Open Access Published by De Gruyter Open Access

Volume 1 Issue 1

January 2015

Issue of Nanospectroscopy

Contents
Journal Overview

Open Access November 22, 2014

Extension of solid immersion lens technology to super-resolution Raman microscopy

Edwin Ostertag, Anita Lorenz, Karsten Rebner, Rudolf W. Kessler, Alfred J. Meixner

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Abstract

Scanning Near-Field Optical Microscopy (SNOM) has developed during recent decades into a valuable tool to optically image the surface topology of materials with super-resolution. With aperture-based SNOM systems, the resolution scales with the size of the aperture, but also limits the sensitivity of the detection and thus the application for spectroscopic techniques like Raman SNOM. In this paper we report the extension of solid immersion lens (SIL) technology to Raman SNOM. The hemispherical SIL with a tip on the bottom acts as an apertureless dielectric nanoprobe for simultaneously acquiring topographic and spectroscopic information. The SIL is placed between the sample and the microscope objective of a confocal Raman microscope. The lateral resolution in the Raman mode is validated with a cross section of a semiconductor layer system and, at approximately 180 nm, is beyond the classical diffraction limit of Abbe.

Open Access January 9, 2015

Chemical stability of plasmon-active silver tips for tip-enhanced Raman spectroscopy

Jana Kalbacova, Raul D. Rodriguez, Vivek Desale, Maximilian Schneider, Ihsan Amin, Rainer Jordan, Dietrich R.T. Zahn

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Abstract

Silver nanostructures are used in tip- and surface-enhanced Raman spectroscopy due to their high electric field enhancement over almost the entire visible spectral range. However, the low chemical stability of silver, compared to other noble metals, promotes silver sulfide and sulfate formation which decreases its plasmonic activity. This is why silver tips are usually prepared on the same day of the experiments or are disregarded in favour of gold that is chemically more stable. Since silver degradation cannot be avoided, we hypothesized that a protection layer may be able to minimize or control degradation. In this contribution, we report the successful preparation of 4-biphenylthiol and 4’-nitro-4-biphenylthiol self-assembled monolayers on silver tips in order to protect them against tarnishing and to investigate the effect on the life-time of the plasmonic activity. The electrochemically etched wire surface was probed via Raman spectroscopy and scanning electron microscopy. The best long term stability and resistance against corrosion was shown by a monolayer of 4-biphenylthiol formed from dimethylformamide which did not display any degradation of the metallic tip during the observed period. Here, we demonstrate an easy and straightforward approach towards increasing the chemical stability of silver TERS-active probes.

Open Access January 19, 2015

Optical properties of silver nanocube surfaces obtained by silane immobilization

Virginia Merk, Alexander Nerz, Sebastian Fredrich, Ulrich Gernert, Sören Selve, Janina Kneipp

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Abstract

Silver nanocubes were synthesized by the polyol method and immobilized on a surface in a simple approach using an aminopropyltriethoxysilane (APTES). The optical and structural properties of the polyvinylpyrrolidone (PVP) stabilized nanocubes were investigated in solution and on glass surfaces. The SERS enhancement factors at two excitation wavelengths for crystal violet were compared with electric fields arising in different nano¬particle configurations using finite-difference time-domain simulations. They are in agreement with the preferred face-to-face orientation in the nanoaggregates on the surfaces. The facile immobilization enables on-demand preparation and use of the nanocubes in real analytical applications.

Open Access March 23, 2015

On the SERS depolarization ratio

Antonino Foti, Cristiano D’Andrea, Elena Messina, Alessia Irrera, Onofrio M. Maragò, Barbara Fazio, Pietro G. Gucciardi

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Abstract

The Raman depolarization ratio is a quantity that can be easily measured experimentally and offers unique information on the Raman polarizability tensor of molecular vibrations. In Surface Enhanced Raman Scattering (SERS), molecules are near-field coupled with optical nanoantennas and their scattering properties are strongly affected by the radiation patterns of the nanoantenna. The polarization of the SERS photons is consequently modified, affecting, in a non trivial way, the measured value of the SERS depolarization ratio. In this article we elaborate a model that describes how the SERS depolarization ratio is influenced by the nanoantenna re-radiation properties, suggesting how to retrieve information on the Raman polarizability from SERS experiments.

Open Access March 24, 2015

Fluorescence imaging of hybrid nanostructures composed of natural photosynthetic complexes and reduced graphene oxide

M. Twardowska, D. Chomicki, I. Kamińska, J. Niedziółka-Jönsson, S. Maćkowski

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Abstract

Herein, we describe the results of fluorescence microscopy imaging of peridinin-chlorophyll-protein (PCP) photosynthetic complex mixed with reduced graphene oxide (rGO). Upon incorporation of rGO the fluorescence image of PCP changes substantially from one characterized by uniform intensity towards a more complex pattern. The isolated bright spots feature up to ten times higher emission intensity compared to the fluorescence of PCP in the reference sample, where no rGO was added. The number of the bright spots increases with increasing rGO concentration. At the same time the fluorescence intensity away from the bright spots in the PCP/rGO hybrid system is quenched in comparison to the PCP – only reference.

