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Plasmonic nanoparticles have potential application in nano-optics, solar cell, catalysis, drug delivery and cancer treatment. Among those, thiol protected gold nanocrystals draw greater attraction due to their superior stability and ability to control the composition with atomic precision. However, the challenges in the synthetic protocol and lack of atom quantification techniques hinder the determination of atomic composition. For the first time, we were able to determine the atomic composition of the three different gold nanoparticles in the size regime of 2-4 nm. The composition was found to be [Au.sub.329][(SR).sub.84], [Au.sub.~500][(SR).sub.~120] and [Au.sub.~940][(SR).sub.~160] by electro-spray ionization mass spectrometry. All of these nanocrystals exhibit surface plasmonic resonance at around ~500 nm. Size-dispersity of the gold nanocrystals was confirmed by mass spectrometry, synchrotron based small angle X-ray scattering and scanning transmission electron microscopy analysis. Possible atomic arrangements of these nanocrystals were determined by high-energy X-ray based pair distribution function analysis. These largest gold nanocrystals with known composition will pave the way to the understanding the origin of surface plasmon resonance and will have greater potential towards application in catalysis and optical devices., INTRODUCTION Surface plasmon resonance (SPR) is a collective oscillation of the free electron density of the metal with the incident radiation (1). Gold nanoparticles shows SPR at 500-550 nm depend [...]

Visualizing individual molecules with chemical recognition is a longstanding target in catalysis, molecular nanotechnology and biotechnology. Molecular vibrations provide a valuable 'fingerprint' for such identification. Vibrational spectroscopy based on tip-enhanced [...]

The influence of the spherical anisotropy (SA) of a middle layer on the plasmon resonance couplings in the sandwiched gold nanoshell (Au/SA/Au) has been investigated by means of a modified Mie theory. It is found that the plasmon couplings in the Au/SA/Au nanoshells are more sensitive to the permittivity along the radial direction of SA layer than the permittivity along the tangential direction. With increasing the anisotropic value of the middle layer, the dipole peaks of antisymmetric [ω-.sup.-] mode and symmetric [ω-.sup.+] mode both show blue-shifts, while the shift of the antisymmetric [ω-.sup.-] mode is larger than that for the symmetric [ω-.sup.+] mode. The larger anisotropic value of the SA layer induces the stronger near-field outside the nanoparticles for the antisymmetric [ω-.sup.-] mode, while the smaller anisotropic value makes the larger near-field for the symmetric [ω-.sup.+] mode. We further have found that the middle SA layer with smaller anisotropic value is helpful to obtain larger electric fields inside the nanoshells, which may be useful for their potential applications in nonlinear optics. Keywords Spherical anisotropy. Sandwiched gold nanoshells. Plasmon coupling. Near-field enhancement, Introduction Metallodielectric layered nanoparticles and nanostructures have attracted increasing scientific and technological interest in recent years due to their importance in the fundamental physics and the potential applications in nano-electronics, [...]

The plasmon resonances of metallic nanoparticles have received considerable attention for their applications in nanophotonics, biology, sensing, spectroscopy and solar energy harvesting. Although thoroughly characterized for spheres larger than ten nanometres in diameter, the plasmonic properties of particles in the quantum size regime have been historically difficult to describe owing to weak optical scattering, metal-ligand interactions, and inhomogeneity in ensemble measurements. Such difficulties have precluded probing and controlling the plasmonic properties of quantum-sized particles in many natural and engineered processes, notably catalysis. Here we investigate the plasmon resonances of individual ligand-free silver nanoparticles using aberration-corrected transmission electron microscope (TEM) imaging and monochromated scanning TEM electron energy-loss spectroscopy (EELS). This technique allows direct correlation between a particle's geometry and its plasmon resonance. As the nanoparticle diameter decreases from 20 nanometres to less than two nanometres, the plasmon resonance shifts to higher energy by 0.5 electronvolts, a substantial deviation from classical predictions. We present an analytical quantum mechanical model that describes this shift due to a change in particle permittivity. Our results highlight the quantum plasmonic properties of small metallic nanospheres, with direct application to understanding and exploiting catalytically active and biologically relevant nanoparticles., The remarkable growth of nanotechnology has been driven by the ability to alter material properties as dimensions are reduced towards the atomic scale. Nanomaterials exhibit physical and chemical properties very [...]

We show that a broadband surface plasmon can be excited in a thin metal film. A train of two plasmons can be excited at conditions near the condition of broadband surface plasmon excitation. Also, a method for independent multichannel checks of biochips by wavelength addressing is proposed. OCIS codes: 240.6680, 130.6010, 110.2970.

Three-dimensional gold nanoarchitecture was fabricated by layer-by-layer (LbL) deposition of gold nanoparticles (AuNPs) and multiwalled carbon nanotubes (MWCNTs) on a glass substrate for a highly sensitive plasmonic biosenser using a conventional UV-vis instrument. Carboxyl-functionalized MWCNTs were reacted with 3-mercaptopropyltriethoxysilane (MPTES) to introduce multiple thiol groups onto MWCNTs. A serf-assembled monolayer (SAM) of AuNPs on a glass chip was sequentially dipped into MPTES-functionalized MWCNTs (MWCNT-Si-SH) and AuNPs to form multilayers of AuNPs on MWCNTs. Such three-dimensionally assembled AuNPs provided a large surface area and multiple binding sites within a few steps of modification and microporous structures of multilayered MWCNTs to allow a high accessibility of target molecules. It was shown that the bulk refractive index (RI) sensitivity of these muitilayered AuNPs (three-dimensional chip) appeared to be 5.6 times better than that of a monolayer of AuNPs on a glass chip (two-dimensional chip). The three-dimensional chips were further used for a biomolecular binding study, showing a detection limit as low as 0.5 nM for streptavidin and 3.33 nM for anti-human serum albumin (HSA), both of which were ~20 times higher than the sensitivity of the two-dimensional chips. 10.1021/ac100346z

