Plasmonic biosensor based on vertical arrays of gold nanoantennas.

Implementing large arrays of gold nanowires as functional elements of a plasmonic biosensor is an important task for future medical diagnostic applications. Here we present a microfluidic-channel-integrated sensor for the label-free detec-tion of biomolecules, relaying on localized surface plasmon resonances. Large arrays (~ 1 cm2) of vertically aligned and densely packed gold nanorods to receive, locally confine and amplify the external optical signal, are used to allow for reli-able biosensing. We accomplish this by monitoring the change of the optical nanostructure resonance upon the presence of biomolecules within the tight focus area above the nanoantennas, combined with a surface treatment of the nanowires for a specific binding of the target molecules. As a first application, we detect the binding kinetics of two distinct DNA strands as well as the following hybridization of two complementary strands (cDNA) with different lengths (25 and 100 bp). Upon immobilization, a redshift of 1 nm was detected; further backfilling and hybridization led to a peak shift of additional 2 nm and 5 nm for 25 and 100 bp, respectively. We believe that this work gives deeper insight into the func-tional understanding and technical implementation of a large array of gold nanowires for future medical applications.