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At least 1,099 records · Page 61Linked to original sources
PubMed1995

Quantification of hepatitis B virus DNA over a wide range from serum for studying viral replicative activity in response to treatment and in recurrent infection.

A new standardized test for hepatitis B virus (HBV) DNA with increased sensitivity and range over previous assays (30 to 10(6) HBV genomes/test) was evaluated in this study. The quantitative results from the test have been validated using international reference specimens of known titer and a reference solution hybridization test. The test has small variability considering the wide dynamic range. The CV was 14% within one experiment and 32% to 39% between independent experiments. Hepatitis B surface antigen (HBsAg)-negative, anti-HBc-positive blood donor sera (n = 25) were all negative for HBV DNA in the new test, whereas 63% (n = 19) of HBsAg-positive healthy carriers had measurable quantities of HBV DNA. In five example cases of chronic hepatitis B patients responding to alfa-interferon treatment but remaining virus positive, HBV DNA was consistently present in posttreatment sera in a titer range 4 x 10(3) to 10(6)/mL not detectable by the conventional hybridization test. In two complete responders, the HBV DNA titer decreased over six orders of magnitude to below cutoff of the test. In four liver transplant recipients with chronic hepatitis B, viral recurrence was detected by the new test at an early stage much before the clinical relapse. Unlike serology, the test was suitable also in patients under anti-HBs immunoprophylaxis. In conclusion, the new colorimetric polymerase chain reaction (PCR) test allowed thousandfold increased sensitivity in quantification of HBV DNA in patient sera. The test may have future applications in improving assessment of efficacy of antiviral treatment and guiding therapeutic interventions.

Adult↗
PubMed2004

Resistance to signal activation governs design features of the MAP kinase signaling module.

Given its broad influence over numerous cell functions, redesigning the mitogen-activated protein (MAP) kinase signaling module would offer a powerful means to engineer cell behavior. Early challenges include identifying quantitative module features most relevant to biological function and developing simple design rules to predictably modify these features. This computational study delineates how features such as signal amplification, input potency, and dynamic range of output may be tuned by manipulating chief module components. Importantly, the model construction identifies a metric of resistance to signal activation that quantitatively predicts module features and design trade-offs for broad perturbations in kinase and phosphatase expression. Its predictive utility extends to dynamic properties such as signal lifetime, which often dictates MAP kinase effect on cell function. Taken together, we propose that predictably altering MAP kinase signaling by tuning resistance is not only a feasible engineering strategy, but also one exploited by natural systems to allow each MAP kinase to exert pleiotropic effects in a context-dependent manner. External stimuli not only activate kinases, but also alter phosphatase expression and activity, thereby reconfiguring a single module for quantitatively distinct modes of signaling such as transient vs. sustained dynamics, each with unique effects on cell function.

Computer Simulation↗
PubMed2003

A study of the chemiluminescence behavior of myoglobin with luminol and its analytical applications.

A chemiluminescence signal at 425 nm was observed when ferric state myoglobin was mixed with luminol in alkaline medium. Because the signal was remarkably enhanced in the presence of Fe(CN)6(4-), analytical applications were investigated in a flow-injection system. The increase in chemiluminescence was linearly dependent on myoglobin concentration in the range 0.1 to 100 nmol L(-1), and the limit of detection was 0.04 nmol L(-1) with relative standard deviation 3.2% (3 sigma). It was also found that binding of Mb with the ligands CN-, SCN-, and F- significantly inhibited the chemiluminescence reaction. The linear dynamic ranges for the ligands were 1.0-300.0, 0.1-3.0, and 0.5-100.0 nmol L(-1), and the limits of detection (S/N=3) 0.4, 0.04, and 0.2 nmol L(-1), for F-, CN-, and SCN-, respectively. The relative standard deviations were 5.32%, 6.13%, and 3.38% for 0.1 nmol L(-1) CN-, 0.5 nmol L(-1) SCN-, and 1.0 nmol L(-1) F-, respectively. At a flow rate of 2.0 mL min(-1) the assay could be accomplished in 1 min, including sampling and washing. The method has been successfully applied to the determination of myoglobin in human urine and F- in water samples. A possible mechanism of chemiluminescence production by myoglobin and luminol is presented.