A research element of the European Union (EU) sixth Framework project BioCop focused on the development of a surface plasmon resonance (SPR) biosensor assay for the detection of paralytic shellfish poisoning (PSP) toxins in shellfish as an alternative to the increasingly ethically unacceptable mouse bioassay. A biosensor assay was developed using both a saxitoxin binding protein and chip surface in tandem with a highly efficient simple extraction procedure. The present report describes the single laboratory validation of this immunological screening method, for this complex group of toxins with differing toxicities, according to the European Decision 2002/ 657/EC in conjunction with IUPAC and AOAC single laboratory validation guidelines. The different performance characteristics (detection capability CC[beta], specificity/selectivity, repeatability, reproducibility, stability, and applicability) were determined in relation to the EU regulatory limit of 800 [micro]g of saxitoxin equivalents (STX eq) per kg of shellfish meat. The detection capability CC[beta] was calculated to be 120 [micro]g/kg. intra-assay repeatability was found to be between 2.5 and 12.3% and interassay reproducibility was between 6.1 and 15.2% for different shellfish matrices. Natural samples were also evaluated and the resultant data displayed overall agreements of 96 and 92% with that of the existing AOAC approved methods of mouse bioassay (MBA) and high performance liquid chromatography (HPLC), respectively. 10.1021/ac1000338

The most general investigation and exploitation of light-induced processes require simultaneous control over spatial and temporal properties of the electromagnetic field on a femtosecond time and nanometer length scale. Based on the combination of polarization pulse shaping and time-resolved two-photon photoemission electron microscopy, we demonstrate such control over nanoscale spatial and ultrafast temporal degrees of freedom of an electromagnetic excitation in the vicinity of a nanostructure. The time-resolved cross-correlation measurement of the local photoemission yield reveals the switching of the nanolocalized optical near-field distribution with a lateral resolution well below the diffraction limit and a temporal resolution on the femtosecond time scale. In addition, successful adaptive spatiotemporal control demonstrates the flexibility of the method. This flexible simultaneous control of temporal and spatial properties of nanophotonic excitations opens new possibilities to tailor and optimize the light--matter interaction in spectroscopic methods as well as in nanophotonic applications. coherent control | nanophotonics | plasmonics | ultrafast spectroscopy www.pnas.org/cgi/doi/10.1073/pnas.0913556107

We present studies on the propagation of plasmon waves in metallic multimode waveguides surrounded by a dielectric medium. The permittivity of the metal was determined by a Drude model. The propagation was simulated by the method of lines. The propagating field exhibited the well-known self-imaging phenomenon known as the Talbot effect. The metallic waveguides are lossy. The influence of various parameters on the losses was examined. By a suitable choice of parameters, propagation distances of several Talbot periods are possible. Our investigation also includes simulations for the propagation of eigenmodes of the waveguides and results for the calculation of the effective index. OCIS codes: 050.1960, 070.6760, 130.2790, 130.3120, 230.7370, 240.6680.

A hexagonal nanostructure formed by seven core shell nanocylinders filled with different dielectric cores is investigated. The surface plasmon resonance in such a hexagonal nanostructure under conditions of different illumination wavelengths, dielectric cores, angles of incidence, and thicknesses of silver shells is studied by use of the finite element method. Simulation results show that the resonant wavelength is redshifted as the dielectric constant and the size of the core increase. The peak resonant wavelength and the local field enhancement are approximately proportional to the radius of the dielectric core. Additionally, the surface plasmon field excited by TM-polarized light at the incident angle of [theta] = 15[degrees] is exactly a linear combination of those excited at incident angles of [theta] = 0[degrees] and 30[degrees], confirming the linear nature of the surface plasmon resonance in a nanostructure formed by linear media. OCIS codes: 240.6680, 250.5403.

We report on microscopic imaging of phospholipid membranes. To achieve nonlabel, noncontact, and high spatial resolution imaging of the membranes, we use optically excited localized surface plasmons as a virtual measurement probe to obtain the local refractive index. This enables significantly higher lateral resolution of ~170nm. We reveal that the developed microscope has the capability of observing lipid bilayers with thickness of 3.0nm deposited into the gaps in a patterned lipid bilayer with thickness of 4.6 nm. We find that the thickness resolution against the deposited lipid bilayer is ~0.33 nm. OCIS codes: 240.6680, 180.0180, 120.6650.

Leakage radiation microscopy (LRM) is used to directly image surface-plasmon-coupled emission (SPCE). When compared with the prism-based setup commonly used in SPCE research, LRM has the advantages of directly giving out the emitting direction without angle scanning, and the image generated of surface plasmon polariton (SPPs) propagation, which helps to understand the optical process of SPCE. LRM also can give a clearer SPCE image than that obtained by a prism-based setup. Based on the LRM, we find that the SPCE pattern and propagation of SPPs can be modified by the shape of PMMA films containing fluorescence molecules. OCIS codes: 180.2520, 240.6680.

