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Biomedical subjects

R Narayanaswamy

Publications and source records attributed to R Narayanaswamy.

14 recordsLinked to original sources
PubMed2006

A novel luminescent lifetime-based optrode for the detection of gaseous and dissolved oxygen utilising a mixed ormosil matrix containing ruthenium (4,7-diphenyl-1,10-phenanthroline)3Cl2 (Ru.dpp).

A novel luminescent lifetime optrode is presented for the detection of gaseous and dissolved oxygen. The optrode utilises ruthenium (4,7-diphenyl-1,10-phenanthroline)(3)Cl(2) as the sensing fluorophore immobilised in a hydrophobic ormosil matrix. The ormosil matrix is synthesised at room temperature from octyltriethoxysilane and methyltriethoxysilane precursors. Investigations of different ormosils were conducted and the most effective one was selected for optrode production. Optrodes were tested for responses to gaseous and dissolved oxygen. Their responses were modelled using traditional two-site or two-exponential methods and feed-forward artificial neural networks. Comparison of the two modelling methodologies is presented and further improvements in modelling and ormosil design are suggested.

Chlorides↗
PubMed2006

Fluorescence sensor using a molecularly imprinted polymer as a recognition receptor for the detection of aluminium ions in aqueous media.

This paper describes the investigation of a molecularly imprinted polymer (MIP) as a sensing receptor for Al(3+) ion detection by using an optical approach. Al(3+) ion was adopted as the template molecule and 8-hydroxyquinoline sulfonic acid ligand as the fluorescence tag. The polymer was synthesised using acrylamide as monomer, 2-hydroxyethyl methacrylate as co-monomer and ethylene glycol dimethracylate as cross-linker. The free radical polymerisation was performed in methanol and initiated by 2,2'-azobisisobutyronitrile at 70 degrees C. The imprinted polymer was fluorometrically characterised using a fibre optic attachment in a self-designed flow-cell. NaF was used to leach the Al(3+) ion from the MIP. The optimum pH for the rebinding of Al(3+) ion with the leached polymer was found to be pH 5 and the fluorescence response was found to be stable within the buffer strength range of 0.05-0.10 M. The fluorescence intensity during Al(3+) ion rebinding was inversely dependent on temperature, and a low interference response (<3%) toward metal ions except for Cu(2+) and Zn(2+) ions was observed. The polymer rebinding repeatability study conducted over 9 cycles with Al(3+) ion (0.8 x 10(-4) M) was found to give an RSD value of 2.82% with a standard deviation of 0.53. The dynamic range of the system was found to be linear up to 1.0 x 10(-4) M Al(3+) ion with a limit of detection of 3.62 microM.

Aluminum↗
PubMed2006

Engineering RNA-based circuits.

Nucleic acids can modulate gene function by base-pairing, via the molecular recognition of proteins and metabolites, and by catalysis. This diversity of functions can be combined with the ability to engineer nucleic acids based on Watson-Crick base-pairing rules to create a modular set of molecular "tools" for biotechnological and medical interventions in cellular metabolism. However, these individual RNA-based tools are most powerful when combined into rational logical or regulatory circuits, and the circuits can in turn be evolved for optimal function. Examples of genetic circuits that control translation and transcription are herein detailed, and more complex circuits with medical applications are anticipated.

Animals↗
PubMed2001

A disposable optrode using immobilized tyrosinase films.

A disposable fiber-optic sensor based on the immobilized tyrosinase enzyme in a composite biopolymer and its application for the detection of 3,4-dihydroxyphenyalanine (L-dopa) and its analog are described. The enzymatic oxidation product of L-dopa was stabilized through formation of an adduct with 3-methyl-2-benzothiazoline hydrazone resulting in enhanced accuracy and sensitivity of the measurements. The response was found to be linear and concentration dependent in the range of 5 x 10(-5) to 4 x 10(-4) M (r(2) = 0.9307) for the substrate l-dopa over the pH range 5.8 to 7.2 with response times of 8 min. The immobilized enzyme films are stable for 4 months when stored under moisture-free conditions at 4 degrees C.

