Development of a micro fluorescence detector for m-TAS based on surface plasmon field enhancement

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The aim of this study is development of a high-performance fluorescence detection method based on surface plasmon enhanced excitation for integration into a micro total analysis system (μ-TAS). We employed a PMMA nanocone array (diameter, 250nm ; height, 750 nm ; pitch, 250 nm ; macroscopic dimension, 5×5mm^2) prepared by nanoimprinting as a substrate. The surface was treated with tannic acid and silver nitrate successively. After immobilization of Texas-Red on the surface, fluorescence enhancement property of the nanocone array was estimated by comparison between the fluorescence intensity of the same areas in the presence and absence of nanocone array upon far-field illumination using a fluorescence microscope. The silver-coated nanocone array showed the fluorescence intensity approximately 50 times larger than that of the flat surface. This result suggests that far-field illumination of the silver-coated nanocone array induces local plasmons and the strongly enhanced electromagnetic field effectively excites the fluorophores immobilized on the surface. Then we have demonstrated a practical application of this excitation method. Anti-IgG was immobilized on a silver coated nanocone arrays and the two sections of the surface were covered with PDMS microfluid channels, respectively. Fluorescence labeled IgG solution and BSA solution were independently introduced into the two channels and then, after careful washing, fluorescence microscopic imaging was carried out. The clear difference in the fluorescence intensity between the two channels demonstrates that the silver-coated nanocone is useful for fluorescence bioassays as a plasmon-enhanced substrate.