Near Infrared Plasmonic Devices
Collaborators: Prof. Gilbert Walker, University of Toronto
                        Dr Joanne Yeh, University of Pittsburgh
                        Dr. Jianjun Wei, CFD Research Corporation, Huntsville Al
This work is supported by funds from a NASA and the NIH
Group Members:  Matthew Kofke, Himadri Mandel
Plasmonics is broadly defined as the field concerned with the understanding and application of surface plasmon based phenomena.  Surface plasmons are the collective oscillations of the free electron gas of a metal (typically Au or Ag) at the interface between the metal and a dielectric environment (such as air) in response to incident light typically at optical frequencies (visible – infrared).  These oscillations can be confined to a metallic nanoparticle or freely propagating along a metal film. These phenomena offer the possibility to use nanoscale structures to manipulate photons on the nanoscale (nanophotonics) to create optical devices with wholly novel characteristics.  The plasmonics program in the Waldeck group focuses on the design and characterization of novel plasmonic devices as well as the implementation of these devices in biological sensing and surface plasmon enhanced spectroscopies.
Nanoparticle based subwavelength transmission:
Figure 1:  The diagram in panel a) shows a 150nm gold film on quartz with nanoparticle chains nested within a subwavelength nanoslit.   Single nanoslits are defined by a width w and fixed spacing P that represents the period of the array.  The nanoparticle chains within the slit are defined by a length along the y-axis L and width along the x-axis d.  The separation between individual nanoparticles within the chain is defined as s.  b) SEM image of a FIB milled nanoparticle/nanoslit array.  For the nanoslit: w = 240nm and P = 517nm, and for the nanoparticles: L = 290nm, d = 160nm, s = 210nm.
One project has focused on understanding the phenomenon known as extraordinary optical transmission, originally discovered by Ebbesen and coworkers[1], which is the transmission of light through subwavelength nanoapertures with efficiency larger than predicted by classical diffraction theory.  By nesting a two-dimensional array of nanoparticles within subwavelength nanoslits [2] (Figure 1) we are able to control both the wavelength of maximum transmission as well as the bandwidth of the resonance in the near-IR region of the electromagnetic spectrum. Through our work, we have shown that nanoparticle based localized surface plasmon resonance (LSPR) plays a significant role and sometimes the dominant role in the subwavelength transmission process.  
Integrated micro/nanofluidic plasmonic biosensor:
The biosensing project is focused on creating a nanofluidic plasmonic device which can easily be integrated into a microfluidic system.  The nanoparticle/nanoslits device shown in figure 1 is particularly promising because it is well known that LSPR based biosensing[3] is a sensitive technique and the nanoslits geometry provides easy integration with a microfluidic system.  By combining nanofluidic LSPR biosensing with microfluidics we expect the device to have significant advantage over other plasmon based biosensing platforms.
1.    T. W. Ebbesen, H. J. Lezec, H. F. Ghaemi, T. Thio, and P. A. Wolff, "Extraordinary optical transmission through sub-wavelength hole arrays," Nature 391, 667-669 (1998).
2.    M. J. Kofke, G. C. Walker, and D. H. Waldeck, “ Composite nanoparticle nanoslit arrays: a novel platform for LSPR mediated subwavelength optical transmission Optics Express, 18   (2010) 7705-7713.  doi:10.1364/OE.18.007705
3.    J. N. Anker, W. P. Hall, O. Lyandres, N. C. Shah, J. Zhao, and R. P. Van Duyne, "Biosensing with plasmonic nanosensors," Nat Mater 7, 442-453 (2008).
Figure 2:  Nanoparticle/Nanoslit array integrated into a microfluidic system.  The fluid containing the analyte will enter the nanochannels containing the nanoparticles.   Binding events will be observed through shifts in the wavelength of maximum transmission as the analytes bind to the nanoparticles.