A new biosensor based on surface plasmon-enhanced fluorescence spectroscopy (SPFS), which employs long-range surface plasmons (LRSP) and a photo-cross-linkable carboxymethyl dextran (PCDM) hydrogel binding matrix, is reported. LRSPs are surface plasmon modes that propagate along a thin metallic film with orders of magnitude lower damping compared to regular surface plasmons. Therefore, their excitation provides strong enhancement of the intensity of the electromagnetic field and a greatly increased fluorescence signal measured upon binding of fluorophore-labeled molecules on the sensor surface. In addition, these modes exhibit highly extended evanescent fields penetrating up to micrometers in distance from the metallic sensor surface. Therefore, a PCDM hydrogel with approximately micrometer thickness was anchored on the sensor surface to serve as the binding matrix. We show that this approach provides large binding capacity and allows for the ultrasensitive detection. In a model experiment, the developed biosensor platform was applied for the detection of free prostate specific antigen (f-PSA) in buffer and human serum by using a sandwich immunoassay. The limit of detection at the low femtomolar range was achieved, which is approximately 4 orders of magnitude lower than that for direct detection of f-PSA based on the monitoring of binbing-induced refractive index changes. 10.1021/ac901662e

The propagation of laser-excited surface plasmons along a gold film with surface roughness is directly observed via scattered light. The attenuation length of surface plasmons in a broad wavelength interval is calculated for smooth gold and silver films. The surface roughness, which was characterized with an AFM, introduces corrections to the attenuation length, angular dependence of the surface plasmon resonance, and the effective dielectric constant of the metal film. These corrections are also taken into account and discussed. OCIS codes: 240.0310, 240.5770, 240.6680.

Surface plasmons are electromagnetic waves that can exist at metal interfaces because of coupling between light and free electrons. Restricted to travel along the interface, these waves can be channeled, concentrated, or otherwise manipulated by surface patterning. However, because surface roughness and other inhomogeneities have so far limited surface-plasmon propagation in real plasmonic devices, simple high-throughput methods are needed to fabricate high-quality patterned metals. We combined template stripping with precisely patterned silicon substrates to obtain ultrasmooth pure metal films with grooves, bumps, pyramids, ridges, and holes. Measured surface-plasmon--propagation lengths on the resulting surfaces approach theoretical values for perfectly flat films. With the use of our method, we demonstrated structures that exhibit Raman scattering enhancements above [10.sup.7] for sensing applications and multilayer films for optical metamaterials.

Nickel thin films thermally evaporated onto glass supports are used to demonstrate surface plasmon coupled fluorescence (SPCF) over a broad 400 nm wavelength range (400-800 nm) for potential assays that can be run in buffer and/or whole blood. In contrast to traditional fluorescence-based assays, SPCF converts otherwise isotropic emission into highly directional and polarized emission, an attractive concept for surface assays. Theoretical Fresnel calculations performed in the ultraviolet to near-infrared spectral range (344-1240 nm) predict the near-field generation of surface plasmons in 15 and 20 nm nickel thin films. The angles of minimum reflectivity for nickel thin films with 10 nm Si[O.sub.x] and 30 nm polymer overcoats over the 428-827 nm wavelength range occur over a 10 degree range. To experimentally corroborate the theoretical calculations, a polymeric solution of five different fluorophores, POPOP ([[lambda].sub.max, emission] : 428 nm), FITC (517 nm), S101 (600 nm), Zn PhCy (710 nm), and IR 780 (814 nm), were spin coated separately onto 15 and 20 nm nickel thin films. SPCF intensity (s- and p-polarized) from fluorophores at the corresponding emission [[lambda].sub.max] was measured at angles between 0-90 degrees. In addition, the free-space emission and SPCF intensity of FITC on 20 nm nickel thin film were also measured to demonstrate the angular-dependent nature of SPCF. SPCF from nickel thin films was p-polarized and highly directional with [[lambda].sub.max] confirmed at an angle of 65 degrees for all the fluorophores as predicted by Fresnel calculations. The utility of nickel thin films for whole blood bioassays is demonstrated with a long-wavelength fluorophore, where the SPCF intensity of Zn PhCy (50 pM-50 [micro]M) in whole blood at 710 nm was measured at 65 degrees. Using Fresnel calculations it is also predicted that the evanescent field above the nickel films penetrates deeper into solution than for other metals used to date for SPCF, an attractive notion in SPCF-based biosensing applications.

A prototype nanoparticle biosensor based on localized surface plasmon resonance (LSPR) spectroscopy was developed to detect drug binding to human membrane-bound cytochrome P450 3A4 (CYP3A4). CYP3A4 is one of the most important enzymes in drug and xenobiotic metabolism in the human body. Because of the inherent propensity of CYP3A4 to aggregate, it is difficult to study drug binding to this protein in solution and on surfaces. In this paper, we use a soluble nanometer scale membrane bilayer disk (Nanodisk) to functionally stabilize monomeric CYP3A4 on Ag nanoparticle surfaces fabricated by nanosphere lithography. CYP3A4-Nanodiscs have absorption bands in the visible wavelength region, which upon binding certain drugs shift to either shorter (type I) or longer wavelengths (type II). On the basis of the coupling between the LSPR of the Ag nanoparticles and the electronic resonances of the heme chromophore in CYP3A4-Nanodiscs, LSPR spectroscopy is used to detect drug binding with high sensitivity. This paper combines LSPR and Nanodisc techniques to optically sense drug binding to a functionally stable membrane protein, with the goal of integrating this with microfluidics and expanding it into a multiarray format, enabling high-throughput screening.

Here we experimentally demonstrate measurements of the wavelength-dependent phase response of a surface plasmon resonance sensor using a spectral interferometric technique. By using a broadband incoherent fiber light source and a polarimetry configuration with a high-birefringence component, the spectral phase response of a surface plasmon resonance sensor can be retrieved. A combination of wavelength interrogation and phase detection is enabled by our proposed scheme. In contrast to the previously demonstrated heterodyne or spatial fringe detection schemes, this in-line optical configuration is much simpler and can be very compact when implemented with advanced fiber optic and integrated components. OCIS codes: 240.6680, 280.4788, 120.5050, 120.2130.

