Application of differential phase measurement technique to surface plasmon resonance sensors

An optical differential phase surface plasmon resonance (SPR) technique capable of performing detection and visualization of refractive index in the order of 10−5 is presented. The system makes use of the s-polarization as the reference beam to interfere with the p-polarization, of which the phase has close relationship with the change of surface plasmon resonance conditions at the sensor surface. The extraction of phase information is achieved by performing fringe analysis on the interference pattern captured by an image digitizer. This technique is shown here to be sensitive enough to image salt–water mixture with a level of 0.1 wt.%. Given that we have now demonstrated the possibility of SPR phase extraction from digitized images, direct application of this technique in two-dimensional biosensor arrays with high measurement throughput is also suggested.