Effect of capillary properties on the sensitivity enhancement in capillary/fiber optical sensors.

The sensitivity enhancement observed in fluorescence signals when a conventional fiber optical sensor is coupled with a quartz or glass capillary results from the partial reflection of the radiation at the sample/internal wall interface and from the internal reflection of the refracted portion within the capillary wall. Thus, the length and absorbing properties of the capillary as well as the nature of the surrounding medium affect the enhancement significantly. To interpret the dramatic changes in enhancement observed experimentally when the absorbing properties of the capillary were changed, a partial reflective waveguide model is reported.