Biomedical subjects

J Bürck

Publications and source records attributed to J Bürck.

4 recordsLinked to original sources

PubMed2001

Prognostic value of codon 918 (ATG-->ACG) RET proto-oncogene mutations in sporadic medullary thyroid carcinoma.

We have determined the frequency of 918 RET proto-oncogene mutations (ATG-->ACG) in primary MTC tumors and metastases and correlated the presence or absence of this mutation with the clinical outcome of patients suffering from sporadic medullary thyroid carcinoma (MTC). A total of 197 samples, consisting of both primary tumors and lymph node metastases from 34 patients with sporadic MTC, were collected for PCR analysis of the RET 918 mutation. In 75 of the samples (38%), codon 918 (ATG-->ACG) mutations could be detected. The mutations showed a heterogeneous distribution: 21/34 patients (62%) had mutations in at least 1 tumor sample, and in 13 patients (38%) the mutation was present in all examined samples. Patients were considered 918mt when at least 1 tumor sample showed the RET 918 mutation. These 918mt and 918 wild-type (918wt) patients did not differ significantly concerning sex, age at diagnosis, TNM stage at diagnosis, number of examined tumor samples or follow-up time. However, 918mt patients showed more aggressive development of distant metastases during follow-up (p = 0.032, Fisher's exact test) with decreased metastases-free survival (p < 0.005, log-rank test). Furthermore, 918mt patients had a significantly lower survival rate than 918wt patients (p = 0.048, log-rank test). These data show that the RET codon 918 mutation has a prognostic impact on patients with sporadic MTC which may influence follow-up treatment.

Adult↗

PubMed1996

Integrated optical NIR-evanescent wave absorbance sensorfor chemical analysis.

A new, long-path integrated optical (IO) sensor for the detection of non-polar organic substances is described. The sensing layer deposited on a planar multimode IO structure is built by a suitable silicone polymer with lower refractive index (RI). It acts as a hydrophobic matrix for the reversible enrichment of non-polar organic contaminants from water or air. Light from the near-infrared (NIR) range is coupled into the planar structure and the evanescent wave part of the light field penetrating into the silicone layer interacts with the enriched organic species. As a result, light is absorbed at the characteristic frequencies of the corresponding C-H, N-H or O-H overtone and combination band vibrations of the analytes. To perform evanescent field absorbance (EFA) measurements, the arc-shaped strip waveguide structure of 172 mm interaction length was adapted to a tungsten-halogen lamp and an InGaAs diode array spectrograph over gradient index fibers. Dimethyl-co-methly(phenyl)polysiloxanes with varying degrees of phenylation were prepared and used as sensitive coating materials for the IO structure. Light attenuation in the arc-shaped waveguides is high and typical insertion losses in the range of 14-18 dB were obtained. When the coated sensors were brought in contact with aqueous samples, the light transmission decreases, which is due to the formation of H(2)O micro-emulsions in the silicone superstrates. Nevertheless, after reaching constant light transmissions, absorbance spectra of aqueous trichloroethene samples were successfully collected. For gas measurements, where water cross sensitivity problems are absent, the sensitivity of the IO device for trichloroethene was tested as a function of the RI of the silicone superstrate. The slope of the TCE calibration function increases by a factor of 10 by using a poly(methylphenylsiloxane) layer with a RI of 1.449 instead of poly(dimethylsiloxane) (RI: 1.41). A comparison of the IO-EFA and an earlier developed fiber-optic EFA sensor for trichloroethene measurements in the gas phase showed an increase in sensitivity per unit length of the waveguide by a factor of up to 120.

Journal Article↗

PubMed1996

Optimisation of an integrated optical evanescent wave absorbance sensor for the determination of chlorinated hydrocarbons in water.

The suitability of an integrated optical chemical sensor for the determination of highly volatile chlorinated hydrocarbons in aqueous solutions has been proven. The analytes are detected by NIR absorption spectrometry in the evanescent field of an integrated optical strip waveguide generated in a BGG31 (Schott, Germany) glass substrate, which is coated with a hydrophobic polymer superstrate as sensing layer. It has been shown that the sensitivity increases when the refractive index of the superstrate is increased from 1.333 up to 1.46. Different UV-cured polysiloxanes with low cross sensitivity to water have been prepared. Due to the good light transmission properties of the IO-sensors prepared by this method, quantitative measurements have been performed with the model system trichloroethene (TCE) in water. A detection limit of 22 ppm has been found and the sensor response times (t(90)-value) are between five and fourteen minutes for a coating thickness of around 30 microm. The sensor response is totally reversible. The analyte desorbes in air within 2 min. The enrichment of trichloroethene in the polysiloxane coating can be described by film diffusion through the aqueous boundary layer as rate determining step.

Journal Article↗

PubMed1996

Determination of hydrocarbons in water by evanescent wave absorption spectroscopy in the near-infrared region.

An home-made EFA (Evanescent Field Absorbance)-sensor has been tested for the determination of hydrocarbons in water. The investigations have been performed both with crude oil emulsions and petrol solutions. Cuvette and evanescent wave spectra of crude oil and petrol in the near-infrared region are presented and discussed. The concentration of aromatic compounds in crude oil can be determined semiquantitatively by the standard addition method. The sorption behaviour of the hydrocarbons in the cladding of the fiberoptic sensor has been investigated and a correlation between the sensor signal and the concentration of the aqueous hydrocarbon emulsion/solution could be shown. The desorption of the enriched molecules after the measurements is also presented. The petrol molecules evaporate in ambient air so that the sensor is easily regenerated. In case of oil measurements the hydrocarbon molecules cannot be removed by rinsing the sensor with clear water or by evaporating them in ambient air. It has to be regenerated by washing it with a high volatile solvent instead.

Journal Article↗