S. N. Shtykov

Nanomaterials and nanotechnologies in chemical and biochemical sensors: Capabilities and applications

The publications reporting on the use of nanomaterials and nanotechnologies in chemical and biochemical sensor designing were reviewed for the recent decade. The capabilities and applications were discussed for nanoparticles based on gold, silver, magnetic and semiconductor materials (quantum dots), lanthanides, and silica compounds, as well as for nanotubes and nanolayers (Langmuir-Blodgett films, selfassembled monolayers) used in optical (absorbance, luminescence, surface enhanced Raman spectroscopy, surface plasmon resonance), electrochemical, and mass-sensitive sensors. It was shown that the unique capabilities of nanosensors might hold the key to improve the analysis of liquids, gases, and especially biochemical and biological objects in the near future.

Determination of warfarin by sensitized fluorescence using organized media

The effect of surfactant micelles and albumin on the fluorescence warfarin of and the fluorescence of Eu3+ and Tb3+ sensitized by warfarin and the second ligand is studied. It was shown that sensitized fluorescence in the system Eu3+-tenoyltrifluoroacetone-warfarin allows a 3800-fold reduction of the detection limit for warfarin. The developed procedure was used to determine warfarin in soil.

Intermolecular forces and the internal pressure of liquids

The problem of the introduction of the term internal pressure from the standpoint of intermolecular forces is solved. It is shown that internal pressure is created by the macrosystem average force field of the structural units of a liquid. Internal pressure is shown to be not an energy characteristic, but a macrosystem average force parameter of the interaction between the structural units of a liquid phase system, although it has the energy density dimension, [J/m3].

Volumetric and Transport Properties of Water–n-Octane–Sodium Dodecyl Sulfate–n-Pentanol Microemulsions

The density, isothermal compressibility, and thermal expansion coefficient of monophase water–n-octane–sodium dodecyl sulfate–n-pentanol microemulsions were measured in a wide range of the water-to-oil ratios. The internal pressure and molar volume of the investigated microemulsion systems were calculated. The conductivity of microemulsions was determined and its percolation character was revealed.

Doxycycline-sensitized solid-phase fluorescence of europium on silica in the presence of surfactants

The effect of the second ligand and surfactant micelles on the solid-phase time-resolved fluorescence of europium sensitized by doxycycline on Silasorb 600 is studied. A procedure of the sorption-luminescence determination of doxycycline using micelles of Triton X-100 nonionic surfactant is developed; the detection limit is 1.1 × 10−7. The analytical range for doxycycline is 3 × 10−7 to 3 × 10−5 M. The procedure is tested on a doxycycline pharmaceutical drug; RSD was no worse than 4%.

Properties of a sodium dodecyl sulfate-Brij 35 binary micellar system and their effect on the alkaline hydrolysis of O-ethyl-O-p-nitrophenylchloromethylphosphonate

It is found that a sodium dodecyl sulfate-Brij 35 binary mixture inhibits the alkaline hydrolysis of O-ethyl-O-p-nitrophenylchloromethylphosphonate. Tensiometric data and variations in cloud point suggest the synergistic effect of the above surfactants caused by the formation of mixed micelles. The method of solvatochromic probe ET(30) shows that the micropolarity of a medium rises at the sites of localization of substrates solubilized in micelles with an increase in ionic surfactant fraction in mixed aggregates. Variations in micellization properties, micropolarity, and surface potential with the composition of the binary mixture of the surfactants influence the catalytic properties of mixed micelles with respect to the examined reaction.

Factors determining the catalytic activity of the mixed micellar system cetyltrimethylammonium bromide-Brij-35 in the hydrolysis of a phosphonic acid ester

The micellization and surface properties, Stern layer micropolarity, and catalytic action of the cetyltrimethylammonium bromide-Brij-35 system in the alkaline hydrolysis of O-ethyl O-p-nitrophenyl chloromethylphosphonate have been investigated at different proportions of the constituent surfactants. This system has unique, invertible catalytic properties ranging from acceleration of the hydrolysis reaction by more than one order of magnitude to strong inhibition of this reaction and even termination of the reaction at certain proportions of the surfactants. The factors in the changes of the catalytic effect under variation of the surfactant ratio are micropolarity in the reaction zone and surface potential. A likely cause of the termination of the process is the shift of the reaction zone from the surface layer to the micelle core, where the environment is less polar.

Determination of volatile organic compounds using piezosensors modified with the Langmuir-Blodgett films of calix[4]resorcinarene

A sensor based on a piezoelectric quartz resonator modified with the Langmuir-Blodgett (LB) films of calix[4]resorcinarene is proposed for the detection of volatile organic compounds. Parameters for the formation of ordered LB films based on calix[4]resorcinarene were optimized, and the effects of the pH and metal ion content of the subphase on the behavior of the Langmuir monolayers of calix[4]resorcinarene were studied. The effects of the number of monolayers in a sensor coating, the pH of the subphase from which the monolayers were transferred, and the presence of copper ions in the subphase on the response of the resulting piezoelectric quartz sensors to the vapors of various volatile organic compounds (ethanol, benzene, toluene, ethylbenzene, ethyl acetate, acetone, hexane, and cumene) were studied. It was found that the proposed sensor was characterized by a short response time and reproducible measurements.

Effect of nucleophilic agents and organized media on the fluorimetric determination of histamine with o-phthalic aldehyde

The addition of nucleophilic agents, 2-mercaptoethanol, 3-mercaptopropionic acid (3-MPA), and N-acetyl cysteine, to the system histamine-o-phthalic aldehyde (OPA) resulted in the following effects: the exclusion of the acidification step, the 1.5-2-fold increase in the time of attaining the optimum fluorescence, the shift of the pH of fluorophore formation of a less alkaline region by 2 units and the widening of its range by two to three times, and the twofold increase in the fluorophore stability (in time in the case of 3-MPA). The addition of surfactant micelles reduced the time of attaining the optimum fluorescence intensity by two times, but its intensity increased (by a factor of 1.3–1.5) only in the presence of nonionic surfactant block copolymers. The widest plateau range (2 pH units), the highest stability of an analytical signal in time (3 h), and the best reaction sensitivity were obtained after the addition of 2-hydroxypropyl-β-cyclodextrin to the histamine-OPA-3-MPA system. Procedures were proposed for the determination of histamine in fish products and wine using nucleophilic agents and different organized media.

Bulk Properties of n-Heptane–Water–Sodium Dodecyl Sulfate–n-Pentanol Microemulsions

The density, isothermal compressibility, and thermal expansion coefficient of macroscopically single-phase n-heptane–water–sodium dodecyl sulfate–n-pentanol microemulsions are measured by a precision dilatometric method at 25°C. The internal pressure and molar volume of the investigated microemulsion systems are calculated. It was shown that the bulk properties of direct microemulsions with various contents of the dispersed phase markedly differ.