Surface plasmon resonance (SPR) sensor using 2ω harmonic lock-in detection

Abstract

Surface plasmon resonance (SPR) sensor has been studied for high sensitivity optical biosensor as a single molecule detection, virus detection, DNA sequencing etc. SPR sensor requires an ultra-small signal detection system that measures very small intensity variation of reflected light along with the change of a refractive index near the sensor surface. In this reason, lock-in detection method which is able to detect small signal buried in noise has been applied to SPR sensor. In general lock-in detection method using multiplier and low pass filter measures DC value of output, and its sensitivity is determined by 1/f noise at DC. Unlike the DC measurement we have proposed 2ω harmonic lock-in detection method using multiplier and band pass filter. Sensitivity of the proposed lock-in detection method is much lower than 1/f noise at DC. In this paper we will show that 2ω harmonic lock-in detection method for SPR sensor system providing the sensitivity enhanced.