Uwe Bindig

Investigations on photolon-and porphyrin-doped sol-gel fiberoptic coatings for laser-assisted applications in medicine

In view of laser-assisted medical applications, the construction of silica-based sol-gel fiberoptic sensors based on photolon (Ph) and protoporphyrin IX (PP IX) is discussed. Electron microscopy and AFM were used to characterize the silica sol-gel coatings. AFM measurements indicate a change in the surface porosity. The PP IX-based sensors were constructed as a one-layer optode as well as a multilayered structure. An additional hybrid sensor made up of alternate layers of PP IX-and Ph-doped sol-gel was also constructed and examined. Sol-gel matrices were prepared from silicate precursor tetraethylorthosilicate (TEOS) mixed with ethanol in acid-catalyzed hydrolysis. The carrier matrices of photosensitive dyes were produced with factor R = 20, where R denotes the ratio of solvent moles (ethanol) to the number of TEOS moles. A multilayered coating was built up using the reverse-dipping technique. The overall coating thickness was determined by electron microscopy. Doped sol-gels with different PP IX concentrations were used to produce fiberoptic coatings. The film optodes with a different number of layers were examined by fluorescence spectroscopy. It was found that photolon and protoporphyrin IX entrapped in sol-gel preserve their chemical reactivity and have contact with the external environment. The hybrid sensor demonstrated clear fluorescence and a reversible behavior in gaseous environments.

Fibre-optic IR-spectroscopy for biomedical diagnostics

The use of microscopy is a valuable means of gaining vital information for medical diagnostics. Due to a number of recent technological developments advances have been made in IR microscopy and in particular, rapid detection methods. Microscopic examination methods usually involve sampling followed by a method of sample purification or preparation. The advantages of the IR analytical method are that it is based on a direct, non‒destructive measurement of sample material and that the resulting IR spectra provide extensive and specific information about the sample composition and structure. The course of a disease can lead to either formation or loss of organic compounds in metabolism as well as changes within the biological matrix. Corresponding changes can also be expected in the IR‒signature in view to the grading of alteration. Our preliminary IR microscopic investigations compared diseased and healthy tissue samples individually and basic information was obtained about the tissue specific spectral signature, taking account of biological variance. Human tissue samples taken from the colon were used for these studies. Given the number of endoscopic applications used in minimally invasive medicine, we hope to establish the IR fibre based procedure as an optical biopsy method for tissue diagnostics. The aqueous environment as well as the IR radiation source, signal detection and the flexible wave guide type will be a limiting factor for an IR system. The hygiene requirements are particularly high for a fibre based system to be used for in vivo applications.

Optical properties of sol-gel fiber optic applicators for laser interstitial therapy

A new type of applicator for interstitial laser coagulation is proposed in this paper. The new fiber optic applicator is made by removing the original fiber cladding and replacing it with a sol-gel coating. The sol-gel coating was prepared from the silicate precursor TEOS (tetraethylorthosilicate), mixed with ethanol in acid, which catalyzes hydrolysis. The material is produced with the factor R = 20, where R denotes the number of solvent moles to the number of TEOS moles. In these studies, optical fibers were used from Laser Components (core diameter 400 µm, HCS, low OH). The external jacket was mechanically removed, leaving a remaining 2-cm length of bare fiber. The modified dip-coating method was used to cover the bare fibers with sol-gel material. Two types of applicators were produced: pure sol-gel coated devices and applicators with sol-gel coating doped with photosensitive dyes. The photodynamic activity of chlorophyll-based Photolon and Protoporphyrin IX (PPIX) incorporated within the sol-gels was studied spectrophotometrically. It was demonstrated that sol-gel applicators are capable of performing laser interstitial coagulation using a semiconductor cw laser at 980 nm. It was also demonstrated that the incorporated photosensibilizers retain their photochemical activity.

Detection of malignant tissues by using infrared microscopy and fiber optic spectroscopy

In this work we present our effort to develop an infrared method to differentiate between malignant and healthy tissue in vivo. This paper will present the technical design of the laboratory set up and the results obtained in experiments carried out on melanoma tumors in the skin of male mice. Silver halide fibers were used to carry our ATR measurements on tumor sections. Further results were compared with detailed measurements carried out using an FTIR-microscope and thin tissue sections in the spectral range of 4000 - 900 cm-1. The results indicate that IR spectroscopy would be a useful tool for biodiagnosis, in vivo and in real time. The fiberoptic method described here will easily lend itself to endoscopic applications.

Examination of light distribution from fibers coated with sol-gel films doped with porphyrine

The modification of optical fibers by exploiting various coatings may be important for construction of fiberoptics, sensors or applicators for interstitial laser therapy. We report here on sol-gel films placed on fiber cores, replacing the original fiber coatings. The silica sol-gel coatings where prepared form silicate precursor TEOS (tetraethylorthosilicate) mixed with ethyl alcohol in acid catalyzed hydrolysis. The matrices were produced with various ratios R=5, 15, 20, 32, 40, 50, whereas R denotes the number of solvent moles (here ethanol) to the number of TEOS moles. Two types of coatings were produced: pure sol-gel matrices and sol-gel doped with Protophyrin IX in two various concentrations. The angular light intensity distribution was examined in order to find out the influence of R factor on the light intensity distribution near the fiber tip. Then, the light pattern was captured by means of CCD camera and the three dimensional luminances were calculated. The same experiments were repeated for silica sol-gel coatings doped with natural porphyrine Protoporphyrine IX and different patterns were observed.

