On-substrate fabrication of a bio-conjugated Au nanoring solution for photothermal therapy application.

The on-substrate fabrication of a bio-conjugated Au nanoring (NRI) solution with the localized surface plasmon (LSP) resonance wavelength in the 1200-1300 nm range is demonstrated. Also, the effects of photothermal therapy through LSP resonance-induced absorption enhancement are illustrated by applying the bio-conjugated Au NRIs to human liver cancer cells and illuminating the cells with a laser of 1315 nm in wavelength. The Au NRI fabrication is based on the techniques of nano-imprint lithography and metal secondary sputtering. The procedure for on-substrate surface modification of Au NRIs leads to a high production yield of bio-conjugated NRIs. The threshold levels of the local laser intensity for injuring cancer cells based on the LSP resonances of Au NRIs of two different samples are determined.

Fabrication of surface metal nanoparticles and their induced surface plasmon coupling with subsurface InGaN/GaN quantum wells.

Based on the fabrication of Ag nanoparticles (NPs) with controlled geometry and surface density on an InGaN/GaN quantum well (QW) epitaxial structure, which contains indium-rich nano-clusters for producing localized states and free-carrier (delocalized) states in the QWs, and the characterization of their localized surface plasmon (LSP) coupling behavior with the carriers in the QWs, the interplay behavior of LSP coupling with carrier delocalization in the QWs is demonstrated. By using the polystyrene nanosphere lithography technique with an appropriate nanosphere size and adjusting the post-fabrication thermal annealing condition, the induced LSP resonance wavelength of the fabricated Ag NPs on the QW sample can match the QW emission wavelength for generating the coherent coupling between the carriers in the QWs and the induced LSP. The coupling leads to the enhancement of radiative recombination rate in the QWs and results in increased photoluminescence (PL) intensity, red-shifted PL spectrum, reduced PL decay time, and enhanced internal quantum efficiency. It is found that the observed effects are mainly due to the LSP coupling with the delocalized carriers in the QWs.

Au nanorings for enhancing absorption and backscattering monitored with optical coherence tomography.

Preparation of a high-concentration Au nanoring (NR) water solution and its applications to the enhancement of image contrast in optical coherence tomography (OCT) and the generation of the photothermal effect in a bio-sample through localized surface plasmon (LSP) resonance are demonstrated. Au NRs are first fabricated on a sapphire substrate with colloidal lithography and secondary sputtering of Au, and then transferred into a water solution through a liftoff process. By controlling the NR geometry, the LSP dipole resonance wavelength in tissue can cover a spectral range of 1300 nm for OCT scanning of deep tissue penetration. The extinction cross sections of the fabricated Au NRs in water are estimated to give levels of 10(-10)-10(-9) cm(2) near their LSP resonance wavelengths. The fabricated Au NRs are then delivered into pig adipose samples for OCT scanning. It is observed that, when resonant Au NRs are delivered into such a sample, LSP resonance-induced Au NR absorption results in a photothermal effect, making the opaque pig adipose cells transparent. Also, the delivered Au NRs in the intercellular substance enhance the image contrast of OCT scanning through LSP resonance-enhanced scattering. By continuously OCT scanning a sample, both photothermal and image contrast enhancement effects are observed. However, by continually scanning a sample with a low scan frequency, only the image contrast enhancement effect is observed.

Characterizing the localized surface plasmon resonance behaviors of Au nanorings and tracking their diffusion in bio-tissue with optical coherence tomography.

The characterization results of the localized surface plasmon resonance (LSPR) of Au nanorings (NRs) with optical coherence tomography (OCT) are first demonstrated. Then, the diffusion behaviors of Au NRs in mouse liver samples tracked with OCT are shown. For such research, aqueous solutions of Au NRs with two different localized surface plasmon resonance (LSPR) wavelengths are prepared and characterized. Their LSPR-induced extinction cross sections at 1310 nm are estimated with OCT scanning of solution droplets on coverslip to show reasonably consistent results with the data at individual LSPR wavelengths and at 1310 nm obtained from transmission measurements of Au NR solutions and numerical simulations. The resonant and non-resonant Au NRs are delivered into mouse liver samples for tracking Au NR diffusion in the samples through continuous OCT scanning for one hour. With resonant Au NRs, the average A-mode scan profiles of OCT scanning at different delay times clearly demonstrate the extension of strong backscattering depth with time. The calculation of speckle variance among successive OCT scanning images, which is related to the local transport speed of Au NRs, leads to the illustrations of downward propagation and spreading of major Au NR motion spot with time.