Current Research
Surface Plasmon Band Gap Sensing
I am working on the development of a new concept of surface plasmon sensor. It uses the properties of the propagation of surface plasmon waves through nanostructures to improve the sensing performance.
Surface plasmons (SP) are electromagnetic waves that propagate at optical frequencies on the surface of common metals such as gold or silver. Since all the energy of the wave is concentrated on the interface, the wave is very sensitive to any change of the optical properties on the surface. SPs are notably very sensitive to any type of molecular binding occurring on the surface, which is why they are used for biosensing purposes using a technique commonly known as surface plasmon resonance (SPR).
Figure 1: Schematic of a Device for Surface Plasmon Resonance (SPR) sensing.
In order to improve the performances of surface plasmon sensing in compact systems, I use periodic nanostructures that modify the propagation properties of the surface plasmon waves. Specifically, in a periodic nano-structure, the SP dispersion relation presents a band gap structure similar to a photon in a photonic crystal or an electron in a lattice: on the edge of the Brillouin zone, when the SP wavelength is equal to half the period of the nanostructures, the SP is Bragg-reflected and its propagation is blocked.
Figure 2: Surface Plasmon Dispersion Relation through periodic nanostructures .
This phenomenon is central in the new sensing concept: the system is prepared so that the excitation frequency lies on the edge of the band gap. The propagation of SP through the device is possible and the excitation light is completely absorbed. When molecular binding occurs on the surface, the SP wavelength is changed so that the system is now within the band gap: the SP propagation through the device is now blocked. This can be seen by monitoring the reflected intensity. The figure below is an illustration of the sensing concept:
Figure 3: Illustration of the concept of Surface Plasmon Band Gap Sensing.
I take advantage of the fact that the density of modes on the edge of the band gap is much higher than what it is outside of the band gap. This allows the fabrication of a SP sensor that is much more resistant to any loss of quality in the optical system. We hope that this new sensing concept, by lowering the requisites on the optical components of the sensor will permit the true integration of SP sensors within lab-on-chip types of systems.
Experimentally, I use holographic lithography to produce the nanostructures. I also developed a novel micro-stamping technique that allows the control of both the period and the height of the nanostructures.
Figure 4: AFM measurement of a typical surface obtained with holographic lithography.
The long-term goal of this project is to enable in-situ algae concentration measurements within a distributed sensor network developed with the Center for Embedded Networked Sensing (CENS).
3D dielectrophoretic trap for cells manipulation within micro-channels
Previously, I was working on the design of a micro trap for single cells. This work was a requisite for the implementation of a smart-Petri dish a device to control accurately the environment of cells.
The main goal of the project, conducted for the CMISE institute, is to integrate cells in MEMS for spatial applications.
I was using high frequency fields to apply dielectrophoretic forces on cells in a 3D configuration. The final device was be able to trap and manipulate single cells.
Figure 5: Finite Element Analysis (FEA) of the trap.
Figure 6: (a) Neuroblastoma trapped in the trap within a micro-channel (b) SEM picture of the trap illustrating its 3D nature.
Education
- Ph.D.,
UCLA,
- M.S.
UCLA,
- Diplome d'Ingenieur,
Ecole Polytechnique, Paris, France
Contact Info
Phone: 310-825-9540
E-Mail: arnaud@seas.ucla.edu