Anastasia E. Goldt

Planar SERS nanostructures with stochastic silver ring morphology for biosensor chips

Surface-enhanced Raman spectroscopy (SERS) of living cells has rapidly become a powerful trend in biomedical diagnostics. It is a common belief that highly ordered, artificially engineered substrates are the best future decision in this field. This paper, however, describes an alternative successful solution, a new effortless chemical approach to the design of nanostructured silver and heterometallic continuous coatings with a stochastic “coffee ring” morphology. The coatings are formed from an ultrasonic mist of aqueous diamminesilver hydroxide, free of reducing agents and nonvolatile pollutants, under mild conditions, at about 200–270 °C in air. They consist of 30–100 micrometer wide and 100–400 nm high silver rings composed, in turn, of a porous silver matrix with 10–50 nm silver grains decorating the sponge. This hierarchic structure originates from ultrasonic droplet evaporation, contact-line motion, silver(I) oxide decomposition and evolution of a growing ensemble of silver rings. The fabricated substrates are a remarkable example of a new scalable and low cost material suitable for SERS analyses of living cells. They evoke no hemolysis and reduce erythrocyte lateral mobility due to suitable “coffee ring” sizes and a tight contact with the silver nanostructure. A high SERS enhancement, characteristic of pure silver rings, made it possible to record Raman scattering spectra from submembrane hemoglobin in its natural cellular environment inside single living erythrocytes, thus making the substrates promising for various biosensor chips.

Constrained growth of anisotropic magnetic δ-FeOOH nanoparticles in the presence of humic substances

Natural polyelectrolytes, humic substances, are suggested to control in situ growth of feroxyhyte nanoparticles of a highly reduced mean size and with enhanced colloidal stability in salt solutions. The feroxyhyte is formed as 2–5 nm thick and 20 × 20 nm wide nanoflakes due to the blocking of developing facets of feroxyhyte and constraints caused by diffusion limitations of ionic constituents across partially charged branches of humic substances.

Chimie douce preparation of reproducible silver coatings for SERS applications

A new soft chemistry preparation method of submicron — thick porous coatings of metallic silver is suggested for possible surface enhanced Raman spectroscopy (SERS) applications. The method is based on facile deposition of diamminesilver (I) aerosols forming instantly a nanostructured layer by fast decomposition and self–reduction of [Ag(NH3)2]+ aqueous solutions onto surfaces of inorganic substrates under mild conditions of 280–300∘C in air. A strong difference in overall microstructures and related SERS signals of model analytes is found for substrates with different deposition time and in comparison with a standard magnetron deposition technique. It is demonstrated that the suggested method is predominant for formation of robust SERS substrates with a stable and reproducible SERS enhancement.

Magnetic Properties of Maghemite Nanoparticles

Magnetic particles of maghemite (spinel γ-Fe2O3) are synthesized by means of aerosol pyrolysis, making it possible to produce chemically uniform highly-dispersed single-phase materials. The magnetic properties of synthesized particles for temperatures ranging from helium temperature up to room temperature and higher are investigated using a SQUID magnetometer. The experimental curves are compared to the results from calculations performed by the Monte Carlo method. It is found that the Curie temperature is lower for γ-Fe2O3 nanoparticles than for bulk samples. Several parameters of the material are estimated by comparing the experimental and calculated results.

Electroplating of porous gold films for SERS analysis of heme derivatives

Abstract Gold porous films with an 2D inverse opal structure were prepared via electrochemical deposition for further application as SERS-active substrates for the on-chip analysis of heme B derivatives. The thickness of the deposited film was controlled through deposition charge while the grain size was dependent significantly on electrolyte content. A semiquantitative surface analysis of film composition and phase analysis of the gold films were performed by XPS and XRD methods while the observed local, Mie and Bragg plasmon resonance modes were discussed based on UV–vis reflectance data.

Optical properties of multilayer films of nanocomposites based on WS2 nanotubes decorated with gold nanoparticles

Multilayer films of WS2 nanotubes decorated with gold nanoparticles are prepared for the first time using nanocomposite assemblage on the water-heptane interface and film transition onto optically transparent or semiconducting surfaces. The film morphology resembles a mosaic structure of 10-25 square micron areas with in-plane textured nanotubes. Optical properties demonstrate several features around 490, 545, and 675 nm connected either with excitonic transitions or scattering guided by high anisotropy of the nanotubes and their texturing peculiarities in the films.

Magnetic Resonance Imaging of Endothelial Cells with Vectorized Iron Oxide Nanoparticles

We propose a method for obtaining superparamagnetic nanoparticles based on iron oxide and their water suspensions. The structure and size of nanoparticles were confi rmed by transmission electron microscopy, dynamic light scattering, and X-ray diffraction analysis. The nanoparticles also contained a fl uorescent dye Dil C18. Cytotoxicity of obtained aqueous suspension was studied by MTT assay; low toxicity of nanoparticles was demonstrated. High T2-relaxivity of nanoparticles allows using them as a contrast agent for MRI. After incubation of cerebellar sections with nanoparticles vectorized with antibodies to antigen AMVB1, specifi c visualization of blood vessels was detected.

Silver Eco-Solvent Ink for Reactive Printing of Polychromatic SERS and SPR Substrates

A new reactive ink based on a silver citrate complex is proposed for a photochemical route to surface-enhanced Raman spectroscopy active substrates with controllable extinction spectra. The drop-cast test of the ink reveals homogeneous nucleation of silver and colloid particle growth originating directly from photochemical in situ reduction in droplets, while the following evaporation of the deposited ink produces small nano- and micron-size particles. The prepared nanostructures and substrates were accurately characterized by electron microscopy methods and optical extinction spectroscopy. Varying the duration of UV irradiation allows tuning the morphology of individual silver nanoparticles forming hierarchical ring structures with numerous “hot spots” for most efficient Raman enhancement. Raman measurements of probe molecules of rhodamine 6G and methylene blue reached the largest signal enhancement of 106 by the resonance effects.

Facile chemical routes to mesoporous silver substrates for SERS analysis

Mesoporous silver nanoparticles were easily synthesized through the bulk reduction of crystalline silver(I) oxide and used for the preparation of highly porous surface-enhanced Raman scattering (SERS)-active substrates. An analogous procedure was successfully performed for the production of mesoporous silver films by chemical reduction of oxidized silver films. The sponge-like silver blocks with high surface area and the in-situ-prepared mesoporous silver films are efficient as both analyte adsorbents and Raman signal enhancement mediators. The efficiency of silver reduction was characterized by X-ray diffraction and X-ray photoelectron spectroscopy. The developed substrates were applied for SERS detection of rhodamine 6G (enhancement factor of about 1–5 × 105) and an anti-ischemic mildronate drug (meldonium; enhancement factor of ≈102) that is known for its ability to increase the endurance performance of athletes.