Usefulness of magnetically-controlled MNPs-enzymes microreactors for the fluorimetric determination of total cholesterol in serum.

A new dynamic method containing a magnetically retained enzyme reactor (MRER) located in the reaction/detection zone of a flow injection (FI) system, has been used for the determination of total cholesterol in serum samples. The MRER was formed by a mixture ratio of 2/1 of immobilized enzymes cholesterol esterase (ChE) and cholesterol oxidase (COx) on magnetic nanoparticles (MNPs). The analytical signal is based on the fluorescence decreasing of the fluorophore naphtofluorescein (NF) due to its oxidation by the HO formed in the enzymatic reactions.

Automatic determination of coenzyme Q10 in food using cresyl violet encapsulated into magnetoliposomes.

A new type of magnetoliposomes (MLs), containing hydrophobic magnetic-gold nanoparticles and the long wavelength fluorophore cresyl violet, has been used for the determination of coenzyme Q10 (CoQ10). MLs were concentrated just before the detector, using a flow system and an external electromagnet device. The subsequent introduction of Triton X-100 and CoQ10 causes the MLs lysis and the cresyl violet oxidation, obtaining a decrease in the fluorescence signal.

Usefulness of palladium impregnated magnetite nanoparticles for polyphenol determination.

Palladium impregnated magnetite nanoparticles (Pd-Fe3O4NPs) have been synthesized and used as reusable catalyst for the fluorometric determination of polyphenols in wines. The method is based on the decrease of the indocyanine green fluorescence, which is ascribed to its oxidation by dissolved oxygen in the presence of the nanoparticles, and the inhibition of the fluorescence decrease by polyphenols, which is proportional to the polyphenol concentration. The dynamic range of the calibration graph is 0.

Automatic determination of polyphenols in wines using laccase and terbium oxide nanoparticles.

The analytical usefulness of the combined use of laccase, terbium oxide nanoparticles (Tb4O7NPs) and 8-hydroxypyrene-3-sulphonate trisodium (HPTS) for the determination of polyphenol compounds in wine samples is described. The system is based on the temporal inhibition by polyphenols on the decrease of the HPTS fluorescence in the presence of laccase and on the activating effect of Tb4O7NPs, which increase the reaction rate of the system, shortening analysis times. The method has been developed in a microplate format using an automatic reader, reaching a sample throughput of 35 samples h(-1).

Fluorometric determination of alkaline phosphatase activity in food using magnetoliposomes as on-flow microcontainer devices.

Liposomes containing magnetic gold nanoparticles (AuNPs) and an enzymatic substrate (4-methylumbelliferyl-phosphate) have been used as on-flow microcontainers for reagent preconcentration in a flow injection method for the determination of alkaline phosphatase (ALP) activity. The dynamic range of the calibration graph was 6.4 × 10(-3)-0.

Application of Tb(4)O(7) nanoparticles for lasalocid and salicylate determination in food analysis.

The usefulness of Tb(4)O(7) nanoparticles (NPs) as analytical reagents using sensitized luminescence as a detection system is described for the first time, and the results obtained are compared with those obtained using Tb(III) ions. Two drugs used in veterinary practice, namely, lasalocid (LAS) and salicylate (SAL), have been chosen as model analytes to carry out this study. The experimental conditions for these systems have been optimized, and their analytical features were obtained.

Gold nanoparticle-biotinylated liposome hybrids as analytical reagents for biotin determination using a competitive assay and resonance light scattering detection.

The preparation of hybrid nanostructures formed by gold nanoparticles (AuNPs) into biotinylated liposomes and their analytical application are presented. The surface of negatively charged AuNPs was modified with 1-dodecanethiol and the NPs were encapsulated into biotinylated liposomes using the rapid solvent evaporation method. Liposomes were resized by both mechanical shaking and ultrasound treatments and filled liposomes were separated from empty liposomes using sucrose density gradient centrifugation.

Determination of monensin in milk samples by front-surface long-wavelength fluoroimmunoassay using nile blue-doped silica nanoparticles as labels.

A heterogeneous immunoassay for monensin determination in milk samples using a tracer formed by anti-monensin antibodies bound to nile blue (NB)-doped silica nanoparticles (NPs), 96-well microplates as solid supports and long-wavelength fluorescence measurements is described for the first time. The assay relies on the competition of the monensin present in the samples with a monensin-bovine serum albumin conjugate, which was immobilized onto the well surface, for the active sites of anti-monensin antibodies. After subsequent incubation and washing steps, the fluorescence of the bound tracer fraction is measured onto the dry surface of the well.

Luminescent determination of flavonoids in orange juices by LC with post-column derivatization with aluminum and terbium.

