Browsing by Author "Lal, Surbhi"

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    Nanoparticle-based all-optical sensors
    (2004-08-17) Halas, Nancy J.; Lal, Surbhi; Nordlander, Peter J.; Jackson, Joseph B.; Moran, Cristin Erin; Rice University; United States Patent and Trademark Office
    The present invention provides a sensor that includes an optical device as a support for a thin film formed by a matrix containing resonant nanoparticles. The nanoparticles may be optically coupled to the optical device by virtue of the geometry of placement of the thin film. Further, the nanoparticles are adapted to resonantly enhance the spectral signature of analytes located near the surfaces of the nanoparticles. Thus, via the nanoparticles, the optical device is addressable so as to detect a measurable property of a sample in contact with the sensor. The sensors include chemical sensors and thermal sensors. The optical devices include reflective devices and waveguide devices. Still further, the nanoparticles include solid metal particles and metal nanoshells. Yet further, the nanoparticles may be part of a nano-structure that further includes nanotubes.
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    Profiling the near field of nanoshells using surface enhanced Raman spectroscopy and fluorescence spectroscopy
    (2006) Lal, Surbhi; Halas, Naomi J.
    Plasmon resonances in metal nanoparticles control the far field and near field optical properties of these metallic structures. The enhanced electromagnetic near field is strongest at the surface of the nanoparticles and rapidly decays away from the surface. This enhanced near field is exploited in surface enhanced spectroscopies including Surface Enhanced Raman Spectroscopy (SERS) and Metal Enhanced Fluorescence Spectroscopy (MEFS). A measurement of the decay profile of the fringing field is important both for further development of surface enhanced spectroscopy for sensor device application, and for understanding from a fundamental physics point of view. Gold nanoshells are spherical colloidal nanoparticles with a silica core covered by a thin gold shell. The plasmon resonance of nanoshells can be controllably tuned in the visible and infrared parts of the spectrum. The near field profile of nanoshells can be theoretically calculated on the basis of Mie scattering theory. The thesis describes a series of experiments designed to experimentally verify the near field profile of nanoshells. A scaffold of ss-DNA is used to place a fluorescein dye molecule at varying distances from the nanoshell surface. The SERS intensity from both the scaffold molecules and the fluorescein placed at the end of the tether is measured simultaneously and self consistently. The fluorescein-ss-DNA nanoshell conjugate structures are also used to study the distance dependence of the fluorescence emission from fluorescein. The thesis discusses the results of the SERS intensity profile agreement with the intensity profile calculated using Mie scattering theory. The quenching and enhancement of the fluorescence emission at varying distances from the nanoshell surface are also discussed.