I. Hołowacz

Optical properties of sol–gel coatings for fiberoptic sensors

Abstract Sol–gel-derived materials can be exploited for the construction of various optoelectronic devices, including sensors optodes and their protective layers, as well as other kinds of coatings. Different types of materials were studied: silica sol–gel matrices made from silica solutions with water or alcohol as solvents. The samples were prepared in the form of single layer films. The films were deposited on glass surfaces. The porous structure of sol–gels layers was examined as well as the transmittance spectra, which were measured in the visible and UV regions. A strong influence of the solvent type on the material optical properties was noted. Alcohol-based samples showed stable homogenous structures, with no cracking. However, the water-based samples demonstrated higher transmittance in the visible region. The obtained results can serve as a basis for choosing a suitable layer when constructing optical sensors or coatings.

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.

Thermal imaging for face recognition in optical security systems

Face recognition belongs to the most fundamental human perceptual capabilities. Today, the technology is encapsulated in commercial software that runs on any low cost personal computer and is capable to detect the human faces anywhere in a scene and rapidly identifying them by matching the face against its database of known faces.

Performance repeatability of fiberoptics applicators for laser therapy

The distribution of light emitted from the sol-gel coated fiberoptic applicator for interstitial laser therapy was examined. The silica sol-gel coatings were prepared from silicate precursor TEOS (tetraethylorthosilicate) mixed with ethyl alcohol in acid catalyzed hydrolysis. The applicator was produced with ratio R = 20, whereas R denotes the number of solvent moles (ethanol) to the number of TEOS moles. Then, the light pattern was captured by means of CCD camera and statistical pattern recognition method was applied to study the repeatability of light distribution. Two methods were applied: Fisher Linear Discriminant Analysis (FLDA) and Principal Component Analysis (PCA). The top match characteristic TM as calculated by statistical pattern recognition methods was taken as a factor corresponding to the performance repeatability. It was demonstrated that is possible to produce the sol-gel applicators with more than 92% repeatability.

Influence of certain screening masks on human face in far infrared spectral region

Recently, the use of far IR spectral region (FIR), especially in range 8-13 micrometers , is widely discussed. One of the main areas of applications is monitoring of human body for health care. On the other hand, the health care and banking industries are faced with fraud. There is a need to elaborate the systems that can be used not only for health diagnosis, but also for unique identification of human bodies. This paper discusses the possibility of exploiting of the registration of FIR images and their computer aided processing for facial recognition systems.

Examination of light distribution from sol-gel based applicators for interstitial laser therapy

We describe here the construction of sol-gel based applicators for interstitial thermotheraphy. The silica sol-gel coatings were prepared from silicate precursor TEOS (tetraethylorthosilicate) mixed with ethyl alcohol in acid catalyzed hydrolysis. The matrices were produced with various ratios R=5, 10, 20, 32, 50, whereas R denotes the number of solvent molds (here ethanol) to the number of TEOS moles. The spatial light intensity distribution was examined in order to find out the influence of R factor on the light distribution shape. It was shows that the most homogeneous patterns are observed for sol-gel coatings with R factors equal 10 and 20.

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.

Sol-gel optics for biomeasurements

Sol-gel technique is a method for producing of glass-like materials without involving a melting process. Organic compounds such as alcoholates of silicon, sodium or calcium can be used. The irregular non-crystalline network forms a gel structure where the metallic atoms are bonded to oxygen atoms. Low-temperature treatment turns this gel into an inorganic glass-like structure. There are numbers of applications of these materials that can be produced in various forms and shapes. Here, silica based sol-gel bulks and thin films optodes for biomedical applications will be presented.

Examination of the haemolytic activity of sol-gel materials

Recently, the sol-gel based biomaterials are extendedly investigated with emphasis on theirs various applications, including medical ones. In this respect it is important to investigate the influence of sol-gel matrices on biological systems. The results of laboratory and biological testing of aqueous extracts of sol-gels are presented in this work. It was proved that it is possible to produce the sol-gel derived materials that will be non-haemolytic. This can be achieved by heating the materials in elevated temperatures. This effect can also be reached by suitably long aging (minimum 6 months).