A new post-column derivatization system is described and applied to the determination of flavonoids in citric beverages after their separation by LC using a monolithic column. The derivatization involves the formation of the chelates of the analytes with aluminum (III) and terbium (III) in the presence of the surfactant SDS and the measurement of the terbium sensitized luminescence at lambda(ex) 360 and lambda(em) 545 nm. Naringin, hesperidin, quercetin, naringenin, and kaempferol have been chosen as analyte models.

High throughput bioassays using nanoparticles.

An overview of the usefulness of different nanoparticles to improve the features of high throughput separation and individual and multiplexed detection bioassays is presented. Although the development of microarray and microfluidic systems has expanded the capabilities of these high throughput assays, the combined use of NPs and these devices has provided them with new applications in drug discovery, proteomic and genomic studies, and clinical diagnosis. This article reviews the wide application field of magnetic, gold, silver, semiconductor and other nanoparticles in high throughput bioassays.

Synthesis and characterization of oxazine-doped silica nanoparticles for their potential use as stable fluorescent reagents.

The synthesis process to obtain silica nanoparticles (NPs) doped with two oxazine dyes, nile blue and cresyl violet, has been investigated using a modification of the reverse micelle microemulsion method and a procedure based on the Stöber method. A micellar medium provided by the non-ionic surfactant Triton X-100 in a hexanol:water mixture and an ethanol:water mixture, have been used to provide the synthesis medium in each case. Tetraethoxysilane has been used as the initiator of the polymerization and condensation reactions after its hydrolysis in basic medium using ammonium hydroxide.

Determination of soluble phosphates in water samples using ytterbium(III) and dynamic measurements of light scattering intensity at long wavelength.

A selective and fast method has been developed for the determination of phosphates by measuring the formation of ytterbium(III) phosphate through the variation of the light scattering intensity with time. The low solubility of this compound causes an efficient dispersion of the radiation at 490 nm, which is measured at 980 nm using the second-order grating effect. This approach minimizes potential background signals from the sample matrix.

Analytical innovations in the detection of phenolics in wines.

A liquid chromatographic method with online photometric and luminescent detection for the determination of 18 phenolic compounds in wines is reported. Photometric detection is performed at four wavelengths, namely, 256, 280, 320, and 365 nm, using a diode array detection system. The luminescent detection is achieved by means of a postcolumn derivatization reaction of 10 of these compounds with terbium(III) in the presence of synergistic agents, such as ethylenediaminetetraacetic acid (EDTA) and n-octyltriphosphine oxide (TOPO).

Long-wavelength fluorescence polarization immunoassay: determination of amikacin on solid surface and gliadins in solution.

The versatility of the fluorescence polarization immunoassay (FPIA) is increased by using two long-wavelength labels, Nile Blue and a ruthenium(II) chelate. The first label has been used to study the potential of FPIA on a solid surface using dry reagent technology. The aminoglycoside antibiotic amikacin has been used as an analyte model, and the method has been applied to the analysis of serum samples.

Determination of some hydroxybenzoic acids and catechins in white wine samples by liquid chromatography with luminescence detection.

A liquid chromatographic method with luminescence detection for the determination of eight phenolic compounds is reported. The method involves postcolumn derivatization with terbium(III). This derivatization is based on the reaction between phenolics and terbium(III) to form luminescent chelates, which were determined at lamda ex 295 and lamda em 545 nm using the fluorescence mode.

Determination of fluoroquinolones in milk samples by postcolumn derivatization liquid chromatography with luminescence detection.

A liquid chromatography (LC) method with luminescence detection for the determination of eight quinolone antibiotics is reported. The system encompasses three consecutive steps: (a) chromatographic separation using reverse-phase mode (RP-LC), (b) postcolumn derivatization reaction, and (c) luminescence detection by monitoring fluorescence (FL) and time-resolved (TR) signals. The derivatization step is based on the reaction between quinolones and terbium(III) to form luminescent chelates, which were determined at lambda(ex) 340 and lambda(em) 545 nm (FL mode) or at lambda(ex) 281 and lambda(em) 545 nm (TR mode).

Usefulness of ytterbium(III) as analytical reagent for total sulfite determination in white wine samples.

Ytterbium(III) is used as reagent for the determination of sulfite by measuring the formation of the Yb(III)-sulfite complex through the variation of the light scattering intensity with time. The low solubility of this complex causes an efficient dispersion of the radiation at 490 nm, which is measured at 980 nm. Each kinetic datum is automatically obtained in only 0.

Stopped-flow fluorescence polarization immunoassay.

A general survey of the analytical application of kinetic methodology in fluorescence polarization immunoassay (FPIA) is presented. Stopped-flow mixing technique (SF) allows the initial rate of the immunochemical reaction between the tracer and the antibody to be obtained, which is used as the analytical parameter instead of the equilibrium signal used in conventional FPIA. The instrumentation required is described and the features of the analytical methods proposed are compared with those obtained by conventional FPIA.