K+ ion measurement via surface plasmon resonance (SPR) using both visible and near infrared light source

K⁺ ion sensors using the surface plasmon resonance (SPR) phenomenon were fabricated. The wavelengths of incident light sources at 670 nm, 830 nm, and 1310 nm were used in these experiments to detect variations of resonance angles in the environment of air and water. Furthermore, the K⁺ concentrations in the range from 10^-8 to 1 M were measured by applying the K⁺ sensing membrane on a thin metal film via the spin coat technique; additionally, wavelength dependent results of SPR measurements were obtained.