using a paste glass carbon electrode (GCE) assembled by the PVP-capped CdS nanoparticles and immobilizing DNA probe was developed as a novel application of nano-semiconductors such as CdS to achieve a notable amplification in sensor response.

Introduction

In recent years quantum-confined semiconductor nanoparticles such as CdS and CdSe which are important groups II–VI semiconductors have attracted considerable attention due to their unique size-dependent chemical properties connecting with their potential applications in light-emitting diodes, optoelectronic devices and even a fluorescence probe in the determination of certain biomacromolecules, such as bovine serum albumin (BSA) [1], [2], [3], [4], [5], [6]. As an important application of semiconductor nanoparticles, the amplification of a novel biosensor for DNA hybridization signals is of central importance for the diagnosis and treatment of genetic diseases, the detection of infectious agents, and reliable forensic analysis [7].

Because of the potential properties of CdS nanoparticles, many synthetic methods have been employed to prepare CdS nanoparticles including soft chemical reaction, solid-state reaction, sol–gel process, spray-pyrolysis methods, sono-chemical preparation. Controlling the size and shape of nanocrystalline material is a key issue in the exploitation of novel properties. Great efforts have focused on the design of effective methods to synthesize 1D nanostructure such as nanowires [8], nanobelts [9] and nanotubes [10] due to the unique properties of these structures. Qian's group has synthesis shape-controlled 3D and 1D structures of CdS in a binary solution with l-cysteine's assistance [6]. However, the realization of the controllable and selective preparation of 3D nanostructures still remains difficult.

In order to improve the uniformity and capability of photonic catalysis, some polymer-assisted synthesis such as PVA [11], PAN [12], PVP [13], PAA [14] have been investigated. Previous researches have indicated that PVP is a good choice as stabilizers on anisotropic growth of Ag, Au and CdS nanowires [15], because it can interact with the metal ions by complex or ion-pair formation.

A variety of techniques have also been developed for the detection of DNA hybridization, such as electrochemical [16], fluorescent [17], radiochemical [18], piezoelectronic [19], [20], surface plasmon resonance spectroscopy and quartz crystal microbalance [21], [22], [23]. Such techniques rely on conversion of the DNA base-pair recognition event into a useful detection signal. Among them, electrochemical technique is very attractive owing to its rapid and direct detection of DNA hybridization, high sensitivity, inherent simplicity and miniaturization and low cost. The large surface area-to-volume ratio, along with the ability to tune the band gap, by choice of particle size, which means that nanodispersed semiconductors (such as CdS) having been used as sensitizers and catalysts in photochemical reaction are universally accepted [24]. In this paper, we use PVP as stabilizer in order to prevent the agglomeration of CdS nanoparticles and improve the quality of CdS nanoparticles through systematic research, then the as-prepared CdS could adsorb onto the surface of the bare glassy carbon electrode (GCE) and immobilize mercapto groups modified target ssDNA to produce DNA–CdS nanoconjugates. Moreover, because of the transference of negative charges, space resistance and semiconductor characteristics of CdS nanoparticles, the use of CdS nanoparticles obviously amplify DNA hybridization detection signals.

Section snippets

Reagents and apparatus

Cadmium chloride (CdCl2·2.5H2O, AR), sodium thiosulfate pentahydrate (Na2S2O3·5H2O, AR), poly(N-vinyl-2-pyrrolidone) (PVP, K30), absolute ethanol were purchased from SCRC used without further purification unless indicated. The various oligonucleotides were purchased from Sangon Bioengineering Ltd. Company (Shanghai, China) having the following sequences:

  • Probe DNA: 5′-AGTGCGCCAGGAGCCT-3′.

  • Complementary target DNA: 5′-SH-AGGCTCCTGGCGCACT-3′.

All the oligonucleotides stock solutions were prepared

X-ray diffraction analysis

Fig. 2(a) shows the XRD pattern of the samples 1, 2, 3 and 4 at different dosages of PVP with the same initial reactant concentrations (concentrations of Cd2+ and S2− were 0.1 and 0.1 mol L−1, respectively). All the reflection peaks of different samples can be indexed to hexagonal CdS with lattice constants of α = 4.141 Å and c = 6.718 Å, which are in great agreement with the literature data (JCPDS card no. 41-1049). The mean crystalline size can be calculated using Scherrer's equation: D = /β cos θ.

Conclusions

In summary, uniform and high quality novel walnut-like CdS structure has been synthesized successfully on a large scale by a solvothermal process using PVP as stabilizer. X-ray diffraction patterns show that the obtained CdS nanoparticles are of hexagonal polycrystalline phase. We conclude that the concentration of PVP, the reaction time and the system temperature are deemed as critical parameters in tailoring the shape and size of CdS nanostructures, the morphology, quality of CdS nanocrystals

Acknowledgements

The financial support of this work by the National Natural Science Foundation of China (project nos. 60574095, 60574094), National High Technology Research and Development Program of China (project no. 2006AA03Z309), and National Key Basic Science Research Program Project (973 project 2007CB936603) are gratefully acknowledged.

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