An SPR detection apparatus has an optical system with a sensor member including a planar metallic layer, the sensor member being removably mountable to a housing. First optics direct an incident beam toward a rear side of the metallic layer at a predetermined range of angles to a normal to the sensor layer. Second optics guide at least one reflected beam, corresponding to the incident beam, from the metallic layer to the transducer. The transducer converts incoming electromagnetic radiation to an electrical signal for transmission to a signal processor disposed in the housing and operatively connected to the at least one opto-electrical transducer so as to detect a surface plasmon resonance angle. The first optics are configured so that the at least one incident beam spans at least about 20°.
