An improved surface plasmon resonance (SPR) sensor is provided based on direct measurement of the Goos-Hänchen effect. Sensor sensitivity is enhanced by selecting the thickness of the metallic layer of the SPR sensor to be close to a critical thickness dcr where the effect of the surface plasmon resonance on the Goos-Hänchen shift is most pronounced. Overall sensor sensitivity is surprisingly found to improve with this approach, even though the measurement is based on a second order effect (i.e., the Goos-Hänchen shift) instead of the first order reflectance change measured in conventional SPR sensor approaches. The invention is also applicable to sensors based on measurements of other non-specular reflection parameters, such as temporal shifts, frequency shifts, and/or angular shifts.