Mikaela Nichkova

University of California, Davis

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Bruce D. Hammock

University of California, Davis

Ian M. Kennedy

University of Waikato

Dosi Dosev

University of California, Davis

Shirley J. Gee

Sage Therapeutics (United States)

M.‐Pilar Marco

Institute of Advanced Chemistry of Catalonia

Kai Liu

Georgetown University

Randy K. Dumas

Quantum Design (United States)

Francisco Sánchez‐Baeza

Biomedical Research Networking Center in Bioengineering, Biomaterials and Nanomedicine

Peter Haglund

Umeå University

Malin L. Nording

Umeå University

Cooperative Institutions

University of California, Davis

South China Agricultural University

Chinese Academy of Sciences

Cancer Research Center

University of California System

Key Laboratory of Guangdong Province

Consejo Superior de Investigaciones Científicas

Instituto de Investigaciones Químicas y Ambientales de Barcelona

Autonomous University of San Luis Potosí

Institute of Advanced Chemistry of Catalonia

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Immunochemical Determination of Industrial Emerging Pollutants

Springer eBooks (2006)

M.‐Carmen Estévez Héctor Font Mikaela Nichkova J.‐Pablo Salvador Begoña Varela

10.1007/b98609

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Citations (7)

Nanomaterial Based Environmental Sensors

PUBLISHED BY IMPERIAL COLLEGE PRESS AND DISTRIBUTED BY WORLD SCIENTIFIC PUBLISHING CO. eBooks (2007)

Dosi Dosev Mikaela Nichkova Ian M. Kennedy

10.1142/9781860948572_0016

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Citations (0)

Novel ELISAs for Screening of the Biogenic Amines GABA, Glycine, β-Phenylethylamine, Agmatine, and Taurine Using One Derivatization Procedure of Whole Urine Samples

Analytical Chemistry (2010)

Han G. Huisman Paul Wynveen Mikaela Nichkova Gottfried Kellermann

The inhibitory neurotransmitters GABA, glycine and agmatine and neuromodulators beta-phenylethylamine (beta-PEA) and taurine are important biogenic amines of the sympathetic and parasympathetic nervous systems in the body. Abnormalities in the metabolism of these biomarkers have been implicated in a vast number of neurological diseases. Novel competitive immunoassays, using one unique whole urine derivatization procedure applicable for all five biomarkers, have been developed. The determination of these biomarkers was highly reproducible: the coefficient of variance of inter- and intra-assay variation is between 3.9% and 9.8% for all assays. The assays show a good linearity in urine samples within the range of 100-400 mg Cr/dL and specificity when urine samples are spiked with biogenic amines. The recoveries are between 76 and 154%. The correlation between HPLC and ELISA for glycine and taurine (n = 10) showed regression coefficients of 0.97 and 0.98, respectively. An in vivo study on the urinary clearance of beta-PEA, agmatine and taurine after oral intake by healthy individuals demonstrated the specificity and clinical significance of these new immunoassays. The immunoassays are useful for clinical and basic research where a fast and accurate assay for the screening of biogenic amines in urine is required, without preclearance of the sample.

Biogenic amine

10.1021/ac100858u

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Citations (31)

Immunochemical Screening of Pesticides (Simazine and Cypermethrin) in Orange Oil

Journal of Agricultural and Food Chemistry (2009)

Mikaela Nichkova Xun Fu Zheng Yang Ping Zhong James R. Sanborn

Pesticide residue analysis in citrus oils is very important for their quality and marketing. This study assessed the reliability and sensitivity of enzyme-linked immunosorbent assays (ELISA) for simazine and cypermethrin screening in orange oil. Simazine was analyzed after extraction of the oil with methanolic phosphate buffer with a limit of quantitation (LOQ) of 40 microg/L for 1-fold and approximately 100 microg/L for 10-fold oils. Due to matrix effects the immunoanalysis of cypermethrin required hexane-acetonitrile partitioning followed by silica solid phase extraction. The method detected levels higher than 0.5 ppm (mg/L). This LOQ is lower than the U.S. EPA tolerance level (0.9 ppm) for cypermethrin in citrus oils. A good correlation (r(2) 0.99) between ELISA and LC-MS/MS was observed for the analysis of both analytes in 1-fold orange oil. Immunochemical screening can be used to reduce instrumental analysis costs by its use in preliminary orange oil screening.

Simazine

10.1021/jf900652a

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Citations (22)

Ase with Carbon Trap Combined with an Immunoassay as a Fast and Reliable Screening Method to Detect Polychlorinated-P-Dioxins and Furans from Soil Samöles

Organohalogen compounds (2006)

Erik Spinnel Malin L. Nording Mikaela Nichkova Ylva Persson Shirley J. Gee

Trap (plumbing)

Source

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Quantum Efficiency and Surface Passivation Effect of Nanocrystalline Y₂O₃:Eu³⁺

Journal of Nanoscience and Nanotechnology (2008)

