Andrei V. Kabashin

Photonic bandgap fiber-based Surface Plasmon Resonance sensors

The concept of photonic bandgap fiber-based surface plasmon resonance sensor operating with low refractive index analytes is developed. Plasmon wave on the surface of a thin metal film embedded into a fiber microstructure is excited by a leaky Gaussian-like core mode of a fiber. We demonstrate that by judicious design of the photonic crystal reflector, the effective refractive index of the core mode can be made considerably smaller than that of the core material, thus enabling efficient phase matching with a plasmon, high sensitivity, and high coupling efficiency from an external Gaussian source, at any wavelength of choice from the visible to near-IR. To our knowledge, this is not achievable by any other traditional sensor design. Moreover, unlike the case of total internal reflection waveguide-based sensors, there is no limitation on the upper value of the waveguide core refractive index, therefore, any optical materials can be used in fabrication of photonic bandgap fiber-based sensors. Based on numerical simulations, we finally present designs using various types of photonic bandgap fibers, including solid and hollow core Bragg fibers, as well as honeycomb photonic crystal fibers. Amplitude and spectrum based methodologies for the detection of changes in the analyte refractive index are discussed. Furthermore, sensitivity enhancement of a degenerate double plasmon peak excitation is demonstrated for the case of a honeycomb fiber. Sensor resolutions in the range 7 * 10(-6) -5 * 10(-5) RIU were demonstrated for an aqueous analyte.

Photon crystal waveguide-based surface plasmon resonance biosensor

The concept of a photonic crystal waveguide-based surface plasmon resonance sensor is proposed, in which plasmons on a surface of a thin metal film are excited by a Gaussian-like leaky mode of an effectively single mode photonic crystal waveguide. The authors demonstrate that effective refractive index of a waveguide core mode can be designed to be considerably smaller than that of a core material, enabling efficient phase matching with plasmons at any wavelength of choice, while retaining highly sensitive response to changes in the refractive index of an analyte layer. This is attractive for the development of portable surface plasmon resonance biochemical sensors.

Fragmentation of colloidal nanoparticles by femtosecond laser-induced supercontinuum generation

A femtosecond laser-based method to control the size characteristics of gold colloidal nanoparticles is reported. The method uses the supercontinuum generation produced through a strong nonlinear-optical interaction of the femtosecond radiation with a liquid to fragment relatively large colloids and reduce their agglomeration. The fragmented species then recoalesce to form smaller, less dispersed, and much more stable nanoparticles in the solution. The size of the nanoparticles after the treatment is independent of the initial characteristics of colloids, but depends strongly on laser parameters and on the presence of chemically active species in the solution.

Properties and sensing characteristics of surface-plasmon resonance in infrared light

Conditions of surface-plasmon resonance (SPR) production with use of IR pumping light (800-2300 nm) in the Kretschmann-Raether prism arrangement were investigated. Both calculations and experimental data showed that SPR characteristics in the IR are strongly influenced by the properties of the coupling prism material. Indeed, quite different regularities of plasmon excitation, polarity of sensing response, and sensitivity are observed for two different glasses and silicon. The observed differences in SPR properties are related to essentially different behavior of dispersion characteristics of materials near the SPR coupling point. Methods for improving sensor performance and miniaturizing the SPR technique using novel coupling materials (silicon) are discussed.

Phase-sensitive time-modulated surface plasmon resonance polarimetry for wide dynamic range biosensing

A novel polarimetry scheme is proposed to improve the performance of phase-sensitive Surface Plasmon Resonance (SPR) biosensors. The scheme uses s-polarized light, not affected by SPR, as a reference beam, while information on the phase of the p-polarized component is obtained from an analysis of phase-polarization state of light of mixed polarization. We utilize temporal modulation of the beam reflected under SPR by a photo-elastic modulator and show that, under certain birefringent geometry, the signals at the 2nd and 3rd harmonics of modulated frequency can provide ultra-sensitive phase-based response to changes of the refractive index (thickness) of thin films on gold. We also show that the proposed configuration significantly improves detection limit compared to conventional intensity-sensitive SPR, yet enables to maintain wide dynamic range of measurements, which is normally difficult with phase-sensitive SPR schemes. Biosensing applications of the proposed scheme are illustrated in a biological model reaction of avidin - biotin binding on gold.

