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Biomedical subjects

C Y Dong

Publications and source records attributed to C Y Dong.

11 recordsLinked to original sources
PubMed2001

In vitro visualization and quantification of oleic acid induced changes in transdermal transport using two-photon fluorescence microscopy.

In a novel application of two-photon scanning fluorescence microscopy, three-dimensional spatial distributions of the hydrophilic and hydrophobic fluorescent probes, sulforhodamine B and rhodamine B hexyl ester, in excised full-thickness human cadaver skin were visualized and quantified. Both sulforhodamine B and rhodamine B hexyl ester were observed to lie primarily in the lipid multilamellae region surrounding the corneocytes within the stratum corneum. From the two-photon scanning fluorescence microscopy scans, the changes in the concentration gradient and the vehicle to skin partition coefficient of each probe induced by the oleic acid enhancer action were calculated relative to the control sample (not exposed to oleic acid), and subsequently applied to theoretically derived mathematical expressions of transdermal transport to quantitatively characterize the oleic acid-induced relative changes in the skin diffusion coefficient and the skin barrier diffusion length of the permeant. For the hydrophobic probe rhodamine B hexyl ester, the permeability enhancement was primarily driven by an increase in the vehicle to skin partition coefficient, leading to an increase in the steepness of the concentration gradient across the skin. The primary oleic acid-induced changes in the transport properties of the hydrophilic probe sulforhodamine B included increases in the vehicle to skin partition coefficient and the skin diffusion coefficient. These findings utilizing the two-photon scanning fluorescence microscopy methodology and data analysis described here demonstrate that, in addition to providing three-dimensional images that clearly delineate probe distributions in the direction of increasing skin depth, the subsequent quantification of these images provides additional important insight into the mechanistic changes in transdermal transport underlying the visualized changes in probe distributions across the skin.

Biological Transport↗
PubMed2001

Resolution enhancement in standing-wave total internal reflection microscopy: a point-spread-function engineering approach.

The theoretical basis for resolution enhancement in standing-wave total internal reflection microscopy (SW-TIRM) is examined. This technique relies on the formation of an excitation field containing super-diffraction-limited spatial-frequency components. Although the fluorescence generated at the object planes contains high-frequency information of the object distribution, this information is lost at the image plane, where the detection optics acts as a low-pass filter. From the perspective of point-spread-function (PSF) engineering, one can show that if this excitation field is translatable experimentally, the high-frequency information can be extracted from a set of images where the excitation fields have different displacement vectors. We have developed algorithms to combine this image set to generate a composite image with an effective PSF that is equal to the product of the excitation field and the Fraunhofer PSF. This approach can easily be extended to incorporate nonlinear excitation modalities into SW-TIRM for further resolution improvement. We theoretically examine high-resolution imaging based on the addition of two-photon, pump-probe, and stimulated-emission depletion methods to SW-TIRM and show that resolution better than 1/20 of the emission wavelength may be achievable.

Journal Article↗
PubMed2000

Time-resolved polarization imaging by pump-probe (stimulated emission) fluorescence microscopy.

We report the application of pump-probe fluorescence microscopy in time-resolved polarization imaging. We derived the equations governing the pump-probe stimulated emission process and characterized the pump and probe laser power levels for signal saturation. Our emphasis is to use this novel methodology to image polarization properties of fluorophores across entire cells. As a feasibility study, we imaged a 15-microm orange latex sphere and found that there is depolarization that is possibly due to energy transfer among fluorescent molecules inside the sphere. We also imaged a mouse fibroblast labeled with CellTracker Orange CMTMR (5-(and-6)-(((4-chloromethyl)benzoyl)amino)tetramethyl-rhodamine). We observed that Orange CMTMR complexed with gluthathione rotates fast, indicating the relatively low fluid-phase viscosity of the cytoplasmic microenvironment as seen by Orange CMTMR. The measured rotational correlation time ranged from approximately 30 to approximately 150 ps. This work demonstrates the effectiveness of stimulated emission measurements in acquiring high-resolution, time-resolved polarization information across the entire cell.