Female↗
PubMed1998

A novel and innovative quantitative kinetic software for virological colorimetric assays.

This study addresses the limited range of quantification with colorimetric assays (ELISA) starting from the analysis of color production in a reference external curve. An automatic ELISA management software, designated Quanti-Kin Detection System (QKDS) is described, which retains the sensitivity of the end-point reading and extends the dynamic range up to five logarithms with mathematical interpretation of color production. The QKDS software is a generic system suitable for different types of ELISA with substrate incubation at room temperature, does not require dedicated instruments, performs accurate quantification (including assay quality control) and has a user friendly interface. Specific applications were developed for three types of analytes: antibodies, viral antigens and nucleic acids. Data are presented on three representative QKDS applications to HIV antibodies, p24 antigen and proviral DNA kits. The precision of quantification is strictly correlated with the precision of the kit; however, for almost all samples with known analyte amount, the error percentage was below 10%, only for two cases in quantification of HIV proviral DNA the error percentage was around 25%. The necessity for a wide quantification range has been demonstrated by measuring clinical samples, which showed a distribution in all possible quantification ranges for all kits.

Animals↗
PubMed2004

Canonical sensitivities: a useful tool to deal with large perturbations in metabolic network modeling.

The dynamic range of metabolic models can be extended to deal with large perturbations by introducing the related concepts of "generalized" kinetic order and "canonical" sensitivities. Generalized kinetic orders are built as a well-defined non linear combination of the canonical sensitivities coefficients, which in turn are obtained by a least-squares regression on central composite factorial design data. In a such way, the whole domain of the operating variables is mapped without need to determine locally neither the first nor the second order model derivatives. The method was validated through numerical simulations, its predictions being compared with those coming from a Michaelis-Menten formalism taken as reference. In parallel, two variants of the Power-law formalism (S-system, least-squares GMA) also were tested. The canonical sensitivities method produced the widest range to predict metabolite concentrations and metabolic fluxes at the steady states. In addition, the variation pattern for the logarithmic gains and for the characteristic eigenvalues have been accurately determined from a unique overall model, being both required to make realistic analysis in metabolic engineering. The achieved information also can be expressed in terms of those typical coefficients derived from the Metabolic Control Analysis (MCA). Even if current first order Power-law or MCA formalisms were used, the canonical sensitivities approach provides a significant advantage, since complete sets of homologous, accurate, locally valid metabolic coefficients can be simultaneously recovered from the array proposed, being representative of the whole range of the operating variables instead of a unique nominal condition as is usual.

Algorithms↗
PubMed2006

Enhanced molecular recognition signal in allosteric biosensing by proper substrate selection.

Among protein biosensors, those based on enzymatic responses to specific analytes offer convenient instruments for fast and ultra-fast molecular diagnosis, through the comparative analysis of the product formed in presence and in absence of the effector. We have explored here the performance of five beta-galactosidase substrates during the activation of a beta-galactosidase sensor by antibodies against the human immunodeficiency virus (HIV). Interestingly, the employed substrate determines the dynamic range of the allosteric signal and significantly influences the sensitivity of the senso-enzymatic reaction. While ortho-nitrophenyl beta-D-galactopyranoside allows the detection of a model anti-gp41 monoclonal antibody below 0.024 ng/microL, phenol red beta-D-galactopyranoside offers the most dynamic response with signal/background ratios higher than 12-fold and a detection limit around 0.071 ng/microL. The hydrolysis of both chromogenic substrates generates linear sensing responses to immune human sera and parallel time-course topologies of the allosteric reaction. Therefore, the obtained results stress the potential of chromogenic substrates versus those rendering quimioluminescent, amperometric, or fluorescent signals, for the further automatization, miniaturization, or adaptation of beta-galactosidase-based biosensing to high-throughput applications.

