Effects of Surface Topography and Cellular Biomechanics on Nanopillar-Induced Bactericidal Activity.

Bacteria are mechanically resistant biological structures that can sustain physical stress. Experimental data, however, have shown that high-aspect-ratio nanopillars deform bacterial cells upon contact. If the deformation is sufficiently large, it lyses the bacterial cell wall, ultimately leading to cell death.

Spatially-Localized Functionalization on Nanostructured Surfaces for Enhanced Plasmonic Sensing Efficacy.

This work demonstrates the enhancement in plasmonic sensing efficacy resulting from spatially-localized functionalization on nanostructured surfaces, whereby probe molecules are concentrated in areas of high field concentration. Comparison between SERS measurements on nanostructured surfaces (arrays of nanodisks 110 and 220 nm in diameter) with homogeneous and spatially-localized functionalization with thiophenol demonstrates that the Raman signal originates mainly from areas with high field concentration. TERS measurements with 10 nm spatial resolution confirm the field distribution profiles predicted by the numerical modeling.

Surface micropatterning for the formation of an in vitro functional endothelial model for cell-based biosensors.

Label-free biosensing, such as with surface plasmon resonance (SPR), is a highly efficient method for monitoring the responses of living cells exposed to pharmacological agents and biochemical stimuli in vitro. Conventional cell culture protocols used in cell-based biosensing generally provide little direct control over cell morphologies and phenotypes. Surface micropatterning techniques have been exploited for the controlled immobilization and establishment of well-defined cell morphologies and phenotypes.

Hydrophilic Mechano-Bactericidal Nanopillars Require External Forces to Rapidly Kill Bacteria.

Nanopillars have been shown to mechanically damage bacteria, suggesting a promising strategy for future antibacterial surfaces. However, the mechanisms underlying this phenomena remain unclear, which ultimately limits translational potential toward real-world applications. Using real-time and end-point analysis techniques, we demonstrate that in contrast to initial expectations, bacteria on multiple hydrophilic "mechano-bactericidal" surfaces remained viable unless exposed to a moving air-liquid interface, which caused considerable cell death.

Nanoplasmonics-enhanced label-free imaging of endothelial cell monolayer integrity.

Surface plasmon resonance imaging (SPRI) is a powerful label-free imaging modality for the analysis of morphological dynamics in cell monolayers. However, classical plasmonic imaging systems have relatively poor spatial resolution along one axis due to the plasmon mode attenuation distance (tens of μm, typically), which significantly limits their ability to resolve subcellular structures. We address this limitation by adding an array of nanostructures onto the metal sensing surface (25 nm thick, 200 nm width, 400 nm period grating) to couple localized plasmons with propagating plasmons, thereby reducing attenuation length and commensurately increasing spatial imaging resolution, without significant loss of sensitivity or image contrast.

Early detection of bacteria using SPR imaging and event counting: experiments with and .

Foodborne pathogens are of significant concern in the agrifood industry and the development of associated rapid detection and identification methods are of major importance. This paper describes the novel use of resolution-optimized prism-based surface plasmon resonance imaging (RO-SPRI) and data processing for the detection of the foodborne pathogens and . With an imaging spatial resolution on the order of individual bacteria (2.

Dielectrophoretic cell trapping for improved surface plasmon resonance imaging sensing.

The performance of conventional surface plasmon resonance (SPR) biosensors can be limited by the diffusion of the target analyte to the sensor surface. This work presents an SPR biosensor that incorporates an active mass-transport mechanism based on dielectrophoresis and electroosmotic flow to enhance analyte transport to the sensor surface and reduce the time required for detection. Both these phenomena rely on the generation of AC electric fields that can be tailored by shaping the electrodes that also serve as the SPR sensing areas.

Performance improvement of plasmonic sensors using a combination of AC electrokinetic effects for (bio)target capture.

Analytes concentration techniques are being developed with the appealing expectation to boost the performance of biosensors. One promising method lies in the use of electrokinetic forces. We present hereafter a new design for a microstructured plasmonic sensor which is obtained by conventional microfabrication techniques, and which can easily be adapted on a classical surface plasmon resonance imaging (SPRI) system without further significant modification.

Monitoring individual cell-signaling activity using combined metal-clad waveguide and surface-enhanced fluorescence imaging.

