Patterned and switchable surfaces for biomaterial applications

Chapter 5 – Surface plasmon resonance imaging of polymer microarraysReflectivity versus angle of incidence curves were measured before and afteraddition of ethanol (Figure 5.11C) allowing the determination of the total shift in theresonance angle. Furthermore, determining the slope of this curve for every angle ofincidence gives the relationship between a change in reflectivity and a change inresonance angle. This enabled the conversion of the change in reflectivity, measuredduring a fixed angle measurement, to the corresponding shift in resonance angle, asdepicted in Figure 5.8. For simplicity, where the relationship between resonanceangle and reflectivity was found to be linear the ratio of the total shift in resonanceangle to the total change in reflectivity was used to convert each change inreflectivity measurement from a fixed angle experiment to a shift in resonance angle.However, when the relationship was not linear each change in reflectivitymeasurement was converted independently using the method outlined in Figure 5.8.The resultant kinetic curves showing changes in resonance angle are shown in Figure5.11B, and here all four spots measure equivalent responses with an average value of-0.147°. As determined by SPR measurements, the phosphate buffer solution usedhas a η = 1.3355. A 1% ethanol solution has a refractive index of 1.3336, thus, thechange in refractive index was 0.0019. This should correspond to a resonance angleshift of -0.141°. This value is very close to the experimentally determined value of -0.147°, well within the limits of the experimental error.5-184