Surface enhanced Raman spectroscopy has become a viable technique for the detection of single molecules. This highly sensitive technique is due to the very large (up to 14 orders in magnitude) enhancement in the Raman cross section when the molecule is adsorbed on a metal nanoparticle cluster. We report here SERS (Surface Enhanced Raman Spectroscopy) experiments performed by adsorbing analyte molecules on nanoscale silver particle clusters within the gelatin layer of commercially available holographic plates which have been developed and fixed. The Ag particles range in size between 5 - 30 nanometers (nm). Sample preparation was performed by immersing the prepared holographic plate in an analyte solution for a few minutes. We report here the production of SERS signals from Rhodamine 6G (R6G) molecules of nanomolar concentration. These measurements demonstrate a fast, low cost, reproducible technique of producing SERS substrates in a matter of minutes compared to the conventional procedure of preparing Ag clusters from colloidal solutions. SERS active colloidal solutions require up to a full day to prepare. In addition, the preparations of colloidal aggregates are not consistent in shape, contain additional interfering chemicals, and do not generate consistent SERS enhancement. Colloidal solutions require the addition of KCl or NaCl to increase the ionic strength to allow aggregation and cluster formation. We find no need to add KCl or NaCl to create SERS active clusters in the holographic gelatin matrix. These holographic plates, prepared using simple, conventional procedures, can be stored in an inert environment and preserve SERS activity after several weeks subsequent to preparation.

In this contribution, we present new tailor-made substrates for surface-enhanced Raman scattering (SERS). They are based on precise control of the mean shape and the average diameter of nanoparticles prepared by self-assembly of atoms on dielectric supports. Tailoring of the SERS substrates have been achieved by precise tuning of the localized surface plasmon polariton resonance of silver nanoparticles to the vicinity of the laser wavelength used for SERS excitation. The underlying method relies on control of the growth kinetics of supported metal nanoparticles which causes a pronounced shape change as a function of particle size. Additionally, the strong dependence of the energetic position of surface plasmon excitation on the shape of the particles is exploited. With this preparation method, SERS substrates with optimized plasmon resonances and field enhancement can be easily produced for specific excitation wavelengths and detection ranges. The nanoparticles have been characterized by optical spectroscopy and atomic force microscopy (AFM). Silver nanoparticles with a plasmon resonance at about 2.4 eV were prepared with and without a protective CaF₂ coating. SERS spectra of pyrene were obtained with excitation at 514.5 nm. They exhibit a good reproducibility. Furthermore, the substrates did not show degradation during the measurements and those with protective coating still yielded 70% of the SERS intensity of uncoated substrates, indicating their potential usefulness for an analytical detection of specific molecules. Further tailoring of supported metal nanoparticles for SERS applications by laser irradiation will be discussed.

This study reports on current work involving the use of Surface Enhanced Raman Spectroscopy (SERS) for the intracellular detection of cell constituents in mouse fibroblast cells using gold nanoshells. Gold nanoshells were acquired from Nanospectra Biosciences that are based on a silica dielectric core and an outer gold shell layer. They have the unique property of a tunable surface plasmon resonance wavelength from the visible through the near infrared which allows control of the electromagnetic field strength on its surface. Hence gold nanoshells can serve as SERS substrates with plasmonic properties that are not aggregation dependent and thus can be expected to overcome the reproducibility problem that is generally associated with aggregation based colloidal metal nanoparticles. These results represent the first steps in the development of a nanoshell-based SERS probe to detect cell organelles and/or intracellular biochemicals with the goal of ultimately improving the ability to monitor intracellular biological processes in real time.

This study utilizes a surface plasmon resonance (SPR) biosensing to investigate the influence of secondary structures on the DNA hybridization and a surface-enhanced Raman scattering (SERS) spectrum to yield analytical data regarding the structure of the oligonucleotides. It is found that the SPR angular shifts associated with the three pairs of 60mer oligonucleotides with prominent secondary structures are lower than those observed for the two pairs of oligonucleotides with no obvious secondary structures. It is also determined that increasing the DNA hybridization temperature from 35 ^oC to 45 ^oC reduces secondary structure effects. On the hybridization with mixture target oligonucleotides, the SPR results demonstrate that secondary structures interfere significantly. Although the kinetics of biomolecular interaction analysis is performed by using SPR sensor, the structural information of the oligonucleotides can not observed directly. The SERS spectrum provides the structural information of the oligonucleotides with silver colloidal nanoparticles adapted as a Raman active substrate. Also, the detection limit of the DNA Raman signal has been successfully improved to reach sub-micro molarity of DNA concentration.

