Dorota Korte

Application of complex geometrical optics to determination of thermal, transport, and optical parameters of thin films by the photothermal beam deflection technique

In this work, complex geometrical optics is, for what we believe is the first time, applied instead of geometrical or wave optics to describe the probe beam interaction with the field of the thermal wave in photothermal beam deflection (photothermal deflection spectroscopy) experiments on thin films. On the basis of this approach the thermal (thermal diffusivity and conductivity), optical (energy band gap), and transport (carrier lifetime) parameters of the semiconductor thin films (pure TiO2, N- and C-doped TiO2, or TiO2/SiO2 composites deposited on a glass or aluminum support) were determined with better accuracy and simultaneously during one measurement. The results are in good agreement with results obtained by the use of other methods and reported in the literature.

Encapsulation efficiency of CdSe/ZnS quantum dots by liposomes determined by thermal lens microscopy.

In this study the encapsulation of core shell carboxyl CdSe/ZnS quantum dots (QDs) by phospholipids liposome complexes is presented. It makes the quantum dots water soluble and photo-stable. Fluorescence self-quenching of the QDs inside the liposomes was observed. Therefore, the thermal lens microscopy (TLM) was found to be an useful tool for measuring the encapsulation efficiency of the QDs by the liposomes, for which an optimum value of 36% was determined. The obtained limit of detection (LOD) for determining QDs concentration by TLM was 0.13 nM. Moreover, the encapsulated QDs showed no prominent cytotoxicity toward Breast cancer cells line MDA-MB-231. This study was supported by UV-visible spectroscopy, high resolution transmission electron microscopy (HRTEM) and dynamic light scattering measurements (DLS).

Theoretical description of thermal lens spectrometry in micro space

For thermal lens spectrometry in micro space, temperature distributions in the sample under continuous-wave modulated excitations of either laser or incoherent light source (ILS) are for the first time deduced with respective considerations of different experimental parameters, such as flow of the sample, excitation beam divergence, effects of top/bottom layers adjacent to the sample, and sidewall effects. On the basis of the temperature distributions, thermal lens (TL) models are built based on the Fresnel diffraction theory. Numerical simulations of the influence of the above factors on the TL signal are made for different detection schemes in search of higher detection sensitivity. We were able to predict the optimum probe beam offset as a function of the flow of the sample, the optimum detection scheme to minimize the effects of fluctuation of the flow velocity and/or excitation beam radius, the optimum excitation beam radius for a given sample length, and propose a three-layer system in an ILS-excite...

Mode-mismatched confocal thermal-lens microscope with collimated probe beam

We report a thermal lens microscope (TLM) based on an optimized mode-mismatched configuration. It takes advantage of the coaxial counter propagating tightly focused excitation and collimated probe beams, instead of both focused at the sample, as it is in currently known TLM setups. A simple mathematical model that takes into account the main features of the instrument is presented. The confocal detection scheme and the introduction of highly collimated probe beam allow enhancing the versatility, limit of detection (LOD), and sensitivity of the instrument. The theory is experimentally verified measuring ethanols absorption coefficient at 532.8 nm. Additionally, the presented technique is applied for detection of ultra-trace amounts of Cr(III) in liquid solution. The achieved LOD is 1.3 ppb, which represents 20-fold enhancement compared to transmission mode spectrometric techniques and a 7.5-fold improvement compared to previously reported methods for Cr(III) based on thermal lens effect.

Influence of Foreign Ions on Determination of Ionic Ag in Water by Formation of Nanoparticles in a FIA-TLS System

The influence of foreign ions on the determination of ionic Ag in an aqueous solution based on the formation of silver nanoparticles, during reduction reaction of Ag+ by , was studied using UV-Vis spectrometry and thermal lens spectrometry combined with flow injection analysis. The analysis was performed for ions that are normally present in drinking water supplies, or can result from contamination, and included Cl−, Br−, I−, , , K+, Mg2+, Fe3+, Cu2+, Cd2+, Mn2+, Pb2+, Zn2+, Hg2+, and . It was demonstrated that some ions are strong interferents in the determination of ionic silver in water by either precipitating the Ag salts or forming compounds and complexes that cause the increase in the detected signal.

