Gold Nanostars Obviate Limitations to Laser Interstitial Thermal Therapy (LITT) for the Treatment of Intracranial Tumors.

Purpose: Laser interstitial thermal therapy (LITT) is an effective minimally invasive treatment option for intracranial tumors. Our group produced plasmonics-active gold nanostars (GNS) designed to preferentially accumulate within intracranial tumors and amplify the ablative capacity of LITT.

Experimental Design: The impact of GNS on LITT coverage capacity was tested in ex vivo models using clinical LITT equipment and agarose gel-based phantoms of control and GNS-infused central "tumors.

Plasmonic nanorod probes' journey inside plant cells for SERS sensing and multimodal imaging.

Nanoparticle-based platforms are gaining strong interest in plant biology and bioenergy research to monitor and control biological processes in whole plants. However, monitoring of biomolecules using nanoparticles inside plant cells remains challenging due to the impenetrability of the plant cell wall to nanoparticles beyond the exclusion limits (5-20 nm). To overcome this physical barrier, we have designed unique bimetallic silver-coated gold nanorods (AuNR@Ag) capable of entering plant cells, while conserving key plasmonic properties in the near-infrared (NIR).

Direct and Label-Free Detection of MicroRNA Cancer Biomarkers using SERS-Based Plasmonic Coupling Interference (PCI) Nanoprobes.

MicroRNAs (miRNAs), small noncoding endogenous RNA molecules, are emerging as promising biomarkers for early detection of various diseases and cancers. Practical screening tools and strategies to detect these small molecules are urgently needed to facilitate the translation of miRNA biomarkers into clinical practice. In this study, a label-free biosensing technique based on surface-enhanced Raman scattering (SERS), referred to as plasmonic coupling interference (PCI), was applied for the multiplex detection of miRNA biomarkers.

Tailoring the Core-Satellite Nanoassembly Architectures by Tuning Internanoparticle Electrostatic Interactions.

The use of plasmonic nanoplatforms has received increasing interest in a wide variety of fields ranging from theranostics to environmental sensing to plant biology. In particular, the development of plasmonic nanoparticles into ordered nanoclusters has been of special interest due to the new chemical functionalities and optical responses that they can introduce. However, achieving predetermined nanocluster architectures from bottom-up approaches in the colloidal solution state still remains a great challenge.

Optical Fano resonances in a nonconcentric nanoshell.

The interaction of light with a metal nanoshell with an off-center core generates multipoles of all orders. We show here that the matrix elements used to compute the multipole expansion coefficients can be derived analytically and, with this result, we can show explicitly how the dipole and quadrupole terms in the expansion are coupled and give rise to a Fano resonance. We also show that the off-center core significantly increases the electric field enhancement at the shell surface compared to the concentric case, which can be exploited for surface-enhanced sensing.

Tunable and amplified Raman gold nanoprobes for effective tracking (TARGET): in vivo sensing and imaging.

We describe the development of a highly tunable, physiologically stable, and ultra-bright Raman probe, named as TARGET (Tunable and Amplified Raman Gold Nanoprobes for Effective Tracking), for in vitro and in vivo surface-enhanced Raman scattering (SERS) applications. The TARGET structure consists of a gold core inside a larger gold shell with a tunable interstitial gap similar to a "nanorattle" structure. The combination of galvanic replacement and the seed mediated growth method was employed to load Raman reporter molecules and subsequently close the pores to prevent leaking and degradation of reporters under physiologically extreme conditions.

Fano resonance in a gold nanosphere with a J-aggregate coating.

We present a facile method to induce J-aggregate formation on gold nanospheres in colloidal solution using polyvinylsulfate. The nanoparticle J-aggregate complex results in an absorption spectrum with a split lineshape due to plasmon-exciton coupling, i.e.

In vivo detection of SERS-encoded plasmonic nanostars in human skin grafts and live animal models.

