Biomedical subjects

T Vo-Dinh

Publications and source records attributed to T Vo-Dinh.

At least 19 recordsLinked to original sources

PubMed2002

Radiation dosimetry using three-dimensional optical random access memories.

The ability to determine particle type and energy plays an important role in the dosimetry of heavy charged particles (HCP) and neutrons. A new approach to radiation dosimetry is presented, which is shown to be capable of particle type and energy discrimination. This method is based on utilising radiation induced changes in the digital information stored on three-dimensional optical random access memories (3D ORAM). 3D ORAM is a small cube (a few mm3) composed of poly(methyl methacrylate) doped with a photochromic dye. and it was originally proposed as a memory device in high speed parallel computers. A Nd:YAG laser system is used to write and read binary information (bits) on the ORAM, which functions as a charged particle detector. Both the read and the write processes use two laser beams that simultaneously strike the material to cause a colour change at their intersection (similar to the darkening of light-sensitive sunglasses when exposed to sunlight.) The laser produces colour changes in the ORAM, which then reverts to the original colour ('bit-flips') at sites where energy is deposited from interaction with incident HCP or neutron-recoil protons. The feasibility of this approach was demonstrated both theoretically and experimentally. Calculations based on track structure theory (TST) predict that when HCP interact with the ORAM material, the local energy deposition is capable of inducing measurable 'bit-flips'. These predictions were recently confirmed experimentally using two types of ORAM systems, one based on spirobenzopyran and the other on anthracene, as the photochromic dyes.

Computer Storage Devices↗

PubMed2002

Nanosensor for in vivo measurement of the carcinogen benzo[a]pyrene in a single cell.

This work describes the fabrication and the application of an antibody-based fiber-optic nanosensor for in situ measurements of the carcinogen benzo[a]pyrene (BaP) in a single cell. This antibody-based spectroscopic nanosensor is miniaturized enabling the detection of fluorescent analytes in single cells. In addition to measuring fluorescent analytes in single cells, the nanosensor has the potential to be applied for both diagnostic and proteomics purposes. In this work, the human breast carcinoma cell line, MCF-7, was used as the model system to perform BaP measurements in single cells. A standard concentration curve for BaP was established and used to perform quantitative analyses of BaP in individual cells. From these analyses, it was estimated that the concentration of BaP in the individual cells investigated was approximately 3.61 x 10(-10) M. The results obtained demonstrate the application of antibody-based nanosensors for performing in situ measurements inside a single cell.

Antibodies↗

PubMed2001

Detection of E. coli using a microfluidics-based antibody biochip detection system.

This work demonstrates the detection of E. coli using a 2-dimensional photosensor array biochip which is efficiently equipped with a microfluidics sample/reagent delivery system for on-chip monitoring of bioassays. The biochip features a 4 x 4 array of independently operating photodiodes that are integrated along with amplifiers, discriminators and logic circuitry on a single platform. The microfluidics system includes a single 0.4 mL reaction chamber which houses a sampling platform that selectively captures detection probes from a sample through the use of immobilized bioreceptors. The independently operating photodiodes allow simultaneous monitoring of multiple samples. In this study the sampling platform is a cellulosic membrane that is exposed to E. coli organisms and subsequently analyzed using a sandwich immunoassay involving a Cy5-labeled antibody probe. The combined effectiveness of the integrated circuit (IC) biochip and the immunoassay is evaluated for assays performed both by conventional laboratory means followed by detection with the IC biochip, and through the use of the microfluidics system for on-chip detection. Highlights of the studies show that the biochip has a linear dynamic range of three orders of magnitude observed for conventional assays, and can detect 20 E. coli organisms. Selective detection of E. coli in a complex medium, milk diluent, is also reported for both off-chip and on-chip assays.

Animals↗

PubMed2001

Microarray sampling-platform fabrication using bubble-jet technology for a biochip system.

The fabrication of microarrays containing PCR-amplified genomic DNA extracts from mice tumors on a Zetaprobe membrane using a modified thermal ink-jet printer is described. A simple and cost-effective procedure for the fabrication of microarrays containing biological samples using a modified bubble-jet printing system is presented. Because of their mass-produced design, ink-jet printers are a much cheaper alternative to conventional spotting techniques. The usefulness of the biochip microarray platform is illustrated by the detection of human fragile histidine triad (FHIT), a tumor suppressor gene. Subcutaneous carcinomas were induced with MKN/FHIT and MKN/E4 cell lines in immunodeficient mice. Several weeks into their development, the tumors from both groups of mice were removed and subjected to DNA extraction by lysis of tissue samples. The extracted DNA samples were amplified by PCR (30 cycles) using the primers corresponding to nucleotides 2 to 18 of the FHIT sequence. The resulting solution was transferred to the individual reservoirs of a three-color cartridge from a conventional thermal ink-jet printer (HP 694C), and arrays were printed on to a Zetaprobe membrane. After spotting, these membranes were used in a hybridization assay, using fluorescent probes, and detected with a biochip.