Silicon nanoparticles produced by femtosecond laser ablation in water as novel contamination-free photosensitizers

We report the synthesis of novel inorganic contamination-free photosensitizers based on colloidal silicon nanoparticles prepared by laser ablation in pure deionized water. We show that such nanoparticles are capable of generating singlet oxygen ((1)O(2)) under laser irradiation with a yield estimated at 10% of that of photofrin, which makes them a potential candidate for therapeutics, antiseptics, or disinfectants. We also discuss a model of (1)O(2) generation and the possibility for optimizing its release. Potential advantages of such novel inorganic photosensitizers include stable and nonphotobleaching (1)O(2) release, easy removal, and low dark toxicity.

Size-controllable synthesis of bare gold nanoparticles by femtosecond laser fragmentation in water

We report a size-controllable synthesis of stable aqueous solutions of ultrapure low-size-dispersed Au nanoparticles by methods of femtosecond laser fragmentation from preliminary formed colloids. Such approach makes possible the tuning of mean nanoparticle size between a few nm and several tens of nm under the size dispersion lower than 70% by varying the fluence of pumping radiation during the fragmentation procedure. The efficient size control is explained by 3D geometry of laser fragmentation by femtosecond laser-induced white light super-continuum and plasma-related phenomena. Despite the absence of any protective ligands, the nanoparticle solutions demonstrate exceptional stability due to electric repulsion effect associated with strong negative charging of formed nanoparticles. Stable aqueous solutions of bare gold nanoparticles present a unique object with a variety of potential applications in catalysis, surface-enhanced Raman spectroscopy, photovoltaics, biosensing and biomedicine.

Photonic Crystal Fiber and Waveguide-Based Surface Plasmon Resonance Sensors for Application in the Visible and Near-IR

Abstract In the proposed photonic crystal waveguide-based surface plasmon resonance (SPR) sensor, a plasmon wave on the surface of a thin metal film is excited by a Gaussian-like leaky mode of an effectively single-mode photonic crystal waveguide. By judicious design of a photonic crystal waveguide, the effective refractive index of a core mode can be made considerably smaller than that of the core material, thus enabling efficient phase-matching with a plasmon, high sensitivity, and high coupling efficiency from an external Gaussian source, at any wavelength of choice from the visible to near infrared (IR), which is, to our knowledge, not achievable by any other design. Moreover, unlike the case of total internal reflection (TIR) waveguide-based sensors, a wide variety of material combinations can be used to design photonic crystal waveguide-based sensors as there is no limitation on the value of the waveguide core refractive index. This sensor design concept was implemented using planar multilayer photonic crystal waveguides, solid and hollow core Bragg fibers, as well as microstructured photonic crystal fibers. Amplitude and spectral-based methodologies for the detection of changes in the analyte refractive index were devised. Sensor resolution as low as 8.3·10−6 refractive-index unit (RIU) was found for aqueous analyte.

Silicon-based surface plasmon resonance sensing with two surface plasmon polariton modes.

Surface plasmon resonance (SPR) sensing on a silicon-based platform is considered. We have studied properties of SPR in a combined silicon-dielectric layer-gold film-sample medium structure and established conditions of the simultaneous excitation of two plasmon polariton modes that provide narrow and well-separated minima of the reflected intensity. It has been shown that the external mode over the gold-sample medium interface demonstrates a highly sensitive response to a change in the refractive index of the sample medium, whereas the internal mode over the dielectric-gold interface is almost insensitive to medium parameters. We propose that the internal mode can be used as an effective reference zero point for miniature and portable SPR-based systems designed for field and multichannel sensing.

Laser-induced treatment of silicon in air and formation of Si/SiOx photoluminescent nanostructured layers

Two different mechanisms of laser-induced treatment of silicon in atmospheric air are compared. In one, silicon target was ablated by pulsed UV radiation, which led to a formation of microscale spikes under the irradiation spot and a deposition of material around it. The treated material contained silicon nanocrystals and exhibited weak photoluminescence (PL) signals, whose peak position was not uniform over the treated surface and varied from 2.0 to 2.3 eV in different points. In another mechanism, silicon target served to provide first electrons in order to initiate a breakdown in surrounding air by pulsed IR radiation. As a result, a highly porous nanostructured layer was formed under the contact of the target with the breakdown plasma. All points of the layer exhibited only 1.95 eV PL signals, whose intensity was stronger than in the case of the UV ablation by at least an order of magnitude. Possible mechanisms of nanostructure formation and PL origin are discussed.