Jiunn-Woei Liaw

Magnetic gold-nanorod/ PNIPAAmMA nanoparticles for dual magnetic resonance and photoacoustic imaging and targeted photothermal therapy

Nanomedicine can provide a multi-functional platform for image-guided diagnosis and treatment of cancer. Although gold nanorods (GNRs) have been developed for photoacoustic (PA) imaging and near infra-red (NIR) photothermal applications, their efficiency has remained limited by low thermal stability. Here we present the synthesis, characterization, and functional evaluation of non-cytotoxic magnetic polymer-modified gold nanorods (MPGNRs), designed to act as dual magnetic resonance imaging (MRI) and PA imaging contrast agents. In addition, their high magnetization allowed MPGNRs to be actively localized and concentrated by targeting with an external magnet. Finally, MPGNRs significantly enhanced the NIR-laser-induced photothermal effect due to their increased thermal stability. MPGNRs thus provide a promising new theranostic platform for cancer diagnosis and treatment by combining dual MR/PA imaging with highly effective targeted photothermal therapy.

Purcell effect of nanoshell dimer on single molecule’s fluorescence

The Purcell effect of a nanoshell dimer on the fluorescence of a single molecule placed within the dimers gap is studied. The numerical results show that the nanoshell dimer acts as an antenna, making the energy transfer from an excited molecule to the dimer more efficient, and as a lowpass filter for the radiation of fluorescence to the far field. Moreover, the enhancement factor of a nanoshell dimer on the fluorescence is much higher than that of a solid Au dimer in the longer-wavelength regime.

Surface-Modified Gold Nanoparticles with Folic Acid as Optical Probes for Cellular Imaging

In this study, we demonstrate that the uptake rate of the surface-modified gold nanoparticles (GNPs) with folic acid by specific cells can be increased significantly, if the membranes of these cells have sufficient folic-acid receptors. Two human breast cancer cell lines were studied; one is MDA-MB-435S cell, and the other T-47D cell. The expression of the folic acid receptors of the former is much higher than that of the latter. These cells were incubated with media containing bare GNPs or GNPs conjugated with folic acid individually. Due to the unique optical behavior (i.e. surface plasmon resonance) of GNPs, the uptake amount of GNPs by cells can be identified by using the laser scanning confocal microscopy. Our experiments show that the uptake amount of GNPs in MDA- MB-435S cells is higher than that in T-47D cells for the same culture time, if the culture medium contains bare GNPs. Moreover, if the GNPs conjugated with folic acid are used for the culture, the uptake rate of GNPs by MDA-MB-435S cells is improved more. In contrast, the uptake rates of both GNPs are almost the same by T-47D cells. The phenomenon indicates that the uptake rate of GNPs can be improved via the ligand- receptor endocytosis, compared with the nonspecific endocytosis. Therefore, the uptake rate of GNPs conjugated with folic acid by MDA-MB-435S cells is higher than that of bare GNPs.

Internalized Gold Nanoparticles Do Not Affect the Osteogenesis and Apoptosis of MG63 Osteoblast-Like Cells: A Quantitative, In Vitro Study

The long-term toxicity effects of gold nanoparticles (GNPs) on the proliferation and differentiation of a progenitor cell line, MG63 osteoblast-like cells, was investigated. These cells were treated for 20 hours with two media that contained 10 nm GNPs at concentrations of 1 ppm and 10 ppm. The mitosis of the GNP-treated MG63 was observed after at least 21 hours using dark-field and fluorescence microscopy. The TEM, LSCM and dark-field hyperspectral images indicated that the late endosomes in cells that contained aggregated GNPs were caused by vesicle fusion. Subsequently, after 21 days of being cultured in fresh medium, the specific nodule-like phenotypes and bone-associated gene expression of the treated MG63 cells exhibited the same behaviors as those of the control group. Statistically, after 21 days, the viability of the treated cells was identical to that of the untreated ones. During the cell death program analysis, the apoptosis and necrosis percentages of cells treated for 8 or fewer days were also observed to exhibit no significant difference with those of the untreated cells. In summary, our experiments show that the long-term toxicity of GNPs on the osteogenetic differentiation of MG63 is low. In addition, because of their low toxicity and non-biodegradability, GNPs can potentially be used as biomarkers for the long-term optical observation of the differentiation of progenitor or stem cells based on their plasmonic light-scattering properties.

Plasmon resonances of spherical and ellipsoidal nanoparticles

Surface plasmon resonance (SPR) of a single metallic nanoparticle is analyzed and simulated via multi-multipole method for 3D problems. The excitation, at optical frequencies, of the SPR leads to an extremely strong field in the vicinity of the nanoparticle. Numerical results indicate that a red shift of SPR is induced for an ellipsoidal nanoparticle, compared to a spherical one. Two structures of core-shelled spherical nanoparticles are also studied; one is a nanosphere of Ag shell with an oxide core, and the other one is Ag core with an oxide shell (ZrO2 or SiO2). Numerical results illustrate the SPR of these two core-shelled structures are quite different from each other and different from that of a solid one. It suggests that one can manipulate the optical response on demand by tuning the core/shell ratio and the permittivity of shell or core.