Surface-enhanced Raman scattering (SERS)-active plasmonic nanomaterials have become a promising agent for molecular imaging and multiplex detection. Among the wide variety of plasmonics-active nanoparticles, gold nanostars offer unique plasmon properties that efficiently induce strong SERS signals. Furthermore, nanostars, with their small core size and multiple long thin branches, exhibit high absorption cross sections that are tunable in the near-infrared region of the tissue optical window, rendering them efficient for in vivo spectroscopic detection.

The three-dimensional inverse-scattering and inverse-source problems with a planar aperture.

When signals are recorded on a planar aperture with point emitters/detectors, from either a three-dimensional (3D) scattering potential or from a 3D spatially-incoherent source distribution, an integral equation arises containing the product of two Green's functions in the weak scattering limit (the Born approximation). This fundamental imaging equation for scatterers or sources is derived and solved analytically.

SERS nanosensors and nanoreporters: golden opportunities in biomedical applications.

This article provides an overview of recent developments and applications of surface-enhanced Raman scattering (SERS) nanosensors and nanoreporters in our laboratory for use in biochemical monitoring, medical diagnostics, and therapy. The design and fabrication of different types of plasmonics-active nanostructures are discussed. The SERS nanosensors can be used in various applications including pH sensing, protein detection, and gene diagnostics.

Plasmonic nanoprobes: from chemical sensing to medical diagnostics and therapy.

This article provides an overview of the development and applications of plasmonics-active nanoprobes in our laboratory for chemical sensing, medical diagnostics and therapy. Molecular Sentinel nanoprobes provide a unique tool for DNA/RNA biomarker detection both in a homogeneous solution or on a chip platform for medical diagnostics. The possibility of combining spectral selectivity and high sensitivity of the surface-enhanced Raman scattering (SERS) process with the inherent molecular specificity of nanoprobes provides an important multiplex diagnostic modality.

Investigating the plasmonics of a dipole-excited silver nanoshell: Mie theory versus finite element method.

This report compares COMSOL's finite element method (FEM) algorithm with the Mie theory for solving the electromagnetic fields in the vicinity of a silica-silver core-shell nanoparticle when excited by a radiating dipole. The novelty of this investigation lies in the excitation source of the nanoshell system: an oscillating electric dipole is frequently used as a model for both molecular scattering and molecular fluorescence; moreover, a common classical model of atomic or molecular spontaneous emission is a decaying electric dipole. The radiated power spectra were evaluated both analytically and numerically by integrating the Poynting vector around 20, 60 and 100 nm nanoshells, thereby solving the total and scattered fields generated by a dipole positioned inside the core and in the surrounding air medium, respectively.

Plasmonic Nanoparticles and Nanowires: Design, Fabrication and Application in Sensing.

This study involves two aspects of our investigations of plasmonics-active systems: (i) theoretical and simulation studies and (ii) experimental fabrication of plasmonics-active nanostructures. Two types of nanostructures are selected as the model systems for their unique plasmonics properties: (1) nanoparticles and (2) nanowires on substrate. Special focus is devoted to regions where the electromagnetic field is strongly concentrated by the metallic nanostructures or between nanostructures.

Plasmonics enhancement of a luminescent or Raman-active layer in a multilayered metallic nanoshell.

Expressions for the enhancement of the far-field scattering cross section of a luminescent or Raman-active compound contained within a multilayered nanosphere are derived, where the active compound resides between an outer metallic shell and a metallic core. The quasi-static approximation is assumed for silver and gold particles using a Lorentz-Drude model of the dielectric function. An attempt has also been made to account for the effect of electron scattering from the boundaries of the shell on the enhancement calculation.

Plasmonics of 3-D nanoshell dimers using multipole expansion and finite element method.

The spatial and spectral responses of the plasmonic fields induced in the gap of 3-D nanoshell dimers of gold and silver are comprehensively investigated and compared via theory and simulation using the multipole expansion (ME) and the finite element method (FEM) in COMSOL, respectively. The E-field in the dimer gap was evaluated and compared as a function of shell thickness, interparticle distance, and size. The E-field increased with decreasing shell thickness, decreasing interparticle distance, and increasing size, with the error between the two methods ranging from 1 to 10%, depending on the specific combination of these three variables.