Allosteric Regulation↗
PubMed2001

Time resolved fluorometric immunoassay, using europium labelled antihuman IgG, for the detection of human tetanus antitoxin in serum.

A time resolved fluorometric immunoassay (TRFIA) has been developed and compared with an in house enzyme linked immunosorbent assay (ELISA) and commercial ELISA (Bindazyme) for the detection of tetanus antitoxin in human sera. A panel of 132 sera submitted for routine testing was used. Scatterplots showed a high degree of correlation between all three assays, although some divergence of results was apparent for low titre sera when comparing in house ELISA results with Bindazyme ELISA and TRFIA results. The TRFIA appeared to be more sensitive than the in house ELISA, and the Bindazyme assay compared well with the TRFIA. The intra-assay precision of all three assays, in terms of percentage coefficient of variation (%CV), was between 2.0% and 4.0%. The interassay precision ranged from 5% to 8% for the in house ELISA, 13% to 19% for the Bindazyme assay, and 11% to 13% for TRFIA. Both Bindazyme and TRFIA assays were simple to perform, accurate, reproducible, and amenable to automation. A particular benefit of the TRFIA was its large dynamic range, enabling tetanus antitoxin values of 0.01 IU/ml to 50 IU/ml to be measured with just one dilution of serum. TRFIA appears to be a useful serological technique worthy of further development.

Confidence Intervals↗
PubMed2002

Monitoring and multiplexing technique for interferometric fiber optic sensors with a linearly chirped Er:fiber laser.

The monitoring of interferometer fiber optic sensors using a laser that is scanned over a wide frequency range is investigated. The interrogation technique is based on the principle that if the light-source frequency varies linearly with time, the optical signal reflected or transmitted is intensity modulated at a frequency that is proportional to the optical path difference (OPD) in the interferometer. Fourier components in the detected optical output signal then correspond to the OPDs of any interferometers that have contributed to this modulation. The temporal position of a peak in the power spectrum of this signal is proportional to the OPD of the interferometer that is responsible for that peak. A fine tuning of the OPD value is determined from the phase of the corresponding Fourier component. Experimentally, an Er:fiber laser scanned over a 48-nm range centered at 1540 nm was used to monitor intrinsic fiber Fabry-Perot interferometers (FFPIs). Variations in the laser scan rate were compensated with the optical signal modulated by a reference FFPI held at a constant temperature. The OPD measurement resolution was 3.6 nm, and the dynamic range was 1.3 x 10(7). The temperature was measured from 20 degrees C to 610 degrees C with a 0.02 degrees C resolution, and multiplexing of three of the sensors arranged in series was demonstrated.

Journal Article↗
PubMed1994

Storage phosphor imaging technique improves the accuracy of RNA quantitation using 32P-labeled cDNA probes.

The use of the storage phosphor imaging technique to quantitate radioactivity on blots generated by hybridization with 32P-cDNA probes was evaluated and compared with screen-enhanced x-ray film autoradiography. Quantitation of RNA dot blots hybridized with a 28S ribosomal RNA-specific cDNA probe showed that storage phosphor imaging was more sensitive than screen-enhanced x-ray film autoradiography in identifying low amounts of total RNA (1-10 micrograms). Evaluation of Northern blots containing 30 micrograms of total RNA from human skin biopsies hybridized with a cDNA probe for the human acidic ribosomal phosphoprotein, PO, showed that both techniques detected random biological variability of this housekeeping gene in a similar manner. The two techniques exhibited a strong linear correlation in their ability to quantitate mRNA levels of a retinoic acid-inducible gene (RIS-1). This correlation was stronger at levels corresponding to 1-fold to 30-fold increases of signal and decreased beyond this range because of the insensitivity of the x-ray film. In conclusion, storage phosphor imaging is more accurate than screen-enhanced x-ray film autoradiography in identifying different RNA amounts (higher sensitivity) and in detecting increasing RNA signals at high levels of radioactivity (higher dynamic range).

Animals↗
PubMed2006

Combining stir bar sorptive extraction and MEKC for the determination of polynuclear aromatic hydrocarbons in environmental and biological matrices.

