| Abstract
| - Surface plasmon resonance (SPR) has been widely usedin a Kretschmann configuration to study optical thicknesschanges of layers on a Au surface in response to ananalyte. The method has been popularized and optimizedfor protein layers, but has also been used in the sameformat for other layers without further optimization including those absorbing at the incident wavelength. In thispaper, we examine whether SPR remains the “best”attenuated reflectivity format for absorbing overlayers.Experimental data from the SPR response of a copperphthalocyanine film to nitrogen dioxide are used as aninput example for a design process using an evolutionaryalgorithm. The data showed a trend toward thinner goldlayer systems (∼25 nm gave an contrast−enhancementof 42.9% compared with ∼50-nm Au) or Au-free solutionsincluding a layer with low refractive index. From theevolutionary design predictions, further modification couldbe tested based on available materials and “redundantlayers” could be eliminated from the final selection. Byinclusion of the external optics, a design could be selectedto accommodate poor precision (±0.5°) in the incidentangle and a possible multilayer solution was shown usingTeflon AF 1600, with refractive index ∼1.3. The predictedNO2 response showed an improvement compared with theclassical SPR configuration, and the incident angle chosenby the SGA for the interrogation of these layers was closeto a stationary point in the absolute response curve, thusoffering very good tolerance to automatic position referencing to the reflectivity minimum.
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