Patterned and switchable surfaces for biomaterial applications

Andrew Hook – Patterned and switchable surfaces for biomaterial applicationsThe resulting surface plasmons are evanescent waves that have an intensitymaximum at the metal/dielectric interface that decays exponentially into thedielectric to a penetration depth of about 200 nm. Thus, changes in the dielectricproperties within 200 nm of the dielectric material in contact with the metal coatingwill alter the excitation of the surface plasmons, the change of which can be detectedby changes in the intensity of the reflected light [248]. In a typical experiment, lightis coupled into the prism at a fixed angle of incidence, whereupon, for a plot ofreflectivity against angle of incidence the absolute value of the differentialof reflectivity versus angle of incidence is maximised. This is typically at an angleslightly lower than the resonance angle. The intensity of the reflected light ismonitored. The reverse side of the metal coating is then primed with a suitable bufferbefore a molecule of interest is flowed over the metal surface (Figure 5.1A). Thedetection of an adsorption event, as injected molecules of interest replace buffermolecules associated with the surface, can be detected by a sudden increase in thereflected light intensity (Figure 5.1B) as a result of a shift in the resonance angle(Figure 5.1C) associated with a change in the refractive index of the dielectric. Thisincrease will reach a plateau as the surface is saturated with the molecule of interest,and will finally decrease with washing of buffer to remove loosely bound moleculeof interest. Thus, the difference in the initial and final intensity of the reflected lightis a result of the adsorption of the molecules of interest and, when a monochromaticlight source is used, can be related to the shift in the resonance angle required tofulfil K ev = K sp (Figure 5.1C) [247].SPRi, or SPR microscopy, is achieved by coupling SPR with imaging [252, 253].Typically, the reflected light from an SPR experiment is detected by a camera orviewed through a microscope, enabling spatial measurements of changes in the5-161