Biopolymers↗
PubMed2001

An optical biosensor employing tiron-immobilised polypyrrole films for estimating monophenolase activity in apple juice.

A method is described for the incorporation of tiron as a substrate for tyrosinase enzyme into a polypyrrole film deposited on indium titanium oxide (ITO) glass. The presence of tiron in the polypyrrole film is verified by cyclic voltammetry (CV). The enzyme activity using the polypyrrole-tiron film is confirmed by the catalytic conversion of immobilised substrate to quinones by the enzyme. The use of both potentiometric and optical methods for the detection of the catalytic activity of the polypyrrole-tiron film and their potential use for the determination of monophenolase activity of apple polyphenol oxidase is described. This is the first report of this kind whereby tiron has been immobilised in a polypyrrole matrix for the enzyme activity determination.

1,2-Dihydroxybenzene-3,5-Disulfonic Acid Disodium ↗
PubMed2001

Simple regression model using an optode for the simultaneous determination of zinc and cadmium mixtures in aqueous samples.

An optical-fiber chemical sensor (optode) is described for the simultaneous determination of Zn2+ and Cd2+ mixtures using 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol immobilized onto XAD-4 (Br-PADAP/XAD-4). A simultaneous analysis was achieved by using a single-wavelength kinetic approach coupled with a regression model. Here, the regression model was derived for the slope response of Br-PADAP/XAD-4 to binary mixtures of the metal ions, Zn2+ and Cd2+, at pH 8. The model was used then to predict the concentration of one metal ion while the other was kept constant. This was found to be reasonably successful for Zn2+ and Cd2+, with deviations of 3% and 10%, respectively. The sensor was also found to provide excellent sensitivity for both metal ions with excellent LODs (< 0.1 ppm) and very short analysis times (< 30 s).

Azo Compounds↗
PubMed1999

Characterisation of a Hg(II) ion optrode based on Nafion-1-(2-thiazolylazo)-2-naphthol composite thin films.

An optrode for Hg2+ ions based on a Nafion-1-(2-thiazolylazo)-2-naphtol (TAN) composite thin film has been developed. This optrode has a wide linear response range of 1-75 microM (pH 6) of Hg2+ ions with a limit of detection of 0.05 microM (10 micrograms l-1), which is sufficiently adequate for many environmental monitoring applications. The reflectance signal response shows a close correlation with the theoretical model derived. The response time of the optrode thin film was within 5-7 min to reach 95% of the final signal, depending on the concentration of Hg2+ ions. The selectivity of optrode to Hg2+ ions in phosphate buffer is good, with Co2+ and Ni2+ ions as the main interferences.

Environmental Monitoring↗
PubMed1995

Transmission maximum-likelihood reconstruction with ordered subsets for cone beam CT.

An iterative algorithm is presented for accelerated reconstruction of cone beam transmission CT data (CBCT). CBCT supplies an attenuation map for SPECT attenuation compensation and anatomical correlation. Iterative algorithms are necessary to reduce truncation artifacts and 3D reconstruction artifacts. An existing transmission maximum-likelihood algorithm (TRML) is accurate but the reconstruction time is too long. The new algorithm is a modified EM algorithm, based on ordered subsets (OSEM). OSEM was evaluated in comparison to TRML using a thorax phantom and a 3D Defrise phantom. A wide range of image measures were evaluated, including spatial resolution, noise, log likelihood, region quantification, truncation artifact removal, and 3D artifact removal. For appropriate subset size, OSEM produced essentially the same image as TRML, but required only one-tenth as many iterations. Thus, adequate images were available in two to four iterations (20-30 min on a SPARC 2 workstation). Further, OSEM still approximately maximizes likelihood: divergence occurs only for very high (and clinically irrelevant) iterations. Ordered subsets are likely to be useful in other geometries (fan and parallel) and for emission CT as well. Therefore, with ordered subsets, high-quality iterative reconstruction is now available in clinically practical reconstructions times.

