Carsten Sönnichsen

Planar Metamaterial Analogue of Electromagnetically Induced Transparency for Plasmonic Sensing

We experimentally demonstrate a planar metamaterial analogue of electromagnetically induced transparency at optical frequencies. The structure consists of an optically bright dipole antenna and an optically dark quadrupole antenna, which are cut-out structures in a thin gold film. A pronounced coupling-induced reflectance peak is observed within a broad resonance spectrum. A metamaterial sensor based on these coupling effects is experimentally demonstrated and yields a sensitivity of 588 nm/RIU and a figure of merit of 3.8.

Mycosynthesis of Silver Nanoparticles Using the Fungus Fusarium acuminatum and its Activity Against Some Human Pathogenic Bacteria

We report extracellular mycosynthesis of silver nanoparticles by Fusarium acuminatum Ell. and Ev. (USM-3793) isolated from infected ginger (Zingiber officinale). An aqueous silver nitrate solution was reduced to metallic silver when exposed to F. acumi- natum cell extract leading to the appearance of a brown color within 15-20 minutes. The color is due to the formation of silver nanoparti- cles and the excitation of surface plasmons. The optical spectrum showed the plasmon resonance at 420 nm and analysis by transmission electron microscopy confirmed the presence of silver nanoparticles. The nanoparticles produced were spherical with a broad size distribu- tion in the range of 5-40 nm with average diameter of 13 nm. The reduction of the silver ions occurs probably by a nitrate-dependent re- ductase enzyme, which we found to be present in the extra-cellular medium. We tested the silver particles for their broad-band antibacte- rial activity on different human pathogens. We observed efficient antibacterial activity against multidrug resistant and highly pathogenic bacteria, including multidrug resistant Staphylococcus aureus, Salmonella typhi, Staphylococcus epidermidis, and Escherichia coli. The synthesis of silver nanoparticles by the fungus F. acuminatum may therefore serve as a simple, cheap, eco-friendly, reliable and safe method to produce an antimicrobial material.

Spectroscopy of single metallic nanoparticles using total internal reflection microscopy

We have developed a simple, fast, and flexible technique to measure optical scattering spectra of individual metallic nanoparticles. The particles are placed in an evanescent field produced by total internal reflection of light from a halogen lamp in a glass prism. The light scattered by individual particles is collected using a conventional microscope and is spectrally analyzed by a nitrogen-cooled charge-coupled-device array coupled to a spectrometer. This technique is employed to measure the effect of particle diameter on the dephasing time of the particle plasmon resonance in gold nanoparticles. We also demonstrate the use of this technique for measurements in liquids, which is important for the potential application of particle plasmons in chemical or biological nanosensors.

Synthesis of Rod-Shaped Gold Nanorattles with Improved Plasmon Sensitivity and Catalytic Activity

We prepared rod-shaped gold nanorattles solid gold nanorods surrounded by a thin gold shell using a galvanic replacement process starting with silver-coated gold nanorods. These structures are very promising candidates for catalytic applications and optimized plasmon sensors. They combine the advantages of rods (low plasmon resonance frequency, large polarizability, small damping) with the high surface area of hollow structures. The plasmon sensitivity to changes in the dielectric environment is up to 50% higher for gold nanorattles compared to gold nanorods with the same resonance frequency and 6x higher than for plasmons in spherical gold nanoparticles. The catalytic activity measured for the reduction of p-nitrophenol is 4x larger than for bare gold nanorods.

Single Unlabeled Protein Detection on Individual Plasmonic Nanoparticles

The ultimate detection limit in analytic chemistry and biology is the single molecule. Commonly, fluorescent dye labels or enzymatic amplification are employed. This requires additional labeling of the analyte, which modifies the species under investigation and therefore influences biological processes. Here, we utilize single gold nanoparticles to detect single unlabeled proteins with extremely high temporal resolution. This allows for monitoring the dynamic evolution of a single protein binding event on a millisecond time scale. The technique even resolves equilibrium coverage fluctuations, opening a window into Brownian dynamics of unlabeled macromolecules. Therefore, our method enables the study of protein folding dynamics, protein adsorption processes, and kinetics as well as nonequilibrium soft matter dynamics on the single molecule level.

LbL multilayer capsules: recent progress and future outlook for their use in life sciences

In this review we provide an overview of the recent progress in designing composite polymer capsules based on the Layer-by-Layer (LbL) technology demonstrated so far in material science, focusing on their potential applications in medicine, drug delivery and catalysis. The benefits and limits of current systems are discussed and the perspectives on emerging strategies for designing novel classes of therapeutic vehicles are highlighted.

Quantitative optical trapping of single gold nanorods.

