K+-ion sensing using surface plasmon resonance by NIR light source

A surface plasmon resonance (SPR) sensor, which detects K+ ion using gold thin film, was constructed at different incident wavelengths, 670 and 830 nm. The properties of gold thin film and wavelength are very important factors in exciting surface plasmon resonance. We investigated the SPR phenomenon at different incident wavelengths when the surface plasmon resonated with evanescent waves. The resonance angle changed about 4.4degrees as the light source changed from 670 to 830 nm wavelengths in pure water. The sensor chip that is coated with a sensing membrane was tested at each wavelength. We found no resonance point at the 670 nm wavelength because the sensing film was too thick when the K+ ion concentration was varied from 10(-8) to 1 M. As the light source was changed to the 830 nm wavelength, we could detect the resonance point even though the film was thick. Therefore, we could detect surface plasmon resonance phenomena at the longer incident wavelength and the smaller resonance angle. We could detect the K+ ion concentration from 10-8 to 1 M by using a 830 nm laser diode and sensing membrane. (C) 2003 Elsevier B.V. All rights reserved.