Evanescent field based biosensing systems such as surface plasmon resonance (SPR), diffraction gratings, or metal-clad waveguides (MCWGs) are powerful tools for label-free real-time monitoring of signaling activity of living cells exposed to hormones, pharmacological agents, and toxins. In particular, MCWG-based imaging is well suited for studying relatively thick objects such as cells due to its greater depth of penetration into the sensing medium, compared to SPR. Label-free methods, however, provide only indirect measurements in that the measured signal arises from local changes in material properties rather than from specific biomolecular targets.

Spatial resolution versus contrast trade-off enhancement in high-resolution surface plasmon resonance imaging (SPRI) by metal surface nanostructure design.

Surface plasmon resonance imaging (SPRI) is an optical near-field method used for mapping the spatial distribution of chemical/physical perturbations above a metal surface without exogenous labeling. Currently, the majority of SPRI systems are used in microarray biosensing, requiring only modest spatial resolution. There is increasing interest in applying SPRI for label-free near-field imaging of biological cells to study cell/surface interactions.

Metal clad waveguide (MCWG) based imaging using a high numerical aperture microscope objective.

Evanescent-field based methods such as surface plasmon resonance (SPR) have been used very effectively for label-free imaging of microscopic biological material in close proximity to a sensing surface. However, the shallow probing depth of SPR (typically less than ~200 nm) can be problematic when imaging relatively thick biological objects such as cells or bacteria. In this paper, we demonstrate how metal-clad waveguides (MCWG) can be used to achieve deeper probing depth compared to SPR while maintaining good imaging spatial resolution.

Label-free visualization and quantification of single cell signaling activity using metal-clad waveguide (MCWG)-based microscopy.

Label-free biosensing methods are very effective for studying cell signaling cascade activation induced by external stimuli. Assays generally involve a large number of cells and rely on the underlying assumption that cell response is homogeneous within a cell population. However, there is an increasing body of evidence showing that cell behavior may vary significantly even among genetically identical cells.

High Figure of Merit (FOM) of Bragg Modes in Au-Coated Nanodisk Arrays for Plasmonic Sensing.

Gold-coated nanodisk arrays of nearly micron periodicity are reported that have high figure of merit (FOM) and sensitivity necessary for plasmonic refractometric sensing, with the added benefit of suitability for surface-enhanced Raman scattering (SERS), large-scale microfabrication using standard photolithographic techniques and a simple instrumental setup. Gold nanodisk arrays are covered with a gold layer to excite the Bragg modes (BM), which are the propagative surface plasmons localized by the diffraction from the disk array. This generates surface-guided modes, localized as standing waves, leading to highly confined fields confirmed by a mapping of the SERS intensity and numerical simulations with 3D finite element method.

Directional surface enhanced Raman scattering on gold nano-gratings.

Directional plasmon excitation and surface enhanced Raman scattering (SERS) emission were demonstrated for 1D and 2D gold nanostructure arrays deposited on a flat gold layer. The extinction spectrum of both arrays exhibits intense resonance bands that are redshifted when the incident angle is increased. Systematic extinction analysis of different grating periods revealed that this band can be assigned to a propagated surface plasmon of the flat gold surface that fulfills the Bragg condition of the arrays (Bragg mode).

Generalized analytical model based on harmonic coupling for hybrid plasmonic modes: comparison with numerical and experimental results.

Metal nanoparticle arrays have proved useful for different applications due to their ability to enhance electromagnetic fields within a few tens of nanometers. This field enhancement results from the excitation of various plasmonic modes at certain resonance frequencies. In this article, we have studied an array of metallic nanocylinders placed on a thin metallic film.

Bimodal behavior and isobestic transition pathway in surface plasmon resonance sensing.

In traditional interpretation of surface plasmon resonance (SPR) sensing and imaging data, total surface coverage of adsorbed or deposited chemical and biological molecules is generally assumed. This homogenous assumption leads to the modeling of monomodal propagation of plasmons on the surface of the metallic film corresponding to a certain relative permittivity and thickness of the medium-such as molecular thin film-next to the metal. In actual SPR Imaging (SPRI) and SPR sensing situations, the plasmonics-active platforms (e.

Angle-dependent resonance of localized and propagating surface plasmons in microhole arrays for enhanced biosensing.

