Specific Features of the Excitation of Surface Plasmons at the Interface between Metal and Aqueous Solution of Extremely Low Concentration

Measurements of optical parameters of media by surface plasmon spectroscopy have a number of advantages: possibility of real-time monitoring, label-free operation, accuracy, and high sensitivity. In addition, surface plasmon spectroscopy is a universal method, used in sensor applications (e.g., biosensors and sensors for volatiles and solutes). This method is especially efficient for detecting trace amounts of materials in gas and liquid media. Its sensitivity is sufficient for measuring the refractive index of a medium with an error of 10–6. Using nanostructured surfaces, one can improve sensitivity to 10–9. In this study, we expanded the possibilities of plasmon spectroscopy (which made it possible to measure impurity concentrations as low as 10–13 mol/L) and described the mechanisms and dynamics of modification of metal–aqueous solution interface (electrical double layer (EDL)). The measurement results for phthalocyanine solutions with concentrations of 10–9 and 10–13 mol/L are reported.