Development of immunosensors for the analysis of 1-naphthol in organic media

Regio- and stereoselective 1,3-dipolar cycloaddition reactions of C-aryl (or hetaryl)-N-phenylnitrones to monosubstituted ylidene malononitriles and 4-benzylidene-2-phenyloxazol-5(4H)-one

The first example of 1,3-dipolar cycloaddition reactions of C-aryl (or hetaryl)-N-phenylnitrones to monosubstituted ylidene malononitriles and 4-benzylidene-2-phenyl-oxazol-5(4H)-one is described. The reaction of C-(4-(dimethylamino)phenyl)-N-phenyl-nitrone (1a) with 2-(4-substituted-benzylidene)malononitriles 2a, b in dry toluene, in the absence of catalyst, at reflux temperature furnished the novel cycloadducts 2-(3-aryl-2-phenyl-2,3-dihydro-1,2,4-oxadiazol-5-yl)-3-(4-methoxyphenyl)acrylonitriles 3a, b. Refluxing C-aryl (or hetaryl)-N-phenylnitrones 1b–i with 2-(4-methoxy-benzylidene)malononitrile (2a) in dry toluene, in the absence of catalyst, gave the unexpected 2-cyano-3-(4-methoxyphenyl)-acrylamide (5), as the sole product. On the other hand, refluxing 4-benzylidene-2-phenyloxazol-5(4H)-one (7) with an equimolar amount of C-aryl (or hetaryl)-N-phenyl-nitrones 1a–c, f–i in absolute EtOH afforded the previously unknown 5-anilino-4-benzoyl-2-phenyloxazole (10), as the only isolable product. The resulting products were formed with a high degree of regio- and stereoselectivity. Quantum chemical calculations were performed to verify stereoselectivity of the studied reaction. A mechanistic proposal is presented to rationalize the formation of these products.

Solid-Phase Spectrophotometric Analysis of 1-Naphthol Using Silica Functionalized with m-Diazophenylarsonic Acid

The m-aminophenylarsonic acid (m-APAA) was immobilized onto the silica gel surface with covalently grafted quaternary ammonium groups via ion exchange. The diazotization of ion-bonded m-APAA resulted in a new solid-phase spectrophotometric reagent for detection of 1-naphtol in environmental water samples. The procedure of solid-phase spectrophotometric analysis is characterized by 20 μg L(-1) limit of detection (LOD) of 1-naphtol, up to 2000 concentration factor, and insensitivity to the presence of natural water components as well as to 30-fold excess of phenol, resorcinol, and catechol.

Single-step cycle pulse operation of the label-free electrochemiluminescence immunosensor based on branched polypyrrole for carcinoembryonic antigen detection

A novel label-free electrochemiluminescence (ECL) immunosensor based on luminol functional-Au NPs@polypyrrole has been developed for the detection of carcinoembryonic antigen (CEA). In this work, polypyrrole prepared by chemical polymerization provided a large surface area to load amounts of gold nanoparticles (Au NPs). Au NPs could not only attach abundant luminol for the enhancement of ECL signal, but also provide a friendly microenvironment for the immobilization of antibodies. Moreover, 1-butylpyridinium tetrafluroborate ([BPy]BF₄) were used to disperse luminol functional-Au NPs@polypyrrole nanocomposites, resulting in the film-formation of composites on the electrode, which could improve the stability of immunosensor. In particular, employment of single-step cycle pulse could limit the consecutive reaction between luminol and H₂O₂ efficiently, thus leading to stable and strong signals. The proposed method presents good ECL response for the detection of CEA allowing a wide linear range from 0.01 pg/mL to 10 ng/mL and a limit of detection as low as 3 fg/mL. The immunosensor would be a promising tool in the early diagnosis of CEA due to its high sensitivity, simplicity and cost-effective.

An expedient synthesis of oxazolones using a cellulose supported ionic liquid phase catalyst

A novel cellulose supported ionic liquid phase catalyst has been synthesized and effectively employed as a heterogeneous catalyst in the synthesis of oxazolones.

Site-directed antibody immobilization techniques for immunosensors

Immunosensor sensitivity, regenerability, and stability directly depend on the type of antibodies used for the immunosensor design, quantity of immobilized molecules, remaining activity upon immobilization, and proper orientation on the sensing interface. Although sensor surfaces prepared with antibodies immobilized in a random manner yield satisfactory results, site-directed immobilization of the sensing molecules significantly improves the immunosensor sensitivity, especially when planar supports are employed. This review focuses on the three most conventional site-directed antibody immobilization techniques used in immunosensor design. One strategy of immobilizing antibodies on the sensor surface is via affinity interactions with a pre-formed layer of the Fc binding proteins, e.g., protein A, protein G, Fc region specific antibodies or various recombinant proteins. Another immobilization strategy is based on the use of chemically or genetically engineered antibody fragments that can be attached to the sensor surface covered in gold or self-assembled monolayer via the sulfhydryl groups present in the hinge region. The third most common strategy is antibody immobilization via an oxidized oligosaccharide moiety present in the Fc region of the antibody. The principles, advantages, applications, and arising problems of these most often applied immobilization techniques are reviewed.

