Comprehensive T-matrix Reference Database: A 2009-2011 Update

The T-matrix method is one of the most versatile and efficient theoretical techniques widely used for the computation of electromagnetic scattering by single and composite particles, discrete random media, and particles in the vicinity of an interface separating two half-spaces with different refractive indices. This paper presents an update to the comprehensive database of peer-reviewed T-matrix publications compiled by us previously and includes the publications that appeared since 2009. It also lists several earlier publications not included in the original database

Comprehensive T-Matrix Reference Database: A 2007-2009 Update

The T-matrix method is among the most versatile, efficient, and widely used theoretical techniques for the numerically exact computation of electromagnetic scattering by homogeneous and composite particles, clusters of particles, discrete random media, and particles in the vicinity of an interface separating two half-spaces with different refractive indices. This paper presents an update to the comprehensive database of T-matrix publications compiled by us previously and includes the publications that appeared since 2007. It also lists several earlier publications not included in the original database

Resonances On-Demand for Plasmonic Nano-Particles

A method for designing plasmonic particles with desired resonance spectra is presented. The method is based on repetitive perturbations of an initial particle shape while calculating the eigenvalues of the various quasistatic resonances. The method is rigorously proved, assuring a solution exists for any required spectral resonance location. Resonances spanning the visible and the near-infrared regimes, as designed by our method, are verified using finite-difference time-domain simulations. A novel family of particles with collocated dipole-quadrupole resonances is designed, demonstrating the unique power of the method. Such on-demand engineering enables strict realization of nano-antennas and metamaterials for various applications requiring specific spectral functions

Surface Morphology of a Gold Core Controls the Formation of Hollow or Bridged Nanogaps in Plasmonic Nanomatryoshkas and Their SERS Responses

Surface-enhanced Raman scattering (SERS) probes with a nanometer-sized interior gap between the Au core and shell, also called nanomatryoshkas (NMs), have attracted great interest in SERS-based bioimaging and biosensing. Recently, seed-mediated growth has been shown to be effective for NM synthesis. We found that the structure of nanogaps inside Au NMs depends strongly on the core surface morphology. Specifically, when the initially citrate-stabilized 15 and 35 nm smooth Au cores were further functionalized with 1,4-benzenedithiol (BDT) in the presence of cetyltrimethylammonium chloride (CTAC), the Au shell growth led to the formation of a subnanometer hollow interior gap containing BDT molecules. In contrast, the use of 23 and 35 nm faceted polygonal CTAC-stabilized Au cores for Au shell growth resulted in NMs with small bridged gaps. The formation of incomplete outer shells with one or two nanometer-sized hollow gaps was also observed for 23 nm polygonal cores but not for 35 nm ones. The experimental SERS response from BDT molecules in bridged-gap NMs was an order of magnitude higher than that for hollow-gap NMs. This finding is in agreement with the finite-difference time-domain (FDTD) simulations predicting stronger electromagnetic fields inside nanobridged gaps, as compared to hollow-gap NMs. The major SERS peaks from BDT inside NMs of both types (two sizes, four samples) was an order of magnitude higher than the near-field SERS peaks recorded for the corresponding 15CIT, 23CTAC, 35CIT, and 35CTAC cores alone after surface functionalization with BDT molecules. This observation is explained by a simple dipole approximation (DA) theory, which was developed to estimate the structure- and wavelength-dependent electromagnetic SERS enhancement in the hollow-gap NMs with good accuracy, as confirmed by comparison with exact multilayered Mie (ML Mie) calculations. With a double increase in the core size, the NM SERS response also increased, and the ratio between the major peak intensities of the larger and smaller NMs was about 2. Finally, the calculated SERS spectra of the hollow-gap NMs agree with the data reported for 532, 633, and 785 nm laser excitations. The physical insights acquired from this study open the way for rational design and efficient optimization of new SERS platforms based on electromagnetic field enhancement in subnanometer gaps within plasmonic nanostructures

Magnetic and Plasmonic Nanoparticles for Biomedical Devices

The design of magnetic, plasmonic, and hybrid nanoparticles is a rapidly growing multidisciplinary field that has found various promising biomedical applications, including bioimaging and focused thermal cancer therapy, targeted delivery of drugs, DNA and siRNA molecules, clinical analytics and chemical and biosensing, etc. In particular, magnetic and plasmonic nanoparticles have led to an emerging trend in nanomedicine, theranostics, which combines diagnosis and therapeutic modalities in a single hybrid nanostructure..

Polydopamine-coated Au nanorods for targeted fluorescent cell imaging and photothermal therapy

Au nanorods (AuNRs) have attracted a great interest as a platform for constructing various composite core/shell nanoparticles for theranostics applications. However, the development of robust methods for coating AuNRs with a biocompatible shell of high loading capacity and with functional groups still remains challenging. Here, we coated AuNRs with a polydopamine (PDA) shell and functionalized AuNR-PDA particles with folic acid and rhodamine 123 (R123) to fabricate AuNR-PDA-R123-folate nanocomposites. To the best of our knowledge, such AuNR-PDA-based composites combining fluorescent imaging and plasmonic phothothermal abilities have not been reported previously. The multifunctional nanoparticles were stable in cell buffer, nontoxic and suitable for targeted fluorescent imaging and photothermal therapy of cancer cells. We demonstrate the enhanced accumulation of folate-functionalized nanoparticles in folate-positive HeLa cells in contrast to the folate-negative HEK 293 cells using fluorescent microscopy. The replacement of folic acid with polyethylene glycol (PEG) leads to a decrease in nanoparticle uptake by both folate-positive and folate-negative cells. We performed NIR light-mediated targeted phototherapy using AuNR-PDA-R123-folate and obtained a remarkable cancer cell killing efficiency in vitro in comparison with only weak-efficient nontargeted PEGylated nanoparticles. Our work illustrates that AuNR-PDA could be a promising nanoplatform for multifunctional tumor theranostics in the future