Templated Techniques for the Synthesis and Assembly of Plasmonic Nanostructures

It is now well-known that the size, shape, and composition of nanomaterials can dramatically affect their physical and chemical properties, and that technologies based on nanoscale materials have the potential to revolutionize fields ranging from catalysis to medicine. Among these materials, anisotropic particles are particularly interesting because the decreased symmetry of such particles often leads to new and unusual chemical and physical behavior. Within this class of particles, triangular Au and Ag nanoprisms stand out due to their structure- and environment-dependent optical features, their anisotropic surface energetics, and the emergence of reliable synthetic methods for producing them in bulk quantities with control over their edge lengths and thickness. This Review will describe a variety of solution-based methods for synthesizing Au and Ag triangular prismatic structures, and will address and discuss proposed mechanisms for their formation.

Colloidal Gold and Silver Triangular Nanoprisms

https://opus.lib.uts.edu.au/bitstream/10453/4361/3/2006003918.pdf

Therapeutic possibilities of plasmonically heated gold nanoparticles

Enhanced near-field at noble metal nanoparticle surfaces due to localized surface plasmon resonance (LSPR) has been researched in fields ranging from biomedical to photoelectrical applications. However, it is rarely explored on nonmetallic nanomaterials discovered in recent years, which can also support LSPR by doping-induced free charge carriers, let alone the investigation of an intricate system involving both. Here we construct a dual plasmonic hybrid nanosystem Au–Cu9S5 with well controlled interfaces to study the coupling effect of LSPR originating from the collective electron and hole oscillations. Cu9S5 LSPR is enhanced by 50% in the presence of Au, and the simulation results confirm the coupling effect and the enhanced local field as well as the optical power absorption on Cu9S5 surface. This enhanced optical absorption cross section, high photothermal transduction efficiency (37%), large light penetration depth at 1064 nm, excellent X-ray attenuation ability, and low cytotoxicity enable Au–Cu9S5 ...

Surface plasmon resonance enhanced light absorption and photothermal therapy in the second near-infrared window.

Drug delivery into biological cells is an important and growing area of application. Among other systems, such as gels, polymeric micelles, liposomes, and colloids, nanoengineered polyelectrolyte multilayer microcapsules offer a unique opportunity to combine surface multifunctionality with design flexibility for the delivery of encapsulated materials into designated compartments and cells. Furthermore, microcapsules can be arranged in arrays for imaging, could be appropriate candidates for a cell-sorting system, and serve as fluorescence markers for the characterization of cells by fluorescence-activated cell sorting (FACS). The capsules are fabricated using the layer-bylayer (LbL) method by alternately adsorbing oppositely charged polymers on colloidal templates followed by core dissolution. In this regard, proteins and biocompatible polymers have also received increased interest. The main advantage of such a method is the precise control over the chemical composition of the surfaces. In the area of biomedical applications, polyelectrolytemultilayer capsules are envisioned for the delivery of encapsulated materials into biological cells. Recently, we have presented the real-time monitoring and remote release of encapsulated materials from polyelectrolyte-multilayer capsules on the single-capsule level. Such an approach is different from the studies reported by other research groups in that it is performed on a single-capsule level, which is the method ideally suited to applications where precise control is necessary. In addition, the distinctive feature reported in reference [10b] is the measurement of the temperature rise induced locally by absorption of laser light by nanoparticles. In general, nanoparticles are becoming ubiquitous components that link chemistry and physics with biology and biochemistry. They can be embedded in the walls of capsules to provide functionality, and they are also finding increasing interest for biological imaging. Herein, we show that polyelectrolyte-multilayer capsules containing metallic nanoparticles in their walls can be remotely activated to release encapsulatedmaterial inside living cells. Fluorescently labeled polymers were chosen as a model system for encapsulated materials. The remote-release experiments were conducted according to the following scheme. The polyelectrolyte-multilayer shells were doped with metal nanoparticles, which served as absorption centers for energy supplied by a laser beam. These absorption centers cause local heating that disrupts the local polymer matrix and allows the encapsulated material to leave the interior of the capsule. When using lasers with biological objects, it is important to minimize the absorption of laser light by cells and tissue. This can be accomplished by choosing the laser wavelength in the biologically “friendly” window—the near-infrared (NIR) part of the spectrum. Usually the spectral properties of water serve as a good criterion, as it constitutes 80–85% of eukaryotic cells. Indeed, in water the temperature rise in the focus of a laser diode with wavelength 850 nm and operating at optical powers up to 100 mW during less than 1 s exposure time was reported to be under 1 K. Other important parameters that control the interaction of laser light with the absorption centers are the size of the nanoparticles and their concentration on the microcapsules. The concentration of metal nanoparticles plays an important role for two reasons: 1) when the distance between the two adjacent nanoparticles is of the order of their size, the thermal effects produced by [*] Dr. A. G. Skirtach, Dr. O. Kreft, K. K hler, Prof. Dr. H. M hwald, Prof. Dr. G. B. Sukhorukov Institut f+r Grenzfl-chen Max-Planck-Institut f+r Kolloidund Grenzfl-chenforschung Am M+hlenberg 1, 14424 Golm/Potsdam (Germany) Fax: (+49)331-567-9202 E-mail: andre.skirtach@mpikg-golm.mpg.de

Laser-induced release of encapsulated materials inside living cells

The reduction of HAuCl4 by Na2S has been reported to produce gold nanoparticles with an optical absorption in the near-infrared along with its characteristic absorption in the visible. The optical resonances in the visible are due to the gold surface plasma, which are a function of the geometry of the particles. The near-infrared absorption had been attributed to the formation of Au2S/Au core/shell structures. In this report we present new electronic absorption, electron microscopy, and X-ray absorption data in several systems to show that the near-infrared absorption does not involve core/shell structures. We further suggest that the near-infrared adsorption is most likely the result of the formation of aggregates of gold nanoparticles. The identification of the origin of the near-infrared resonance is critical in understanding the optical properties of metal nanoparticle systems.

R. Yoshizaki

Papers

Near Infrared Optical Absorption of Gold Nanoparticle Aggregates