Sensitive plasmonic biosensor using gold nanoparticles on a nano fiber tip

We propose a fiber-optic biosensor based on the generation of local surface plasmons (LSR) near a nano fiber tip. The nano-optical fiber biosensor was made by shaping the fiber to form a taper with a tip size less than 100nm. Gold nanoparticles with 12nm diameter were immobilized to the tapered fiber's tip by modifying tip surface with NH 2 groups. Most of light in the fiber tip is confined by the total internal reflection. It generates substantial evanescent wave near the tip and effectively excites LSR on the nanogolds. The evanescent wave excitation results in very low background light and high signal to noise ratio. Using this nanofiber sensor, we have achieved a sensitivity of reflective index unit, ~4800 (% RIU -1 ) in the intensity measurement. Furthermore, the LSR is excited only near the tip region. It takes advantage of ultra small detection area. Only micro-liter sample solution is needed for the detection.