Measurement System For Surface Plasmon Resonance Based On Virtual Instrumentation

Surface plasmon resonance (SPR) is an optical phenomenon taking place on the interface of metal-dielectric medium. Because of sensitive response to the refractive indices of dielectric in contact with the metal surface, SPR sensors are used for monitoring the variation of physical quantities corresponding to the change of refractive indices. SPR technology is widely utilized in the field of biochemistry, immunology and pharmacy etc.By using the software development platform of LabVIEW, as well as improving on the optical paths of the SPR sensor in Kretschmann configuration, a measurement system for SPR based on virtual instrumentation is designed.Firstly, in order to lower the artificial error margin, increase accuracy and operability, strengthen the ability of data processing and analyzing, and make it convenient to extend the system's functions, virtual instrumentation is utilized in this measurement system, as well as rotating stage with high-precision stepping motor, and Butterworth low-pass filter in the software for eliminating the high-frequency disturbances caused by interference noise from the output ray.Furthermore, a double-prism adaptive optical design is proposed, which regulates the optical path so that the photodetector can be immovable in the process of angular scanning. Complicated structure of 8/20 rotating stage with which a prism and a photodetector rotates at θ and 2θ respectively in conventional angular scanning SPR sensor is avoided; Thus new design reduces movable components, makes structure simple, and compact.Finally, a function of auto-calibration of initial position is developed based on the self-mixing interference, by designing a functional module in the software platform without additional hardware, which implements low-cost calibration with precision up to 0.005°.In the experiment, refractive indices of air, distilled water and alcohol are measured by this system respectively, and the result is in agreement with theoretical values approximately, and has good repetition and high resolution.