Surface Plasmon Resonance microscopy (SPRm) Impedance measures both SPR and EIS simultaneously and is capable of imaging local electrochemical impedance in real time with high spatial resolution. This technique relies on detecting surface plasmon waves propagating on a metal thin film which are created by a laser beam incident on the metal film, typically via a prism at a resonant angle. In the same way as for EIS, an AC voltage is applied to the surface to create a surface charge density modulation (delta q), which induces a SPR signal change (delta theta). The surface plasmon resonance condition is sensitive to the dielectric constant of the metal film, which is a function of the surface charge density. Compared to SPR, the impedance signal measured by SPRm Impedance is insensitive to nonspecific binding and solution bulk index changes and because the signal scales with the surface area, it is suitable for detecting small molecules. In conclusion, by measuring SPR in an electrolyte, interfacial impedance can be measured by applying a potential modulation to the sensor surface. By measuring the amplitude and phase of the resonance angle produced by the changes in the surface charge modulation, submicron spatial resolution impedance information can be obtained to study the cellular responses dynamics or to study electrochemical reactions of nanoparticles.