The surface plasmon resonance (SPR) biosensor was recently introduced to the analytical biochemical society for measuring small drug--protein interactions. However, the technique has many times been used without specifying the type of enantiomeric form of the chiral drug measured and/or with using a too narrow drug concentration range resulting in biased values of binding coefficients and sometimes even assumptions about single-site bindings although the binding in reality comprises a multisite interaction. In this study we will give guidelines for reliable experimental and methodological approaches to avoid these pitfalls. For this purpose, we also introduce a new tool, based on physical chemistry, to the sensor community; the calculation of the adsorption energy distribution (AED). The AED-calculations reveal the degree of heterogeneity directly from the SPR raw data and thus guide us into a narrower selection of probable models before the rival model titling procedure. We demonstrate how to measure reliable equilibrium data for the two typically different cases: drug binding to (i) transport (plasma) proteins and to (ii) a target protein. Both the binding of the chiral [beta]-blocker propranolol to [[alpha].sub.1]-acid glycoprotein (AGP) and that of the anticoagulant warfarin to human serum albumin were heterogeneous, with a few strong enantioselective sites and many weak nonselective sites. We also demonstrate how the multisite binding rapidly falsely turns to single-site as the concentration range is narrowed and how adding dimethyl sulfoxide to the buffer affects multisite drug--protein data. The binding of the enantiomers of the thrombin inhibitor melagatran was investigated on both thrombin and the transport proteins, revealing clear enantioselectivity for thrombin in favor of the active enantiomer, but almost similar binding properties for both enantiomers to the transport protein AGP. The AED-ealculations verified that both these system has a unimodal energy distribution and are best described with a homogeneous adsorption model.

We have applied surface plasmon resonance (SPR) spectroscopy to study the cooperative interactions of estrogen receptor a (ERa) and transcription factor Sp1 with a composite DNA element, containing an estrogen response element (ERE) half-site upstream of two adjacent Sp1 sites (+571 ERE/Sp1 composite site in promoter A of the human PR gene). Using nuclear extracts of MCF-7 breast cancer cells as sample, we have shown that Sp1 is associated with Sp1-binding sites only, whereas ERa can be recruited to DNA both through direct binding to the ERE half-site and/or through protein-protein interactions with DNA-bound Sp1. The ERE half-site and the proximal Sp I site are only 4 bp apart, and our data suggests that one transcription factor bound to DNA constitutes a sterical hindrance of the accessibility of the binding site for the other transcription factor. Our data confirms previous observations that ERa increases the amount of Sp1 recruited to the composite binding site in a dose-dependent manner. Using recombinant proteins, we have unambiguously proved the formation of a ternary complex of ERa/Sp1--composite DNA, for which previously published electrophoretic mobility shift assay (EMSA) results are contradictive. With this study, we have demonstrated that the solid--liquid-phase SPR assay is a powerful alternative for studying multiprotein--DNA interactions and is superior to the EMSA experiments as it is capable of real-time measurements, can quantify the amount of protein bound, and can capture transient and weak binding interactions. The comprehensive characterization of the synergistic interactions between ERa--DNA, Sp1--DNA, and ER[alpha]--Sp1 contributes to the understanding of how ERa and Sp1 influence and activate gene transcription.

We present a fractional sensitivity analysis of a competitive microfluidic heterogeneous immunoassay for a small molecule analyte. A simple two-dimensional finite element model is used to determine the fractional sensitivity of the assay signal with respect to analyte concentration, flow rate, initial surface density of binding sites, and antibody concentration. The fractional sensitivity analysis can be used to identify (1) the system parameters for which it is most crucial to control or quantify the variability between assays and (2) operating ranges for these parameters that improve assay sensitivity (within the constraints of the experimental system). Experimental assay results for the drug phenytoin, obtained using surface plasmon resonance imaging, are shown to be consistent with the predictions of the model.

We present nanohole arrays in a gold film integrated with a six-channel microfluidic chip for parallel measurements of molecular binding kinetics. Surface plasmon resonance effects in the nanohole arrays enable real-time, label-free measurements of molecular binding events in each channel, while adjacent negative reference channels can record measurement artifacts such as bulk solution index changes, temperature variations, or changing light absorption in the liquid. With the use of this platform, streptavidin--biotin specific binding kinetics are measured at various concentrations with negative controls. A high-density microarray of 252 biosensing pixels is also demonstrated with a packing density of 106 sensing elements/[cm.sup.2], which can potentially be coupled with a massively parallel array of microfluidic channels for protein microarray applications.

Thermally responsive hydrogel gratings were micro-patterned and immobilized on a gold coated glass substrate using a photochemical cross-linking and attachment method. The thermoresponsive behavior of hydrogels with different thicknesses was studied in MilliQ water by the surface plasmon diffraction (SPD) technique. The diffraction intensity can be substantially increased by surface plasmon field enhancement. Because of its self-reference property, SPD offers considerable advantages in the characterization of the thin hydrogel film. The real-time kinetic observation of the volume phase transition in thin hydrogel films can be achieved by monitoring the diffraction intensity variation as a function of temperature. Little diffraction intensity of the hydrogel grating was observed in the swollen state while strong intensity peaks were observed in the collapsed state owing to the large change in the optical contrast upon the volume phase transition.

Rapid, sensitive, and accurate detection of analytes present in low concentrations in complex matrixes is a critical challenge. One issue that affects many biosensor protocols is the number and nature of the interferences present in complex matrixes such as plasma, urine, stool, and environmental samples, resulting in loss of sensitivity and specificity. We have developed a method for rapid purification, concentration, and detection of target analytes from complex matrixes using antibody-coated superparamagnetic nanobeads (immunomagnetic beads, or IMBs). The surface plasmon resonance (SPR) detection signal from staphylococcal enterotoxin B (SEB) was dramatically increased when the IMBs were used as detection amplifiers. When SEB detection included a 10-fold concentration/purification IMB protocol, a substantial increase in detection sensitivity was observed. This procedure was used to successfully purify and concentrate SEB from serum and stool samples, then amplify the SPR detection signal. SEB at a concentration of 100 pg/mL was easily detected in both buffer and stool samples using this procedure. The IMB protocol also served to verify the analyte detection by using two different anti-SEB antibodies, mouse monoclonal antibodies attached to the magnetic nanobeads and rabbit polyclonal antibodies on the SPR sensor surface. Multiple detections of SEB in stool were performed using the same sensor surface by regenerating the sensor surfaces with a pH 2.2 buffer wash.