Acid Anhydride Hydrolases↗

PubMed2001

Laser-induced fluorescence studies of polycyclic aromatic hydrocarbons (PAH) vapors at high temperatures.

In this work, we present the fluorescence spectra of anthracene and pyrene vapors at different elevated temperatures (from 150 to 650 degrees C) excited with the 337 nm line of a nitrogen laser. We describe the high temperature effects on the resulting spectral properties including spectral intensity, spectral bandwidth and spectral shift. We found that the PAH fluorescence spectral bandwidths become very broad as the temperature increases. The broadening is mainly due to thermal vibrational sequence congestion. We also have found that the fluorescence intensity of pyrene vapor increases with increasing temperature, which results from the increase of the pyrene vapor absorption cross section at 337 nm.

Anthracenes↗

PubMed2001

Biomedical implications of protein folding and misfolding.

A review of protein-folding mechanisms is presented to indicate (i) the formation of correctly folded and misfolded forms, and (ii) the biomedical implications involved. Protein mechanisms may be classified into series and series-parallel mechanisms. The mechanism may involve one or more stable intermediate (partially folded, misfolded, with some structure) states. It is the parallel or the 'off-pathway' step(s) that lead to the aggregate (misfolded state). This aggregate state yields the amyloid deposits in human tissue that lead to diseases in humans that are resistant to treatment. Means by which the off-pathway step may be minimized and the correct folding pathway enhanced are presented. Particular emphasis is placed on the in vivo machinery (chaperones) that is in place in the cells, and how it functions to allow the proteins to fold in the correct and active form, thus minimizing the amyloid deposits in tissues. More effort needs to be placed to understand the function of these chaperones, and thus help facilitate the formation of active and stable proteins in the cells. Though more effort needs to be placed in the present treatment strategies, novel treatment procedures also need to be explored in order to develop effective strategies to treat these seemingly intractable diseases.

Fractals↗

PubMed2001

A kinetic analysis using fractals of cellular analyte-receptor binding and dissociation.

A fractal analysis is presented for cellular analyte-receptor binding and dissociation kinetics using a biosensor. Data taken from the literature may be modelled, in the case of binding, using a single-fractal analysis or a dual-fractal analysis. The dual-fractal analysis represents a change in the binding mechanism as the reaction progresses on the surface. The predictive relationship developed for the equilibrium constant, K (affinity which is equal to k(d)/k(1or2)), as a function of the analyte concentration is of particular value since it provides a means by which the affinity may be manipulated. This should be of assistance in cell-surface reactions, drug-candidate optimization and for the design of immunodiagnostic devices. Relationships are also presented for the binding and dissociation rate coefficients as a function of their corresponding fractal dimension, D(f) or the degree of heterogeneity that exists on the surface, and the analyte concentration in solution. When analyte-receptor binding or dissociation is involved, an increase in the heterogeneity on the surface (increase in D(f) or D(fd) as the case may be) leads to an increase in the binding and the dissociation rate coefficients. It is suggested that an increase in the degree of heterogeneity on the surface leads to an increase in the turbulence on the surface owing to the irregularities on the surface. This turbulence promotes mixing, minimizes diffusional limitations and leads subsequently to an increase in the binding and the dissociation rate coefficients. The binding and dissociation rate coefficients are rather sensitive to the degree of heterogeneity, D(f) and D(fd), respectively, that exists on the biosensor surface. The heterogeneity on the surface in general affects the binding and dissociation rate coefficients differently. In general, the analyte concentration in solution has a mild affect on the fractal dimension for binding or the fractal dimension for dissociation. This is indicated by the low values of the exponent in the predictive relationships developed.

Fractals↗

PubMed2000

Three-dimensional optical random access memory materials for use as radiation dosimeters.

This article describes the development of the first three-dimensional optical random access memory (3D-ORAM) material and readout system for monitoring energetic neutrons. Two different photochromic dyes, 5'-chloro-6-nitro-1',3',3'-trimethylspiro-[2H-1-benzopyran-2,2'-in doline] (spirobenzopyran) and anthracene, have been investigated for use in these 3-D ORAM dosimeter materials. These dyes were immobilized in a poly(methyl methacrylate) support, and the resulting dosimeter materials were irradiated with neutrons from a Cf-252 source. Fluorescence measurements from the dosimeter show a dramatic decrease in the overall fluorescence intensity of the 3D-ORAM dosimeter exposed to the Cf-252, relative to a nonirradiated dosimeter. In addition, a two-photon excitation readout system has been developed for determining characteristics of the radiation that are necessary for estimating dose.