Open Access March 25, 2015

Liquid Crystals as an Active Medium: Novel Possibilities in Plasmonics

Roberto Caputo, Giovanna Palermo, Melissa Infusino, Luciano De Sio

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Abstract

The peculiar properties of Liquid Crystals (LCs) foster new possibilities in plasmonics. The combination of the intrinsic tunability of LCs with the plasmonic properties of metallic nanoparticles (NPs) provides novel and intriguing features of systems commonly identified as active plasmonics. Being LCs, one of the media whose refractive index can be controlled through the application of external stimuli, they represent a convenient host for enabling plasmonic tunability. On the other hand, the localized plasmonic resonance, typical of NPs, can strongly influence and control the behaviour of LCs. In this paper, we overview several systems of NPs combined with LCs arranged in different configurations. The properties of the resulting systems suggest novel, intriguing outcomes in both fundamental and applied research.

Open Access May 27, 2015

Spectrophotometric observations of thiacyanine dye J-aggregation on citrate capped silver nanoparticles

Bojana B. Laban, Vesna Vodnik, Vesna Vasić

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Abstract

The J-aggregation of anionic cyanine dye, 5,5’ – disulfopropyl-3,3’ – dichloro - thiacyanine sodium salt (TC) in the presence of 2x10-3 M KCl and citrate capped silver nanoparticles (AgNPs, diameter ~10nm) was investigated. The influence of added salt (KCl), as well as AgNPs and TC concentration on the intensity of the absorption bands with the maxima at 464 and 481 nm, characteristic of the J-aggregation of the dye in solution and on AgNPs surface, respectively, was studied. The spectrophotometric and fluorescence spectra confirmed that AgNPs induced the decomposition of J-aggregates formed in solution on the account of their formation on NPs surface. The obtained results enabled the evaluation of number of TC molecules per AgNPs participating in J-aggregate formation. The experimental results yielded about 320 molecules of TC per AgNPs in at least three layers in a slanted orientation.

Open Access August 28, 2015

Integrated plasmonic double bowtie / ring grating structure for enhanced electric field confinement

N. Rahbany, W. Geng, S. Blaize, R. Salas-Montiel, R. Bachelot, C. Couteau

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Abstract

Metallic nanoparticles and nanoantennas have been extensively studied due to their capability to increase electromagnetic field confinement which is essential in numerous applications ranging from optoelectronics to telecommunication and sensing devices. We show that a double bowtie nanoantenna has a higher electric field confinement in its gap compared to a single bowtie nanoantenna, which is expected to give better fluorescence enhancement of a single emitter placed in the gap. We show that the electric field intensity can be further increased by placing the double bowtie inside a ring grating structure where the excitation of surface plasmon-polaritons (SPPs) is achieved. We perform FDTD simulations to characterise the double bowtie nanoantenna and study the effect of its dimensions on the electric field enhancement in the gap. Our proposed integrated structure with gratings is shown to increase the electric field by a factor of 77 due to a double cavity effect. Next steps would be to study the fluorescence enhancement of emitters placed inside our double bowtie / ring grating nanocavity to see if the strong coupling regime can be attained.

Open Access February 2, 2016

Plasmon spectroscopy: Theoretical and numerical calculations, and optimization techniques

Rogelio Rodríguez-Oliveros, Ramón Paniagua-Domínguez, José A. Sánchez-Gil, Demetrio Macías

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Abstract

We present an overview of recent advances in plasmonics, mainly concerning theoretical and numerical tools required for the rigorous determination of the spectral properties of complex-shape nanoparticles exhibiting strong localized surface plasmon resonances (LSPRs). Both quasistatic approaches and full electrodynamic methods are described, providing a thorough comparison of their numerical implementations. Special attention is paid to surface integral equation formulations, giving examples of their performance in complicated nanoparticle shapes of interest for their LSPR spectra. In this regard, complex (single) nanoparticle configurations (nanocrosses and nanorods) yield a hierarchy of multiple-order LSPR s with evidence of a rich symmetric or asymmetric (Fano-like) LSPR line shapes. In addition, means to address the design of complex geometries to retrieve LSPR spectra are commented on, with special interest in biologically inspired algorithms. Thewealth of LSPRbased applications are discussed in two choice examples, single-nanoparticle surface-enhanced Raman scattering (SERS) and optical heating, and multifrequency nanoantennas for fluorescence and nonlinear optics.

Open Access February 3, 2016

Optical Detection of core-gold nanoshells inside biosystems

Mario D’Acunto, Simone Dinarelli, Antonio Cricenti, Marco Luce

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Abstract

Metal nanoshells having a dielectric core with a thin gold layer are generating new interest due to the unique optical, electric and magnetic properties exhibited by the local field enhancement near the metal – dielectric core interface. These nanoshells possess strong, highly tunable local plasmon resonances with frequencies dependent upon the nanoshell shape and core material. These unique characteristics have applications in biosensing, optical communication and medicine. In this paper, we developed a theoretical, numerical and experimental approach based on a scanning near optical microscope to identify nanoshells inside mouse cells. Taking advantage of the characteristic near-infrared transparency window of many biological systems, i.e. the low light absorption coefficient of biological systems between 750−1100 nm, we were able to identify a 100−150 nm diameter barium titanate-gold nanoshell inside the h9c2 mouse cells.