Advanced homogeneous-heterogeneous immunosensing format employing restricted access supports

A rapid immunosensing methodology that employs the so-called homogeneous-heterogeneous assay mode is presented. The immunosensor is based on the homogeneous competition among the analyte, a fluorescent tracer, and the antibody, followed by separation of free and bound species by means of a restricted access alkyl-diol silica C18 reversed-phase chromatographic support. In order to develop a general labeling methodology, fluorescent tracers are synthesized from oligonucleotides covalently bound to the hapten in 3' position and the marker in 5'. The immunosensor principle is demonstrated by determining atrazine in a completely automated manner at 2 min/sample without regeneration of the support and a limit of detection of 1.0 microg/L with the optimized system. Preliminary assays employing multilabeled tracers indicate that sensitivity can be improved. Organic solvents 2-propanol and acetonitrile up to 15% (v/v) are well tolerated, while methanol can be added to 50%. The sensor capabilities are demonstrated through the analysis of natural waters.

Immunosensors for pollutants working in organic media. Study of performances of different tracers with luminescent detection

A comparative study of enzymatic and non-enzymatic labels combined with luminescence detection, developed for immunosensing of pesticide residues (carbaryl, 1-naphthol, irgarol 1051) in organic media, is presented. Peroxidase and alkaline phosphatase enzymes with fluorogenic (3-p-hydroxyphenylpropanoic acid) and luminogenic (AMPPD derivative) substrates, respectively, were assessed as enzymatic markers. As an alternative, terbium(III) chelate, with time-resolved fluorescence detection, was evaluated as a non-enzymatic label. The best sensitivity was achieved by use of alkaline phosphatase in an immunocomplex capture assay format (I (50) values 0.06, 0.27, and 7.45 microg L(-1) in buffer, 1:1 methanol-buffer, and methanol, respectively). Results were also good (I (50) 1.00 and 6.30 microg L(-1) for water and aqueous-organic mixture, respectively) for Tb(III) chelate in an immobilized conjugate assay format. Use of alkaline phosphatase label to measure carbaryl (100 ng L(-1)) in different spiked river water samples, after solid-phase extraction and analyte elution with an ethyl acetate-methanol mixture, resulted in recoveries ranging from 81 to 98%, with acceptable precision (CV 4-14%, n=4).

Analysis of zearalenone in cereal and Swine feed samples using an automated flow-through immunosensor

The development of a sensitive flow-though immunosensor for the analysis of the mycotoxin zearalenone in cereal samples is described. The sensor was completely automated and was based on a direct competitive immunosorbent assay and fluorescence detection. The mycotoxin competes with a horseradish-peroxidase-labeled derivative for the binding sites of a rabbit polyclonal antibody. Control pore glass covalently bound to Prot A was used for the oriented immobilization of the antibody-antigen immunocomplexes. The immunosensor shows an IC(50) value of 0.087 ng mL(-1) (RSD = 2.8%, n = 6) and a dynamic range from 0.019 to 0.422 ng mL(-1). The limit of detection (90% of blank signal) of 0.007 ng mL(-1) (RSD = 3.9%, n = 3) is lower than previously published methods. Corn, wheat, and swine feed samples have been analyzed with the device after extraction of the analyte using accelerated solvent extraction (ASE). The immunosensor has been validated using a corn certificate reference material and HPLC with fluorescence detection.

Noninvasive biomonitoring approaches to determine dosimetry and risk following acute chemical exposure: analysis of lead or organophosphate insecticide in saliva

There is a need to develop approaches for assessing risk associated with acute exposures to a broad range of metals and chemical agents and to rapidly determine the potential implications to human health. Noninvasive biomonitoring approaches are being developed using reliable portable analytical systems to quantitate dosimetry utilizing readily obtainable body fluids, such as saliva. Saliva has been used to evaluate a broad range of biomarkers, drugs, and environmental contaminants, including heavy metals and pesticides. To advance the application of noninvasive biomonitoring a microfluidic/electrochemical device has also been developed for the analysis of lead (Pb), using square-wave anodic stripping voltametry. The system demonstrates a linear response over a broad concentration range (1-2000 ppb) and is capable of quantitating saliva Pb in rats orally administered acute doses of Pb acetate. Appropriate pharmacokinetic analyses have been used to quantitate systemic dosimetry based on determination of saliva Pb concentrations. In addition, saliva has recently been used to quantitate dosimetry following exposure to the organophosphate insecticide chlorpyrifos in a rodent model system by measuring the major metabolite, trichloropyridinol, and saliva cholinesterase inhibition following acute exposures. These results suggest that technology developed for noninvasive biomonitoring can provide a sensitive and portable analytical tool capable of assessing exposure and risk in real-time. By coupling these noninvasive technologies with pharmacokinetic modeling it is feasible to rapidly quantitate acute exposure to a broad range of chemical agents. In summary, it is envisioned that once fully developed, these monitoring and modeling approaches will be useful for evaluating acute exposure and health risk.