Analysis of a Bowtie Nanoantenna for the Enhancement of Spontaneous Emission

A 2-D metallic bowtie nanoantenna, consisting of two nearby metallic nanotriangles and containing a molecule within the gap, is studied for the enhancement of a single emitters spontaneous emission. For simplicity, a transverse-magnetic model is used for simulation and a set of new surface integral equations is developed for the calculation. The process of spontaneous emission is simply divided into two stages: the first stage is the excitation of the emitter irradiated by an incident plane wave and the second is the emission of the excited emitter. For the latter, the excited emitter is modeled as an electric dipole to interact with the nanoantenna. The results show that a metallic bowtie nanoantenna behaves as a nanolens as well as a polarizer to provide a strong local electric field with a polarization parallel to the axis of the bowtie in the gap for the emitters excitation, and its quantum yield exhibits a function of a low-pass filter as well as an orientizer for the emitters emission.

Wavelength-dependent longitudinal polarizability of gold nanorod on optical torques

This study theoretically investigates the wavelength-dependent longitudinal polarizability of a gold nanorod (GNR) irradiated by a polarized laser beam. The resultant optical torque in terms of the Maxwell stress tensor was analyzed quantitatively using the multiple multipole method. Our results indicate that the real part of the longitudinal polarizability of GNR can be either positive or negative, leading to the parallel or perpendicular modes, respectively. For the parallel and perpendicular modes, the long axis of GNR is rotated to align parallel and perpendicular, respectively, to the polarization direction of the illuminating light. The turning point between these two modes, depending on the aspect ratio (AR) and the size of GNR, nearly coincides with the longitudinal surface plasmon resonance (LSPR). The perpendicular mode ranges from the transverse SPR to LSPR, and the range of the parallel mode is broadband from LSPR to the near infrared regime. Owing to that a larger optical torque and less plasmonic heating are of concern, an efficiency of optical torque is defined to evaluate the performance of different wavelengths. Analysis results indicate that lasers with wavelength in the perpendicular mode are applicable to rotate and align a GNR of a higher AR. For example, the laser of 785 nm (the perpendicular mode) is superior to that of 1064 nm (the parallel mode, off-resonant from LSPR of 955 nm) for rotating a GNR of AR = 4 and radius 20 nm with an orientation of 45° with respect to the laser polarization.

Thermal damage potential during hip resurfacing in osteonecrosis of the femoral head: An experimental study

Hip resurfacing arthroplasty has become an attractive treatment option for young, active patients with femoral head necrosis. However, little information is available about the potential thermal damage to the remaining femoral head when a cemented component is used. We used an experimental model to measure the temperature profile at the cement–bone interface during hip resurfacing. We compared four simulated lesion sizes—15, 25, 33, and 50%—of the femoral head, and a control group with no cystic lesion. Temperatures were measured with the specimens in a 37°C saline bath or with copious pulsed lavage. With specimens tested in the bath, peak temperatures were higher, and durations of temperatures above 50°C were longer, in femoral heads with necrotic lesions (88.8 ± 7.5°C; 17.6 ± 1.1 min for a 15% lesion; 96.2 ± 7.2°C; 22.86 ± 1.3 min for a 25% lesion; 99.7

Simulation of surface plasmon resonance of metallic nanoparticles by the boundary-element method

A set of new surface integral equations (Fredholm equations of the second kind) has been systematically derived from the Stratton-Chu formulation of Maxwells equations for a two-dimensional TM mode to investigate the interactions of an incident electromagnetic wave with nanostructures, especially metals. With these equations, the surface components (the tangential magnetic field, the normal displacement, and the tangential electric field) on the boundary are solved simultaneously by the boundary-element method numerically. For nanometer-sized structures (e.g., dimension of 10 nm), our numerical results show that surface plasmon resonance causes a strong near-field enhancement of the electric field within a shallow region close to the interface of metal and dielectric. In addition, the corresponding pattern of the far-field scattering cross section is like a dipole. For the submicrometer-sized cases (dimension of several hundreds of nanometers), the numerical results indicate the existence of a standing wave on the backside surface of metals. This phenomenon could be caused by two surface plasmon waves that creep along the contour of metals clockwise and counterclockwise, respectively, and interfere with each other.

Average enhancement factor of molecules-doped coreshell (Ag@SiO 2 ) on fluorescence

Average enhancement factor (AEF) of a coreshell (Ag@SiO(2)) on the fluorescence of molecules doped within the silica shell is proposed and studied to estimate the overall performance of a large number of coreshells. Using Mie theory and dyadic Greens functions, the enhancement factor (EF) of a coreshell is first calculated for any arbitrarily oriented and located electric dipole embedded in the shell. AEF is then obtained by averaging the individual EF over all possible orientations and positions of the electric dipoles. AEF of a FITC-doped coreshell (radius of Ag core: 25 nm, thickness of shell: 15 nm) irradiated by a laser of 488 nm for FITCs emission at 518 nm is 2.406. It is much smaller than the maximum EF (30.114) of a coreshell containing a single molecule with a radial orientation at its optimal position. For Alexa 430-doped coreshell excited at 428 nm, AEF is 12.34 at the emission of 538 nm.