We report a quantitative analysis of the forces acting on optically trapped single gold nanorods. Individual nanorods with diameters between 8 and 44 nm and aspect ratios between 1.7 and 5.6 were stably trapped in three dimensions using a laser wavelength exceeding their plasmon resonance wavelengths. The interaction between the electromagnetic field of an optical trap and a single gold nanorod correlated with particle polarizability, which is a function of both particle volume and aspect ratio.

Electrically controlled light scattering with single metal nanoparticles

A concept to electrically control the scattering of light is introduced. The idea is to embed noble metal nanoparticles in an electro-optical material such as a liquid crystal in order to induce a spectral shift of the particle plasmon resonance by applying an electric field. Light scattering experiments on single gold nanoparticles show that spherically shaped nanoparticles become optically spheroidal when covered by an anisotropic liquid crystal. The two particle plasmon resonances of the optically spheroidal gold nanoparticles can be spectrally shifted by up to 50 meV when electric fields of more than 10 kV/cm are applied.

Nanoassembled Plasmonic-Photonic Hybrid Cavity for Tailored Light-Matter Coupling

We propose and demonstrate a hybrid cavity system in which metal nanoparticles are evanescently coupled to a dielectric photonic crystal cavity using a nanoassembly method. While the metal constituents lead to strongly localized fields, optical feedback is provided by the surrounding photonic crystal structure. The combined effect of plasmonic field enhancement and high quality factor (Q approximately 900) opens new routes for the control of light-matter interaction at the nanoscale.

Au@MnO Nanoflowers: Hybrid Nanocomposites for Selective Dual Functionalization and Imaging

Recently, the development of hybrid nanostructures consisting of various materials has attracted considerable interest. The assembly of different nanomaterials with specific optical, magnetic, or electronic properties to multicomponent composites can change and even enhance the properties of the individual constituents. Specifically tuning the structure and interface interactions within the nanocomposites has resulted in novel platforms of materials that may lead the way to various future technologies, such as synchronous biolabeling, protein separation and detection, heterogeneous catalysis, and multimodal imaging in biomedicine. Of the various kinds of nanomaterials, gold nanorods show an unusually high polarizability at optical frequencies arising from the excitation of localized surface-plasmon resonances (LSPRs). Furthermore, gold nanorods have promising therapeutic properties as hyperthermal agents because the local temperature around the gold nanorods can be increased by laser illumination through the tunable surface plasmon bands in the near infrared (NIR) region. Using NIR radiation for hyperthermal therapy is beneficial because of the low absorption and low scattering by blood and tissue in this spectral range. Magnetic nanoparticles constitute another major class of nanomaterials that have attracted much research effort over the past decades. In particular, exchange-coupled magnetic nanocomposites, such as antiferromagnetic/ferromagnetic core–shell nanoparticles, such as MnO/Mn3O4, have magnetic properties that are quite different from those of the individual components. Concerning biomedical applications, superparamagnetic nanoparticles are attractive as contrast agents for magnetic resonance imaging (MRI). The majority of nanoparticles that have been investigated in this field comprise iron oxides (Fe3O4, g-Fe2O3), which are known to shorten the transverse (or spin–spin) relaxation time T2. [11] Recently, manganese oxide nanoparticles (MnO NPs) have been shown to be interesting candidates as contrast agents for shortening of the longitudinal (or spin-lattice) relaxation time T1. [12] Consequently, a nanoparticulate system containing both an optically active plasmonic gold unit and a magnetically active MnO component would be advantageous for simultaneous optical and MRI detection. Although considerable research efforts have been put into the chemical design of suitable surface ligands, one of the major obstacles for biocompatible applications remains the lack of surface addressability. Therefore, a nanocomposite made up of individually addressable Au and MnO domains offers two functional surfaces for the attachment of different kinds of molecules, thus increasing both diagnostic and therapeutic potential. Furthermore, the size of either of the two components can be varied to optimize the magnetic and optical properties. Herein we present the successful synthesis of Au@MnO nanocomposites consisting of both paramagnetic MnO NPs and Au crystallites followed by separate surface functionalization of both domains with fluorescent ligands. Scheme 1 depicts a functionalized Au@MnO nanoflower with selective attachment of catechol anchors to the metal oxide petals and thiol anchors to the gold core. The nanoflowers were synthesized by decomposition of manganese acetylacetonate [Mn(acac)2] in diphenyl ether in the presence of preformed Au NPs (“seeds”), with oleic acid and oleylamine as surfactants, following a similar procedure for the preparation of Au@Fe3O4 heteroparticles by Sun et al. [15] The [*] T. D. Schladt, Dr. M. I. Shukoor, K. Schneider, Dr. M. N. Tahir, O. K hler, Prof. Dr. W. Tremel Institut f r Anorganische Chemie und Analytische Chemie Johannes-Gutenberg-Universit t Duesbergweg 10–14, 55099 Mainz (Germany) Fax: (+49)6131-39-25605 E-mail: tremel@uni-mainz.de