Journal Article↗

PubMed2000

Intracellular measurements in mammary carcinoma cells using fiber-optic nanosensors.

Submicrometer fiber-optic biosensors have been developed and used to measure toxic chemicals within single cells. Optical fibers that have been pulled to a distal-end diameter of less than 1 micrometer are coated with antibodies to selectively bind the species of interest. This paper describes the use of these fibers to selectively measure the concentration of benzo[a]pyrene tetrol (BPT), a metabolite of benzo[a]pyrene, within individual cells of two different cell lines, human mammary carcinoma cells and rat liver epithelial cells. The results from these measurements have been used to determine the sensitivity, reproducibility, and usefulness of these nanosensors. The detection limit of these biosensors has been determined to be 0.64 +/- 0.17 x 10(-11) M for BPT.

Animals↗

PubMed2000

The development of optical nanosensors for biological measurements.

This article discusses and documents the basic concepts of, and developments in, the field of optical nanosensors and nanobiosensors. It describes the progression of this field of research from its birth up to the present, with emphasis on the techniques of sensor construction and their application to biological systems. After a brief overview of the techniques for fabricating nanometer-sized optical fibers, we describe the various types of transducer and bioreceptor molecule presently used for nanosensor and nanobiosensor fabrication.

Animals↗

PubMed2000

Native fluorescence and mag-indo-1-protein interaction as tools for probing unfolding and refolding sequences of the bovine serum albumin subdomain in the presence of guanidine hydrochloride.

Changes in the fluorescence spectrum of tryptophans Trp 134 and Trp 212 in bovine serum albumin (BSA) and of Trp 214 of human serum albumin in the presence of the chaotropic agent guanidine hydrochloride (Gnd) were studied. A detailed analysis of the fluorescence spectrum of native BSA yielded the fluorescence spectrum for each tryptophan of BSA. Modifications in the binding of Mag-indo-1 to BSA, which results in a specific quenching of the fluorescence spectrum of Trp 134 associated with an energy transfer from Trp 134 to the protein-bound Mag-indo-1, were also investigated. Changes occurring when the Gnd concentration is decreased stepwise cover a larger concentration scale of Gnd than the reverse protocol, allowing one to suggest that the resulting conformational changes in the subdomain IA of BSA involve at least three different steps.

Animals↗

PubMed2000

Antibody-based nanoprobe for measurement of a fluorescent analyte in a single cell.

We report here the application of an antibody-based nanoprobe for in situ measurements of a single cell. The nanoprobe employs antibody-based receptors targeted to a fluorescent analyte, benzopyrene tetrol (BPT), a metabolite of the carcinogen benzo[a]pyrene (BaP) and of the BaP-DNA adduct. Detection of BPT is of great biomedical interest, since this species can serve as a biomarker for monitoring DNA damage due to BaP exposure and for possible precancer diagnosis. The measurements were performed on the rat liver epithelial clone 9 cell line, which was used as the model cell system. Before making measurements, the cells were treated with BPT. Nanoprobes were inserted into individual cells, incubated 5 min to allow antigen-antibody binding, and then removed for fluorescence detection. We determined a concentration of 9.6+/-0.2x10(-11) M for BPT in the individual cells investigated. The results demonstrate the possibility of in situ measurements inside a single cell using an antibody-based nanoprobe.

Animals↗

PubMed2000

Antibody-based biosensor for breast cancer with ultrasonic regeneration.

We describe a novel method and instrumental setup for regenerating antibodies immobilized on a fiberoptic probe of an immunosensor using ultrasonic irradiation with broadband imaging transducers. The instrumental setup and irradiation conditions for antibody regeneration using ultrasound are described. The results of the measurements with antibody against breast cancer antigen illustrate the effectiveness and potential of the regenerable immunosensor. A 65% removal of the antigens bound to the Mab immobilized on the fiber surface is attained after ultrasound regeneration.

Antibodies, Monoclonal↗

PubMed1999

DNA biochip using a phototransistor integrated circuit.

