Differential surface plasmon resonance imaging for high-throughput bioanalyses

A new imaging technique for high-throughput surface plasmon resonance (SPR) measurements is described. It is the application of a CCD camera for simultaneous processing of two images at two different wavelengths provided by two laser diodes. The two lasers are brought to resonance by tuning of the angle of incidence so that the detection power and the dynamic range are optimized for the wavelength pair selected. Applying a special differential processing of the two images, SPR measurements can be performed near the shot noise limit taking into account the number of CCD pixels involved. It is shown that the detection limit of imaging methods can be improved significantly if the working point is set near to the reflection minimum instead of choosing the angle with the steepest slope of the reflection curve. The technique is demonstrated by simultaneous measurement of hybridization reactions of three different types of thiolated oligonucleotides in 30 small areas set by a commercial spotter. A noise level of 1.5 x 10(-6) refractive index units (RIU) was obtained for single, 500 x 500 mu m(2) reaction areas. The noise level was about 6 x 10(-7) RIU when five areas were taken into account. The present arrangement and the particular spotter applied would allow simultaneous measurements of up to 400 binding reactions with a noise level of about 1.5 x 10(-6) RIU.