Photoactive sol-gel biocoatings

In this work we investigated the photoactive properties sol-gel biocoatings doped with Protoporphyrin IX (PP IX). It was demonstrated that PP IX entrapped in sol-gel preserves its chemical activity and may have contact with the external environment. The chemical reactions with zinc cations and pyridine, as well as protonation, occurred quite fast. This indicates, that the interconnected porous network could be easily penetrated by relatively large molecules (e.g. mentioned by pyridine molecule). Further, we observed that PP IX molecules do not leave the pores. Structural changes caused by the addition of PP IX to the sol-gel matrix influence not only on the optical properties, but also on durability of the coatings. The altering of PP IX doped silica sol-gel coatings is quite slow.

IR fiber optic sensing on biological tissue

A diagnostic method is described to detect differences between diseased and normal tissue from bladder carcinoma by FTIR-microspectroscopy and fiber-optics methods. Regions of interest on 10 μm thin tissue sections were mapped using an IR-microscope in transmission mode. Afterwards the specimens were analyzed using standard pathological techniques. Quadratic discriminant as well as correlation analysis was applied for data analysis. IR optical fibers, not only allowed measurements to be made in the attenuated total reflectance (ATR)-mode but also absorption measurements to be carried out at a remote location. The IR-sensor is in contact with the sample which shows characteristic absorption lines. This method can be used to determine the absorption of a sample in a non-destructive manner. In this paper we report our efforts to develop a fiber-optic infrared sensor to differentiate between malignant and healthy tissue in vivo. Silver halide fibers and a special sensor tip were used for the ATR measurements on human tissue specimens. The results indicate that IR-spectrometry will be a useful tool for bio-diagnostics.

Recent developments in fiber optic IR sensors

Although there is an ongoing effort to use infrared- spectroscopy for tissue differentiation and classification, there is still a need for the development of a sensor for use in the quick and non-destructive detection of spectral changes resulting from, for example, the influence of temperature. It is our intention to investigate flat IR- sensors and their suitability as a tool for detection within bio-organic compounds. Initial investigations using bio- liquids, tissues in the native and coagulated state, and micro-organisms have already been carried out. According to the literature, major IR-spectroscopic differences can be expected in the fingerprint region (1500-1000 cm-1). An experimental set up was based on an FTIR-spectrometer, fiber optic cables, sensor and an external detector. A sensor was used whereby a segment of 1.5 cm at the center of the fiber was flattened to approx. 150 micrometers . Transmission spectra of flattened fibers have been compared to those of the cylindrical fibers. Spectral differences were obtained indicating a possible use for the study of thermal damage in tissues. The fiber-optic based results are comparable to micro-ATR-FTIR-spectroscopy (attenuated total reflectance) measurements. IR-sensing was performed either using circular or flat silver halide wave guides.

IR-Spectroscopic imaging applied to human colon biopsy

Tissue samples from colon biopsy have been analyzed using FT-IR microscopy. For differentiation of cancerous versus normal tissue and for imaging of tissue structure linear and quadratic discriminant analysis was applied. A large number of samples has been used for statistical parametrization. After IR mapping, the samples have been analyzed with common pathological techniques. Comparing the pathological classification with the results of the discriminant analysis the resolving power of the later is estimated. The influence of filtering (using derivative spectra, baseline correction, and normalization) has been investigated. In vivo application of IR-spectroscopy using IR laser diodes or grating spectrometers for fast measurements will lead to a reduction of data concerning spectral range and resolution. The accompanying loss in differentiation of tissue is discussed. Images constructed with the discriminant analysis are compared to corresponding images from visible microscopy.

IR spectroscopy: new results due to fiber optic sensing in view of biomedical application

Optical fibers transparent in the mid-infrared (IR) enable absorption measurements in remote location. New techniques will enhance the possibility using IR fibers for measurements in ATR-mode. If the fiber is in contact with a sample that has characteristic absorption lines, the total transmission of the fiber and sample of these lines will decrease. In this way the absorption of a sample can be determined using a non-destructive method. This work has proven the suitability of flattened IR-Fiber as a tool for detection of organic substances. Initial investigations using bio-organic compounds, bio-liquids, tissue in the native and coagulated state, and micro-organisms have already been carried out with a view to bio-medical usage. An experimental set up was based on an FTIR-spectrometer, fiber optic cables and an external detector. A segment of 1.5 cm at the center of the fiber was flattened to approx. 150 micrometers . Transmission spectra of flattened fibers have been compared to those of the cylindrical fibers. Spectral differences were obtained indicating a possible use for the study of thermal damage in tissues.