Animals↗
PubMed2000

Two-photon excitation fluorescence microscopy.

Two-photon fluorescence microscopy is one of the most important recent inventions in biological imaging. This technology enables noninvasive study of biological specimens in three dimensions with submicrometer resolution. Two-photon excitation of fluorophores results from the simultaneous absorption of two photons. This excitation process has a number of unique advantages, such as reduced specimen photodamage and enhanced penetration depth. It also produces higher-contrast images and is a novel method to trigger localized photochemical reactions. Two-photon microscopy continues to find an increasing number of applications in biology and medicine.

Animals↗
PubMed1998

New time-resolved techniques in two-photon microscopy.

Microscopy is traditionally a tool for determining biological structures. Many recent advances in optical microscopy involves the incorporation of spectroscopy techniques to monitor biochemical states of microscopic structures in living cells and tissues. By minimizing tissue photodamage, two-photon excitation microscopy provides a new opportunity to study the dynamics of biological systems on time scales from nanoseconds to hours. This review will focus on a number of these new methods: two-photon time-lapse microscopy, two-photon photoactivation, two-photon correlated spectroscopy, two-photon single particle tracking and two-photon lifetime microscopy.

Animals↗
PubMed1995

Fluorescence lifetime imaging by asynchronous pump-probe microscopy.

We report the development of a scanning lifetime fluorescence microscope using the asynchronous, pump-probe (stimulated emission) approach. There are two significant advantages of this technique. First, the cross-correlation signal produced by overlapping the pump and probe lasers results in i) an axial sectioning effect similar to that in confocal and two-photon excitation microscopy, and ii) improved spatial resolution compared to conventional one-photon fluorescence microscopy. Second, the low-frequency, cross-correlation signal generated allows lifetime-resolved imaging without using fast photodetectors. The data presented here include 1) determination of laser sources' threshold powers for linearity in the pump-probe signal; 2) characterization of the pump-probe intensity profile using 0.28 microns fluorescent latex spheres; 3) high frequency (up to 6.7 GHz) lifetime measurement of rhodamine B in water; and 4) lifetime-resolved images of fluorescent latex spheres, human erythrocytes and a mouse fibroblast cell stained by rhodamine DHPE, and a mouse fibroblast labeled with ethidium bromide and rhodamine DHPE.

Animals↗
PubMed1989

An analysis of prognostic factors in cirrhosis.

To develop a more comprehensive index for predicting the prognous of liver cirrhosis. 300 consecutive patients with cirrhosis were studied in terms of survival from 1975 to 1986. Median follow-up period was 5.3 years. A multivariable survival analysis (Cox's regression model) using clinical biochemical data obtained at admission disclosed eight factors of value in predicting prognosis: age, frequency of previous GI bleeding, ascites, hepatic encephalopathy, serum albumin, serum bilirubin, hemoglobin and prothrombin time. A prognostic index was constructed for the calculation of the estimated survival probability.

Adult↗
PubMed1983

Prevention of type 2 herpes simplex virus induced cervical carcinoma in mice by prior immunization with a vaccine prepared from type 1 herpes simplex virus.

Repeated intra-vaginal inoculation of mice with inactivated type 2 herpes simplex virus induced cervical carcinoma in approximately 50% of mice. Prior immunization with subunit vaccine Ac NFU1(S-) BHK reduced the frequency of cervical carcinoma to 19%. Inoculation of mice with a control preparation of uninfected cell extract never induced preinvasive or invasive cervical cancer. There was evidence of an antibody response in every vaccinated and/or innoculated animal. Mice developing cervical cancer had a significantly higher antibody titre to type 2 herpes virus than mice not developing cancer. These results are in general accord with sero-epidemiological studies of preinvasive and invasive cervical carcinoma in human subjects and suggests that this experimental model may be appropriate for further investigation of prevention of human cervical cancer by vaccination.

Animals↗