Biomedical subjects

J M Zwier

Publications and source records attributed to J M Zwier.

4 recordsLinked to original sources

PubMed2005

Characterization of sectioning fluorescence microscopy with thin uniform fluorescent layers: Sectioned Imaging Property or SIPcharts.

Thin, uniformly fluorescing reference layers can be used to characterize the imaging conditions in confocal, or more general, sectioning microscopy. Through-focus datasets of such layers obtained by standard microscope routines provide the basis for the approach. A set of parameters derived from these datasets is developed for defining a number of relevant sectioned imaging properties. The main characteristics of a particular imaging situation can then be summarized in a Sectioned Imaging Property-chart or SIPchart. We propose the use of such charts for the characterization of imaging properties in confocal and multiphoton microscopy. As such, they can be the basis for comparison of sectioned imaging condition characteristics, quality control, maintenance or reproduction of sectioned imaging conditions and other applications. Such charts could prove useful in documenting the more relevant properties of the instrumentation used in microscopy studies. The method carries the potential to provide the basis for a general characterization of sectioned imaging conditions as the layers employed can be characterized and fabricated to standard specifications. A limited number of such thin, uniformly fluorescing layers is available from our group for this purpose. Extension of the method to multiphoton microscopy is discussed.

Journal Article↗

PubMed2004

Image calibration in fluorescence microscopy.

A fluorescence image calibration method is presented based on the use of standardized uniformly fluorescing reference layers. It is demonstrated to be effective for the correction of non-uniform imaging characteristics across the image (shading correction) as well as for relating fluorescence intensities between images taken with different microscopes or imaging conditions. The variation of the illumination intensity over the image can be determined on the basis of the uniform bleaching characteristics of the layers. This permits correction for the latter and makes bleach-rate-related imaging practical. The significant potential of these layers for calibration in quantitative fluorescence microscopy is illustrated with a series of applications. As the illumination and imaging properties of a microscope can be evaluated separately, the methods presented are also valuable for general microscope testing and characterization.

Animals↗

PubMed2003

New glycosylated porphyrins for PDT applications.

A good sensitizer for photodynamic therapy (PDT) should be a very selective reagent, which should fastly eliminate from healthy tissues. Furthermore it should have a strong absorption in the red light and good energy transfer properties to molecular oxygen to produce singlet oxygen. All these specifications imply that many second generation photosensitizers (porphyrins, chlorins, bacteriochlorins...) have been modified in order to improve their properties, but however, few have received the approval by regulatory authorities. One way to increase the selectivity of a photosensitizer is coupling it to a vector. Carbohydrate-bound porphyrins were found to be of great interest because of the specific affinity of particular carbohydrates for some tumour cells, the increasing of plasmatic life time and solubility. In this study, we report the synthesis and the photophysical properties (absorption, fluorescence, singlet oxygen formation) of new glycosylated porphyrins. Then, in vitro photocytotoxic properties were evaluated on the human colon adenocarcinoma cell line HT29.

Computer Graphics↗

PubMed2001

Computational study of radical cations of saturated compounds with sigma-type and pi-type N-N bonds.

Geometrical and electronic properties have been calculated and are compared with experimental data for three saturated diaza compounds and their radical cations and dications. The molecular geometries in the different oxidation states are consistently reproduced very well using the B3PW91 and B3LYP three-parameter density functional methods, with a modest 6-31G* basis set. The performance of the pure density functionals BLYP and BPW91 is less satisfactory. The Hartree-Fock method yields excellent results in some cases but poor results in others. Ionization potentials and electron-nuclear hyperfine interactions are reproduced moderately well with B3LYP and B3PW91. Electronic excitation energies calculated with time-dependent density functional theory agree very well with experiment in most cases. For 2,7-diazatetracyclo[6.2.2.2(3,6).0(2,7)]tetradecane 2 and its radical cation and dication, the reorganization parameters for self-electron exchange were calculated and compared with experimental and earlier computed data. The calculations allow a good estimate of the different contributions to the energy barrier, i.e., the internal and solvent reorganization energies and the work term in the case of 2+/2++.

Journal Article↗