This paper presents an optical device capable of the simultaneous measurement of the surface plasmon resonance (SPR) spectrum, which provides information regarding the change in the dielectric constant of the binding analytes, and the surface-enhanced Raman scattering (SERS) spectrum, which yields analytical data regarding the structural changes of the analytes. SPR sensing is an established technology in the field of direct real-time analysis of biomolecular interactions such as antibodies/antigens, DNA hybridization, receptors/ligands, etc. Meanwhile, SERS sensing techniques represent a powerful means of acquiring and diagnosing structural information relating to analyte binding. This study adopts the attenuated total reflection (ATR) method and an Au nanocluster-embedded dielectric sensing film in developing a biosensor which integrates the SPR and SERS sensing techniques. The results confirm the effectiveness of the proposed multi-functional device in developing a detailed understanding of the mechanisms of biomolecular recognition.

We report recent achievements in metal-enhanced fluorescence. Several fluorophore systems have been studied on metal particle-coated surface and in colloid suspensions. In particular, we describe a distance dependent enhancement on silver island films (SIFs), release of self-quenching of fluorescence near silver particles, and the applications of fluorescence enhancement near metalized surfaces to bioassays. We discuss a number of methods for various shpae silver particle deposition on surfaces.

Fluorescence is widely used as a spectroscopic tool or for biomedical imaging, in particular for DNA chips. Nanostructured metallic substrates permit to locally enhance the fluorescence signal which offer the possibility both to detect very small fluorophore concentrations and to trace precisely the bio-markers. We have developed substrates made of silver or gold nanoparticles covered with a spacer layer of alumina. Double metallic and dielectric gradients permit to directly map the fluorescence enhancement factor and to determine the best condition for maximum enhancement. One and two photons excitations are studied. Fluorescence enhancement reaches two orders of magnitudes. Lifetime measurements reveal additional information on the decay channels induced by the nanoparticle presence.

Directional fluorescence emission of a sulforhodamine 101 in polyvinyl alcohol film has been observed from samples deposited on semi-transparent silver mirror. The fully p-polarized fluorescence emerges through the glass prism in form of hollow cone. The angle of this cone of emission depends on the thickness of the sample, and does not depend on the mode of excitation. The angular dependence of surface plasmon-coupled emission (SPCE) on the sample thickness has been discussed as well as its relevance to the surface plasmon resonance (SPR) analysis.

In this presentation we describe a novel methodology for ultra-sensitive fluorescence immunoassays based on a new class of fluorescent biomarkers, which are strongly enhanced by nano-size metallic particles. Specifically, we discuss development of the immunoassay on the surfaces coated with metallic particles for high sensitivity detection of cardiac markers. This technology will allow detection of the biomarkers in serum and blood without separation and amplification steps. We present an experimental platform that uses front-face excitation in total internal reflection mode for efficient rejection of background fluorescence.

We present the fabrication and characterization of silver island films with SiO₂ coatings for application in plasmonic sensors based on surface-enhanced fluorescence and Raman detection. The emission spectral properties of goat anti-mouse immunoglobulin (IgG) F(ab')₂ labeled with one or two fluorescein residues were examined on substrates with metallic silver islands. The self-quenching of fluorescein emission was mostly eliminated when this antibody fragment was held 60-90 Å from the surface of metallic silver islands, and our preliminary experiments demonstrated an 8-fold emission intensity increase. Similar surfaces were also examined for surface-enhanced Raman analysis of Rhodamine 123, a potential drug for photodynamic therapy.

Surface plasmon resonance phase-shift interferometry (SPR-PSI) is a novel technique which combines SPR and modified Mach-Zehnder phase-shifting interferometry to measure the spatial phase variation caused by biomolecular interactions upon a sensing chip. The SPR-PSI imaging system offers high resolution and high-throughout screening capabilities for microarray DNA hybridization without the need for additional labeling, and provides valuable real-time quantitative information. Current SPR-PSI imaging systems measure the spatial phase variation caused by tiny biomolecular changes on the sensing interface by means of a five-step phase reconstruction algorithm and a novel multichannel least mean squares (MLMS) phase unwrapping algorithm. The SPR-PSI imaging system has an enhanced detection limit of 2.5 × 10^-7 refraction index change, a long-term phase stability of π/100 in 30 minutes, and a spatial phase resolution of π/500 with a lateral resolution of 10μm. This study successfully demonstrates the kinetic and label-free observation of 5-mer DNA microarray hybridization.

