Enabling Ultrasensitive Optical Measurements with Plasmonics

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Metallic nanostructures have enabled critical advances in a variety of applications ranging from photonic devices that perform a logical function, medical research to better target tumors for further localized photothermal treatment, solar cells technology to high sensitivity optical sensors. An electromagnetic field such as a laser light confined in the vicinity of a single silver or gold nanoparticle or an ensemble of interacting particles, displays resonances that are dependent on the opto-geometric properties of the nanostructure. Under the right experimental conditions, the excitation of such local resonance can yield enhancement of the electromagnetic field by several orders of magnitude which can be exploited for ultrahigh sensitivity optical spectroscopy. Its application in materials science and biomaterial is tremendous offering improved spatial resolution and sensitivity at a level down to the detection of a single molecule. This research program aims at providing solutions to enable ultrahigh sensitivity measurements in optical spectroscopy and is articulated along four principal objectives:****(i) High spatial resolution vibrational spectroscopy of biomaterials using tip-enhanced Raman spectroscopy will be conducted. We will focus on DNA strands and develop a strategy to better evaluate lesions in DNA strands. Our setup offers a resolution in the 10 nm range allowing one to probe and manipulate a sequence of a few bases that compose the DNA. (ii) Plasmon mediated detection of biomolecular exchanges between neuronal cells will be developed using surface-enhanced effects. We will combine surface patterning to direct cell growth over plasmonic sensor enabling to probe chemical and biochemical exchanges occurring in the vicinity of the cell membrane. Fluorescence and Raman enhancements will be used to probe chemical exchanges. (iii) We will develop strategies to design and optimize mid-infrared plasmonics platforms. To yield a large enhancement over a wide spectral domain in the mid-IR we will develop fractal plasmonic structures. Because of the small size (typically 100x100 micron square) of the plasmonic platform, the use of a bright infrared source such as the one accessible at the Canadian Light Source will be of great value for the study of these platforms. (iv) Finally, nonlinear optical effects generated in plasmonic structures will be conducted. Non-centrosymmetric geometries should lead to large optical nonlinearities will be probed by second-harmonic generation microscopy. Ultimately the chirality of the plasmonic structure will also be a parameter that will be valued for chiral sensing using nonlinear effects opening a variety of applications in optical biosensing.This program aims at providing cutting-edge approaches in nanoscale imaging to probe the intimate nature of chemical and biochemical processes involved in the most basic cellular processes. **