Plasmon resonance microsensor for droplet analysis

Microscale fiber tip sensors based on the plasmon resonance are reported. The fabrication process derived from our previous approach for manufacturing near-field scanning optical microscopy probes has been optimized for sensing applications. A typical tip sensor is a tapered fiber 400 microm in length, coated with a nanoporous thin silver film. The miniaturized geometry of the sensor allows detection in a single droplet of liquid solution (approximately 20 microl). The tip sensor is sensitive for refractive indices between 1.33 and 1.40 with a sensitivity of at least 3 x 10(-4) refractive index unit (RIU)/nm. The Raman scattering enhancement through these microsensors demonstrates the important role played by the localized plasmon resonance. The sensors' linear response covers a large region, interesting for biosensing in aqueous environments such as biomedical applications.