Optical antenna is a nanoscale miniaturisation of radio or microwave antennas that is also governed by the rule of plasmonics. We introduce various types of optical antenna and make an overview of recent developments in optical antenna research. The role of local and surface plasmons in optical antenna is explained through antenna resonance and resonance conditions for specific metal structures are explicitly obtained. A strong electric field is shown to exist within a highly localised region of optical antennas such as antenna feed gap or apertures. We describe physical properties of field enhancement in apertures (circular and rectangular holes) and gaps (infinite slit and feed gap), as well as experimental techniques measuring enhanced electric vector field. We discuss the analogies and differences between conventional and optical antennas with a projection for future developments. Keywords: optical antenna; subwavelength; resonance; surface plasmon; enhancement; metal

The dependence of the surface plasmon resonance (SPR) phase difference curve on the complex refractive index of a sample in Kretschmann configuration is discussed comprehensively, based on which a new method is proposed to measure the complex refractive index of turbid liquid. A corresponding experiment setup was constructed to measure the SPR phase difference curve, and the complex refractive index of turbid liquid was determined. By using the setup, the complex refractive indices of Intralipid solutions with concentrations of 5%, 10%, 15%, and 20% are obtained to be 1.3377 + 0.0005i, 1.3427 + 0.0028i, 1.3476 + 0.0034i, and 1.3496 + 0.0038i, respectively. Furthermore, the error analysis indicates that the root-mean-square errors of both the real and the imaginary parts of the measured complex refractive index are less than 5 x [10.sup.-5]. OCIS codes: 240.6680, 170.7050, 120.4530.

Label-free biomolecular binding measurement methods, such as surface plasmon resonance (SPR), are becoming increasingly more important for the estimation of real-time binding kinetics. Recent advances in surface plasmon resonance imaging (iSPR) are emerging for label-free microarray-based assay applications, where multiple biomolecular interactions can be measured simultaneously. However, conventional iSPR microarray systems rely on protein printing techniques for ligand immobilization to the gold imaging surface and external pumps for analyte transport. In this article, we present an integrated microfluidics and iSPR platform that uses only electrokinetic transport and guiding of ligands and analytes and, therefore, requires only electrical inputs for sample transport. An important advantage of this new approach, compared to conventional systems, is the ability to direct a single analyte to a specific ligand location in the microarray, which can facilitate analysis parallelization. Additionally, this simple approach does not require complicated microfluidic channel arrangements, external pumps, or valves. As a demonstration, kinetics and affinity have been extracted from measured binding responses of human IgG and goat antihuman IgG using a simple 1:1 model and compared to responses measured with conventional pressure driven analyte transport. The measured results indicate similar binding kinetics and affinity between the electrokinetic and pressure-driven sample manipulation methods and no cross contamination to adjacent measurement locations has been observed.

In this contribution, we established a sandwich immunoassay system with a common spectrofluorometer to collect the plasmon resonance scattering (PRS) signals from silver nanoparaticles (AgNPs) immunotargeted on glass slides. By taking the immunoreactions of goat antihuman IgG (Fc fragment specific) antibody (GAH-IgG), human immunoglobulin (H-IgG), and rabbit antihuman IgG (Fab fragment specific) antibody (RAH-IgG) as an example, we found that if a primary antibody (GAH-IgG) was first immobilized on the surface of glass slides and applied to capture target antigen (H-IgG), AgNPs-labeled secondary antibody (RAH-IgG) could be employed to detect the target antigen (H-IgG) by forming a sandwich immune complex on the surface of the glass slide. It was found that the PRS signals resulting from the AgNPs immunotargeted on the glass slides could be applied to the quantitative detection of H-IgG target antigen in the range of 10-1000 ng/mL with the limit of determination of 1.46 ng/mL (3[sigma]) under optimal conditions, which is sensitive and comparable with reported chemiluminescence immunoassays. With a dark-field microscope coupled with a spectral system, we measured the PRS features of single AgNPs immunotargeted on the glass slides, showing that the PRS of single nanoparticles might have potential applications in analytical chemistry. Further findings showed that the strong PRS signals from the AgNPs immunotargeted on the glass slides can be clearly seen and distinguished by naked eyes under the excitation of a common white light-emitting diode (LED) torch. Therefore, a visual PRS immunoassay system can be established easily with common glass slides and an LED torch.

Composite films consisting of a ceramic matrix with embedded metal nanoparticles have received increased interest due to their numerous potential applications in the field of optics and optoelectronics. Numerous studies have been dedicated to the fabrication of these composite materials and it has been shown that nanocermet films can be obtained by successive deposition of alternate dielectric and metal films of thicknesses opportunely chosen. In this case, stacks of dielectric layers alternated with layers of metal nanoclusters (NCs) are obtained. However, until now, optical characterization of these kinds of multilayer stack has been used to retrieve mainly qualitative information on the dimension, shape, and geometric distribution of nanoparticles inside the dielectric matrix. An easy-to-handle model that quantitatively links the optical properties to the main features of the NCs embedded in the matrix is presented. This model can be applied to multilayer stacks of dielectric layers alternated with metal NC layers and is shown to be a valid alternative to a recently published model [Nanotechnology 19, 125709 (2008)] that was applied to the case of a three-layer structure (dielectric/metal:dielectric/dielectrict. OCIS codes: 310.6860, 240.6680, 160.4236.

