Cavity ring-down detection of surface plasmon resonance in an optical fiber resonator

An apparatus to detect binding events for use with a coherent source that emits radiation, the apparatus comprising:

• a passive, closed fiber optic ring;
• a sensor having a predetermined shape, a conductive coating, and being in line with the passive, closed fiber optic ring, the conductive coating capable of supporting a surface plasmon driven by a propagating field in the passive, closed fiber optic ring and responsive to a level of the binding events at a surface of the conductive coating;
• coupling means for i) optically coupling at least a portion of the radiation emitted by the coherent source into the passive, closed fiber optic ring to generate the propagating field in the passive, closed fiber optic ring and ii) transmitting a detection portion of the propagating field from the passive, closed fiber optic ring;
• a detector for detecting a power level of the detection portion of the propagating field transmitted by the coupling means and generating a signal responsive thereto;
• and
• a processor electrically coupled to the detector for determining the level of the binding events on the surface of the conductive coating of the sensor based on a rate of decay of the power level of the detection portion of the propagating field detected by the detector.

An improved method of detecting environmental changes in a fluid using a surface plasmon cavity ring-down detection (SPCRD) system that comprises a surface plasmon resonance (SPR) sensor optically coupled within an optical cavity, the SPR sensor formed of a metal-coated tapered optical fiber section, the method comprising:

• coupling coherent optical radiation into the optical cavity of the SPCRD system, the coherent optical radiation comprising a predetermined wavelength;
• monitoring a power level of the coherent optical radiation in the optical cavity;
• determining a baseline cavity loss of the optical cavity based on the monitored power level;
• exposing the SPR sensor to the fluid;
• determining a detection cavity loss of the optical cavity based on the monitored power level following exposure of the SPR sensor to the fluid;
• and
• detecting environmental changes in the fluid based on differences between the baseline cavity loss and the detection cavity loss of the optical cavity.