Response of surface-plasmon resonance sensor based on gold surfaces modified by self-assembled monolayer to nonionic surfactants

A chemical sensor for the determination of nonionic surfactants (NISs) based on surface-plasmon resonance (SPR) phenomenon was fabricated using a gold thin film, the surface of which was modified with a self-assembled monolayer (SAM). Stearylmercaptan was used for the SAM constituent. The magnitude of the angle shift of SPR sensor to NISs increases in this order: Triton X-100 < heptaethyleneglycol dodecyl ether (HEEG) < hexaethyleneglycol dodecyl ether (HEG) < pentaethyleneglycol dodecyl ether (PEG). This order of magnitude of angle shift is in accord with the sequence of the hydrophobicity of the NISs. The linear relationships between Δθ (the change in the resonance angle relative to the baseline value) and the concentration of NISs were obtained in the concentration range from 2 × 10 -6 M to 1 × 10 -5 M. The coexistence of common inorganic cations and anions at 100 times excess to the Triton X-100 gives only a positive error less than ca. +5%. The coexistence of an anionic surfactant (sodium dodecylbenzene sulfonate) at 10 times excess to the Triton X-100 gives a very serious positive error of ca. +320%. This serious positive error was completely eliminated by using the flow system with an anion-exchange resin column.