Phosphorescence of molecules of polycyclic aromatic hydrocarbons in aqueous micellar solutions of sodium dodecylsulfate at room temperature

Deactivation of the excited states of pyrene, benzanthracene, and fluorene molecules in aqueous micellar solutions of sodium dodecylsufate is studied using steady and pulsed fluorimetry. Quenching of the singlet states of polyatomic hydrocarbons by thallium ions is considered. Effective, micellar, and biomolecular constants for the quenching rate are obtained. Phosphorescence constants for the aforementioned compounds are determined. Reasons behind the possibility of observing phosphorescence of polyaromatic compounds in micellar solutions at room temperature are ascertained. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 2, pp. 201–204, March–April, 1999.     

Tetraphenylporphyrin Sensors with High Cross Sensitivity for “Electronic-Tongue” Analyzers

Tertaphenylporphyrin-based film sensors were prepared with anionic and cationic lipophilic ionic additives introduced into polyvinyl chloride membranes plasticized with various solvents. The data obtained with these sensors were used to calculate the parameters of the cross sensitivity of the sensors. A multisensor system of the electronic tongue type was developed on the basis of the sensors studied.     

A gel-based visual immunoassay for non-instrumental detection of chloramphenicol in food samples

A gel-based non-instrumental immuno-affinity assay was developed for the rapid screening of chloramphenicol (CAP) in food samples with the limit of detection (LOD) of 1 μg L⁻¹. The immuno-affinity test column (IATC) consisted of a test layer containing anti-CAP antibody coupled gel, and a control layer with anti-HRP antibody coupled gel. Based on the direct competitive immuno-reaction and the horseradish peroxidase enzymatic reaction, the test results could be evaluated visually. Basically, blue color development represented the negative results, while the absence of color development represented the positive results. In this study, CAP spiked samples of raw milk, pasteurized milk, UHT milk, skimmed milk powder, acacia honey, date honey, fish and shrimp were tested. Little or none sample pretreatment was required for this assay. The whole procedure was completed within 10 min. In conclusion, the gel-based immuno-affinity test is a simple, rapid, and promising on-site screening method for CAP residues in food samples, with no instrumental requirement.     

INDENTATION OF A RIGID CYLINDER WITH A ROUGH FLAT BASE INTO A THIN VISCOELASTIC LAYER

Journal of Applied Mechanics and Technical Physics - Interaction between a thin viscoelastic layer and a rigid cylinder whose contacting end surface is nominally flat but has a microrelief is...     

Fluorescent properties of aflatoxins in organized media based on surfactants,cyclodextrins, and calixresorcinarenes

Fluorescent properties aflatoxin B1 (AfB1) and its metabolites, aflatoxins B2, G1, and G2 in the presence of surfactants, cyclodextrins, and calix[4]resorcinarenes are studied. It is found that surfactants and cyclodextrins enhance the fluorescence of aflatoxins B1 and G1. Using the example of AfB1, it is shown that the fluorescence intensity in solution attains a maximum in the presence of 2-hydroxypropyl-β-cyclodextrin. The effects observed increase the sensitivity of the fluorimetric determination of AfB1: the detection limit in water is 3.1 × 10^?8 M and decreases to 2.1 × 10^?9 M in a solution of cyclodextrin.     

Novel gel-based rapid test for non-instrumental detection of ochratoxin A in beer

A rapid easy-to-use immunoassay was optimised for the non-instrumental detection of ochratoxin A (OTA) in beer. The analytical method involves preconcentration on the immunoaffinity layer inside a column followed by direct competitive ELISA detection in the same layer. The visual cut-off value, i.e. the lowest OTA concentration resulting in no colour development, was 0.2 μg L^-1. Assay validation was performed using samples spiked with OTA. Thirty-seven naturally contaminated samples were screened with the gel-based method developed and no false-negative results were obtained. The method described offers a simple, rapid and cost-effective screening tool, thus contributing to better health protection of consumers. Figure Gel-based immunoassay of spiked beer samples.     

