The microminiature SPR fiber probe creates an SPR sensing surface on the end of a multimode optical fiber. White light travels down the fiber and strikes the active surface, where certain wavelengths are attenuated by SPR. A mirror deposited on the fiber end then reflects the light back down the fiber. The reflected light is directed to a spectrophotometer, and the measured spectra are analyzed to determine the refractive index near the active surface of the fiber. The small size and simple construction of the SPR fiber probe make it unique among SPR sensors.