Imaging surface plasmon resonance (SPR) photonic sensors

Abstract

Imaging surface plasmon resonance (SPR) sensors have been studied in this project. SPR imaging sensors provide measurements on a two-dimensional scale, which means that parallel detection of many different analytes may be achieved using the arrays of sensing spots in the sensor surface. While such sensors are compatible with micro-array chips, they are an effective tool for high-throughput biomolecular interaction scanning. Two types of 2D SPR imaging sensors based on spectral and phase interrogations are demonstrated. Spectral interrogation of SPR sensing is first demonstrated with the application for gas pressure detection. This is a new type of optical pressure sensor that offers the benefits of wide dynamic range and no moving part. Experimental results show a resolution of 4.4 x 10-5 RIU, which corresponds to a pressure resolution of 16 kPa. A data processing algorithm has also been developed for determining the SPR resonance minimum (SPRdip) in the spectral curve. Spectral SPR sensing is further expanded into a one-dimensional (1D) detection technique by scanning a spectrometer probe across the spectral SPR image. We have used this technique for studying elastohydrodynamic lubrication (EHL) dimples commonly encountered in tribology. The refractive index and pressure distributions in highly pressurized EHL contacts are measured. A resolution of 8.6 x 10-4 RIU is reported. This value is 198 times better than that reported by the conventional technique. The SPR technique also ensures direct determination of refractive index distribution irrespective of the absolute film thickness h. This is not possible with conventional technique. The one-dimensional detection is further developed into a two-dimensional (2D) spectral SPR imaging. Since the variation in SPR spectral characteristics relates to the refractive index change, a calibration curve is constructed to convert image color (Hue) into refractive index. The spectral SPR image of a PB2400 lubricant dimple is successfully converted into a 2D refractive index distribution. A resolution of 9.4 x 10-4 RIU is demonstrated. Because of the 2D measurement capability of the spectral SPR imaging technique, high-throughput micro-array applications, such as those involving bio-screening will be readily possible. In the study of phase-sensitive SPR imaging sensor arrays, phase interrogation of SPR is first demonstrated in a Mach-Zender interferometer. With differential phase measurement, a resolution of 6.2 x 10-5 RIU is demonstrated. A novel design of multi-pass SPR sensor is further introduced to enhance the sensor sensitivity. In an optical cavity, the incident beam is permitted to impinge on the sensing surface at least twice, the total phase shift caused by the presence of the target analyte is enhanced. Detection resolution improvement of over two times is demonstrated. This reveals that the multi-pass approach is an effective way to enhance the phase response of existing phase-sensitive SPR sensors. In our experiments, we have developed a phase extraction algorithm for analyzing from interferograms. This is an essential achievement towards phase imaging sensor. Biosensor arrays based on SPR phase imaging is demonstrated. By using the differential phase detection approach, each pixel in the phase image can serve as an individual sensing element. Therefore, a SPR phase map can be constructed. The sensor resolution is found to be 9.8 x 10-5 RIU, which is compatible with the sensor resolution reported by conventional phase imaging sensors based on fringe shift analysis. Array detection of the bioaffinity interactions between anti-H3 antibody and target virus has been successfully demonstrated. The imaging SPR sensor schemes presented in this dissertation are compatible with micro-array chip for providing high sensitivity and high-throughput biological detection, which may find promising applications in biotechnology, medical diagnostics, drug screening, food safety and environmental protection etc.

Date of Award	2 Oct 2007
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Ho Pui Aaron HO (Supervisor) & Kwok Sum CHAN (Supervisor)