A combination of interdisciplinary analytical tools for evaluation of multi-layered coatings on medical grade stainless steel for biomedical applications

Graphical abstract Figure. No caption available. HighlightsCombination of interdisciplinary analytical tools for analysis of multi‐layered coatings.First use of photothermal beam deflection spectroscopy for coating evaluation.New testing platform for medical grade steel materials for biomedical applications. Abstract In this comprehensive study several analytical techniques were used in order to evaluate multi‐layered biomedical surface coatings composed of a drug (diclofenac) and a polymer (chitosan). Such a thorough examination is of paramount importance in order to assure safety and prove efficiency of potential biomedical materials already at the in vitro level, hence leading to their potentially faster introduction to clinical trials. For the first time a novel technique based on thermal diffusivity and conductivity measurements (photothermal beam deflection spectroscopy – BDS) was employed in order to analyse in a non‐destructive way the thickness of respective layers, together with their thermal diffusivity and conductivity. In addition to attenuated total reflection Fourier‐transform infrared spectroscopy (ATR‐FTIR), BDS confirmed successive surface layers of the prepared coatings. Scanning electron microscopy and atomic force microscopy were used to examine structural information on the macro‐ and micro/nano‐scale, respectively. Surface hydrophobicity was measured with the contact angle analysis, which clearly showed differences in hydrophobicity between coated and non‐coated samples. Considering the targeted application of the prepared coatings (as implant in orthopaedic treatments), the in vitro drug release was analysed spectrophotometrically to examine the coatings potential for a controlled drug release. Furthermore, the material was also tested by electrochemical impedance spectroscopy and cyclic polarisation techniques, which were able to detect even minor differences between the performance of the coated and non‐coated materials. As the final test, the biocompatibility of the coatings with human osteoblasts was determined.

Trace Detection and Photothermal Spectral Characterization by a Tuneable Thermal Lens Spectrometer with White-Light Excitation

In the thermal lens experimental set-up we replaced the commonly employed pump laser by a halogen lamp, combined with an interference filter, providing a tuneable, nearly monochromatic pump source over the range of wavelengths 430-710 nm. Counter-propagating pump and probe beams are used and a 1 mm path-length sample cell together with the interference filter makes an optical cavity, providing amplification of the thermal lens signal, which leads to enhancement of the measurement sensitivity, and enables detection of absorbances on the order of 5 × 10-6. Amplified thermal lens signal allows us to replace the typical lock-in amplifier and digital oscilloscope with a silicon photodetector, Arduino, and a personal computer, offering the possibility for a compact, robust and portable device, useful for in-field absorption measurements in low concentration or weakly absorbing species. The use of a white light source for optical pumping, an interference filter for wavelength selection and direct diagnostic of the thermal lens signal increase the versatility of the instrument and simplifies substantially the experimental setup. Determination of Fe(II) concentrations at parts per billion levels was performed by the described white-light thermal lens spectrophotometer and the absorption spectrum for 50 μgL-1 Fe(II)-1,10-phenanthroline was well reproduced with an average measurement precision of 4%. The obtained limits of detection and quantitation of Fe(II) determination at 510 nm are 3 µgL-1 and 11 µgL-1, respectively. The calibration curve was linear in the concentration range of LOQ-500 µgL-1 with reproducibility between 2% and 6%, confirming that this instrument provides good spectrometric capabilities such as high sensitivity, tuneability and good reproducibility. In addition, the versatility of the instrument was demonstrated by recording the photothermal spectrum of gold nanostructured material and determination of excitation wavelength with most efficient optical to thermal energy conversion, which differs considerably (cca 100 nm) from the absorption maximum of the investigated sample.

Transparent Photocatalytic Thin Films on Flexible Polymer Substrates

Self-cleaning and/or photocatalytic films on polymer substrates have found numerous applications during the past decades. However, the common demand for high-temperature post synthesis treatment limits the application to temperature resistant substrates only. Herein, we prepared self-cleaning photocatalytic films on four thermosensitive polymeric substrates: polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), and acryl coated polyester (PES) fabric (D2) with poly(vinylidene fluoride) (PVDF) containing lacquer (D1). TiO2 was prepared via a low-temperature sol-gel process using titanium(IV) isopropoxide and zirconium(IV) butoxide as precursors with various loading levels of Zr; 0, 5, 10, and 20 mol.%, and deposited on the substrates by using a SiO2 binder in form of thin films (ca. 200 nm thick) via dip-coating. The films were characterized by SEM, hardness test, UV-Vis, photothermal beam deflection spectroscopy, and IR spectroscopy, while photocatalytic activity was measured by the fluorescence-based method of the terephthalic acid probe and wetting by contact angle measurements. Films containing 10 mol.% of Zr showed the best compromise regarding photocatalytic activity and mechanical stability while from substrates point of view PVC performed the best, followed by PMMA, D1, and D2. The beneficial role of SiO2 binder was not only guaranteeing excellent mechanical stability, but also to prevent the D1 polymer from deterioration; the latter was found to be labile to long-term solar-light exposure due to degradation of the top PVDF layer.

Absorption Spectra of Ethanol and Water Using a Photothermal Lens Spectrophotometer

In this work we report on the absorption spectra of ethanol and water in the region 430–700 nm using a homemade halogen lamp-based photothermal lens spectrophotometer with a multipass probe-beam configuration. The spectra also include well resolved, higher absorption overtones. The instrument achieves high sensitivity due to multiple reflections within the optical cavity containing the sample. Finally, an Arduino board was used for collecting and digitizing the signal, thus enabling a more compact device.