Underlying subwavelength pinhole affects the optical properties of microcavity surface plasmon resonance biosensors

Our previous work showed that submicron dielectric cores covered in gold proved to be a very sensitive surface plasmon biosensors capable of real-time monitoring of selected biomolecular interactions. The microcavity surface plasmon resonance sensors (MSPRS) were used to analyze conformational changes of bound biomolecules as the oxidation state changes. However, the biosensor gold shell generates a subwavelength nanoaperture at the point of contact between the dielectric core and the glass substrate. The surrounding structure is believed to excite stationary plasmon resonances at the biosensor’s surface evidentiated through spectral minima and maxima in the visible range. In this work we present data showing that the size of the underlying pinhole drastically affects the optical properties of the biosensor and therefore its sensitivity. Visible range optical spectroscopy is used to study the wavelength shift and spectral light intensity as the refractive index is changing at the outer shell surface. Scanning Electron Microscopy (SEM) and Focused Ion Beam (FIB) were used to study the characteristics of the underlying subwavelength aperture and microfluidics was used as a flexible platform for housing fabricated biosensors.