In this work, stir bar sorptive extraction and liquid desorption was combined with MEKC and diode-array detection (SBSE-LD-MEKC-DAD) for the determination of polynuclear aromatic hydrocarbons (PAHs) in aqueous medium, using biphenyl, fluorene, anthracene, phenanthrene, fluoranthene and pyrene as model compounds. MEKC-DAD conditions and parameters affecting SBSE-LD efficiency are fully discussed. Assays performed on aqueous samples spiked at trace levels, yielded recoveries ranging from 55.5 +/- 6.1% (pyrene) to 70.7 +/- 7.1% (anthracene), under optimized experimental conditions. The methodology proved to be nearly described by the octanol-water partition coefficients (K(PDMS/W) approximately K(O/W)). The analytical performance showed good precision (<12.0%), suitable detection limits (2-11 microg/L) and convenient linear dynamic ranges (r(2)>0.99) from 5 to 25 microg/L for anthracene and 25 to 125 microg/L for the remaining compounds. The application of the proposed methodology to environmental water, sediments and fish bile matrices demonstrated good selectivity and accuracy. SBSE-LD combined with MEKC-DAD was shown to be an easy, reliable and robustness methodology, as well as a good analytical alternative to monitor environmental priority pollutants.

Animals↗
PubMed1993

High-performance liquid chromatographic method for simultaneous determination of clodronate and some clodronate esters.

A quaternary alkylmethylamine-bonded stationary phase has been used for the liquid chromatographic resolution of bisphosphonates. Clodronate and three of its esters were separated by this technique. Nitric acid (30 mM) was used as the mobile phase. The effect of the pH of the mobile phase on the retention, resolution, capacity factor and theoretical plates of the column was examined. Thorium-ethylenediaminetetraacetic acid-xylenol orange mixed ligand complex was used as a postcolumn reagent for bisphosphonates. Bisphosphonates react quantitatively with this complex in slightly acidic solutions, and a change in the absorbance of postcolumn reagent is used as a measure of the bisphosphonate concentration. The relative standard deviation (R.S.D.) values for samples in aqueous solutions were in the range 2.3-15.5% (area) and 1.7-5.9% (height). The detection limits for different compounds, Cmin, varied from 0.3 to 1.4 mg/l (area) and from 0.3 to 0.5 mg/l (height). In urine samples the R.S.D. (%) varied from 3.1 to 18.9 (area) and from 1.1 to 6.3 (height). The linear dynamic range was from the detection limit up to 16 mg/l.

Chromatography, High Pressure Liquid↗
PubMed1999

Loudness growth functions and EABR characteristics in Digisonic cochlear implantees.

Electrically evoked auditory brainstem responses (EABRs) and loudness functions were measured in 14 subjects equipped with an MXM Digisonic cochlear implant. EABRs were evoked by 75-Hz pulse trains presented on the apical electrode. Loudness functions at the same rate and at a rate more conventional for psychoacoustic measurements (300 Hz) were measured using a categorical loudness-scaling procedure. The results revealed a significant difference in the loudness functions measured at 75 and 300 Hz, loudness increasing more steeply with stimulus intensity for the latter rate. Significant correlations between EABR wave V thresholds and perceptual thresholds measured at both 75 and 300 Hz were observed. Furthermore, in 8 out of the 14 patients, EABR wave V saturated at a stimulus level corresponding precisely to the loudest bearable, i.e. "Too loud" level for the 300-Hz stimulation rate; this same level corresponded to the "Comfortable" loudness level for the 75-Hz stimulation rate. On average, an almost linear relationship was observed over the first half of the loudness range between the stimulus intensity, expressed as a pulse duration in log units, and wave V amplitude in dB. Although further investigation is required before maximum comfort levels can be predicted reliably from EABR measures in individual subjects, these results indicate new directions regarding the estimation of perceptual dynamic range limits on the basis of EABR measures in cochlear implantees.

Adult↗
PubMed2003

Method for simultaneous measurement of antibodies to 23 pneumococcal capsular polysaccharides.

