Differential SPR immunosensing

In this work we describe a surface plasmon resonance (SPR) sensor with a differential detection of the SPR angle, and demonstrate it. The angle of incidence is modulated by a simple piezo-electric actuator, and the reflectance signal is measured with a lockin-amplifier. When the conditions for SPR are fulfilled, the differential signal is zero. The shift of the resonance conditions can be measured as an increase of the differential signal, or using feedback on the angle of incidence. The sensor will be demonstrated by monitoring an adsorption and an immunoreaction at the sensor surface with sub-mdeg. resolution. The modulated incident beam can also be scanned past a number of sensing areas, making multichannel measurements possible, as will be demonstrated.