Pae C. Wu

Shape matters: plasmonic nanoparticle shape enhances interaction with dielectric substrate.

Numerical analyses of the ultraviolet and visible plasmonic spectra measured from hemispherical gallium nanostructures on dielectric substrates reveal that resonance frequencies are quite sensitive to illumination angle and polarization in a way that depends on nanostructure size, shape, and substrate. Large, polarization-dependent splittings arise from the broken symmetry of hemispherical gallium nanoparticles on sapphire substrates, inducing strong interactions with the substrate that depend sensitively on the angle of illumination and the nanoparticle diameter.

Personalized diagnostics and biosensors: a review of the biology and technology needed for personalized medicine

Abstract Exploiting the burgeoning fields of genomics, proteomics and metabolomics improves understanding of human physiology and, critically, the mutations that signal disease susceptibility. Through these emerging fields, rational design approaches to diagnosis, drug development and ultimately personalized medicine are possible. Personalized medicine and point-of-care testing techniques must fulfill a host of constraints for real-world applicability. Point-of-care devices (POCDs) must ultimately provide a cost-effective alternative to expensive and time-consuming laboratory tests in order to assist health care personnel with disease diagnosis and treatment decisions. Sensor technologies are also expanding beyond the more traditional classes of biomarkers – nucleic acids and proteins – to metabolites and direct detection of pathogens, ultimately increasing the palette of available techniques for the use of personalized medicine. The technologies needed to perform such diagnostics have also been rapidly evolving, with each generation being increasingly sensitive and selective while being more resource conscious. Ultimately, the final hurdle for all such technologies is to be able to drive consumer adoption and achieve a meaningful medical outcome for the patient.

Real-time plasmon resonance tuning of liquid Ga nanoparticles by in situ spectroscopic ellipsometry

Liquid Ga nanoparticles have been deposited on sapphire substrates at room temperature. The optical evolution of Ga nanoparticle surface plasmon resonance during deposition has been characterized by in situ real-time spectroscopic ellipsometry to control and tune the plasmon resonance photon energy. The existence of both longitudinal and transverse modes for spheroidal Ga nanoparticles supported on a sapphire substrate is demonstrated and the dependence of the longitudinal and transverse plasmon energies on particle size is discussed. Stability of the Ga surface plasmon resonance to air exposure and high temperature is also demonstrated.

Demonstration of surface-enhanced Raman scattering by tunable, plasmonic gallium nanoparticles

Size-controlled gallium nanoparticles deposited on sapphire were explored as alternative substrates to enhance Raman spectral signatures. Galliums resilience following oxidation is inherently advantageous in comparison with silver for practical ex vacuo nonsolution applications. Ga nanoparticles were grown using a simple molecular beam epitaxy-based fabrication protocol, and monitoring their corresponding surface plasmon resonance energy through in situ spectroscopic ellipsometry allowed the nanoparticles to be easily controlled for size. The Raman spectra obtained from cresyl fast violet (CFV) deposited on substrates with differing mean nanoparticle sizes represent the first demonstration of enhanced Raman signals from reproducibly tunable self-assembled Ga nanoparticles. Nonoptimized aggregate enhancement factors of approximately 80 were observed from the substrate with the smallest Ga nanoparticles for CFV dye solutions down to a dilution of 10 ppm.

Plasmonic gallium nanoparticles on polar semiconductors: interplay between nanoparticle wetting, localized surface plasmon dynamics, and interface charge.

