Optical Trap-Mediated High-Sensitivity Nanohole Array Biosensors with Random Nanospikes.

We clarify an unconventional principle of the light-driven operation of a biosensor for enhanced sensitivity with the help of random nanospikes added to the surface of a nanohole array. Such a system is capable of optically guiding viruses and trapping them in the vicinity of a highly sensitive site by an anomalous light-induced force arising from random-nanospike-modulated extraordinary optical transmission and the plasmonic mirror image in a virus as a dielectric submicron object. In particular, after guiding the viruses near the apex of nanospikes, there are conditions where the spectral peak shift of extraordinary optical transmission can be greatly increased and reach several hundred nanometers in comparison with that of a conventional nanohole array without random nanospikes.

Multiple Resonances Induced by Plasmonic Coupling between Gold Nanoparticle Trimers and Hexagonal Assembly of Gold-Coated Polystyrene Microspheres.

Optical properties of a gold nanoparticle trimer assembly coupled with gold-coated hexagonally close-packed polystyrene microspheres were investigated by linear and nonlinear spectroscopy. The observed reflection spectrum shows multiple peaks from the visible to near-infrared spectral regions. The spectroscopic properties were also examined by a finite-difference time-domain simulation.