Sub-wavelength periodic structures imprinted in metallic films give rise to enhanced transmission features which are sensitive to changes in refractive index at the surface. Variations in the transmission spectral output can be quantified to detect the concentration of analyte in a solution and the surface of the film can be readily modified with a variety of synthetic recognition elements, biomolecules, and well-established silane chemistry to allow for molecule recognition at the surface of the grating. These nanohole gratings can also be used to couple light into planar optical waveguides, which make ideal signal transducers because of their sturdiness, easy patterning of reagents, and easy incorporation of polymer materials.
In previous work, nanohole structures imprinted on aluminum thin films were characterized as refractive index sensors that can be incorporated as transduction elements into biosensing technologies as well as to provide a path to optimization of an integrated biosensing device. The ability of this potential transduction element to detect affinity reactions occurring at the surface was evaluated using well known biomolecular recognition experiments as well as synthetic recognition experiments using molecularly imprinted polymer films (MIPs). MIPs are biomimetic recognition elements that can be created for a variety of molecular structures, enable large-scale chip fabrication, are reusable, and offer superior stability when exposed to solvents and temperature extremes.
Currently, a novel coaxial nanopillar structure is being evaluated for biosensing appications. It has already demonstrated a theoretical figure of merit(FOM) of 45, which we believe could lead to single molecule sensitivty in a biosensor.
This is a picture taken through a 500nm pitch nanohole array imprinted on aluminum with the hole diameters = 150nm. Theoretically, the film should be opaque and not allow wavelengths larger than the hole diameter to penetrate, but coupling between incident light and surface plasmons promotes light penetration. Thus the film appears much more transparent and you can see Alyssa through the grating.
A. Bellingham, A Characterization of Nanohole Grating Refractive Index Sensors for Biosensing Applications Masters Diss. Politecnico di Milano, Milano, 2012.
Canalejas-Tejero, V., Herranz, S., Bellingham, A., Moreno-Bondi, M. C., & Barrios, C. A. (2013). Passivated Aluminum nanohole arrays for label-free biosensing applications. ACS applied Materials & interfaces.
Terranova B., Bellingham A., Herbert S., Fontecchio A. K., “Cylindrical channel plasmon resonance for single-molecule sensing.” SPIE Photonics West Conference(2014)