Fluorescence is widely used in biological research. Future advances in biology and medicine often depend on the advances in the capabilities of fluorescence measurements. In this overview paper we describe how a combination of fluorescence, and plasmonics, and nanofabrication can fundamentally change and increase the capabilities of fluorescence technology. This change will be based on the use of surface plasmons which are collective oscillations of free electrons in metallic surfaces and particles. Surface plasmon resonance is now used to measure bioaffinity reactions. However, the uses of surface plasmons in biology are not limited to their optical absorption or extinction. We have shown that fluorophores in the excited state can create plasmons which radiate into the far field; additionally fluorophores in the ground state can interact with and be excited by surface plasmons. These interactions suggest that the novel optical absorption and scattering properties of metallic nanostructures can be used to control the decay rates, location and direction of fluorophore emission. We refer to this technology as plasmon-controlled fluorescence. We predict that plasmon-controlled fluorescence (PCF) will result in a new generation of probes and devices. PCF is likely to allow design of structures which enhance emission at specific wavelengths and the creation of new devices which control and transport the energy from excited fluorophores in the form of plasmons, and then convert the plasmons back to light.

We report our latest progresses in the design and synthesis of fluorescent silica nanoparticles. Two different approaches are proposed: the first one is adopted for the inclusion of the dye to prepare doped silica nanoparticles (DSN). The second strategy allows the grafting of the surface of nanoparticles with the dye molecules and is suitable for the synthesis of covered silica nanoparticles (CSN). The two families of nanoparticles are radically different. While DSN are water soluble, surface coverage can dramatically lower the solubility in aqueous solvents. From the point of view of inter-chromophoric interactions, inclusion in DSN allows a good control of the average distance between the dye molcecules but, on the other hand, by surface modification a higher density of fluorophores can be reached making effective short range interactions (in particular electron transfer processes). Finally because of segregation, the interection of dye molecules with the external environment and macromolecules is less effective in the case of DSN. Three different examples are reported. In the first one energy transfer between fluorescein molecules in DSN is demonstrated though fluorescence anisotropy studies. The average distance between the fluorophores was tuned by controlling the degree of loading in order to have energy transfer inside the nanoparticles and in the mean time avoid a too large quenching because of self quenching processes. In the second example extended quenching via electron transfer processes on the surface of CSN is reported showing a simple case of 'amplified' quenching of the fluorescence upon protonation. Finally this last concept was applied to increase the sensibility in the field of metal ion sensing: a case of a water soluble nanosensor for metal ion with amplified response is, in fact, reported.

Our ultimate objective is to develop a low-cost, surface-enhanced fluorescence microarray detection system for highly multiplexed bioassays based on surface plasmon resonance (SPR) coupled fluorescence. For convenience we refer to this approach as SPREFE (SPR-coupled Enhanced Fluorescence Emission). Our implementation employs grating coupler sensor chips that consist of gold-coated plastic substrates with a periodic surface profile that enables resonant coupling of incident optical radiation into surface plasmons. With this architecture, emission from fluorophores suitably bound to ligands on the chip is modified in two striking ways: first, excitation is enhanced by the evanescent plasmon field, and second emission is highly directional, which can significantly improve optical collection efficiency. In this work we explore the feasibility of this approach for biodetection.

The objective of this effort is to improve upon a microarray-based system for label-free, high-throughput proteomic analysis. The system operation is based on a novel grating-coupled surface plasmon resonance imaging (GCSPRI) technology that enables measurement of hundreds to possibly thousands of binding events simultaneously without the limitations of reporter molecules. We expect that this technology will provide a powerful new tool for highly multiplexed analysis of an organism's global protein profile, reflecting metabolic and physiologic activity in relation to time, development and interaction with the environment. It will be applicable to the detection of a broad range of metabolic products, signaling molecules, hormones, enzymes, receptors and other proteins. We present improvements by way of SPR-dispersion compensation with a properly oriented transmission grating placed in the excitation path. This illumination technique is broad-band which reduces the effects of thin-film interference, permitting a 20-fold decrease in sample volume as well as providing more interrogation light.

Functionality of biosensor arrays based on SPR imaging is mainly defined by quality of patterned SAM, which is used for sensing of biological substances of interest. The monolayers are commonly not uniform in the micrometer scale. In the current work we describe experimental setups for PM-IRRAS mapping and SPR imaging of self assembly monolayer (SAM) formed by octadecyl phosphonic acid (CH₃(CH₂)₁₇PO(OH)₂) on a patterned Au/Al₂O₃ surface. By combining highly resolved surface plasmon resonance (SPR) images of the surface with the corresponding PM-IRRAS maps we achieved enhancement of the resolution. In this work we show, that changes of molecular structure in the thin films also induce changes in the SPR signal. Contrary, changes in SPR have their origin in molecular structure within the film.

We propose a fiber-optic biosensor based on the generation of local surface plasmons (LSR) near a nano fiber tip. The nano-optical fiber biosensor was made by shaping the fiber to form a taper with a tip size less than 100nm. Gold nanoparticles with 12nm diameter were immobilized to the tapered fiber's tip by modifying tip surface with NH₂ groups. Most of light in the fiber tip is confined by the total internal reflection. It generates substantial evanescent wave near the tip and effectively excites LSR on the nanogolds. The evanescent wave excitation results in very low background light and high signal to noise ratio. Using this nanofiber sensor, we have achieved a sensitivity of reflective index unit, ~4800 (% RIU^-1) in the intensity measurement. Furthermore, the LSR is excited only near the tip region. It takes advantage of ultra small detection area. Only micro-liter sample solution is needed for the detection.

