Patterned and switchable surfaces for biomaterial applications

Chapter 5 – Surface plasmon resonance imaging of polymer microarrays5.4.2. Standardising SPR signal on a polymer microarrayPLL was arrayed onto bare SPR gold chips from a concentration series rangingfrom 0-2 mg/ml. A surface plot of the resultant SPR signal intensity obtained of thearray formed from such a concentration series is shown as Figure 5.4. Formation ofpolymer arrays of PAA, PEI, PLL and polyvinylpyrrolidone (PVP) has previouslybeen characterised (see section 4.3.3). No method was devised for crosslinking PVPto the surface, which limits the ‘shelf life’ of this polymer array, thus, PVP, used forpolymer arrays in CHAPTER 4, was excluded from SPRi measurements.For the polymer array formed in Figure 5.4, the polymer spots range in thicknessfrom 0-54 nm as determined by profilometry (Figure 4.5). At a given angle, thisresults in differences in the attenuation of a light beam impinging upon the surface ascompared with the uncoated regions, which allows each spot to be spatially resolvedby SPR imaging. The reflectivity is enhanced at the PLL spots formed from thehigher concentrations due to the displacement of the resonance angle to higher anglesas a result of the local increase in the refractive index. For thicker spots formed fromhigher polymer concentrations the shift in resonance angle is greater resulting in alarger increase in reflectivity.A fixed angle SPR adsorption experiment is conducted at an angle at which thegreatest absolute value of the differential of SPR reflectivity occurs for the surfacebeing studied (Figure 1.1C) [248]. This is obtained from the reflectivity against angleof incidence curve for the surface. However, for a polymer array of varied thicknessor refractive index, for instance taking an array of PLL of thickness ranging from 0 –200 nm, described theoretically in Figure 5.5A by 4-phase Fresnel equations usingWinspall software [248, 279] (Fresnel reflectivity calculations were based on a four-5-174