Surface Plasmon Resonance (SPR) in metallic nanostructures is an optical effect that can be exploited for the detection of small molecules. There is a broad range of metallic nanostructures supporting different SPR modes, and nanostructures can be even geometrically combined leading to the creation of new hybridised SPR modes. In our study, we investigated the properties of a hybridised SPR mode (gap modes GM) created by the placement of metallic nanoparticles onto metallic layers and its use as a sensitive sensor. A tunneling current passing through a metal-insulator-semiconductor structure can generate supported SPR modes that can be scattered through GM, which was experimentally confirmed. Moreover, we were able to experimentally follow the degradation of anisotropic (silver nanoprism) nanoparticles under ambient conditions in real time. Using atomic force microscopy and optical spectroscopy we observed an anisotropic corrosion that is starting from the tips of the nanoparticles.
Plasmonic nanostructures promise to provide sensing capabilities with the potential for sensitive and robust assays in a high parallelization. We present here the use of individual nanostructures for the detection and manipulation of biomolecules such as DNA based on optical approaches . The change in localized surface plasmon resonance of individual metal nanoparticles is utilized to monitor the binding of DNA directly or via DNA-DNA interaction. The influence of different size (length) as well as position (distance to the particle surface) is thereby studied . Holes in a Cr layer present another interesting approach for bioanalytics. They are used to detect plasmonic nanoparticles as labels or to sense the binding of DNA on these particles. This hybrid system of hole and particle allows for simple (just using RGB-signals of a CCD ) but a highly sensitive (one nanoparticle sensitivity) detection. On the other hand, the binding of molecular layers around the particles can be detected using spectroscopic features of just an individual one of these systems. Besides sensing, individual plasmonic nanostructures can be also used to manipulate single biomolecular structures such as DNA. Attached particles can be used for local destruction  or cutting as well as coupling of energy into (and guiding along) the molecular structure .
A newly emerging field in bioanalytics based on biomolecular binding detected label-free at single metal
nanoparticles is introduced. Thereby particles which show the effect of localized surface plasmon resonance
(LSPR) are used as plasmonic transducers. They change their spectroscopic properties (a band in the UV-VIS
range) upon binding of molecules. This effect is even observable at the single nanoparticle level using micro
spectroscopy and presents the base for a new field of single particle bioanalytics with the promise of highly
parallel and miniaturized sensor arrays. The paper describes this approach and shows first result from our work regarding the detection of DNA binding at single nanoparticle sensors.
Charge carrier distribution changes in solid substrates induced by the presence of biomolecules have the potential as
sensoric principle. For a high surface-to-bulk ratio as in the case of nanostructures, this effect can be used for highly
Plasmonic nanosensors represent one possible implementation: The resonance wavelength of the conductive electron
oscillation under light irradiation is changed upon molecular binding at the structure surface. This change can be detected
by spectroscopic means, even on a single nanoparticle level using microspectroscopy.
Other examples are nanowires in electrodes gaps, either by metal nanoparticles arranged in a chain-like geometry or by
rod-like semiconductor nanowires directly bridging the gap. Molecules binding at the surface will lead to changes in the
electrical conductivity which can be easily converted into an electrical readout. The various geometries will be discussed
and their sensoric potential for an electrical detection demonstrated.
In this paper, we report on a strategy, which produces enhancement of fluorescence using the so-called plasmonic effect whereby the presence of adjacent metallic nanoparticles can dramatically alter the fluorescence emission and absorption properties of a fluorophore. The effect, which is a result of the surface plasmon resonance of the metal surface, can lead to increases in quantum efficiency, radiative decay rates and photostability of the fluorophore, and depends very sensitively on parameters such as geometry of the nanoparticles, nanoparticle-fluorophore separation and fluorophore type. The work is aimed at improving the efficiency of optical biochips. Key benefits from this enhancement include lower limits of detection, reduced reagent requirements and better resolution. This study is part of a comprehensive investigation of plasmonic enhancement using a range of metal nanoparticle (NP) fabrication techniques and a range of measurement configurations. The focus here is on the fabrication of chemically prepared silver-gold alloy spherical NP with a variable thickness silica shell on the surface of which is immobilised a layer of fluorescent dye molecules. The variable thickness shell serves to control the dye-NP separation, which plays a key role in the enhancement mechanism. Transmission electron microscopy (TEM) was used to characterise the NP. The dye used here was the ruthenium polypyridyl complex [Ru(II)-tris(4,7-diphenyl-1,10-phenanthroline)], abbreviated to [Ru(dpp)3]2+. This paper reports the tuning of the NP plasmon resonance via NP size and alloy composition. The wavelength of the plasmon peak as a function of NP size and composition correlated very well with theoretical predictions based on the Mie scattering theory. Preliminary fluorescence enhancement measurements on this system yielded an enhancement factor of approximately 5.
It is well established that the presence of metallic surfaces or particles in the vicinity of a fluorophore can dramatically increase the radiative decay rate, and consequently the quantum efficiency, of the fluorophore. This effect, which depends on parameters such as metal particle size and fluorophore-particle separation, is manifest as a substantial enhancement in fluorescence emission intensity. This presentation will focus on optimisation strategies to maximise the enhancement for important applications such as fluorescence-based biochip platforms.
Ordered arrays of metallic nano-islands were fabricated on a range of substrates by a process of natural lithography using monodisperse polystyrene nanospheres. The metal particle dimensions were tailored in order to match the plasmon resonance wavelength to the spectral absorption of the fluorophore. The fluorophore Cy5 dye, which is widely used in optical immunoassays and has a medium quantum efficiency (~0.3), was used in this study of the plasmonic enhancement effect.
The morphology of the metallic arrays was investigated using scanning electron microscope (SEM) and atomic force microscope (AFM). Absorption and emission spectroscopies were used to elucidate the enhancement effect and its dependence on metal island morphology. Results were correlated with existing theoretical models. The applicability of this important technique to sensor platforms, such as fluorescence-based biochips, will be discussed.