Abstract: A biological sensor 10 having a beam/light shaper 30 which is adapted to inject light into the sensor at substantially the critical angle with respect to the side surface of the sensor. The sensor 10, of the preferred embodiment of the invention, further may undergo a surface treatment which reduces/eliminates non-specific binding to the sensor surface and a treatment process to reduce light energy losses occurring by mounting and/or inserting the fiber portion of the sensor into the medium of interest. Both the light injection and surface treatment methodologies have utility apart from the biological immunoassay sensor embodiment described and claimed in this Application and may be independently applied to a biological sensor.