We report a microfabrication approach to generate well-defined, addressable, and regenerable lipid membrane arrays in poly(dimethylsiloxane) (PDMS) microchips for label-free analysis of lipid-protein interactions with surface plasmon resonance imaging (SPRi). The multiplexed detection is demonstrated with a tethered bilayer membrane array built in parallel microchannels. These channels allow multiple measurements to be carded out simultaneously, showing low deviations for element-to-element variation in quantifiable signal. Lipid-conjugated receptors were utilized as model systems for protein binding analysis, and the feasibility of regenerating the tethering sublayer after binding was investigated. The results show that the lipid membrane can be removed effectively by nonionic surfactant Triton X-100. The small variance in SPR signal for the buildup process, i.e.,

We demonstrate surface plasmon resonance (SPR) fiber devices based upon ultraviolet inscription of a grating-type structure into both single-layered and multilayered thin films deposited on the flat side of a lapped D-shaped fiber. The single-layered devices were fabricated from germanium, while the multilayered ones comprised layers of germanium, silica, and silver. Some of the devices operated in air with high coupling efficiency in excess of 40 dB and an estimated index sensitivity of [DELTA][lambda]/[DELTA]n = 90 nm from 1 to 1.15 index range, while others provided an index sensitivity of [DELTA][lambda]/[DELTA]n = 6790 nm for refractive indices from 1.33 to 1.37. OCIS codes: 060.2370, 060.2310.

Aflatoxins are extremely toxic metabolites from Aspergillus species that can adulterate a wide range of human foodstuff. Herein, we propose a novel assay designed as an analytical test for aflatoxin [B.sub.1] and [G.sub.1] (AF[B.sub.1] and AF[G.sub.1], respectively) that could represent an alternative screening technique for this class of mycotoxins. The approach for the determination of these toxins is based on surface plasmon resonance using neutrophil porcine elastase as a 'bait' for these aflatoxins. The selection and optimization of the analytical procedure involved a preliminary investigation on the type of inhibition by AF[B.sub.1]: the level of the protease inhibition exerted by AF[B.sub.1] depended upon the incubation time and the concentration of the binding partners, showing the competitiveness and the reversibility of the inhibition. A posteriori, the nature of the interaction granted a rapid analysis, a single detection test requiring only a few minutes. For the development of the assay, the experimental conditions were evaluated and optimized with both calibration solution and aflatoxin-spiked samples. To apply this method to aflatoxin-contaminated maize, a rapid solid-phase extraction treatment was developed. The proposed assay for AF[B.sub.1] and AF[G.sub.1] was validated by comparison with both a chromatographic reference method and a standard enzyme linked immunosorbent assay procedure. This enzyme-based biosensor represents a new approach for the detection of aflatoxins based on the reversible interaction between a blocked macromolecule and a soluble ligand, having the major advantages in the relative rapidity, the reusability of the capturing surface, and low cost per single test.

We investigated the effect of surface roughness on the sensor performance of extinction-based localized surface plasmon resonance (LSPR) biosensors. The sensor measures resonance wavelength shifts in transmittance caused by biomolecular interactions that are amplified by periodic nanostructures. The numerical computation was conducted using rigorous coupled-wave analysis with Gaussian random surface profiles. The results suggest that, when a surface has a roughness smaller than 2 nm in height deviation, the sensitivity of a LSPR biosensor is not significantly influenced regardless of correlation length (CL). However, we found that the extinction peak amplitude and curve width are affected substantially by a decrease in CL. At a less than 100 nm CL, surface roughness can induce interference between localized surface plasmons excited by the surface and nanowires, which can lead to major degradation of sensor performance. OCIS codes: 050.2770, 130.6010, 240.5770, 240.6680.

We report a rapid and ultrasensitive surface plasmon resonance (SPR) assay of chloramphenicol (CAP) by using large gold nanoparticles (40 nm) for signal enhancement on a mixed self-assembled monolayer (mSAM) sensor surface. After immobilization of the target antibiotic CAP through its ovalbumin (OVA) conjugates with an oligoethylene glycol (OEG) linker on the mSAM surface, sequential binding of anti-CAP antibody and IgG/nanogold (40 nm) onto the sensor surface afforded a rapid (< 10 min) and ultrasensitive assay format for CAP. A limit of detection (LOD) for CAP as low as 0.74 fg/mL was achieved in aqueous buffer, and the linear working range was between 1-1000 fg/mL. While the LOD of CAP in a honey spiked-specimen is 17.5 fg/mL, the detection range is 80-5000 fg/mL. The mSAM sensor surface was also shown to be highly stable with over 400 binding/ regeneration cycles performed.

The interaction of light with metal nanoparticles leads to novel phenomena mediated by surface plasmon excitations. In this article we use single molecules to characterize the interaction of surface plasmons with light, and show that such interaction can strongly modulate the polarization of the emitted light. The simplest nanostructures that enable such polarization modulation are asymmetric silver nanocrystal trimers, where individual Raman scattering molecules are located in the gap between two of the nanoparticles. The third particle breaks the dipolar symmetry of the two-particle junction, generating a wavelength-dependent polarization pattern. Indeed, the scattered light becomes elliptically polarized and its intensity pattern is rotated in the presence of the third particle. We use a combination of spectroscopic observations on single molecules, scanning electron microscope imaging, and generalized Mie theory calculations to provide a full picture of the effect of particles on the polarization of the emitted light. Furthermore, our theoretical analysis allows us to show that the observed phenomenon is very sensitive to the size of the trimer particles and their relative position, suggesting future means for precise control of light polarization on the nanoscale. generalized Mie theory | single-molecule Raman scattering | plasmonics

We present a flexible new sensor system that combines the joint advantages of (i) discretely functionalized, code-bearing, microparticles and (ii) label-free detection using grating-coupled surface plasmon resonance. This system offers the possibility of simultaneously investigating the real-time binding kinetics of a variety of molecular interactions. One single multiplexed assay could employ a wide range of immobilization chemistries, surface preparation methods, and formats. Thus, the new system offers a very high level of assay conformability to the end user, particularly when compared to fixed microarrays.