We describe a fluorescent covalent microsphere immunoassay (FCMIA) method for the simultaneous (multiplexed) measurement of immunoglobulin G (IgG) antibodies to 23 pneumococcal capsular polysaccharide (PnPS) serotypes present in the pneumococcal polysaccharide vaccine (PPV23) licensed by the Food and Drug Administration, i.e., PnPSs 1, 2, 3, 4, 5, 6B, 7F, 8, 9N, 9V, 10A, 11A, 12F, 14, 15B, 17F, 18C, 19A, 19F, 20, 22F, 23F, and 33F. In addition, the assay incorporates an internal control that allows for contemporaneous evaluation of the effectiveness of pneumococcal cell wall polysaccharide (C-PS) preadsorption and a second control of PnPS 25 (which is not present in any polysaccharide or conjugate vaccine), which can be used to evaluate interassay reproducibility (useful for pre- versus postvaccination studies). The FCMIA was standardized with U.S. reference antipneumococcal serotype standard serum 89S-2. Preadsorption of 89S-2 with each PnPS and C-PS yielded homologous inhibition for serotypes 1, 6B, 9N, 9V, 11A, 12F,14, 15B, 18C, 19A, 19F, 20, 22F, 25, and 33F; heterologous inhibition for serotypes 9V, 10A, 11A, 12F, 15B, 17F, 20, and 23F; and neither homologous nor heterologous inhibition for serotypes 2, 3, 4, and 5. The minimum detectable concentrations for the 24 multiplexed (PnPS and C-PS) FCMIAs ranged from 20 pg/ml for PnPS 3 to 600 pg/ml for PnPS 14. The PnPS FCMIA method has numerous benefits over enzyme-linked immunosorbent assays commonly used to measure anti-PnPS-specific IgG levels, including increased speed, smaller sample volumes, equivalent or better sensitivity, and increased dynamic range.

Animals↗
PubMed1986

Response characteristics of neurons in the ventral posterior lateral nucleus of the monkey thalamus.

The activity of 132 neurons in the caudal part of the ventral posterior lateral nucleus (VPLc) of the thalamus was recorded from 23 anesthetized monkeys. All single thalamic units that could be excited by electrical search stimuli applied to the contralateral sciatic nerve were investigated. Responses of these cells to mechanical, thermal, and electrical stimuli applied in the periphery indicated that at least half of the sampled cells were nociceptive. Based on responses to graded mechanical stimuli applied to the periphery, 110 of the sampled cells that received a predominant input from cutaneous receptive fields were classified. There were 56 low-threshold, 39 wide dynamic range, and 15 high-threshold cells. The same neurons were also classified into five mechanical types based on a cluster analysis: types 1-5 contained 25, 34, 17, 10, and 24 cells, respectively. The fact that about half the population of cells belonged to either the wide dynamic or the high threshold group (or mechanical types 3-5) suggested that a large population of VPLc neurons respond to mechanical nociceptive stimuli either exclusively or preferentially. Responses of 63 thalamic neurons were tested to noxious heat pulses applied to their cutaneous receptive fields with a contact thermostimulator. Of these, 47 cells were excited, whereas only 16 cells did not respond. The peripheral nerve that innervated the receptive field of each of 82 thalamic neurons was stimulated with graded strengths to activate A fibers only or both A and C fibers. All tested cells responded to peripheral A fiber volleys. In addition, 42 of these cells responded to peripheral C fiber volleys. The C fiber responses could be either short lasting (a few hundreds of milliseconds) or long lasting (up to several seconds). The recording sites of 80 cells were reconstructed. Of these, 78 were in the VPLc nucleus and the remaining two were in the reticular nucleus of the thalamus. No obvious relationship between the response characteristics and the locations of the cells within the VPLc nucleus was found. Sampled thalamic units had a variety of sources of input from the periphery, including both cutaneous and/or deep tissue receptive fields. The majority of the cells, however, had exclusively cutaneous receptive fields. The sizes of the cutaneous receptive fields were often very small, so that nearly half (41%) of the receptive fields of cells sampled occupied an area of skin smaller than half the foot.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1996

Simultaneous determination of danofloxacin and N-desmethyldanofloxacin in cattle and chicken edible tissues by liquid chromatography with fluorescence detection.

