Localized Surface Plasmon Resonance Biosensor Using Ag Nanostructured Films Fabricated by a Reduction Method
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0915-R02-08
Localized Surface Plasmon Resonance Biosensor Using Ag Nanostructured Films Fabricated by a Reduction Method Tomofumi Arai1, Penmetcha K. R. Kumar2, Koichi Awazu1, and Junji Tominaga1 1 Center for Applied Near Field Optics Research (CAN-FOR), National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, 305-8562, Japan 2 Functional Nucleic Acids Group, Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, 3058562, Japan
ABSTRACT In this paper, an optical biosensor based on the localized surface plasmon resonance (LSPR) of Ag nanostructured films is proposed and demonstrated. The Ag nanostructured films, which are fabricated by the reduction of AgOx thin films, exhibit a strong LSPR at wavelengths around 370 nm in an air environment. The reflectance spectra of the Ag nanostructured film represent that the shift in the LSPR wavelength follows a linear dependence on the refractive index of the surrounding medium. By varying the concentration of streptavidin solution, we demonstrate that the Ag nanostructured films functionalized with thiol and biotin molecules can sensitively detect a binding event between biotin and streptavidin molecules. INTRODUCTION The phenomenon of localized surface plasmon resonance (LSPR) has been attracting much attention for a highly sensitive and label-free biosensing method [1-19]. Characteristically, nanoparticles of noble metals such as Ag or Au exhibit a strong absorption and scattering of specific lights due to the collective oscillation of the conduction electrons, which is known as LSPR. The biosensing using LSPR is based on the shift of the resonance wavelength depending on the dielectric properties in the vicinity of nanoparticles [20], and the fabrication method of noble-metal nanoparticles is one of the key factors in the development of LSPR biosensors. Recently, we have developed a novel fabrication method of Ag nanostructured films by the reduction of reactively sputtered AgOx thin films [21]. This fabrication technique possesses several advantages over other methods as follows: (i) a uniformly Ag nanostructured surface is obtained on large area (> 100 cm2); (ii) no additional heating is required; and (iii) only several minutes are needed for the reduction of the AgOx films. It is expected that these advantages enable a reliable mass production of Ag nanostructured films and facilitate cost-effective LSPR biosensors. In this paper, we report the use of the Ag nanostructured films for a LSPR biosensor that monitors the binding event between a biotinylated surface and streptavidin molecules. EXPERIMENT AgOx thin films were deposited by reactive rf magnetron sputtering using a pure Ag target (99.99%) on polished Si wafers (10 ×10 mm2 in size) in a gas mixture of 40% argon and
60% oxygen under a total pressure of 0.5 Pa. The thickness of as-deposited AgOx thin films was 50 nm. The AgOx films were subsequently reduced through two different et
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