Novel Sensing Concepts Based on Localized Field Enhancement around Nanostructures

Optical field enhancement by localized surface plasmon resonance(LSPR) occurs typically on a nano-structured metallic surface. Upon binding of biomolecules on the surface the resonance frequency shifts due to the change of the refractive index, which can be practically applied to an adsorption detector. In this project we develop a new sensing technique (not limited to "bio"-sensing) based on nano-structuring and numerical field calculation. Currently we are also working on the combinaiton of electrochemical sensing.

Detection of Single Binding Events

We were able to detect single binding events of nanoparticle-labeled DNA strands as stepwise peak shifts by single particle measurement. We confirmed the number of binding events by observing label particles by scanning electron microscopy. Our simulation based on a multiple multipole program (MMP) showed that the peak shift is dependent on interparticle gap size and binding position. The experimental peak shift distribution was also reproduced by simulation.

Densely Packed and Optically Coupled Gold Particle Array

We investigated densely packed gold particle array for biosensing applications. In such arrays, gold particles are optical coupled creating a strong field between the particles. This is useful for high sensitivity biosensing. The optical and sensor properties are studied with the aid of MMP simulation. The sensitivity limit to detect streptavidin within 3000 s is estimated to be less than 150 pm.

Symmetry Decomposed MMP Calculation

We simulated plasmonic nano particles on a glass substrate with various coating layers by MMP. The rotationally symmetric geometry of these structures is broken by the obliquely incident plane wave illumination. It was shown that numerically much more efficient axi-symmetric models can still be applied for the computation of the resonance peak positions when the illumination is decomposed in its symmetry-adapted terms. The validity of this procedure was demonstrated for 100 nm gold particles with silicon oxide coating layers of different thicknesses by comparing the scattering spectra of symmetry decomposed models, full 3D models, and experiments.

References

In situ sensing of single binding events by localized surface plasmon resonance
T. Sannomiya, Ch. Hafner, J. Vörös
Nano Letters, 8(10): 3450-3455, 2008.

Biosensing by Densely Packed and Optically Coupled Plasmonic Particle Arrays
T. Sannomiya, P. K. Sahoo, D. I. Mahcicek, H. H. Solak, Ch. Hafner, D. Grieshaber, J. Vörös
Small, 2009 DOI: 10.1002/smll.200900284

Symmetry Decomposed MMP Calculation of Plasmonic Particles on Substrate for Biosensing Applications
T. Sannomiya, J. Vörös, Ch. Hafner
J. Comput. Theor. Nanosci., 6, 749–756, 2009.

Partner

• Prof. Christian Hafner, Computational Optics Group, IFH, ETH Zürich
• Dr. Harun Solak, Laboratory for Micro and Nanotechnology, Paul Scherrer Institute (PSI) Villigen, Switzerland
• Dr. Pratap Sahoo, Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
• Prof. Juergen Brugger & Oscar Vazquez, Microsystems Laboratory LMIS1, EPFL, Lausanne, Switzerland
  

Contact

• Takumi Sannomiya
• Janos Vörös