A. V. Sidorov

Microbead silica decorated with polyhedral silver nanoparticles as a versatile component of sacrificial gel films for SERS applications

A new method of microbead silica preparation with superficially built-in 2–3 nm silver seeds is suggested by using a simple reaction of Stoeber SiO2 microspheres with hot aqueous solutions of diamminesilver(I) hydroxide without addition of reducing agents. The seeding beads initiate growth of polyhedral 20–50 nm silver nanoparticles encrusting silica surface after an instant heterogeneous contact with a mixture of silver nitrate and ascorbic acid solutions with concentrations of as low as 1 mM. The unique microstructure results in a pronounced, about 100 nm, red shift of the silver plasmonic band allowing fast and robust tuning of optical properties of the nanocomposites. Such microengineered building blocks are stored safely in a sacrificial biopolymer (ethylcellulose) film as its versatile component to be applied on demand in aqueous environment since polymer swelling absorbs water-soluble analytes and allows for the advanced SERS analysis.

Correction: Inkjet printing of silver rainbow colloids for SERS chips with polychromatic sensitivity

Correction for ‘Inkjet printing of silver rainbow colloids for SERS chips with polychromatic sensitivity’ by K. E. Yorov et al., RSC Adv., 2016, 6, 15535–15540.

Novel Multilayer Nanostructured Materials for Recognition of Polycyclic Aromatic Sulfur Pollutants and Express Analysis of Fuel Quality and Environmental Health by Surface Enhanced Raman Spectroscopy

A novel concept of advanced SERS (surface enhanced Raman spectroscopy) planar sensors is suggested for fast analysis of sulfur-containing hazardous oil components and persistent pollutants. The main advantage of the proposed sensors is the utilization of an additional preconcentrating layer of optically transparent chitosan gel, which is chemically modified with appropriate π-acceptor compounds to selectively form charge-transfer complexes (CTCs) at the interface with nanostructured silver coatings. The CTCs shift absorption bands of polycyclic aromatic sulfur heterocycles (PASHs) and other important analytes in a controllable way and thus provide a surplus enhancement of vibration modes due to resonant Raman scattering. This novel indicator system provides multiplex determination of PASHs in different forms in a small volume of oil without any tedious sample pretreatment steps. This approach opens new possibilities of increasing either spectral and concentration sensitivity or specificity of SERS-based sensors, allowing for new developments in the fields of ecology, advanced fuel analysis, and other prospective applications.

Inkjet printing of silver rainbow colloids for SERS chips with polychromatic sensitivity

Pristine and artificially mixed silver colloids of diverse anisotropic silver nanoparticles were used as “rainbow” colloidal silver inks for inkjet printing of cellulose-based active elements with polychromatic sensitivity for surface-enhanced Raman spectroscopy optical sensors. Platelet silver nanocrystallites possessing different plasmonic bands in the visual spectral range were grown in water–polyol liquors of different viscosities to prevent nanoparticle agglomeration and provide colloidal stability for at least one year. SERS tests of model photostable dyes revealed bright enhanced signals under several standard wavelengths of laser irradiations thus demonstrating better practical applications of such substrates.

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.

Immobilization of nanostructured metal silver at the surface of anodic titanium dioxide for the creation of composites with the surface plasmon resonance

X-ray-amorphous anodic titanium dioxide is proposed as a carrier of nanostructured silver with a controllable surface roughness for the creation of composite films with an effect of the surface plasmon resonance in the visible region for the spectroscopy of giant combinational scattering (GCS). A comparative analysis of GCS composites obtained by different methods of silver immobilization at the surface of a semiconductor TiO2 (photolysis of silver nitrate (I), magnetron sputtering, and thermal decomposition of ammonium silver complex (I)) has shown a substantial dependence of the functional characteristics on preparation history in the case of model analytes with different spectral characteristics, i.e., dyes of rhodamine 6G and methylene blue in low concentrations of 1 × 10−8 mol/L by an aliquot volume of less than 10 μL.

Bioprotective polymer layers for surface enhanced Raman spectroscopy of proteins

Abstract A challenging problem of modern surface-enhanced Raman spectroscopy (SERS) analysis is related to the design of new composite materials with bioprotective properties providing either a reproducible signal of small quantities or intactness of protein molecules. A new way of modification of silver-based SERS-active substrates with polymer materials is proposed here to achieve large enhancement factors of SERS signals for hemoproteins. It is found that the factors grow in the order: chitosan < bare silver < alginic acid sodium salt ≤ polyacrylic acid. This demonstrates an important role of the polymer origin and its charge state in the retention of protein on the sensor surface and protecting the proteins from silver ions of the nanostructured layer in the sake of future medical diagnostics.

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.

Investigation of kinetics of the process of formation of gold and silver nanoparticles and composites based on them

This article is devoted to studying the kinetics of formation of individual nanoparticles of noble metals and composites based on them. The effect of the concentration of the reducing agent and temperature on the rate of formation of nanoparticles of noble metals is studied. In order to characterize the morphology, phase composition, and optical properties of the synthesized nanomaterials, X-ray diffraction, transmission electron microscopy, UV–visible spectroscopy, and Raman scattering (RS) are used. It is shown that the formation of nanoparticles of noble metals and composites based on them is a three-step process consisting of an induction period, the process of nucleation, and the particle growth stage (which has an autocatalytic character). The formed nanoparticles of noble metals catalyze the further process of reduction of ions remaining in the solution. It has been confirmed that an important factor for amplifying the signal from the analyte molecules in Raman spectroscopy is the resonance absorption by nanoparticles of noble metals in a wavelength range close to the wavelength of the excitation laser.

Reduced graphite oxide decorated with gold nanoparticles for Raman scattering spectroscopy

Surface-enhanced Raman scattering (RS) spectroscopy is a sensitive analytical method that makes it possible to detect individual molecules. The substantial enhancement of the intensity of the signals in this method when compared to traditional Raman scattering is associated with two mechanisms, namely, electromagnetic and chemical. The first mechanism is associated with the enhancement of both the impinging and scattered radiation (electromagnetic enhancement), while the second mechanism is explained by the electron interaction between the molecule being analyzed and metal nanoparticles, namely, by the change in the polarizability of the adsorbed molecule, which results in the displacement and broadening of the electron levels of the adsorbed molecule or in the occurrence of new levels and promotes the enhancement of the signal in the Raman scattering spectrum. Graphene and material associated with it such as graphene oxide, graphite oxide, and reduced forms of graphene and graphite oxides are advanced materials for the creation of a significant chemical enhancement. Taking into account the different nature of the enhancement of the signal from the nanoparticles of noble metals and graphene and its derivatives, it is reasonable to study the effectiveness of hybrid structures on the basis of derivatives of graphene and noble metal nanoparticles in the Raman scattering spectroscopy of the analyte molecules with an aromatic structure.