Abstract
This paper describes theoretical and experimental study of the fundamentals of using surface plasmon resonance (SPR) for label-free detection of voltage. Plasmonic voltage sensing relies on the capacitive properties of metal-electrolyte interface that are governed by electrostatic interactions between charge carriers in both phases. Externally-applied voltage leads to changes in the free electron density in the surface of the metal, shifting the SPR position. The study shows the effects of the applied voltage on the shape of the SPR curve. It also provides a comparison between the theoretical and experimental response to the applied voltage. The response is presented in a universal term that can be used to assess the voltage sensitivity of different SPR instruments. Finally, it demonstrates the capacity of the SPR system in resolving dynamic voltage signals; a detection limit of 10mV with a temporal resolution of 5ms is achievable. These findings pave the way for the use of SPR systems in the detection of electrical activity of biological cells.
Highlights
Surface plasmons (SPs) are light-excitable surface waves that are described as longitudinal oscillations of free electrons at the metal-dielectric interface
Voltage effects on the surface plasmon resonance (SPR) curve To investigate the sensitivity of SPR systems in the detection of voltage perturbations, we start with characterising the effect of the externally applied voltage on the SPR curve
We present the fundamentals of using SPR systems for voltage sensing applied to biological research questions
Summary
Surface plasmons (SPs) are light-excitable surface waves that are described as longitudinal oscillations of free electrons at the metal-dielectric interface They oscillate with a spatial frequency greater than that of light in air. An oil immersion high numerical aperture objective lens [3] is used In both cases, surface plasmon resonance is achieved at specific angle of incidence. The excitation of SPs results in a drop of the intensity of the reflected light [2] and a sharp phase transition [4, 5] at the resonance angle [6] or wavelength [7] This resonance is sensitive to the properties of the dielectric layer adjacent to the metal as well as the metal surface. This feature has been widely used to develop chemical and bio-sensors [8,9,10]
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