Biotemplated Synthesis of CdSe Nanowires

Introduction

Hybrid systems based on semiconductor quantum dots attached to biomolecules find increasing attention in the development of nanobiotechnology [1, 2, 3]. Many experimental approaches have been made to fabricate nanorods by template driven synthesis using chemical routes [1, 2]. However, the electrochemical approach to fabricate semiconductor nanorods using DNA as the template is promising because of its simplicity in depositing the material directly on a conducting substrate. Presence of negatively charged phosphate group in the DNA backbone gives the polyelectrolyte nature to it. Such a polyelectrolyte can interact with positively charged ions and make them ideal templates to grow nanoparticles [4, 5]. Thus, such nanoparticles tag with DNA can produce nanostructures, which are of interest to biosensor applications [6, 7]. The present work reports a novel and simple strategy to grow CdSe nanobiorods using (Oligo) single stranded DNA (ssDNA) and its complementary DNA as a template by an electro deposition technique. The surface, morphology and structural properties have been studied by using Atomic Force Microscopy (AFM) and X-ray Diffractometry (XRD) technique.

Synthesis

CdSe-DNA nanowire thin films were deposited onto Indium Tin Oxide (ITO) conducting glass substrates by a electro-technique cathodic deposition under galvanostatic condition from a solution containing CdSO4 (0.92 M), SeO2 (0.018 M), and ssDNA, Guanine (Poly-G- 60base pair) and oligonucleotides ssDNA, Cytosine (Poly-C- 60base pair) at room temperature [7]. Typically the electrolysis current density was 5mA/cm2 and the deposition time was kept as 2 minute to synthesize CdSe- DNA complex nanowires. Two samples were prepared for the investigation, namely, sample S1, CdSe nanocrystals analysis shows the XRD peaks at 2θ = 25 o, 42 o, and 49 o corresponds to the prominent planes (111) and (220) and (311), confirms the polycrystalline cubic phase in the deposit for both the samples. The peaks marked with a * corresponds to the X-Ray diffraction peaks of ITO substrate in both the sample. Note that for sample S1, the X-ray peak intensities are weak and broad compared to the CdSe-DNA complex suggesting the S1 crystallite sizes are small. Since the CdSe-DNA complex shows a wire like structure (discussed in the latter section), the observed XRD spectra shows intense X-ray peak intensities and narrow peak similar to bulk CdSe materials.

(NCs) without DNA and sample, S2, CdSe nanowire with DNA. The morphology and structural properties of samples were investigated by Atomic Force Microscopic (AFM), and X-ray diffraction XRD where X-ray diffractometer equipped with a monochromatic CuKα radiation source (1.54178Å ).

Results and Discussion

The XRD patterns of CdSe nanocrystalline (S1) and CdSe-DNA complex (S2) are shown in Figure1. Structural

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nanowire morphology as marked in dotted line in figure 2(b). The explanation for nanowire formation using ssDNA and its conjugate is that, initially the CdSe nanocrystals are tagged to ssDNA along its string then the interdiffucion of CdSe nanocrystals with its conjugate DNA make the whole system rigid to form a nanowire.

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Conclusion

Biotemplated synthesis of CdSe nanowire is possible using single strand oligonucleotides (ssDNA) and its conjugate. The CdSe-DNA nanowire have been grown by an electro-deposition technique. XRD results identify the presence of cubic phase in both CdSe nanocrystal and biotemplated CdSe-DNA nanowire. The AFM results identify the shape of the CdSe in nanoparticle form whereas the shape of biotemplated CdSe-DNA complex is in nanowire form.

Acknowledgement

The author is grateful to the late Professor S. N. Sahu then at Institute of Physics for his support on this work.