Daniil N. Bratashov

Gold nanoisland films as reproducible SERS substrates for highly sensitive detection of fungicides.

A wet-chemical approach is used to fabricate centimeter-scale gold nanoisland films (NIFs) with tunable morphology of islands and with strong electromagnetic coupling between them. The approach consists in a uniform seeding of small gold nanoparticles on a glass or silicon substrate, followed by controllable growth of the seeds into small nanoislands. A special technique for TEM sampling was developed to follow the gradual formation of larger-sized isolated nanoparticles, nanoislands of sintered overgrown seeds, and a complete gold layer with nanoscale cracks. The electromagnetic field distribution inside the fabricated NIFs was calculated by FDTD simulations applied to actual TEM images of the fabricated samples rather than to artificial models commonly used. SERS measurements with 1,4-aminothiophenol (ATP) molecules demonstrated the analytical enhancement factor about of 10(7) and the fundamental enhancement factor about of 10(8) for optimized substrates. These values were at least 1 order of magnitude higher than that for self-assembled arrays of gold nanostars and silver nanocubes. SERS spectra of independent samples demonstrated good sample-to-sample reproducibility in terms of the relative standard deviation (RSD) of the main peaks less than 20%. Additionally, Raman maps with 1 μm increment in X-Y directions of NIFs (800 spectral spots) demonstrated good point-to-point repeatability in the intensity of the main Raman vibration modes (RSD varied from 5% to 15% for 50 randomly selected points). A real-life application of the fabricated SERS substrates is exemplified by the detection of the thiram fungicide in apple peels within the 5-250 ppb linear detection range. Specifically, the NIF-based SERS technology detected thiram on apple peel down to level of 5 ng/cm(2).

Nanoencapsulated and microencapsulated SERS platforms for biomedical analysis.

The problems of layer-by-layer-based surface enhancement Raman scattering (SERS)-sensor application for pharmaceutical analysis were discussed. Layer-by-layer (LbL) method allows fabrication of encapsulated SERS platforms with high reproducibility of enhancement factor and increased signal/noise ratio of Raman scattering. LbL encapsulation approach opens an avenue to implement a novel type of theranostic systems combining SERS based sensing and drug delivery in one entity. The area of encapsulation development toward smart multifunctional theranostic systems could bring benefits for personalized medicine and should minimize costs and resources at preclinical and clinical study in pharmacology while testing new bioactive compounds.

Liquid crystal-in-water emulsion stabilized by layer-by-layer adsorption of polyelectrolytes and magnetite nanoparticles

We propose a method for stabilizing and modifying the dispersed phase of a liquid crystal-in-water (LC/water) emulsion using the sequential adsorption of polyelectrolytes and magnetite nanoparticles, which leads to the formation of LC-filled nanocomposite microcapsules. The obtained samples were studied by optical microscopy and Raman spectroscopy. It is established that the LC-filled nanocomposite microcapsules can move under the action of an external magnetic field.

Quantitative and multiplex dot-immunoassay using gap-enhanced Raman tags

Dot immunoassay has been proposed as a simple and fast method for detection of various analytes. However, this qualitative method has a narrow working range and is limited to multiplex detection. To overcome these drawbacks, we suggest a highly specific, quantitative, and multiplex dot immunoassay using plasmonic gap-enhanced Raman tags (GERTs) and a nitrocellulose membrane as a substrate. The assay principle is based on reading surface-enhanced Raman scattering (SERS) spectra from analyte drops on the membrane strip after incubation with GERTs conjugated to biospecific probes. Three types of GERTs were synthesised by embedding nitrobenzenethiol (NBT), naphthalenethiol (NT), and acetamidothiophenol (AcTP) Raman molecules inside Au core/shell nanoparticles. For proof-of-concept experiments, the NBT, NT, and AcTP GERTS were further functionalized with rabbit anti-rat, anti-human, and anti-chicken antibodies, respectively. For all three corresponding antigens, the detected Raman signals linearly depended on the analyte amount within the range from 10 to 300 ng. The multiplex capability of the assay is illustrated by simultaneous one-step determination of rat, human, and chicken IgGs with a mixture of functionalized GERTs by recording Raman maps for whole membrane to avoid the point-to-point repeatability problem. Thus, GERTs are promising SERS nanotags for advanced versions of immunoassays instead of common plasmonic SERS labels with Raman reporters excited by the external near field.

