Antoine Lesuffleur

Periodic nanohole arrays with shape-enhanced plasmon resonance as real-time biosensors

The authors report a combination of the enhanced transmission effect and shape resonances in a periodic array of nanoscale double-hole structures in a gold film to enhance the detection sensitivity of surface plasmon biosensors. Finite-difference time-domain calculations are used to quantify field enhancement at the apexes of the double-hole structure. The double-hole array was used to measure the formation of a self-assembled monolayer and for real-time sensing of protein adsorption onto a gold surface. This result demonstrates the potential to integrate propagating surface plasmons and localized shape resonances to improve real-time biosensors.

Three-dimensional plasmonic nanofocusing

We demonstrate three-dimensional plasmonic nanofocusing of light with patterned metallic pyramids obtained via template stripping. Gratings on the faces of these pyramids convert linearly polarized light into plasmons that propagate toward and converge at a approximately 10 nm apex. Experiments and computer simulations confirm that optical energy is focused into a nanoscale volume (5 x 10(-5) wavelength(3)). Because these structures are easily and reproducibly fabricated, our results could benefit many applications, including imaging, sensing, lithography, and nonlinear spectroscopy.

Membrane protein biosensing with plasmonic nanopore arrays and pore-spanning lipid membranes

Integration of solid-state biosensors and lipid bilayer membranes is important for membrane protein research and drug discovery. In these sensors, it is critical that the solid-state sensing material does not have adverse effects on the conformation or functionality of membrane-bound molecules. In this work, pore-spanning lipid membranes are formed over an array of periodic nanopores in free-standing gold films for surface plasmon resonance (SPR) kinetic binding assays. The ability to perform kinetic assays with a transmembrane protein is demonstrated with α-hemolysin (α-HL). The incorporation of α-HL into the membrane followed by specific antibody binding (anti-α-HL) red-shifts the plasmon resonance of the gold nanopore array, which is optically monitored in real time. Subsequent fluorescence imaging reveals that the antibodies primarily bind in nanopore regions, indicating that α-HL incorporation preferentially occurs into areas of pore-spanning lipid membranes.

Plasmonic nanoholes in a multichannel microarray format for parallel kinetic assays and differential sensing.

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 10(6) sensing elements/cm(2), which can potentially be coupled with a massively parallel array of microfluidic channels for protein microarray applications.

Laser-illuminated nanohole arrays for multiplex plasmonic microarray sensing

Surface plasmon resonance (SPR) imaging is a powerful technique for high-throughput, real-time, label-free characterization of molecular interactions in a microarray format. In this paper, we demonstrate SPR imaging with nanohole arrays illuminated by a laser source. Periodic nanoholes couple incident photons into SPs, obviating the need for the prism used in conventional SPR instruments, while a laser source provides the intensity, stability and spectral coherence to improve the detection sensitivity. The formation of a self-assembled monolayer of alkanethiolates on gold changed the laser transmission by more than 35%, and binding kinetics were measured in parallel from a 5 x 3 microarray of nanohole sensors. These results demonstrate the potential of nanohole sensors for high-throughput SPR imaging on microarrays.

Atomic Layer Deposition of Dielectric Overlayers for Enhancing the Optical Properties and Chemical Stability of Plasmonic Nanoholes

Fabricating plasmonic nanostructures with robust optical and chemical properties remains a challenging task, especially with silver, which has superior optical properties but poor environmental stability. In this work, conformal atomic layer deposition (ALD) of thin alumina overlayers is used to precisely tune the optical transmission properties of periodic nanohole arrays made in gold and silver films. Experiments and computer simulations confirm that ALD overlayers with optimized thicknesses tune and enhance the transmitted intensity due to refractive index matching effects and by modifying the dielectric properties of each nanohole. Furthermore, encapsulating silver nanohole arrays with thin alumina overlayers protects the patterned surfaces against unwanted oxidation and contamination. The ability to precisely tune the optical properties while simultaneously providing robust chemical stability can benefit a broad range of applications, including biosensing and fluorescence imaging.

Surface plasmon resonance for high-throughput ligand screening of membrane-bound proteins.

Technologies based on surface plasmon resonance (SPR) have allowed rapid, label‐free characterization of protein‐protein and protein‐small molecule interactions. SPR has become the gold standard in industrial and academic settings, in which the interaction between a pair of soluble binding partners is characterized in detail or a library of molecules is screened for binding against a single soluble protein. In spite of these successes, SPR is only beginning to be adapted to the needs of membrane‐bound proteins which are difficult to study in situ but represent promising targets for drug and biomarker development. Existing technologies, such as BIAcoreTM, have been adapted for membrane protein analysis by building supported lipid layers or capturing lipid vesicles on existing chips. Newer technologies, still in development, will allow membrane proteins to be presented in native or near‐native formats. These include SPR nanopore arrays, in which lipid bilayers containing membrane proteins stably span small pores that are addressable from both sides of the bilayer. Here, we discuss current SPR instrumentation and the potential for SPR nanopore arrays to enable quantitative, high‐throughput screening of G protein coupled receptor ligands and applications in basic cellular biology.

Plasmonic nano-structures for optical data storage

We propose a method of optical data storage that exploits the small dimensions of metallic nano-particles and/or nano-structures to achieve high storage densities. The resonant behavior of these particles (both individual and in small clusters) in the presence of ultraviolet, visible, and near-infrared light may be used to retrieve pre-recorded information by far-field spectroscopic optical detection. In plasmonic data storage, a femtosecond laser pulse is focused to a diffraction-limited spot over a small region of an optical disk containing metallic nano-structures. The digital information stored in each bit-cell modifies the spectrum of the femtosecond light pulse, which is subsequently detected in transmission (or reflection) using an optical spectrum analyzer. We present theoretical as well as preliminary experimental results that confirm the potential of plasmonic nano-structures for high-density optical storage applications.

Lateral confinement of surface plasmons and polarization-dependent optical transmission using nanohole arrays with a surrounding rectangular Bragg resonator

Enhanced optical transmission and surface plasmon resonant cavity effects are studied for subwavelength aperture arrays surrounded by rectangular-shaped Bragg mirrors. A circular nanohole array with a surrounding rectangular Bragg resonator exhibits the introduction of polarization-dependent enhanced optical transmission by constructive and destructive interference effects generated within the cavity. The feasibility for high-density packing of several individually distinct nanohole arrays is demonstrated by also using the Bragg mirrors to block surface plasmon interference between multiple such neighboring devices spaced 5μm apart.

Periodic modulation of extraordinary optical transmission through subwavelength hole arrays using surrounding Bragg mirrors

The enhanced light transmission through an array of subwavelength holes surrounded by Bragg mirrors is studied, showing that the mirrors act to confine the surface plasmons associated with the extraordinary optical transmission effect, forming a surface resonant cavity. The overall effect is increased light transmission intensity by more than a factor of 3 beyond the already enhanced transmission, independent of whether the Bragg mirrors are on the input or the output side of the incident light. The geometry of the Bragg mirror structures controls the enhancement and can even reduce the transmission by half. By varying these geometric parameters, we were able to periodically modulate the transmission of light for specific wavelengths, consistent with the propagation and interference of surface plasmon waves in a resonant cavity. Finite difference time domain simulations and a wave propagation model verify this effect.