Algorithms↗
PubMed1994

Development of an optical formaldehyde sensor based on the use of immobilized pararosaniline.

The colorimetric indicator pararosaniline has been immobilized onto the cation-exchange resins Amberlite IRC-50, Dowex 50W-X8 and cellulose phosphate by electrostatic bonding. The reflectance of each reagent phase was measured using a bifurcated fibre-optic system and a flow cell. Pararosaniline immobilized on cellulose phosphate was found to respond to formaldehyde without requiring the addition of sulfite to develop the purple chromogen. This immobilized system demonstrated a linear response to 50-2500 micrograms of formaldehyde and had a correlation coefficient of 0.9979. Acetaldehyde and butyraldehyde did not produce any interference. However, exposure to the unsaturated aldehydes, acrolein and crotonaldehyde, gave rise to responses that were much greater than that observed with formaldehyde.

Colorimetry↗
PubMed1993

An optical hydroxyl radical sensor.

A hydroxyl radical (.OH) fibre-optic sensor has been developed. An .OH radical-sensitive reagent phase (nitrophenol) was immobilized onto XAD-7 methacrylate beads. Subsequently the beads were attached to the distal end of a polymethylmethacrylate fibre optic. Nitrocatechol, generated from the attack of .OH radical on nitrophenol, exhibits a strong absorption band in the visible region of the electromagnetic spectrum (lambda max = 510 nm). Here, reflectance spectroscopy was employed to monitor the concomitant intensity decrease in the reflectance spectrum upon .OH radical attack. The sensor exhibited excellent stability and linearity of response to .OH generated by a Fenton reaction system (EDTA, Fe(II) and H2O2) with H2O2 over the concentration range of 3.6 x 10(-6)-8.0 x 10(-2) M.

Fiber Optic Technology↗
PubMed1992

Serum analysis for potassium ions using a fibre optic sensor.

A fibre optic potassium ion sensor has been developed based on reflectance measurements of the pH-dependent chromogenic crown ether 'Takagi reagent' immobilized on the non-ionic polymeric resin Amberlite XAD2. The sensor response is in the 1.5-100 mM range with a detection limit of 0.25 mM K+. The selectivity factor over sodium is 20. The proposed sensor works with a reproducibility of +/- 0.8% at the 5 mM K+ level. Advantageous design features include ease of construction, simplicity of use, reversibility, short response time (approximately 1 min) and an optimum working pH range (7.0-8.0) for biological fluids. This optical sensor was applied successfully to the direct determination of potassium in human serum. Aqueous potassium standards containing 0.13 M NaCl and a buffer of pH 8 were used for calibration.

Biosensing Techniques↗
PubMed1991

Current developments in optical biochemical sensors.

By combining modern fibre optics and opto-electronic instrumentation with chemical and biochemical reagent systems, it has become possible to fabricate optical biosensors. The current state of the art in this development is reviewed in this paper. Many developments describe selective and sensitive methods for sensing bioanalytes and it is likely that such a development will continue to be a very active area of analytical research. However, these biosensing devices can be regarded as successful only if their practicality and reliability can be demonstrated.

Albumins↗
PubMed1989

Transducer mechanisms for optical biosensors. Part 2: Transducer design.

Optical fibre biosensors basically require two components, namely optical fibres, to enable remote measurements to be made, and immobilised reagents. The propagation of light along fibres is discussed and various effects causing attenuation and a fall in transmission efficiency, viz. coupling of light into the fibre and attenuation characteristics of the fibre itself, are considered. The modes of interaction of electromagnetic radiation with the immobilised reagent, viz. absorption alone, absorption followed by luminescence, reflection, or scattering, are discussed and followed by methods by which these effects can be utilised to provide an optically detectable signal. Practical sensor configurations are described and the associated optical instrumentation is outlined. Finally a brief overview is presented of the current state of the art of these sensors.

Blood Chemical Analysis↗