Modeling of friction at different scale levels

We construct a model for studying the common influence of the imperfect elasticity of actual bodies, the microgeometry of their surfaces, and their adhesive interaction on the contact characteristics (the contact pressure distribution, the region of actual contact) and on the sliding friction force. The model is based on the solution of a plane contact problem of sliding of a rigid body with a regular relief on the boundary of a viscoelastic foundation with surface molecular attraction in the gap between the surfaces taken into account. We analyze the influence of the surface microgeometry parameters at different scale levels on the character of the surface interaction (the saturated or discrete contact) and the friction force for different sliding velocities of the contacting bodies.     

Determination of Ochratoxin A in colored food products: Sample preparation and an immunoassay test method

A method is proposed for the purification of highly colored food products (red wine, red pepper) for the immunochemical test determination of Ochratoxin A (OTA) with visual detection. The method is based on passing an analyzed sample (wine diluted with a solution of polyethylene glycol and sodium hydrocarbonate or water-ethanol extract of pepper diluted with a solution of sodium hydrocarbonate) though an adsorbent layer. Criteria for selecting the adsorbent are considered, and silica gels with aminopropyl and trimethylaminepropyl groups are used as the optimal ones. A test system for the determination of OTA combines the indicated purification method with the immunoaffinity preconcentration and immunoenzyme detection. The developed approach has allowed the test determination of OTA in red wine and red pepper at levels of 2 μg/L and 10 μg/kg, respectively.     

Multiplex flow-through immunoassay formats for screening of mycotoxins in a variety of food matrices

Two multi-analyte flow-through immunoassay formats for rapid detection of mycotoxins in a variety of food matrices (peanut cake, maize, and cassava flour) were developed and evaluated. The selected food matrices are typical staple foods and export products for most low-income communities around the world. The assay formats included gel-based and membrane-based flow-through assays and were based on the principle of indirect enzyme-linked immunosorbent assay. Using the same immunoreagents, the performance characteristics of both assays were compared. To the best of our knowledge, this is the first report on such a comparison. The gel-based format was developed to screen for ochratoxin A, fumonisin B₁, deoxynivalenol, and zearalenone detection at cut-off values of 3, 1,250, 1,000, and 200 μg kg⁻¹, respectively, while the membrane-based format can be used to screen ochratoxin A, aflatoxin B_1, deoxynivalenol, and zearalenone at the following cut-offs: 3, 5, 700, and 175 μg kg⁻¹, respectively. The applicability of these assay formats was demonstrated by evaluating the performance characteristics of both tests through performing multiple experiments on different days. Both assays were further evaluated by analyzing naturally contaminated samples in the laboratory and also in the field under tropical conditions (Cameroon, West Africa). The false-negative rate with both formats was less than 5%, which is in good agreement with Commission Decision 2002/657/EC regarding the performance of analytical methods intended for screening purposes.     

Quantum dot based rapid tests for zearalenone detection

Three different kinds of immunosorbent assays with luminescence detection were developed for the determination of zearalenone (ZEN), a secondary toxic metabolite of Fusarium fungi. CdSe/ZnS core/shell quantum dots (QDs) were used as a label in quantitative micro-well plate immunoassays (fluorescent-labeled immunosorbent assay, FLISA) and in qualitative column test methods. As carriers for QD-based column tests, sepharose gel (for covalent binding of antibody) and polyethylene frits (for physical absorption of antibody) were used and compared. The application of QDs as a label resulted in a fourfold decrease in the IC(50) value with FLISA (0.1 ng mL(-1)) with a detection limit of 0.03 ng mL(-1) when compared with the traditional immunosorbent assay which makes use of horseradish peroxidase as the enzyme label. The cutoff levels for both qualitative column test methods were selected based on the maximum level for ZEN in unprocessed cereals established by the European Commission (100 μg kg(-1)) as 5 ng mL(-1) taking into account extraction and dilution. The different developed immumoassays were tested for ZEN determination in raw wheat samples. As a confirmatory method, liquid chromatography coupled to tandem mass spectrometry was used. The obtained results allow using FLISA and both qualitative column test methods for the analysis of analytes with very low established maximum limits, even in very complicated food matrices, owing to the high dilution of the sample extract.