Application of a high-resolution SPR technique for monitoring real-time metal/dielectric interactions

We present a high-sensitivity (1 μs,) high-resolution (10−5 to 10−8 refractive index units (RIU)) method for monitoring the real-time molecular interactions at a metal/dielectric interface. Surface plasmon resonance (SPR) spectroscopy is a surface analysis technique for detecting and characterizing molecule/metal interactions. The technique is based on attenuated total reflection (ATR) and uses changes in the refractive index at a dielectric/metal interface to monitor molecular adsorption. We studied the adsorption rates of three concentrations of the synthesized organic molecule dinaphtho[2,1-c:1′,2′-e][1,2]dithiin self-assembled on an Au(1 1 1) surface. This molecule is of interest because its chiral structure and response to optical stimulation when chemically anchored to a metal surface make it a desirable candidate for studying its photoswitching properties. Our results were in agreement with theoretical predictions on the process of chemical molecular adsorption on metal surfaces that predicted a two-stage adsorption process, with the first stage being relatively short (on the order of minutes) and dependent on solution concentration. SPR spectroscopy is a relatively simple method of analysis and it involves portable equipment compared to alternative surface analysis techniques such as angle scan methods. In future experiments, we will use the technique described in this paper to exploit the optical response properties of the synthesized molecule used in this work.