Ga nanoparticles supported on large band gap semiconductors like SiC, GaN, and ZnO are interesting for plasmon-enhanced UV-emitting solid-state devices. We investigate the influence of the polarity of the SiC, GaN, and ZnO wurtzite semiconductors on the wetting of Ga nanoparticles and on the resulting surface plasmon resonance (SPR) by exploiting real time plasmonic ellipsometry. The interface potential between polar semiconductors (SiC, GaN, and ZnO) and plasmonic nanoparticles (gallium) is shown to influence nanoparticle formation dynamics, geometry, and consequently the SPR wavelength. We invoke the Lippman electrowetting framework to elucidate the mechanisms controlling nanoparticle dynamics and experimentally demonstrate that the charge transfer at the Ga nanoparticle/polar semiconductor interface is an intrinsic method for tailoring the nanoparticle plasmon resonance. Therefore, the present data demonstrate that for supported nanoparticles, surface and interface piezoelectric charge of polar semiconductors also affects SPR along with the well-known effect of the media refractive index.

In situ spectroscopic ellipsometry to monitor surface plasmon resonant group-III metals deposited by molecular beam epitaxy

The evolution of the surface plasmon resonance of Al, Ga, and In deposited by molecular beam epitaxy on GaN surfaces was monitored in real-time using spectroscopic ellipsometry. The correlation between the metal plasmon resonance modes, the particle size, and the growth mode is addressed. Ga and In deposited on GaN substrates form nanoparticles while the Al is shown to form a nearly coalesced thin film. The plasmon resonance of the Ga and In nanoparticles redshift with increasing average particle size while the pseudodielectric function of Al approaches that of a Drude metal.

GaMg alloy nanoparticles for broadly tunable plasmonics.

Manipulating the properties of well understood materials systems for novel technological applications can be achieved by creating nanoscale structures and mixed compounds. The design of novel nanomaterials that underpin plasmonic applications drives the rapid progress in advancing plasmonic materials over the last few years. [ 1 , 2 ] Control of metal nanoparticle shape, [ 3 , 4 ] density, and spacing [ 5 ] is continually improving with novel synthetic techniques. Nevertheless, to continue advancing plasmonics, new metallic nanostructure systems must be developed that offer unique properties and are superior to Ag, [ 6 ] Au, [ 3 , 7 ] and mixtures thereof—the most widely exploited metals [ 8–10 ] and bimetallic systems. [ 11 ]

Cysteamine-Based Functionalization of InAs Surfaces: Revealing the Critical Role of Oxide Interactions in Biasing Attachment

Attaching functional molecules such as thiols and proteins to semiconductor surfaces is increasingly exploited in functional devices such as sensors. Despite extensive research to understand this interface and demonstrate a robust protocol for attachment, the bonding chemistry of thiolates to III-V surfaces has been under great debate in the literature. This study provides a comprehensive chemical model for the attachment of thiols to InAs, an increasingly device-relevant III-V semiconductor, using cysteamine as a model molecule. We examine the attachment of cysteamine to InAs via the thiol group using X-ray photoelectron spectroscopy and spectroscopic ellipsometry and confirm that thiolate bonding to the substrate occurs preferentially to As sites over In sites as a limit. These experiments explore the interplay of the native oxide chemical properties, the cysteamine concentration, and the evolving InAs surface chemistry with functionalization. The thiol-InAs interaction can be framed as a general acid-base reaction, where the nucleophilic and/or electrophilic attack of the surface (i.e., binding to In sites and/or As sites) depends on the acidity of the thiol. The roles of the initial oxide composition, the solvent of the functionalizing solution, and the cysteamine as a limiting reagent in fully displacing the oxide and creating In-S and As-S bonds are highlighted.

Point-of-Care Devices

The growing need for point-of-care testing and reliability of proteomic, genomic, and metabolomic biomarker discovery has accelerated the development of point-of-care devices. Technological considerations critical to designing the analytical element for a device, including choice of sensing modality, active/transduction material, and integration within a portable system are overviewed in this chapter.

Novel, Real-Time Measurement of Plasmon Resonance: Tailoring Nanoparticle Geometry Optically

We demonstrate novel use of in situ spectroscopic ellipsometry to probe in real-time metal nanoparticle deposition. Real-time monitoring of NP assembly plasmon resonance enables control of NP size via the plasmon resonance and vice versa.