J. Phys. Chem. C 2009, 113, 9121–9127
9121
Biomineralization of BSA-Chalcogenide Bioconjugate Nano- and Microcrystals Mandeep Singh Bakshi,*,† Vivek Sheel Jaswal, Gurinder Kaur,§ Todd W. Simpson,| Parampaul Kaur Banipal,# Tarlok Singh Banipal,∇ Fred Possmayer,⊥ and Nils O. Petersen‡ Department of Chemistry, Acadia UniVersity, 6 UniVersity AVe., Elliot Hall, WolfVille, NoVa Scotia, B4P 2R6; National Institute for Nanotechnology, Edmonton, Alberta, Canada; Nanotechnology Research Laboratory, College of North Atlantic, Labrador City, Newfoundland and Labrador, A2 V 2K7; Nanofabrication Laboratory, Physics and Astronomy Building, Department of Biochemistry, UniVersity of Western Ontario, London, Ontario N6A 3K7 Canada; and Departments of Chemistry and Applied Chemistry, Guru Nanak DeV UniVersity, Amritsar 143005, Punjab, India ReceiVed: January 11, 2009; ReVised Manuscript ReceiVed: April 12, 2009
Lead selenide (PbSe), cadmium selenide (CdSe), and selenium (Se) nano- and microcrystals were synthesized by using respective metal acetate salts along with sodium selenite as the Se source in the presence of bovine serum albumen (BSA) as the capping/stabilizing agent. Aqueous phase hydrazine reduction at 85 °C produced fine crystalline morphologies within 48 h. Both PbSe and CdSe reactions produced Se microrods (MRs) as reaction byproduct. The concentrations of metal acetate and sodium selenite used were always 1:1 (i.e., 1.25 mM in each case) and that of hydrazine was fixed at 0.78 M. The amount of BSA was changed systematically from 1-10 × 10-4 g/mL to determine its influence on the crystal growth of these chalcogenides. Their morphologies and chemical compositions were determined with FESEM, TEM, and EDX analysis. A selective and precise EDX analysis of a single particle helped us to elucidate its shape and chemical composition. Such analyses lead to the finding that both reactions produced Se rods, their sizes varied from the nano to micro scale with an increase of the amount of BSA. PbSe polyhedral nanocrystals were obtained at a low BSA amount, which ultimately attained the shape of thick MRs. However, no rod formation was observed for CdSe particles, which were always present in the form of groups of small nanoparticles along with Se MRs. Protein estimation indicated the presence of adsorbed BSA on the surface of chalcogenide particles. A potential reaction mechanism was proposed to explain the Se MRs formation as byproduct. Finally, the results were discussed on the basis of selective adsorption of denatured BSA on specific crystal planes of the rock salt (PbSe) geometry in order to produce rod like morphologies. Introduction Semiconductor nanocrystals (NCs) have demonstrated several remarkable and attractive characteristic features especially suited to analytical applications in the biochemical field. Bioconjugated NCs1 have become the focus of intensive research due to their applications in drug delivery, biological labeling, luminescence tagging, etc. Semiconductor chalcogenides have been widely used as optical filters, optical recording materials, thermoelectric cooling materials, sensors, solar cells, superionic materials, and laser materials.2 Lead selenide (PbSe) is an attractive semiconducting material that has been employed to produce photoresistors, photodetectors, photovoltaic absorbers, photographic plates, and so forth. PbSe has been the subject of particular attention because of its narrow band gap (in bulk) of 0.28 eV (at room temperature) and strong quantum confinement effects due to its large Bohr radius (∼rB ≈ 46 nm).3 Many recent reports4 have focused on the synthesis of various shapes, and physics of PbSe NCs. CdSe, another chalcogenide, has a much lower rB in comparison to PbSe. It is equally important material * To whom correspondence should be addressed. E-mail: ms_bakshi@ yahoo.com. † Department of Chemistry, Acadia University. ‡ National Institute for Nanotechnology. § Nanotechnology Research Laboratory, College of North Atlantic. | Nanofabrication Laboratory. # Department of Chemistry, Guru Nanak Dev University. ∇ Department of Applied Chemistry, Guru Nanak Dev University. ⊥ Department of Biochemistry, University of Western Ontario.
for use in opto-electronic devices, laser diodes, nanosensing, biomedical imaging, and high-efficiency solar cells.5 Considering the rapid miniaturization of technology in all fields, we have synthesized two important chalcogen-based materials, i.e., PbSe and CdSe at the nanoscale using aqueous solution phase synthesis at relatively mild temperature of 85 °C with particular emphasis on their biocompatible applications. For appropriate biocompatible applications of bioconjugated chalcogenides,6 carefully designed synthetic routes involving biological molecules such as amino acids, proteins, and biopolymers are required. Colloidal synthesis of nanochalcogenides is an exciting branch of synthetic inorganic chemistry in which surface active compounds provide charge and steric stabilizations for the growing nucleating centers in order to attain desired morphologies. Many groups7 have followed this route to obtain fine morphologies at relatively elevated temperatures. However, in order to synthesize biomaterials involving biomolecules, it is desirable to have relatively low temperature (
