Surface Enhanced Spectroscopies.

Increasing surface sensitivity of IR, Fluorescence, Raman measurements

Discovered almost four decades ago, surface enhanced Raman spectroscopy (SERS) and subsequent techniques such as surface enhanced Fluorescence (SEF) and surface enhanced infrared spectroscopy (SEIRS) have developed into mature methods to give unprecedented levels of sensitivity. SERS in particular provides ultra-high sensitivity down to attomolar concentrations and even to a single molecule level. More importantly, the use of these surface enhanced techniques has enabled biosensing and biomolecular recognition with ultrahigh sensitivity, opening possibilities for a wealth of applications to probe intimate biological processes with minimal intrusion, better specifity and high reproducibility. The interactions between biomolecules and their changes in conformation in response to stimuli are processes that can be probed at the monolayer level with lower light irradiance and shorter acquisition time, thereby reducing experimental invasion and physiological stress. Keys to the success of surface-enhanced spectroscopies are advances in micro and nanofabrication techniques such as electron-beam lithography and focused ion beam milling that allow one to reproducibly fabricate plasmonic platforms with a 10 nm resolution. The opto-geometric parameters of these platforms can be finely tailored to tune the localized surface plasmon resonance to a selected probe wavelength. Nanosphere lithography is an inexpensive and high throughput technique ideally suited to produce large surfaces of 2D and 3D periodic nanostructures with a variety of shapes such as nanoscale triangles, pyramids, rings, overlaps, gaps, rod chains, and holes.

Theme 2: Surface enhanced spectroscopies. Our group is conceiving and fabricating a variety of platforms with surface-enhanced properties. From the classical, nanosphere lithography to more advanced electron beam lithography and nanoimprint lithography, we have have fabricated a variety of structures that can be exploited from the visible range to the mid-Infrared range with excellent tunability. Some of these strctures have several resonances and are compatible for multiplexed measurements using either Raman, fluorescence and infrared on the same platorms. These structures have been used to detected monolayers as well as single molecules with sensititivity down to femtomolar range for specific analytes. These surface active substrates are generally made or gold or silver and have been used more recently to promote plasmon mediated surface reactions utilizing the EM confinement in the vicinity of these structures.

Selected Relevant Manuscripts

"In search of the Hot-Spot" , D. M. McRae, F.Lagugné-Labarthet*, Nature Nanotechnology, 2019, 14,922-923.

"Probing mid-infrared plasmon resonances in extended radial fractal structures", G. Q. Wallace, D. M. McRae, and F. Lagugné-Labarthet* , Opt. Lett., 2019, 44, 3865-3868.

"Tunable 3D Plasmonic Cavity Nanosensors for Surface-Enhanced Raman Spectroscopy with Sub-femtomolar Limit of Detection" , M. Tabatabaei, M. Najiminaini, K.Davieau, B. Kaminska, M. R. Singh, J. J. L. Carson,* and F.Lagugné-Labarthet,* ACS Photonics, 2015, 2, 752-759.