Disclosed is a horizontal SPR sensor apparatus that provides a simplified beam path, ease of sample handling with concomitant ease of analysis. The horizontal SPR device disclosed herein includes an input and output transfer mirror pair that translates vertically along an axis perpendicular to the beam path. The invention includes an input/output scanner mirror pair that is operatively linked to the transfer mirror pair. This allows for rotation of the scanner mirror pair in response to the vertical translation of the transfer mirror pair and maintains the incident light focus on the metal film/sample layer while varying the angle of incidence and thereby exciting the surface plasmon resonance at the thin metal film layer. Further, this allows the detector and detector optics to be fixed providing for the implementation of heavier multi-stage cooled detectors. Finally, the invention provides an SPR device having a smaller footprint than known alternatives.