Editorial: Special Issue "Laser Synthesis and Processing of Nanostructured Materials".

The fabrication of functional nanomaterials and nanotextured surfaces assisted by spatially and temporally confined laser radiation has matured from laboratory-scale methods to application-ready technology during recent decades [...

Scattering Amplitude of Surface Plasmon Polariton Excited by a Finite Grating.

Unusual optical properties of laser-ablated metal surfaces arise from the excitation of local plasmon resonances in nano- and microstructures produced by laser-processing and from the mutual interaction of those structures through surface plasmon polariton (SPP) waves. This interaction provides a synergistic effect, which can make the optical properties of the composite nanostructure drastically different from the properties of its elements. At the same time, the prediction and analysis of these properties are hampered by the complexity of the analytical solution to the problem of SPP excitation by surface objects of arbitrary configuration.

Editorial for the Special Issue Applications of Nanomaterials in Plasmonic Sensors.

Further progress in the modern sensor industry is associated with the widespread application of new solutions and principles from the field of nanooptics and nanophotonics [...

Electrically Controlled Enrichment of Analyte for Ultrasensitive SERS-Based Plasmonic Sensors.

Recently, sensors using surface-enhanced Raman scattering (SERS) detectors combined with superhydrophobic/superhydrophilic analyte concentration systems showed the ability to reach detection limits below the femto-molar level. However, a further increase in the sensitivity of these sensors is limited by the impossibility of the concentration systems to deposit the analyte on an area of less than 0.01 mm.

Analytical Calculations of Scattering Amplitude of Surface Plasmon Polaritons Excited by a Spherical Nanoantenna.

Since surface plasmon polaritons (SPPs) are surface waves, they cannot be excited by an incident plane wave, because free-space photons do not possess a sufficient in-plane momentum. Phase matching between the incident light and SPP can be achieved using a high-refractive-index prism, grating, or nanoantennas. In this work, we found an expression for the amplitude of SPP excited by an arbitrary 3D current distribution placed near a metal interface.

Ultrasensitive SERS-Based Plasmonic Sensor with Analyte Enrichment System Produced by Direct Laser Writing.

We report an easy-to-implement device for surface-enhanced Raman scattering (SERS)-based detection of various analytes dissolved in water droplets at trace concentrations. The device combines an analyte-enrichment system and SERS-active sensor site, both produced via inexpensive and high-performance direct femtosecond (fs)-laser printing. Fabricated on a surface of water-repellent polytetrafluoroethylene substrate as an arrangement of micropillars, the analyte-enrichment system supports evaporating water droplet in the Cassie-Baxter superhydrophobic state, thus ensuring delivery of the dissolved analyte molecules towards the hydrophilic SERS-active site.

Multi-Purpose Nanovoid Array Plasmonic Sensor Produced by Direct Laser Patterning.

We demonstrate a multi-purpose plasmonic sensor based on a nanovoid array fabricated via inexpensive and highly-reproducible direct femtosecond laser patterning of thin glass-supported Au films. The proposed nanovoid array exhibits near-IR surface plasmon (SP) resonances, which can be excited under normal incidence and optimised for specific applications by tailoring the array periodicity, as well as the nanovoid geometric shape. The fabricated SP sensor offers competitive sensitivity of ≈ 1600 nm/RIU at a figure of merit of 12 in bulk refractive index tests, as well as allows for identification of gases and ultra-thin analyte layers, making the sensor particularly useful for common bioassay experiments.

On-demand concentration of an analyte on laser-printed polytetrafluoroethylene.

Controllable targeted deposition of an analyte dissolved in a liquid drop evaporating on a superhydrophobic surface has recently emerged as a promising concentrator approach with various applications ranging from ultrasensitive bioidentification to DNA molecule sorting. Here, we demonstrate that surface textures with non-uniform wettability fabricated using direct easy-to-implement femtosecond-pulse filament-assisted ablation of polytetrafluoroethylene substrates can be used to concentrate and deposit an analyte at a designated location out of a water droplet. The proposed surface textures contain a central superhydrophilic trap surrounded by superhydrophobic periodically arranged pillars with a hierarchical roughness.

Lens-free laser nanopatterning of large-scale metal film areas with structured light for biosensing applications.

Pulsed laser nanotexturing of metal films represents an ultra-fast, high-performance and cost-effective processing technology for fabrication of various functional surfaces widely used in plasmonics, biosensing, and photovoltaics. However, this approach usually requires high-NA lenses to focus a laser beam onto a few-micron spot as well as a micropositioning platform to move this spot along the sample surface, which increases the cost of the produced functional surfaces and limits the performance of laser-assisted nanotexturing techniques. In this paper we report on a laser-assisted technology for the fabrication of large-scale nanotextured metal substrates.

On-Fly Femtosecond-Laser Fabrication of Self-Organized Plasmonic Nanotextures for Chemo- and Biosensing Applications.

Surface-enhanced Raman scattering (SERS) and surface-enhanced photoluminescence (SEPL) are emerging as versatile widespread methods for biological, chemical, and physical characterization in close proximity of nanostructured surfaces of plasmonic materials. Meanwhile, single-step, facile, cheap, and green technologies for large-scale fabrication of efficient SERS or SEPL substrates, routinely demonstrating both broad plasmonic response and high enhancement characteristics, are still missing. In this research, single-pulse spallative micron-size craters in a thick Ag film with their internal nanotexture in the form of nanosized tips are for the first time shown to demonstrate strong polarization-dependent enhancement of SEPL and SERS responses from a nanometer-thick covering Rhodamine 6G layer with average enhancement factors of 40 and 2 × 10(6), respectively.

Ion-beam assisted laser fabrication of sensing plasmonic nanostructures.

Simple high-performance, two-stage hybrid technique was developed for fabrication of different plasmonic nanostructures, including nanorods, nanorings, as well as more complex structures on glass substrates. In this technique, a thin noble-metal film on a dielectric substrate is irradiated by a single tightly focused nanosecond laser pulse and then the modified region is slowly polished by an accelerated argon ion (Ar(+)) beam. As a result, each nanosecond laser pulse locally modifies the initial metal film through initiation of fast melting and subsequent hydrodynamic processes, while the following Ar(+)-ion polishing removes the rest of the film, revealing the hidden topography features and fabricating separate plasmonic structures on the glass substrate.

Fabrication of porous metal nanoparticles and microbumps by means of nanosecond laser pulses focused through the fiber microaxicon.

We present a novel optical element - fiber microaxicon (FMA) for laser radiation focusing into a diffraction-limited spot with Bessel-like profile as well as for precision laser nanostructuring of metal film surfaces. Using the developed FMA for single-pulse irradiation of Au/Pd metal films on quartz substrate we have demonstrated the formation of submicron hollow microbumps with a small spike atop as well as hollow spherical nanoparticles. Experimental conditions for controllable and reproducible formation of ordered arrays of such microstructures were defined.

Mapping the refractive index of optically transparent samples by means of optical nanoantenna attached to fiber microaxicon.

We demonstrate analytically and numerically that the detection of the spectral response of a single spherical Au nanoantenna allows one to map very small (down to 5·10(-4) RIU) variations of the refractive index of an optically transparent sample. Spectral shift of the dipole local plasmon resonance wavelength of the nanoantenna and the spectral sensitivity of the method developed was estimated by using simple analytical quasi-static model. A pointed scanning probe based on fiber microaxicon with the Au spherical nanoantenna attached to its tip was proposed to realize the RI mapping method.