This work describes the development of an integrated biosensor based on phototransistor integrated circuits (IC) for use in medical detection, DNA diagnostics, and gene mapping. The evaluation of various system components developed for an integrated biosensor microchip is discussed. Methods to develop a microarray of DNA probes on nitrocellulose substrate are discussed. The biochip device has sensors, amplifiers, discriminators, and logic circuitry on board. Integration of light-emitting diodes into the device is also possible. To achieve improved sensitivity, we have designed an IC system having each phototransistor sensing element composed of 220 phototransistor cells connected in parallel. Measurements of fluorescent-labeled DNA probe microarrays and hybridization experiments with a sequence-specific DNA probe for the human immunodeficiency virus 1 system on nitrocellulose substrates illustrate the usefulness and potential of the DNA biochip.

Biosensing Techniques↗

PubMed1998

Surface-enhanced Raman gene probe for HIV detection.

We report, for the first time, the use of surface-enhanced Raman (SERS)-active labels for primers used in polymerase chain reaction amplification of specific target DNA sequences. This method has the potential for combining the spectral selectivity and high sensitivity of the SERS technique with the inherent molecular specificity offered by DNA sequence hybridization. The effectiveness of the detection scheme is demonstrated using the gag gene sequence of the human immunodeficiency virus. The potential use of multiple probes for simultaneous detection of multiple biological targets is discussed.

Base Sequence↗

PubMed1998

Laser-induced fluorescence for esophageal cancer and dysplasia diagnosis.

A method using laser-induced fluorescence (LIF) for in vivo cancer diagnosis of the esophagus is described. Autofluorescence of normal and malignant tissues was measured directly using a fiberoptic probe inserted through an endoscope. The measurements were performed in vivo during routine endoscopy. Measurement of the fluorescence signal from the tissue was performed using laser excitation at 410 nm. The methodology was applied to differentiate normal and malignant tumors of the esophagus. The results of this LIF approach were compared with histopathology results of the biopsy samples and indicated excellent agreement in the classification of normal and malignant tumors for the samples investigated. The LIF procedure could lead to the development of a rapid and cost-effective technique for cancer diagnosis.

Barrett Esophagus↗

PubMed1996

Endoscopic fluorescence detection of high-grade dysplasia in Barrett's esophagus.

BACKGROUND & AIMS: Early detection and treatment of esophageal cancer in Barrett's esophagus may improve patient survival if dysplasia is effectively detected at endoscopy. Typically, four-quadrant pinch biopsy specimens are taken at 2-cm intervals. This study was conducted to determine whether laser-induced fluorescence spectroscopy could be used to detect high-grade dysplasia in patients with Barrett's esophagus. METHODS: Four hundred ten-naonometer laser light was used to induce autofluorescence of Barrett's mucosa in 36 patients. The spectra were analyzed using the differential normalized fluorescence (DNF) index technique to differentiate high-grade dysplasia from either low-grade or nondysplastic mucosa. Each spectrum was classified as either premalignant or benign using two different DNF indices. RESULTS: Analysis of the fluorescence spectra from all patients collectively using the DNF intensity at 480 nm (DNF480) index showed that 96% of nondysplastic Barrett's esophagus samples were classified as benign, all low-grade dysplasia samples as benign, 90% of high-grade dysplasia samples as premalignant, and 28% of low-grade with focal high-grade dysplasia samples as premalignant. Using the two DNF indices concurrently, all patients with any high-grade dysplasia were classified correctly. CONCLUSIONS: Laser-induced fluorescence spectroscopy has great potential to detect high-grade dysplasia in Barrett's esophagus when using the DNF technique.

Adult↗

PubMed1995

In vivo cancer diagnosis of the esophagus using differential normalized fluorescence (DNF) indices.

BACKGROUND AND OBJECTIVE: We report the use of new diagnostic parameters based on the differential normalized fluorescence (DNF) signals for malignant tumor diagnosis. STUDY DESIGN/MATERIALS AND METHODS: Over 200 measurements of endogenous fluorescence from normal and malignant esophageal tissues were performed during routine endoscopy in 48 patients. A pulsed nitrogen-pumped dye laser was used to provide in situ excitation at 410 nm. Direct collection of the fluorescence signal emitted by the tissue was achieved using an intensified photodiode array detector equipped with a fiberoptic probe. RESULTS: The fluorescence signals were normalized with respect to the total fluorescence signal area. The cancer diagnosis indices were defined by the difference between the normalized fluorescence signal of a tumor and the mean value of a reference set of normal tissues. The results of the DNF approach were compared with endoscopic examinations and histopathology interpretations of the biopsy samples. Excellent correlation in the classification of normal and malignant tumors for the samples was found. CONCLUSION: The data indicated that the DNF approach has a significant potential to provide a direct, real-time, and in-situ technique for cancer diagnosis of the esophagus without requiring biopsy of the tumors and time-consuming histopathology tests.

Adenocarcinoma↗