Plasmonic nanostructures for optical biosensing

Year: 2011

Assoc. Prof. Jiří Homola, Ph.D., DSc.

Label-free biosensors represent a disruptive technology that enables the direct observation of biomolecular interactions in real-time and rapid and sensitive detection of chemical and biological species with potential applications in areas such as medical diagnostics, environmental monitoring and food safety. Optical biosensors based on surface plasmons represent the most advanced and mature label-free photonic biosensor technology. Researchers at the Institute of Photonic and Electronics, AS CR, v. v. i. have investigated various types of plasmonic nanostructures to further improve performance and expand utility of plasmonic biosensors. In collaboration with researchers at the University of Washington, Seattle (USA), they researched special quasi-3D nanostructures consisting of thin metal films with nanoholes separated from a layer of metal nanodiscs that face nanoholes by a thin dielectric layer [1, 2]. It was demonstrated that Fabry-Pérot resonances in these structures allow for achieving strong localization of the electromagnetic field which makes the structures attractive for surface-enhanced Raman spectroscopy (SERS) [2]. Sensing properties of plasmonic nanoparticle arrays have been investigated in collaboration with the Karl-Franzens University Graz (Austria). We have investigated the local sensitivity of gold nanorods to changes in the refractive index both theoretically and experimentally and demonstrated that the spatial distribution of sensitivity matches the profile of electric field intensity [3]. We have developed a new biosensor based on an array of gold nanorods [4]. The sensor was shown to be able to detect DNA molecules at levels down to 100 pM and the lowest detectable surface coverage corresponding to less than one DNA molecule per nanoparticle [4].

Extinction spectra of plasmonic nanostructure consisting of an array of gold nanorods for two different refractive indices of the surrounding medium. The inset shows an SEM image of an array.

1. Xu, J. – Guan, P. – Kvasnička, P. – Gong, H. – Homola, H. – Yu, Q.: Light transmission and surface-enhanced Raman scattering of quasi-3D plasmonic nanostructure arrays with deep and shallow Fabry-Pérot nanocavities, Journal of Physical Chemistry C, Vol. 115, (2011), 10996–11002.
2. Xu, J. – Kvasnička, P. – Idso, M. – Jordan, R. W. – Gong, H. – Homola, J. – Yu, Q.: Understanding the effects of dielectric medium, substrate, and depth on electric fields and SERS of quasi-3D plasmonic nanostructures, Optics Express Vol. 19, (2011), 20493-20505.
3. Piliarik, M. – Kvasnička, P. – Galler, N. – Krenn, J. R. – Homola, J.: Local refractive index sensitivity of plasmonic nanoparticles, Optics Express Vol. 19, (2011), 9213–9220.
4. Piliarik, M. – Šípová, H. – Kvasnička, P. – Galler, N. – Krenn, J. R. – Homola J.: High-resolution biosensor based on localized surface plasmons, Optics Express, Vol. 20, (2012), 672–680.