Polarization phenomena in the optical absorption and emission of metallic, semiconducting or composite nanowires are considered theoretically. Most nanowire-based structures are characterized by a dramatic difference in dielectric constant ε between the nanowire material and environment. Due to image forces caused by such ε mismatch in nanowire structures, coefficients of their absorption and emission become essentially different for light polarized parallel or perpendicular to the nanowire axis. As a result, the intensity and spectra of absorption, luminescence, luminescence excitation, and photoconductivity in nanowires or arrays of parallel nanowires are strongly polarization-sensitive. In light-emitting nanowire core-shell structures, the re-distribution of a.c. electric field caused by the image forces may result in essential enhancing of core luminescence in frequency regions corresponding to luminescence from the semiconducting core or when the frequency of optical excitation coincides to the frequency of the plasmon resonance in the metallic shell. Random nanowire arrays acquire some properties typical for nematic liquid crystals. In such arrays, the effect described above may result in "polarization memory", where polarization of luminescence is determined by the polarization of the exciting light.

Microsphere resonators, i.e., photonic atoms, have found wide area of application in optical spectroscopy, quantum optics, cavity QED, switching, and sensing. Photonic atoms have unique optical properties such as high quality factor (Q-factor) morphology dependent resonances (MDR's), and relatively small volumes. High-Q MDR's are very sensitive to the refractive index change and microsphere uniformity. These tiny optical cavities, whose diameters vary from a few to several hundred micrometers, have resonances with reported Q-factors as large as 3x10⁹. Due to their sensitivity, MDR's are also considered for biosensor applications. Binding of a protein or other biomolecules can be monitored by observing the wavelength shift of MDR's. A biosensor, based on this optical phenomenon, can even detect a single molecule, depending on the quality of the system. In this work, elastic scattering spectra from photonic atoms of different materials are experimentally obtained and MDR'S are observed. Preliminary results of unspecific binding of biomolecules are presented. Elastic light scattering spectra of MDR's for biosensor applications are calculated numerically for biomolecules such as Bovine Serum Albumin (BSA) and for Deoxyribo Nucleic Acid (DNA).

We proposed a simple and low cost approach for fabricating SPR biosensor chips. For SPR imaging sensor applications, the requirement of the sensing chip design is different from typical flow-cell configurations in terms size, number of channels and optical coupling surface quality. In order to fulfill the requirements of practical applications, we present several designs for both single and multi-channel bio-chips. Moreover these modules are easy to fabricate with no special requirements on tools. This leads to low-cost and multi-channel bio-chips integrated with a flow-cell for a range of customized SPR sensing applications.

In this study, we use the finite-difference time-domain (FDTD) method and an attenuated-total-reflection (ATR) fluorescent optical microscope to investigate into the enhancement of near electro-magnetic (EM) field via plasmonic effects. In order to enhance the near EM field on the sensing surface, a metallic particle layer is added under the Kretschmann configuration of the conventional surface plasmon resonance sensor based on the ATR method. The affiliation by the simulation and experimental results can help us to understand the mechanisms of surface plasmons and particle plasmons on the sensor surface, and the effects of the EM field enhancement are classified as the surface plasmon effect, particle plasmon effect, interparticle coupling effect, and gap mode effect. By analyzing and comparing the results based on the FDTD method and the ATR fluorescent microscope, we can understand more about the plasmonic effects in order to deign a novel ultra-high resolution plasmonic biosensor.

In this study, localized surface plasmon resonance (SPR) biosensors with gold nanowires regularly patterned on a gold film are considered for sensitivity enhancement. The theoretical investigation was conducted using rigorous coupled wave analysis (RCWA) in terms of various design metrics, such as the resonance angle shift, the SPR curve angular width (SPR CAW), and the minimum reflectance at resonance (MRR). Especially, when LSP modes couple resonantly, broad SPR CAW and shallow MRR as well as a large shift of the resonance angle can be observed due to absorptive damping and localized coupling. The results show that, in general, nanowires of a T-profile present more effective sensitivity enhancement than an inverse T-profile. The sensitivity enhancement mediated by the presence of nanowires has been clarified qualitatively based on the dispersion relation between metal film involving nanowires and surrounding dielectric medium. Moreover, optimal design parameters of nanowires are determined based on quantitative metrics that measure the sensor performance and the fabrication reliability.

In this study, we investigate the impact of the cross sectional profile of an array of metallic nanowires on the feasibility of a localized surface plasmons resonance (LSPR) biosensor. Calculations were performed using rigorous coupled wave analysis with an emphasis on the extinction properties of the LSPR structure. It was confirmed that the resonance spectrum strongly depends on the nanowire period and profile. Our numerical results indicate that the nanowire structure, particularly that of a T-profile, delivers extremely linear sensing performance over a wide range of target refractive index with much enhanced sensitivity. The extinction-based LSPR structure also involves relatively large dimension and thus is expected to provide a feasible biosensor using current semiconductor technology.