No abstract

No abstract

Urease has been covalently immobilized on a 3-D networking silica gel (SG) using dimethyldichlorosilane (DMDCS) as second generation silane coupling reagent and m-nitroaniline as linker component in a robust methodology and subsequently characterized as [{Si­(OSi)4(H2O)0.05}205.2] n=4{OSi­(CH3)2–NH–C6H4–NN-urease}·282.5H2O (molecular mass 263 445 g or 263.4 kDa). Selective coupling of tyrosine residue with an identifiable m-nitroaniline modified SG unit prevents enzyme–enzyme cross-linking leading to enhancement of enzymatic activity. The material worked at room temperature and its activity (luminescent and ammonia releasing efficiency) was enhanced by 3-fold (for both synthetic and real sample) compared to native enzyme values at neutral pH. Up to 30 days and 30 cycles, this 3-fold activity remains as such but reduces gradually to native enzyme level after 60 days and 60 cycles of reuse.

A strategy for rapid in situ elimination of interfering substances that are present in extracts of food samples during assay is described in this article. The novel feature of this method is that the sample purification is carried out as a part of the assay, and a separate sample cleanup step is not required. The assay procedure involves the sequential addition of standard or sample, cleaning solutions, and aflatoxin B1-horseradish peroxidase conjugate (AFB1-HRP) over antibody-spotted zones of a membrane, and 3,3'-diaminobenzidine was used as the substrate for visualization. We have determined that trifluoroacetic acid and propionic acids at concentrations of 100 mM are highly effective for cleaning groundnut, wheat, corn, and poultry feed samples and that NaHCO3 (100 mM) is successful in cleaning processed soybean. In all cases, subsequent washing was performed with phosphate-buffered saline solution to facilitate the removal of traces of adhering interfering substances. A batch of 12 samples can be analyzed within 8 min either by visual comparison of the color intensity (inversely related to the analyte concentration) of a sample spot with those of reference standards or, more precisely, by densitometry. The method was tested for the analysis of AFB1 in groundnut, wheat, corn, processed soybean, chili, and poultry feed. The detection limit obtained was 5 microg/kg, except for chili, where it was 10 microg/kg. The average recoveries from different noninfected food samples spiked with AFB1 at concentrations of 5 to 100 microg/kg were between 99 and 105%. The values obtained for infected corn and groundnut samples correlated well with the estimates obtained by high-pressure liquid chromatography. The absence of a sample extraction step reduces the cost and labor involved in the assay. The method may be potentially applicable to the assay of other mycotoxins and environmental pollutants.

By the use of a new silane coupling reagent, dimethyldichlorosilane (DMDCS), effective and instantaneous immobilization of 8-hydroxyquinoline (HQ) on an inorganic carrier (silica gel, SG) has been carried out for the facile synthesis of an extractor material (composition: {Si­(OSi) p=4(H2O) x=0.16} n=11[−Si­(CH3)2–NH–C6H4–NN–HQ] z=4·25H2O; molar mass: 4010.3 g/mol). The material (thermal stability: ≤100 °C; chemical stability: ≤8 M HNO3) possesses a high Brunauer–Emmett–Teller surface area (BET-SAFe(III): 1170 m2·g–1), an appreciable preconcentration factor (PFFe(III): 145.1), and high breakthrough capacity (BTCFe(III): column exchange capacity, 269 μmol·g–l; Langmuir Q 0, 278.6 μmol·g–1) for Fe­(III). Along with these discernible analytical qualities, a high level of reusability (<800 cycles @ 95% recovery) reflects the material warranty. Fe­(III), present as [Fe­(OH)­(H2O)5]2+ at the recommended pH (1.90 ± 0.15), binds at the highest occupied molecular orbital (HOMO) of the sorbent (η = 7.69 eV) through hard–soft binding with an appreciable binding energy (−14.2 eV). The breakthrough capacity (BTC: 269–278.6 μmol·g–1) was found to be the product of the amount of extractor HOMO (280 μmol·g–1) and the degree of polymerization of the adsorbed metal ion, x (i.e., BTC = [amount of HOMOextractor (μmol·g–1)] × x for monomeric (x = 1) and polymeric (x > 1) species). The findings reveal substantial improvement of Weetall–Hill immobilization of chelating ligands on inorganic carriers.

nCA anchored to SSG surface generates 121 μM g−1 H-bonded metal-trapping cores with 10-fold increase in surface area for selective uptake of {Th2(OH)2(H2O)2}6+.

Under optimum sorption conditions, FSG–PAN forms 1 : 1 ‘ion pairs’ with {Be3O(OH)2}2+, {Al3(OH)3(H2O)2}6+ and {(UO2)2(OH)2(H2O)7}2+.

The catalyzed reporter deposition (CARD) method of signal amplification, also called "tyramide signal amplification", has been used in immunoassays not only to increase sensitivity but also to reduce assay time. The current approach to tyramide amplification in immunoassays involves slow incubation with agitation. In this paper we describe new filtration-based tyramide amplification and substrate visualization techniques. Compared with the standard method, this new approach greatly enhances spot intensities in membrane immunoassay and reduces biotinylated tyramide (B-T) and substrate consumption approximately fiftyfold, without loss of specificity. An improved test device and a cost-effective method for preparation of membranes for Super-CARD amplification have also been developed. The techniques have been used for rapid detection of aflatoxin B(1) (AFB(1)) in a variety of foodstuffs with a detection limit of 12.5 microg kg(-1). The assay procedure involves sequential addition of standards or sample, AFB(1)-horseradish peroxidase (HRP) conjugate, B-T, avidin-HRP, and substrate solution over anti-AFB(1) antibody-spotted zones of the membrane surface. The method saves time, improves reproducibility, eliminates many washing steps and avoids manipulation of the membranes between the different steps, while maintaining the sensitivity of the standard method. Average recoveries from different non-infected food samples spiked with AFB(1) at concentrations from 25 to 100 mg kg(-1) were between 95 and 105%. AFB(1) results obtained on different days for Aspergillus parasiticus infection of corn and groundnut samples correlated well with estimates obtained by HPLC.