High-resolution surface plasmon resonance biosensing

Abstract

Surface plasmon resonance (SPR) sensors are optic ally-interfaced devices that detect the refractive index of a thin layer of analyte in contact with the sensor surface. For biosensing applications such as food toxin or biological warfare agent detection, high-resolution detection of the target species provides an improvement in the detection limit of the SPR sensor.We present the design, modeling, and implementation of an improved SPR biosensor based on long-range surface plasma wave (LRSPW) spectroscopy. An LRSPW consists of two surface plasma waves coupled across a thin metal layer. The LRSPW has lower attenuation than a single surface plasma wave, producing a narrower absorption minimum in the sensor spectral response. This narrower minimum results in improved resolution due to reduced uncertainty in the position of the minimum.Theoretical design curves presented for an LRSPW sensor using a Teflon AF buffer layer and gold metal layer show that the sensor can have sensitivity as high as 1 x 105 nm RIU-1, an order of magnitude or more improvement over conventional SPR sensors. Results of a biosensing experiment conducted with the LRSPW sensor showed a resonance width of only 15 nm (full-width at half-minimum), a sensitivity of 3.1 x 104 nm RIU-1, and a corresponding resolution of 1.9 x 10-7 RIU. Compared with a similar experiment conducted using a conventional SPR sensor, the LRSPW sensor had 25 times better resolution.To further improve the resolution of SPR sensor systems, we also present methods for evaluating the performance of data-processing algorithms for analyzing SPR spectra, including a method for predicting the instrument resolution based on measured system and detector noise. A new interpolated tracking centroid data-processing algorithm is presented, and its performance in terms of resolution, linearity, and resistance to environmental drift is shown to be superior to that of a simple centroid algorithm.