Paper-Based Plasmonic Surface for Chemical Biosensing by the Attenuated Total Reflection Method
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Paper-Based Plasmonic Surface for Chemical Biosensing by the Attenuated Total Reflection Method Nobuko Fukuda, Srimongkon Tithimanan, Hirobumi Ushijima, and Noritaka Yamamoto Flexible Electronics Research Center (FLEC), National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba 305-8565, Japan
ABSTRACT We demonstrate the detection of an increase in refractive index and/or thickness by specific adsorption of proteins on a plasmonic surface on a paper substrate in the Otto configuration. Propagating surface plasmon resonance is observed on a gold surface deposited onto polymer-coated papers through angular scans of reflectivity in the Otto configuration under attenuated total reflection conditions. According to a surface analysis with atomic force microscope, the gold surface roughness on a polyvinyl chloride (PVC)-coated paper is comparable to that of a Si wafer, leading to the achievement of protein detection. On the other hand, the propagating length of the surface plasmons is shorter than that on the Si wafer. According to an observation of the gold surface with scanning electron microscope, the gold grain size on the PVC-coated paper is smaller than that on the Si wafer. Thus, many boundaries cause a reduction in the propagating length on the PVC-coated paper. INTRODUCTION Attenuated total reflection conditions using a prism provide simple optical configurations for propagating surface plasmon resonance (SPR). The Kretschmann configuration is employed in typical chemical and biochemical plasmonic sensors. In the Kretschmann configuration, a surface plasmon polariton is excited at the interface between metal with a finite thickness and a dielectric with an infinite thickness [1]. Thus, a thickness-controlled thin metal layer is deposited onto glass and plastic plates as substrates. In addition, the transparency of the wavelengths of incident light is required for the glass and plastic substrates. This is because the p-polarized incident light enters from the backside of the transparent substrates into the metal thin layer without depolarization. On the other hand, the Otto configuration also provides a plasmonic field on a metal surface [2]. In this case, a surface plasmon polariton is excited at the interface between a dielectric with a finite thickness and metal with an infinite thickness. If a distancecontrolled dielectric gap can be formed between the prism and the metal surface, the surface plasmon polariton can be excited at the metal surface on opaque substrates [2–4]. Paper is a candidate for a substrate to be used in chemical and biochemical sensing in the Otto configuration. The advantages of paper are that it is cheap, lightweight, easy to handle, and combustible. According to typical guidelines in Japan, when biological and toxic samples are used as analytes, conventional glass and plastic substrates must be sterilized before disposal. Paper substrate can be easily incinerated without requiring autoclave treatment for sterilization, which saves on disposal costs. I
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