The ability to recognize the conformational changes and structural variations of a protein when immobilized in a solid surface is of great importance in a variety of applications. Surface plasmon resonance (SPR) sensing is an appropriate technique for investigating interfacial phenomena, and enables the conformational changes of proteins to be monitored through the variation in the SPR angle shift. Meanwhile, the surface-enhanced Raman scattering (SERS) system can also assist in clarifying the changes in protein structure. The present study utilizes a 1 mM CrO₃ phosphate buffer solution (PBS) to induce conformational changes of human serum albumin (HSA). Monitoring the corresponding SPR angle shifts and the SPR reflectivity spectrum enables the relationships between the conformational changes of the surface-immobilized protein and the thickness and dielectric constants of the protein layer to be estimated. The experimental SPR results indicate that the Cr⁶⁺ ions cause significant conformational change of the protein. It is established that the ions are not merely absorbed into the protein as a result of electrostatic forces, but that complex protein refolding events also take place. Furthermore, the data acquired from the SERS system yield valuable information regarding the changes which take place in the protein structure.

The represented work is aimed at the problem of optimization of optical biosensors based on the surface plasmon resonance (SPR) effect in thin gold films. Using it, one can characterize biomolecular interactions by detection of the resonance angle shift in a real time scale without any labels. To provide reliable operation of a sensor chip, we deposited a sensitive gold film onto glass substrates using an intermediate chromium layer capable to improve adhesion of the following layers. Performed is the analysis of the chromium layer influence on structural and optical properties of the gold film as well as on processes of transducer regeneration after operation cycles. The influence of low-temperature annealing (80÷300°C) on gold film properties was investigated. As it was observed with SPR spectroscopy and atomic force microscopy, minimal energy losses during excitation of surface polariton states as well as smoothing the small-scale relief of polycrystalline gold surface are reached with annealing temperatures close to 120°C. It is these samples that provide formation of defectless self-organized thiol monolayers, which results in stabilization and passivation of SPR transducer sensitive surface. Modification of the transducer gold surface with a monolayer matrix system containing two types of mercaptanes of different lengths and structure enabled to realize the idea of molecular recognizing some low-molecular compounds (barbituric acid) against the background of close structural analogs (veronal). To avoid influence of non-specific sorption, for the first time, we used the electrochemically deposited films of nickel hydroxide Ni(OH)₂.

We report on the development of a highly sensitive and cost efficient analysis system based on surface plasmon resonance spectroscopy. The advantage of our system consists of optical components being integrated into the sensor element. These enable the uncritical optical coupling and, therefore, a simplified handling of the sensor plates without additional optical adjustment. Manufacture by hot embossing or injection molding allows for a low cost production of disposable sensor elements. Furthermore, up to 50 measurement spots are arranged in parallel on a sensor plate to simultaneously detect a multitude of different substances. The range of analytes to be determined is only limited by the specific affinity of the immobilized capture molecules on the sensor surface. Optimized protein capture molecules for use in medical diagnosis chips have to be developed for this purpose. The label free detection principle simplifies the probe preparation and leads to a cost reduction compared with common fluorescence techniques. The development of a sensor element containing a number of parallel measurement spots sufficient for a medically significant screening of relevant parameters in blood samples or other body fluids as well as the reliable detection of characteristic virus proteins will be shown in this paper.

We are using a gold nanoparticle coated film to achieve high spatially resolved biosensing that is based on localized surface plasmon resonance (LSPR). This special film possesses the unique optical properties of being not sensitive to the changes of incident angle and relies exclusively on the spectral shift of absorption peak for biosensing. This uniqueness enables it to be compatible with high numerical aperture (NA) optics and to achieve high spatial resolution. We demonstrate a spatial resolution of 25μm assuming a maximum of spectral fluctuation of 0.1nm is acceptable.

Surface Plasmon Resonance (SPR) effect is considered in conditions of the absorption sensing. This sensing implies a formation of a thin absorbent layer with non-zero imaginary part of the dielectric constant on the sensor surface. We study the sensing response of the prism-based coupling system to the thickness increase of different absorbent layers (Au, Cu, Pt, Ag, Al, Si) in both the Attenuated Total Reflection (ATR) and Kretschmann-Raether geometries. The obtained results are of importance for the characterization of the absorbent metal- or semiconductor-based layers and development of nanoparticle-enhanced SPR sensors

We have recently developed a new approach to glucose sensing based on the aggregation of nanometer-sized noble-metal nanoparticles and their respective change in plasmon absorption upon glucose addition. High molecular weight Dextran coated nanoparticles are aggregated with Concanavalin A, (Con A), where the aggregation results in a significant shift in metal-plasmon absorption. The addition of glucose competitively binds to Con A, reducing nanoparticle aggregation, and therefore the plasmon absorption when monitored at 650 nm. We have optimized our plasmonic glucose sensing mechanism with regard to nanoparticle stability, the dynamic range for glucose sensing and the wavelength of observation, to be compatible with both clinical glucose requirements and measurements.