We present a new microscopy technique that we call transmission angle deviation microscopy (TADM). It is based on common-path heterodyne interferometry and geometrical optics. An ultrahigh sensitivity surface plasmon resonance (SPR) angular sensor is used to expand dynamic measurement ranges and to improve the axial resolution in three-dimensional optical microscopy. When transmitted light is incident upon a specimen, the beam converges or diverges because of refractive and/or surface height variations. Advantages include high axial resolution (~32 nm), nondestructive and noncontact measurement, and larger measurement ranges ([+ or -]80 [micro]m) for a numerical aperture of 0.21 in a transparent measurement medium. The technique can be used without conductivity and pretreatment. OCIS codes: 120.0120, 040.2840, 050.5080, 180.5810, 120.3180, 240.6680.

A simple strategy for increasing the collection efficiency of surface plasmon-coupled emission (SPCE) is demonstrated. SPCE is a near-field phenomenon occurring when excited fluorophores are in close proximity to a subwavelength metal film. The energy of the fluorophores induces surface plasmons that radiate the coupled energy at highly specific angles. In an attempt to maximize the collected emission, a conical mirror was placed around the coupling prism. The result was a nearly 500 fold enhancement over the free space signal as detected from a single point from a poly(vinyl alcohol) layer doped with ruthenium. Coupling this large enhancement with LED excitation could lead to the development of inexpensive, handheld fluorescent devices with high sensitivity. OCIS codes: 080.2740, 240.0310, 300.2530.

We report the development of an air-stable, supported membrane array by use of photolithography for label-free detection of lipid--protein interactions. Phosphoinositides and their phosphorylated derivatives (PIPs) were studied for their binding properties to proteins with lipid microarray in combination with surface plasmon resonance imaging (SPRi). We have demonstrated a simple method to fabricate lipid arrays using photoresist and carried out a series of surface characterizations with SPRi, ac impedance, cyclic voltammetry, and fluorescence microscopy to validate the array quality and lipid bilayer formation. A number of lipid compositions have been tested for the robustness of resulting membranes when undergoing dehydration and rehydration procedures, and the 1,2dioleoyl-sn-glycero -3-ethylphosphocholine/poly(ethyl- ene glycol)-phosphatidylethanolamine (DOPC+/PEG-PE) system stands out as the best performer that yields the recovery to within 2% of the original state according to SPR sensorgrams. Limits of detection on the dehydrated/ rehydrated DOPC+/PEG-PE membranes were determined to be 33 nM for avidin binding to biotinylated lipids, 73.5 nM for cholera toxin to GM1, and 25 nM for PtdIns(4,5)P2-binding protein ([P.sub.4,5]BP) to PtdIns(4,5)P2 lipid, respectively. These results demonstrate the suitability and sensitivity of this membrane for constructing membrane arrays for SPRi analysis under ambient conditions. With the use of this addressable and functional lipid membrane array, the screening of specific lipid--protein interactions has been conducted. Strong and specific interactions between [P.sub.4,5]BP and PtdIns(4,5)[P.sub.2]/DOPC+/ PEG-PE membrane were observed as expected, while cross reactions were spotted for [P.sub.4,5]BP/PtdIns(4)P and avidin/GM1 at varied degrees. The air-stable membrane array demonstrated here presents a simple, effective approach for constructing functional membrane surfaces for screening applications, which opens a new avenue for the label-free study of membrane proteins and other forms of lipid--membrane interactions.

Nanodiscs are self-assembled soluble discoidal phospholipids bilayers encirculated by an amphipathic protein that together provide a functional stabilized membrane disk for the incorporation of membrane-bound and membraneassociated molecules. The scope of the present work is to investigate how nanodiscs and their incorporated membrane receptors can be attached to surface plasmon resonance sensorchips and used to measure the kinetics of the interaction between soluble molecules and membrane receptors inserted in the bilayer of nanodiscs. Cholera toxin and its glycolipid receptor [G.sub.M1] constitute a system that can be considered a paradigm for interactions of soluble proteins with membrane receptors. In this work, we have investigated different technologies for capturing nanodiscs containing the glycolipid receptor [G.sub.M1] in lipid bilayers, enabling measurements of binding of its soluble interaction partner cholera toxin B subunit to the receptor with the sensorchip-based surface plasmon resonance (SPR) technology. The measured stoichiometric and kinetic values of the interaction are in agreement with those reported by previous studies, thus providing proof-of-principle that nanodiscs can be employed for kinetic SPR studies.

We present a complete palm-sized, battery-operated bio-detection system based on highly sensitive localized surface plasmon resonance (LSPR). We have replaced the spectrum analyzer by four pulse-powered light-emitting diodes (LED), each with different emission spectra. The reflected light beams from all LEDs were detected by a single photodiode. Its composite output current was demultiplexed by a four-channel lock-in amplifier. Device performance was demonstrated using an LSPR chip covered with a mixture of ethanol/water and 2-propanol/ water at different concentrations. The miniaturized system does not require any external power supply or personal computer and it is therefore suitable for point-of-care and field applications.

Low-attenuation waveguides based on the propagation of long-range surface plasmon polaritons (LRSPPs) along thin Au stripes embedded in low absorption perfluorocyclobutane (PFCB) polymer are presented. A new low in propagation loss of OCIS codes: 230.7390, 240.6680, 310.6860, 160.5470.

A subwavelength corrugated metal wavegnide is studied and designed to slow down the light at terahertz frequencies. The waveguide consists of two parallel thin metal slabs with periodic corrugations on their inner boundaries. Compared with structures based on engineered surface plasmons, the proposed structure has smaller group velocity dispersion and lower propagation loss. The origin of the slow wave is also explained. OCIS codes: 260.3910, 230.7370, 040.2235, 230.4555.