A rugged, simple, and selective method for the determination of danofloxacin and its primary metabolite, N-desmethyldanofloxacin, in cattle (liver, muscle, kidney, and fat) and chicken (liver and muscle) tissues was developed. The method is selective for danofloxacin and N-desmethyldanofloxacin over other veterinary important fluoroquinolones, such as enrofloxacin, ciprofloxacin, norfloxacin, and ofloxacin. Selectivity is achieved through a combination of extraction, chromatography, and fluorescence detection. The analytes were extracted from homogenized tissues using a methanol-perchloric-phosphoric acid solution. After centrifugation, direct injection of extraction supernate was possible. The limit of quantitation was 20 pg on column. Separation was achieved on an Inertsil C8 (5 microns, 100 A) column with dimensions of 250 x 4.6 mm I.D. The mobile phase consisted of 0.05 M phosphate buffer (pH 3.5)-acetonitrile (88:12). A fluorescence detector was utilized with an excitation wavelength of 280 nm and an emission wavelength of 440 nm. The assay was accurate and reproducible within the range of 10 to 500 ng/g for both danofloxacin and N-desmethyldanofloxacin. Intra-assay accuracy was between 98 and 101%, and precision was less than 4%. Inter-assay accuracy was between 99 and 102%, while precision was less than 2%. Recoveries for both analytes over the dynamic range were greater than 90% for all the tissues.

Adipose Tissue↗
PubMed1977

Fundamental frequency-sound pressure level profiles of adult male and female voices.

Fundamental frequency-sound pressure level (fo-SPL) profiles were determined for 12 female and 10 male subjects. Profiles were obtained by having each subject produce the maximum and minimum sound pressure level of which he was capable, at 10% intervals of his fo range. Comparison of male and female profiles showed similar values for frequency range in semitones, maximum and minimum SPL output, and total SPL range. A minimum SPL of 50 dB was necessary to produce a steady-state frequency for all subjects, and the maximum level ofr an acceptable fo was 126 dB SPL. The fo-SPL profiles obtained with the amateur subjects used in this study had a somewhat wider dynamic range than those obtained in earlier studies which utilized trained singers producing musically acceptable tones.

Adult↗
PubMed2002

Aluminium nitrate ceramics: a potential UV dosemeter material.

The ceramic material AlN-Y2O3 is proposed as a potential ultraviolet radiation (UVR) dosemeter using optically stimulated luminescence (OSL) and thermally stimulated luminescence (TL). Experimental studies have shown that AIN ceramics exhibit attractive characteristics suitable for practical UV dosimetry applications. The features are: (1) the spectral sensitivity covers the 200-350 nm range, in the UV-B region it is similar to that of human skin; (2) the angular dependence of the incident radiation follows the cosine law; (3) high yields of both UVR-induced OSL and TL signals compared to those of Al2O3:C; and (4) a large dynamic range TL signal (5 orders of magnitude). Although there is relatively high fading, it is demonstrated that AIN is a feasible material for UVR dosimetry using short integration times.

Aluminum Compounds↗
PubMed1988

Test-retest reliability of the Arden Grating Test: inter-tester variability.

The aim of this study was to investigate the test-retest reliability of the Arden Grating Test (AGT), and to assess the extent to which any variance in AGT score on retest can be attributed to intra-subject and inter-tester differences. Twelve patients with various pathologies and whose contrast sensitivity covered a wide range were each tested twice by six testers. It was shown that variance attributable to testing by different clinicians accounted for approximately 25% of the total variance, and that the 95% confidence limits about any observed score were +/- 15 AGT units, which is about one quarter of the total dynamic range of the test. The large range of scores encompassed by the 95% confidence limits represents considerable unreliability, the consequence of which is a high misclassification rate, i.e. many false positives and false negatives, especially in the context of primary vision screening for which it was designed.

Adult↗