Creating micron regions with modified luminescent properties and topology on CdSxSe1 − x films by laser annealing

Laser annealing of thin polycrystalline films of CdSxSe1 − x solid solutions has a threshold character, modifies the local topological relief, and produces a jumplike change in the luminescent properties of the material in the processed region. The possibility of creating local regions with sharply modified physical properties on a micron-precise scale makes the proposed technique a promising tool for the production of semi-conductor sensor chips.

Low-temperature plasma pulsed deposition of thin films with nanoscale periodicity of properties

Film formation in low-temperature plasma in the pulsed mode was studied. The voltage’s pulse sequence in the sputtering system contained trains of short and long pulses; the short pulse time was chosen shorter than the stabilization time of the glow discharge mode. The formation of the nanoscale composition periodicity in grown films was confirmed by secondary-ion mass spectrometry. Photoluminescence of the films synthesized in the pulsed mode was studied, as well as the possibility of controlling the luminescence behavior and intensity.

Carbon dot aggregates as an alternative to gold nanoparticles for the laser-induced opening of microchamber arrays

Carbon dots (CDs) are usually used as an alternative to other fluorescent nanoparticles. Apart from fluorescence, CDs also have other important properties for use in composite materials, first of all their ability to absorb light energy and convert it into heat. In our work, for the first time, CDs have been proposed as an alternative to gold nanostructures for harvesting light energy, which results in the opening of polymer-based containers with biologically active compounds. In this paper, we propose a method for the synthesis of polylactic acid microchamber arrays with embedded CDs. A comparative analysis was made of the damage to microchambers functionalized with gold nanorods and with CD aggregates, depending on the wavelength and power of the laser used. The release of fluorescent cargo from the microchamber arrays with CD aggregates under laser exposure was demonstrated.

Layer-by-layer polyelectrolyte coating for surface-enhanced Raman scattering on gold nanostars inside hollow core photonic crystal fibers

Photonic crystal fibers with hollow core (HC PCFs) are a specific class of optical fibers characterized by microstructure with periodic holes oriented along fiber. The combination of HC PCF with Raman spectroscopy for biosensors creation is attractive in the terms of the low sample volume, the possibility to increase the integration time without sample degradation and maintaining constant focus during experiments. Here we propose layer-by-layer polyelectrolyte coating of HC PCF inner surface in order to obtain charge-selective absorption of analyte, stabilization of Surface-Enhanced Raman scattering (SERS)-active gold nanoparticles. Distance between SERS hotspots and glass reduces nonlinear signals from glass, and increases signal-to-noise ratio of SERS spectra.

Flexible surface-enhanced Raman scattering-active substrates based on nanofibrous membranes

Surface-enhanced Raman scattering (SERS) has emerged as an excellent analytical tool for the effective detection and fingerprint identification of various chemicals. Recently, significant progress has been made in the fabrication of SERS-active substrates using simple, inexpensive, and affordable methods. The full potential of universal SERS diagnostics will likely be realized with the development of approaches and devices capable of effectively detecting analytes on various surfaces as well as in multicomponent media. In addition, the combination of implantable or wearable SERS-active substrates and remote portable devices enables real-time diagnostics that ideally fit the concept of personalized medicine. In this paper, we summarize recent achievements in fabricating flexible SERS substrates made of cellulose paper, polymer membranes, and textile fibrous films. Emphasis is placed on the in-situ extraction and detection of various chemicals in real-world surfaces and complex media using flexible nanofibrous SERS platforms. The potential SERS applications and future perspectives in on-site diagnostics are also discussed.

Microstructured Waveguides with Polyelectrolyte-Stabilized Gold Nanostars for SERS Sensing of Dissolved Analytes

A sensor based on microstructured waveguides (MWGs) with a hollow core inner surface covered with polyelectrolyte-layer-stabilized gold nanostars was developed for the SERS sensing of dissolved analytes. A polyelectrolyte-layer coating over the inner surface of glass cladding served as a spacer, reducing nonlinear optical effects in the glass near plasmonic hotspots of nanoparticles, as a stabilizing agent for thermodynamically unstable gold nanostars and as an optical coating for the fine-tuning of MWG bandgaps. This approach can be used to construct different kinds of SERS sensors for dissolved analytes, providing conservation, the prevention of coagulation, and the drying of a liquid sample for the time required to record the signal.