Comparison of FDTD numerical computations and analytical multipole expansion method for plasmonics-active nanosphere dimers.

This paper describes a comparative study of finite-difference time-domain (FDTD) and analytical evaluations of electromagnetic fields in the vicinity of dimers of metallic nanospheres of plasmonics-active metals. The results of these two computational methods, to determine electromagnetic field enhancement in the region often referred to as "hot spots" between the two nanospheres forming the dimer, were compared and a strong correlation observed for gold dimers. The analytical evaluation involved the use of the spherical-harmonic addition theorem to relate the multipole expansion coefficients between the two nanospheres.

Optical response of linear chains of metal nanospheres and nanospheroids.

A semi-analytical method for computing the electric field surrounding a finite linear chain of metal nanospheres and nanospheroids is described. In treating chains or clusters of spheres, a common approach is to use the spherical-harmonic addition theorem to relate the multipole expansion coefficients between different spheres. A method is described here that avoids the use of spherical-harmonic addition theorems, which are not applicable to spheroidal chains.

Spectral bounds on plasmon resonances for Ag and Au prolate and oblate nanospheroids.

Analytical expressions for the plasmon resonance frequencies of prolate and oblate spheroids and their dependence on ellipticity have been derived, and approximate bounds on these frequencies established. These formulas may be useful in tuning the plasmon resonance within certain limits. With increasing aspect ratio, the prolate spheroid resonance is red shifted relative to a sphere with no lower limit under the assumptions of a Drude dispersion model.

Noise propagation in linear and nonlinear inverse scattering.

The propagation of noise from the data to the reconstructed speed of sound image by inverse scattering within the framework of the Lippmann-Schwinger integral equation of scattering is discussed. The inversion algorithm that was used consisted in minimizing a Tikhonov functional in the unknown speed of sound. The gradient of the objective functional was computed by the method of the adjoint fields.

Imaging the distribution of magnetic nanoparticles with ultrasound.

Magnetic nanoparticles can be caused to oscillate under the influence of an incident ultrasonic wave. If the particles are momentarily aligned with a magnetizing pulse creating a macroscopic magnetization, this oscillation will result in a time-varying magnetic moment which should be detectable as an induced voltage in a nearby pickup coil. In this way, focused ultrasound can be used to map, or image, the spatial distribution of the magnetic particles after these particles have been introduced into the body.

Plasmon Resonances of Nanoshells of Spheroidal Shape.

Plasmon resonances are computed for nanoshells of prolate and oblate spheroidal shape. Both longitudinal and transverse resonances are investigated as a function of aspect ratio and shell thickness. Formulas for the surface charge density on the outside and inside shell surfaces are derived.

Optoacoustic diffraction tomography: analysis of algorithms.

We consider the problem of using the photoacoustic effect to image the optical properties of tissue. A region of tissue is assumed to be illuminated by frequency-modulated light that creates an ultrasonic wave of the same frequency. This wave is detected on a passive array of receiving transducers distributed over a circular or a cylindrical aperture.

Can ultrasound be used to stimulate nerve tissue?

Background: The stimulation of nerve or cortical tissue by magnetic induction is a relatively new tool for the non-invasive study of the brain and nervous system. Transcranial magnetic stimulation (TMS), for example, has been used for the functional mapping of the motor cortex and may have potential for treating a variety of brain disorders.

Methods And Results: A new method of stimulating active tissue is proposed by propagating ultrasound in the presence of a magnetic field.

Synthetic aperture imaging with arrays of arbitrary shape--part II: The annular array.

It has been previously shown that full aperture resolution can be achieved with an annular transducer array by transmitting and receiving between all pairs of elements around the array circumference and applying an appropriate weighting function. If there are N elements in the array, this requires N transmissions. This paper shows that full aperture resolution can be obtained with a much smaller number of transmissions (two to four) by using a certain aperture phase weighting on transmit and receive.

Synthetic aperture imaging with arrays of arbitrary shape--part I: General case.

The problem of synthesizing full-aperture resolution with linear transmitting and receiving arrays of arbitrary shape is considered. The arrays are assumed to lie in the same plane and can be open (e.g.