Nanopatterned substrates increase surface sensitivity for real-time biosensing

In this paper, we report critical design rules for improving the sensitivity of plasmonic biosensors. We use a scalable, parallel method to fabricate Au plasmonic crystal substrates patterned with an array of pits for real-time sensing. Capture ligands printed selectively in these pits resulted in a strong response to the binding of macromolecules. Angle-resolved sensorgrams showed quantitative differences between wavelength shifts produced by protein analyte bound within regions supporting localized and long-range electromagnetic fields. Contributions from the localized fields dominated the sensing response, especially at high angles. The angle-dependent far-field and near-field optical properties of selectively functionalized plasmonic crystals suggest that optimal performance is achieved at excitation parameters that produce an intense resonance with narrow spectral bandwidth and highly localized electromagnetic fields.