Multiple-angle incidence resolution spectrometry (MAIRS) that was originally developed in an infrared region for analysis of molecular orientation in a thin film on a substrate has been extended to develop a novel UV-visible spectrometry. The new technique, named Vis-MAIRS, has been employed for analysis of anisotropic surface plasmon excitation in a silver thin film with a thickness of 5 nm deposited on a glass slide. The Vis-MAIRS spectra yield two spectra at a time, which correspond to absorption spectra whose transition moments are parallel and perpendicular to the film surface. The two spectra of the silver thin film were largely different from each other in shape, which strongly suggested that the silver nanoparticles in the thin film were in an ellipsoidal shape. In addition, absorption due to long-range surface plasmon propagation across the nanoparticles aligned parallel to the film surface, which is a result of the dipole or quadruple couplings of plasmon in each particle, was clearly monitored for the first time in the Vis-MAIRS spectra. In this manner, Vis-MAIRS is expected to be a useful tool to study aggregates of metal nanoparticles in a film.

In this paper, a novel differential-phase-sensitive surface plasmon resonance biosensor (DP-SPRB) is proposed and developed, in which a two-frequency laser is integrated with a differential amplifier in order to analytically convert the phase modulation into amplitude modulation. With the use of the conventional envelope detection technique, the differential phase is precisely decoded in real time in terms of the demodulated amplitude. In order to verify high detection sensitivity of the DP-SPRB, a sucrose-water solution and glycerin-water solution at low concentrations were both tested, and the experimental results confirm that the detection sensitivity on wt % concentration of the sucrose solution is 0.00001%. Moreover, the real-time monitoring mouse IgG/antimouse IgG interaction shows the minimum concentration of mouse IgG to be at 10 fg/mL. To our knowledge, this is the highest sensitivity ever measured by a surface plasmon resonance biosensor. However, because of the limited dynamic range of DP-SPRB, it can only apply to biomolecule interactions at extremely low concentration.

We have integrated a surface plasmon grating coupler into a quartz crystal microbalance (QCM) for studying surface association/dissociation reactions. In the integrated system only QCM measurement is needed to record both the optical and the acoustic signals in the same association/ dissociation reaction. This integration considerably simplifies a conventional combination instrument of a grating-coupled surface plasmon resonance (SPR) spectrometer and a quartz crystal microbalance by eliminating a number of SPR components. Moreover, in the integrated system detection of the light reflections is not needed by which one bypasses the interference problem caused by two coherent light reflections off the glass window used to seal the fluid sample and off the sensor surface. The utility of the integrated system is demonstrated using a layer-by-layer polyelectrolyte multilayer deposition protocol, in which the complete features of a conventional grating-coupled SPR/QCM combination instrument are retained, including detection of optical and acoustic changes, as well as monitoring of adsorption kinetics.

Arrays of Au nanowells (NWs) were fabricated by electron-beam lithography (EBL) and characterized by surface plasmon resonance (SPR) and surface-enhanced Raman scattering (SERS). It is revealed that these Au NW arrays exhibit multiple SP resonances that can be tuned by adjusting the geometrical characteristics of the NWs. SERS activity of Au NWs was confirmed for a range of excitation wavelengths and a number of model compounds including rhodamine 6G (R6G), phthalazine, and single-stranded oligonucleotides. According to numerical simulations based on the discrete dipole approximation (DDA), SERS enhancement originates from high electromagnetic fields (hot spots) localized both inside and outside individual NWs. In addition, far-field intercoupling effects between NWs have been observed experimentally in arrays with subwavelength pitch sizes. We show that the SERS enhancement factors can also be tuned and optimized by adjusting the geometry of NWs.

The combination of high-performance liquid chromatography (HPLC) with surface plasmon resonance (SPR) for continuous separation and label-free detection of protein samples is described. The detection was realized by electrostatic adsorption of proteins bearing positive and negative charges onto chemically modified SPR sensors in two separate SPR channels. One SPR channel is coated with carboxymethylated dextran which facilitates the detection of positively charged proteins, whereas the other, devoted to the monitoring of negatively charged proteins, is covered with ethylenediamine molecules attached onto a dextran surface. Renewal of the sensor surface in the channels can be accomplished by introducing regeneration solutions through two six-port valves. The coupled technique (HPLC-SPR) was assessed for its analytical figures of merit and applied to the quantification of lysozyme in human milk samples. Unlike the SPR detection of bulk solution refractive index changes during chromatographic peak elutions, the highest sensitivity of SPR is retained in this work since the measurement is performed at the SPR sensor surface where the evanescent field is the strongest. The renewable SPR detection of continuous separations is reproducible and versatile and does not require the separated proteins to contain chromophores otto be prelabeled with a tag (e.g., a redox-active or fluorescent molecule). Such generality makes SPR complementary to other types of chromatographic detectors.

In this work, we present a novel surface and assay for the simultaneous detection of DNA and protein analytes on a surface plasmon resonance (SPR) imaging sensor. A mixed DNA/oligo (ethylene glycol) (OEG) self-assembled monolayer (SAM) is created using a microarrayer. Thiol-modified single-stranded DNA sequences are spotted onto a gold-coated glass substrate. Backfilling with an OEG-modified alkanethiol creates a protein-resistant surface background. Antibodies conjugated to complementary single-stranded DNA sequences are immobilized on the surface through DNA hybridization. By converting only part of the DNA array into a protein array, simultaneous detections of DNA and protein analytes are possible. A model system of two cDNA sequences and two human pregnancy hormones are used to demonstrate the assay. No cross-reactivity was observed between DNA or protein analytes and nontargeted immobilized cDNA sequence or antibodies. A response from a detection of a single analyte in a mixture of protein and DNA analytes corresponds well with that of a single-analyte solution.