Ahjeong Son Mikaela Nichkova Dosi Dosev Ian M. Kennedy Krassimira R. Hristova

We report application of lanthanide nanoparticles for DNA quantification in a microarray platform as a substitute for conventional organic fluorophores. A non-PCR based DNA microarray assay for quantifying bacteria capable of biodegrading methyl tertiary-butyl ether (MTBE) was demonstrated. Probe DNA was immobilized on a glass surface, hybridized with biotinylated target DNA and subsequently incubated with Neutravidin-biofunctionalized nanoparticles. The fluorescence spot intensities, measured by a commercial laser scanner, show a linear relationship (R2 = 0.98) with bacterial 16S rDNA over a range of target DNA concentrations, while the background fluorescence remained low. In addition, nanoparticles fluorescence shows a stronger intensity than Quasar570 (Cy3). Present sensitivity of the assay is 10 pM of target DNA. The selectivity of the DNA-nanoparticle-probes to discriminate a non-target DNA with two base pairs mismatch in the 16S rDNA gene sequence was shown. The use of Eu:Gd2O3 nanoparticles as biolabels provides a relatively non-toxic, inexpensive, rapid and sensitive alternative to the materials currently used in DNA microarrays.

10.1166/jnn.2008.347

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Citations (12)

Nanomaterial-based Environmental Sensors

IMPERIAL COLLEGE PRESS eBooks (2012)

Dosi Dosev Mikaela Nichkova Ian M. Kennedy

Nanomaterials

10.1142/9781848168053_0020

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Citations (1)

Enzyme‐linked immunosorbent assay for screening dioxin soil contamination by uncontrolled combustion during informal recycling in slums

Environmental Toxicology and Chemistry (2008)

Mirta Trindade Malin L. Nording Mikaela Nichkova Erik Spinnel Peter Haglund

Uncontrolled combustion due to garbage recycling is a widespread activity among slum dwellers in distressed economy countries and has been indicated as a major source of dioxin contamination. However, because of the high cost and complexity of gas chromatography/high-resolution mass spectrometry (GC-HRMS) analysis, the magnitude of the problem remains largely unknown. The present study describes a first approach toward the use of a dioxin antibody-based enzyme-linked immunosorbent assay (ELISA) as the basis for a sustainable, simple, and low-cost monitoring program to assess the toxicological impact of uncontrolled combustion in slums. A panel of 16 samples was analyzed by GC-HRMS and ELISA on split extracts. Close to 20% of the analyzed samples showed dioxin concentrations up to almost twice the guidance level for residential soil in several countries, pointing out the need for performing a large-scale monitoring program. Despite the potential for variations in dioxin congener distribution due to the mixed nature of the incinerated material, there was a good correlation between the toxic equivalents as determined by GC-HRMS and ELISA. Furthermore, an interlaboratory ELISA validation showed that the capacity to perform the dioxin ELISA was successfully transferred between laboratories. It was concluded that the ELISA method performed very well as a screening tool to prioritize samples for instrumental analysis, which allows cutting down costs significantly.

Congener

10.1897/07-660.1

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Competitive Quenching Fluorescence Immunoassay for Chlorophenols Based on Laser-Induced Fluorescence Detection in Microdroplets

Analytical Chemistry (2002)

Mikaela Nichkova Jun Feng Francisco Sánchez‐Baeza M.‐Pilar Marco Bruce D. Hammock

An improved biomonitoring system for the analysis of 2,4,6-trichlorophenol (TCP) in urine samples has been developed. The principle of the biosensor device is the detection of laser-induced fluorescence (LIF) in single microdroplets by a homogeneous quenching fluorescence immunoassay (QFIA). The competitive immunoassay occurs in microdroplets (d = 58,4 microm) produced by a piezoelectric generator system with 10-microm-diameter orifice. A continuous Ar ion laser (488 nm) excites the fluorescent tracer; its fluorescence is detected by a spectrometer attached to a 512 x 512 cooled, charge-coupled device camera. Fluorescence is quenched by specific binding of TCP polyclonal antibodies to the fluorescent tracer (hapten A-fluorescein); the quenching effect is diminished by the presence of the analyte. Thus, an increase in the signal is produced in a positive dose-dependent manner when TCP is present in the sample. In 10 mM PBS buffer, the IC50 of the LIF-microdroplet QFIA is 0.45 microg L(-1) reaching a LOD of 0.04 microg L(-1). The QFIA with the same reagents performed in microtiter plate format achieved a LOD of 0.36 microg L(-1) in buffer solution. Performance in human urine was similar to that observed in the buffer. A LOD of 1.6 ,g L(-1), with a dynamic range between 4 and 149.5 microg L(-1) in urine, was obtained without any sample treatment other than dilution with the assay buffer. The detectability achieved is sufficient for occupational exposure risk assessment.

Fluorescence spectrometry

Microtiter plate

10.1021/ac025933n

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Citations (25)

Assessment of Dioxin-Like Soil Contamination in Mexico by Enzyme-Linked Immunosorbent Assay

Archives of Environmental Contamination and Toxicology (2009)

Edelmira Garcı́a-Nieto Mikaela Nichkova Leticia Yáñez Rogelio Costilla‐Salazar Arturo Torres‐Dosal

Brick

10.1007/s00244-009-9422-8

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Citations (8)