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Surface plasmon resonance: instrumental resolution using photo diode arrays

2000; IOP Publishing; Volume: 11; Issue: 11 Linguagem: Inglês

10.1088/0957-0233/11/11/313

1361-6501

Knut Johansen, Ralph Stålberg, Ingemar Lundström, Bo Liedberg,

Optical Coatings and Gratings

Surface plasmon resonance (SPR) sensors are used to study biomolecular interactions. We have performed a theoretical analysis of a SPR instrument using a convergent beam, a linear detector with various numbers of pixels and various analogue-to-digital converters (ADCs) with a corresponding resolution ranging from 8 to 16 bits. Studies of small molecules at low concentrations or with low affinities are limited by the instrumental set-up, e.g. by the resolution, linearity and noise. The amplitudes of these parameters are highly dependent on the detector, ADC and dip-finding algorithm used. We have studied several dip-finding algorithms, e.g. intensity measurements, second- and third-order polynomial fits and centroid algorithms. Each algorithm used with the ADC and the detector has a resolution associated with it. Some algorithms also have an intrinsic algorithm error that is dependent on the number of pixels and the shape of the dip. A weighted centroid algorithm that has an excellent overall performance is described. If an accuracy of 10-6 refractive index units (RIU) is satisfactory, a 12-bit ADC and a 64-pixel detector are appropriate. Theoretically, by using a 16-bit ADC and a 1024-pixel detector, a resolution of better than 10-9 RIU is obtainable.