Label-free metal ion imaging using surface plasmon resonance microscopy

Label-free metal ion imaging based on surface plasmon resonance (SPR) has been developed by utilizing ion selective membrane formed on SPR substrate. Since the membrane contains ionophores that bind only to specific metal ions, SPR imaging enables real-time observation of local refractive index changes due to the capture of the metal ions by the ionophores. The angle of incidence to the substrate was fixed close to the SPR angle, and the refractive index change of the membrane depending on the ion concentration in the aqueous solution was imaged under a microscope as a change in the intensity of reflected light. Specifically, when a potassium ion solution was dropped onto the ion selective membrane in pure water, the diffusion and propagation of potassium ions were successfully observed at a video rate.