Line Shape Analysis and Extended Instrumental Operation of Surface Plasmon Resonance Sensors

Line shape effects of the surface plasmon resonance (SPR) at the gold-water interface have been exploited, towards extending instrumental performance in the angular interrogation mode. Comprising a micro-fluidic set-up both, SPR-line broadening and associated signal symmetry/asymmetry features have been monitored in real time for selected adsorption systems and are compared with the simultaneously taken resonance angle that represents the commonly recorded SPR feature. Four angular broadening contributions have been identified: an intrinsic, temperature independent fraction, a temperature dependent part that dominates at ambient temperature, a surface morphology/roughness contribution and an adsorption related fraction. The latter, and substantially smaller contribution, is crucially affected by surface conditions, as the transition from hydrophobic to a hydrophilic surface state. Anionic sub-monolayer adsorption has been clearly resolved, along with detection of a pronounced calorimetric effect that originates from an exothermic surface reaction upon exposure of the protein covered gold surface to a strong chemical oxidant.