Recently, an extraordinary transmission of light through small holes (<200 nm) in a thin metallic film has been described. This phenomenon has been shown to be the result of the photon-plasmon interaction in thin films where a periodic structure (such as a set of holes) is embedded in the film. One of the extraordinary results is that the beam that passes through a hole has a very small diffraction in extreme contrast to the wide angle predicted by diffraction theory. Based on this effect, we propose here a new type of microscopy that we term mid-field microscopy. It combines an illumination of the sample through a metallic hole-array with far-field collection optics, a scanning mechanism and a CCD. When compared to other high resolution methods, what we suggest here is relatively simple because it is based on a thin metallic film with an array of nano-sized holes. Such a method can be widely used in high-resolution microscopy and provide a novel simple-to-use tool in many life-sciences laboratories. When compared to near-field scanning optical microscopy (NSOM), the suggested mid-field method provides a significant improvement. This is chiefly for three reasons: 1. The penetration depth of the microscope increases from a few nanometers to a few micrometers, hence the name mid-field microscope. 2. It allows one to measure an image faster because the image is measured through many holes in parallel rather then through a single fiber tip used in conventional near-field microscopy, and 3. It enables one to perform three-dimensional reconstruction of images due to a semi-confocal effect. We describe the physical basics of the photon-plasmon interaction that allows the coupling of light to the surface plasmons and determines the main spectral characteristics of the device. This mechanism can be ascribed due to the super-periodicity of the electron oscillations on the metallic surface engendered by the grating-like structure of the hole-array.

Scanning near-field optical microscopy (SNOM) has proven to be very powerful in terms of both resolution and efficiency. We report on new advances of this technique using metallic tips to scatter the optical field and induce dramatic field enhancements. We also present a new technique under development using multiple nanometric beads as scattering probes dispersed in the volume of the sample, rather than using a single tip. The bead positions are determined in three dimensions (3-D) with a precision better than the diffraction limit, making possible high-resolution 3-D imaging of hollow structures in relatively transparent materials.

The present study proposes the use of a novel optical biosensor with Au nanoclusters embedded in a dielectric film to achieve a 10-fold improvement in the resolution performance. The proposed optical biosensor based on the attenuated total reflection (ATR) method excites both the surface plasmons (SPs) and particle plasmons (PPs) to enhance the local electro-magnetic field by controlling the size and volume fraction of the embedded Au nanoparticles to increase the resolution of the device. A co-sputtering method utilizing a multi-target sputtering system is used to fabricate the present dielectric films (SiO2) with embedded Au nanoclusters. It is shown that the sensitivity of the developed SPR biosensor can be improved by adjusting the size and volume fraction of the embedded Au nanoclusters in order to control the surface plasmon effect. The present gas detection and DNA hybridization experimental results confirm that the proposed Au nanocluster-enhanced SPR biosensor provides the potential to achieve an ultrahigh-resolution detection performance of approximately 0.1 pg/mm² surface coverage of biomolecules.

Current surface plasmon resonance (SPR) modes based on the attenuated total reflection (ATR) method can broadly be categorized as: conventional SPR, long-range SPR (LRSPR), coupled plasmon-waveguide resonance (CPWR), and waveguide-coupled SPR (WCSPR). Although the features of optical biosensors are dependent upon their particular SPR mode, a common requirement for all biosensors utilized for biomolecular interaction analysis (BIA) is a high degree of sensitivity. The current paper presents a theoretical analysis and comparison of the sensitivity and resolution of these four types of SPR biosensors when employed in three of the most prevalent detection methods, namely angular interrogation, wavelength interrogation, and intensity measurement. This study develops a detailed understanding of the influences of various biosensor design parameters in order to enhance the sensitivity and detection limit capabilities of such devices.

Currently, separate diagnostic and therapeutic modalities are required for the diagnosis and treatment of cancer. In many cases, the present standard of care requires invasive surgical procedures and/or other treatments associated with significant side effect profiles, high cost, and poor clinical outcome. A single technology with dual diagnostic/therapeutic capabilities would potentially yield significant savings in the time and cost associated with diagnosing and treating many cancers. In this paper, we discuss gold nanoshell bioconjugates and their role in the development of an integrated cancer imaging and therapy application. Nanoshells are a novel class of nanomaterials that have unique properties including continuous and broad wavelength tunability, far greater scattering and absorption coefficients, increased chemical stability, and improved biocompatibility. Here, we describe the development of an integrated cancer imaging and therapy application using near-infrared (NIR) gold nanoshell bioconjugates.

The intense color of noble metal nanoparticles has inspired artists and fascinated scientists for hundreds of years. These rich hues are due to the interaction of light with the nanostructure's localized surface plasmon (LSPR). Here, we describe three optical sensing modalities that are dependant on the effects of the LSPR. Specifically, we will demonstrate the use of LSPR supporting particles as analogues to fluorescent probes and labels for multiplex detection, sensing based on observation of changes in the LSPR spectrum caused by alteration of the local refractive index upon analyte binding, and the spectroscopic labeling of cells and tissues with Surface Enhanced Raman Scatting (SERS) active nanoparticles probes.