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R Kopelman

Publications and source records attributed to R Kopelman.

At least 37 records · Page 2Linked to original sources
PubMed1996

Miniature sodium-selective ion-exchange optode with fluorescent pH chromoionophores and tunable dynamic range.

An extension into the fluorescence mode of ion-exchange optodes is described, allowing miniaturization and its concomitant benefits. A micrometer-size, fluorescent fiber-optic sodium sensor is described, based on a highly sodium-selective, crown ether-capped calix[4]arene ionophore, capable of ratiometric operation. Three sensor configurations are given, employing different lipophilic, fluorescent pH chromoionophores (Nile Blue derivatives), demonstrating the ability to improve the detection limit and tune the dynamic range to the desired region of interest. Two of the sensors are of special interest in that their working ranges lie within those desired for measuring intracellular cytosolic or blood levels of sodium at the respective physiological pH. These optodes have excellent sodium selectivity, with other physiologically relevant cations (e.g., potassium, calcium, and magnesium) being highly discriminated. Three simple mathematical relationships are given for the three experimentally used fluorescent signal mechanisms (intensity, intensity ratios, and inner-filter or energy transfer effects), permitting visualization on a single graph and enabling direct comparison of the different sensors' optical responses on a common platform. Finally, these optodes measure the sample's sodium activity, rather than the concentration, provided that the sample's pH is measured simultaneously by another sensor, such as a glass electrode.

Fiber Optic Technology↗
PubMed1996

Analytical properties and sensor size effects of a micrometer-sized optical fiber glucose biosensor.

A micrometer-sized fiber-optic fluorescence biosensor for glucose has been fabricated. The sensor is 100 times smaller than existing glucose optodes. It is based on the enzymatic reaction of glucose oxidase that catalyzes the oxidation of glucose to gluconic acid and hydrogen peroxide while consuming oxygen. Tris(1,10-phenanthroline)ruthenium chloride, an oxygen indicator, is used as a transducer. The ruthenium complex and glucose oxidase are incorporated into acrylamide polymer that is attached covalently to a silanized optical fiber tip surface by photocontrolled polymerization. A study of the dependence of the fluorescence intensity on sensor size shows that, under normal operating conditions, the signal decreases with the sensor diameter rather than its volume. Also, the response of micrometer-sized sensors is improved by about 20% compared to that of larger fiber-optic glucose sensors. Due to its small size and the lack of membrane support, the response time of the sensor is only 2 s. An absolute detection limit of around 1 x 10(-15) mol is achieved. The new glucose sensor is at least 25 times faster and its absolute sensitivity 5-6 orders of magnitude higher than that of current glucose optodes.

Biosensing Techniques↗
PubMed1996

Fluorescent fiber-optic calcium sensor for physiological measurements.

A new optical sensor based on covalent immobilization of a newly synthesized calcium-selective, long-wavelength, fluorescent indicator has been constructed, with a response dynamic range optimal for physiological measurements. Immobilization occurs via photoinitiated copolymerization of the indicator with acrylamide on the distal end of a silanized 125 micrograms diameter multimode optical fiber. The working lifetime of this sensor is limited only by photobleaching of the indicator. Due to the inherent hydrophilic nature of the acrylamide polymer, the response time of this new sensor is governed by simple aqueous diffusion of the ionic calcium. This results in sensor response times fast enough to monitor some concentration fluctuations at physiological rates. The ability to monitor calcium concentration fluctuations in a high background level of magnesium is also demonstrated with a calculated selectivity of 10(-4.5).

Biosensing Techniques↗
PubMed1995

Development of a submicrometer optical fiber oxygen sensor.

A submicrometer optical fiber oxygen sensor has been fabricated, based on the fluorescence quenching of tris-(1,10-phenanthroline)ruthenium(II) chloride in the presence of oxygen or dissolved oxygen. The Ru compound has been incorporated into acrylamide polymer that is attached covalently to a silanized optical fiber tip surface by photoinitiated polymerization. Leaching of the sensing reagent from the polymer host matrix has been minimized by the optimization of the ratio between the acrylamide monomer and the cross-linker, N,N-methylenebisacrylamide. The sensor is fully reversible and highly reproducible. A standard deviation of approximately 2% for 10 consecutive fluorescence measurements has been observed for several oxygen concentrations. The sample volume required for measurements is 100 fL. An absolute detection limit of 1 x 10(-17) mol is achieved. This is an improvement by a factor of 10(6) as compared to other existing optical fiber oxygen sensors.

Fiber Optic Technology↗
PubMed1995

Implementation of an NSOM system for fluorescence microscopy.

We describe our progress toward an NSOM system intended for fluorescence imaging of biological samples. This process included integration of shear-force feedback into an existing NSOM system. Topographic images acquired using uncoated tips are presented. We also present our initial effort at simultaneous acquisition of topographic and fluorescence data using an aluminum coated tip.

