Surface Plasmon Resonance : Sensitivity and Resolution

Sammanfattning: Surface plasmon resonance (SPR) is a frequently used technique for detection of biomolecular interactions at surfaces. The SPR phenomenon emanates from an electromagnetic surface wave that is exited by a light source. At excitation, the incident light is absorbed, either at a certain angle of incidence of the light, or at a certain wavelength, depending on the configuration of the SPR apparatus.There is always a need for higher sensitivity, i.e. lower detection limits. This work shows how different parameters, like the SPR-metal, the prism, the wavelength, the detector, and the SPR-dip finding algorithm influence the sensitivity.Many biochemical and biological interactions are complex, e.g. different interaction sites have different kinetic properties, or reaction complexes may show conformational changes. A measurement of a complex biochemical reaction often leads to a small signal superimposed on a large background. To be able to resolve the small signal, linearity errors of the instrument should be small. An SPR instrument utilizing an array detector will introduce linearity errors that may lead to misinterpretation of kinetic data. The linearity errors are quantified, both theoretically and experimentally, and possible misinterpretations are shown.The response from an SPR apparatus is calculated from the relative change in position of the SPR dip using a dip finding algorithm. There are several different dip finding algorithms, which all have different properties. A dip finding algorithm should suppress noise, drifts, linearity errors, and enhance the resolution. The resolution is the smallest increment of the response that can be observed. It is limited by the resolution of the analogue to digital converter (ADC), and is highly dependent on the dip finding algorithm used and the number of pixels in the detector. Simulations show the relationships between the resolution of the response and the resolution of the ADC, the number of pixels in a detector, and the shape of an SPR-dip. By using a 1024-pixel detector anda 16-bit ADC, it is found that an instrumental resolution of 10-9 refractive index units should be possible to obtain.There is a need for high throughput analysis of biochemical interactions, e.g. screening of medical substances. Therefore a multi wavelength imaging SPR apparatus is described that allows simultaneous analysis of many interactions with a high sensitivity.