The presence of microhole arrays in thin Au films is suited for the excitation of localized and propagating surface plasmon (SP) modes. Conditions can be established to excite a resonance between the localized and propagating SP modes, which further enhanced the local electromagnetic (EM) field. The co-excitation of localized and propagating SP modes depends on the angle of incidence (θ(exc)) and refractive index of the solution interrogated.

Biochip data normalization using multifunctional probes.

Using a biochip with stable probe functionalization and a detection system capable of real time measurements, it is demonstrated that acquired probe-target interaction data are more reproducible in time--on a given probe spot using sequential target runs--than in space, using many probe spot replicates on the biochip in one single parallel target run. To increase the biochip data precision, a normalization method that quantifies and corrects the surface inhomogeneity without the use of complex data post-processing has been developed. This simple and effective method is based on adding a common reactive group to all probes and quantifying the biochip response to a calibration target, thus quantifying the spatial heterogeneity in the biosensor responsiveness.

Narrow groove plasmonic nano-gratings for surface plasmon resonance sensing.

We present a novel surface plasmon resonance (SPR) configuration based on narrow groove (sub-15 nm) plasmonic nano-gratings such that normally incident radiation can be coupled into surface plasmons without the use of prism-coupling based total internal reflection, as in the classical Kretschmann configuration. This eliminates the angular dependence requirements of SPR-based sensing and allows development of robust miniaturized SPR sensors. Simulations based on Rigorous Coupled Wave Analysis (RCWA) were carried out to numerically calculate the reflectance - from different gold and silver nano-grating structures - as a function of the localized refractive index of the media around the SPR nano-gratings as well as the incident radiation wavelength and angle of incidence.

Angulo-spectral surface plasmon resonance imaging of nanofabricated grating surfaces.

We present a surface plasmon resonance imaging (SPRI) setup, based on the Kretschmann configuration, capable of simultaneously acquiring the complete spectral and angular plasmonic reflectivity response on all points of the sensing area. Several line poly(methyl methacrylate) grating regions were fabricated on a thin-film gold surface and characterized with this SPRI system. Reflectivity maps of the corrugated regions showing plasmon bandgaps were obtained to illustrate the capability of the setup.

Polarimetric surface plasmon resonance imaging biosensor.

We report the realization of a polarimetric surface plasmon resonance imaging system capable of dynamically resolving a change in the optical anisotropy of biochemical films. Anisotropies as small as 10(-3) refractive index unit on nanometer-thick samples can be resolved. As an example, we present here the dynamical anisotropy obtained by the electrical patterning of a film consisting of a self-assembled monolayer deposited on gold, covered with a phospholipid hemimembrane.

Surface plasmon resonance spectro-imaging sensor for biomolecular surface interaction characterization.

Surface plasmon resonance (SPR) techniques have become, over the last ten years, powerful tools to study biomolecular surface interaction kinetics in real-time without any use of labels. The highest resolution is currently obtained using spectroscopic SPR systems through the measurement of the complete surface plasmon resonance curve in angular or spectral configuration. But, these systems are limited to a few independent channels (<10).

Absorption and related optical dispersion effects on the spectral response of a surface plasmon resonance sensor.

Surface plasmon resonance (SPR) sensing is an optical technique that allows real time detection of small changes in the physical properties, in particular in the refractive index, of a dielectric medium near a metal film surface. One way to increase the SPR signal shift is then to incorporate a substance possessing a strong dispersive refractive index in the range of the plasmon resonance band. In this paper, we investigate the impact of materials possessing a strong dispersive index integrated to the dielectric medium on the SPR reflectivity profile.

Surface plasmon resonance imaging as a multidimensional surface characterization instrument--application to biochip genotyping.

Surface plasmon resonance imaging (SPRI) sensors allow the characterization of a metal/dielectric interface. Providing proper biochemical functionalization and spatial structuration of the functionalized surface, an optical biochip system--label free and real time--can be achieved. We study the impact of the different physical parameters on the quality of the measurements.

Generalization of the Rouard method to an absorbing thin-film stack and application to surface plasmon resonance.

In the context of surface plasmon resonance (SPR) kinetic biochips, it is important to model the SPR phenomenon (i.e., extinction of reflectivity) toward biochip design and optimization.