Equipment Design↗
PubMed1994

Presentation of native epitopes in the V1/V2 and V3 regions of human immunodeficiency virus type 1 gp120 by fusion glycoproteins containing isolated gp120 domains.

The immune response to viral glycoproteins is often directed against conformation- and/or glycosylation-dependent structures; synthetic peptides and bacterially expressed proteins are inadequate probes for the mapping of such epitopes. This report describes a retroviral vector system that presents such native epitopes on chimeric glycoproteins in which protein fragments of interest are fused to the C terminus of the N-terminal domain of the murine leukemia virus surface protein, gp70. The system was used to express two disulfide-bonded domains from gp120, the surface protein of human immunodeficiency virus type 1 (HIV-1), that include potent neutralization epitopes. The resulting fusion glycoproteins were synthesized at high levels and were efficiently transported and secreted. A fusion protein containing the HXB2 V1/V2 domain was recognized by an HIVIIIB-infected patient serum as well as by 17 of 36 HIV-1 seropositive hemophiliac, homosexual male and intravenous drug user patient sera. Many of these HIV+ human sera reacted with V1/V2 domains from several HIV-1 clones expressed in fusion glycoproteins, indicating the presence of cross-reactive antibodies against epitopes in the V1/V2 domain. Recognition of gp(1-263):V1/V2HXB2 by the HIVIIIB-infected human patient serum was largely blocked by synthetic peptides matching V1 but not V2 sequences, while recognition of this construct by a broadly cross-reactive hemophiliac patient serum was not blocked by individual V1 or V2 peptides or by mixtures of these peptides. A construct containing the V3 domain of the IIIB strain of HIV-1, gp(1-263):V3HXB2, was recognized by sera from a human and a chimpanzee that had been infected by HIVIIIB but not by sera from hemophiliac patients who had been infected with HIV-1 of MN-like V3 serotype. The reactive sera had significantly higher titers when assayed against gp(1-263):V3HXB2 than when assayed against matching V3 peptides. Immunoprecipitation of this fusion glycoprotein by the human serum was only partially blocked by V3 peptide, indicating that this infected individual produced antibodies against epitopes in V3 that were expressed on the fusion glycoprotein but not by synthetic peptides. These data demonstrated that the chimeric glycoproteins described here effectively present native epitopes present in the V1/V2 and V3 domains of gp120 and provide efficient methods for detection of antibodies directed against native epitopes in these regions and for characterization of such epitopes.

3T3 Cells↗
PubMed1994

Intravenous pulse cyclophosphamide treatment of severe lupus nephritis: a prospective five-year study.

Despite its widespread use, there are only a few published studies of the use of intravenous high dose pulse cyclophosphamide in systemic lupus nephritis. There are few data about the long-term efficacy and safety of this form of therapy. This study evaluates the clinical efficacy, toxicity, and effects on renal morphology of this regimen in patients with severe lupus nephritis followed prospectively over a five-year period. Twenty consecutive patients with severe active lupus nephritis were enrolled in a treatment regimen of six monthly intravenous pulses of cyclophosphamide (0.5 to 1 g/m2) together with high dose corticosteroid therapy which was rapidly tapered. Efficacy was assessed by improvement or stabilization of clinical, serologic and renal functional parameters. Repeat renal biopsies were performed in 15 patients. Potential toxicity related to therapy was documented. Over the first six months of treatment, this regimen resulted in improvement of clinical activity, lupus serology, stabilization of renal function and decreased proteinuria in 19/20 patients. Nephrotic syndrome remitted in 8/10 patients by one year. Over five years of follow-up, there were five treatment failures defined as a doubling of serum creatinine over baseline. At five years, 3 patients required renal replacement therapy. Elevated plasma creatinine at time of first biopsy, degree of proteinuria, histologic activity and chronicity were not statistically correlated with treatment failure. Patients who failed to respond to this treatment were, however, more likely to have diffuse proliferative lupus nephritis (WHO Class IV) lesions on initial biopsy.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Submicrometer intracellular chemical optical fiber sensors.

A thousandfold miniaturization of immobilized optical fiber sensors, a millionfold or more sample reduction, and at least a hundredfold shorter response time, all simultaneously, were achieved by combining nanofabricated optical fiber tips with near-field photopolymerization. Specifically, pH optical fiber sensors were prepared with internal calibration, making use of the differences in both fluorescence and absorption of the acidic and basic dye species. The submicrometer sensors have excellent detection limits, as well as photostability, reversibility, and millisecond response times. Successful applications include intracellular and intraembryonic measurements. Potential applications include spatially and temporally resolved chemical analysis and kinetics inside single biological cells and their substructures.

Aluminum↗