Sensitive metal layer-assisted guided-mode resonance SU8 nanopillar array for label-free optical biosensing

A novel polymer nanopillar lattice architecture for label-free optical biosensing based on the metal layer assisted guided-mode resonance (MaGMR) effect is presented. The device consists of a 2D array of SU8 nanopillars fabricated by e-beam lithography (EBL) on an optically-thick aluminum layer. EBL proximity effect, that is, the influence of the electron irradiation in the regions adjacent to those exposed by the e-beam - which is usually considered an undesirable fabrication issue - is positively used to create a non-uniform thickness, crosslinked SU8 film among the SU8 nanopillars on the aluminum layer. The optical response of the resulting SU8 nanostructure array exhibits a MaGMR under normally incident light interrogation. Spectral reflectance monitoring of the MaGMR upon the adsorption of water, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) and bovine serum albumin (BSA) molecules is employed to evaluate the surface sensing characteristics of the resonant nanostructure. The figure of merit of the device, defined as the quotient of the surface sensitivity and the resonance spectral width, is increased by two orders of magnitude (0.127 nm−1 versus 0.009 nm−1) as compared with previous SU8 nanopillar array surface sensing architectures because of the high sensitivity and narrow spectral width of the MaGMR feature.