Modulation of MS2 virus adsorption on TiO 2 semiconductor film by nitrogen doping
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Nitrogen was doped into titanium dioxide film to alter its surface electrostatic properties, and subsequently modulate the interaction force between MS2 virus and semiconductor films for control of the adsorption behavior of MS2 on semiconductor surfaces. By combining atomic force microscopy (AFM) height profile and phase profile, adsorptions of MS2 virus on TiO2-based semiconductor surfaces were observed in solutions over a range of pH values. The adsorption behavior was shown to agree with the theoretical analysis of colloidal interactions.
I. INTRODUCTION
Fabrication of nanostructures by biomolecular assembly and interactions has been investigated recently1–13 as an alternative fabrication method to the lithographic patterning process for future generations of electronic and photonic devices. For example, viruses have been used as molecular building blocks to create numerous novel nanostructures.8–13 For these purposes, a good control of virus adsorption onto semiconductor surfaces is essential if these molecular building blocks are to be successfully integrated with semiconductors in creating the nanostructures. To compete with the current lithographic patterning process, smaller viruses with feature sizes well below 100 nm would be of most interest. However, although adsorption of large viruses (with feature sizes over 100 nm) on semiconductor surfaces has been directly observed using atomic force microscopy (AFM),12–16 and other biological techniques such as ELISA17 can detect smaller viruses in solution above certain critical concentration, direct observations of smaller viruses on semiconductor substrates with similar feature sizes present a serious challenge because of the identification difficulty. Here we developed a new strategy of using AFM for observing nano-sized biomolecules on substrates with similar feature sizes by combining information from both height profile and phase profile, and applied this strategy to demonstrate chemical doping of thin film as a method to engineer adsorption behavior of a very small virus, MS2, on semiconductor surfaces. Bacteriophage MS2 is a nonpathogenic virus widely used as a model system for a)
Address all corresopndence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0389 3036 J. Mater. Res., Vol. 22, No. 11, Nov 2007 http://journals.cambridge.org Downloaded: 20 Mar 2015
immunological studies, drug delivery, and gene delivery studies.18–21 It was chosen in this study as a model virus particle. It is a spherically shaped virus with a diameter at ∼27.5 nm, and its molecular structure is well characterized.22,23 The surface charge of MS2 virus originates from the ionization of amino acid residues located on the exterior of the virus particle, which is significantly influenced by the pH value of the surrounding medium.24 Its isoelectric point (IEP) is ∼pH 4.0, so that it is positively charged when the solution pH value is below ∼4.0, but negatively charged when the solution pH value is over ∼4.00. Recently, the attachment of a variety of amino acids w
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