ИСТИНА

Thermal-lens spectrometry (TLS) as a sensitive technique combining thermophysical and optical molecular spectroscopy is applied for complex characterization of various disperse systems. Such applications are usually based on microscopic techniques and precise instrumentation combined with data visualization and sophisticated data treatment. However, TLS can also be implemented as simpler conventional (macroscale) setups still providing high sensitivity of measurements in rather small-volume samples [1]. However, in the case of finely dispersed systems, ensuring neasurement accuracy is very significant considering the diversity of factors introducing systematic and random errors in photothermal experiments [2]. Still, it is not yet fully considered. In this talk, we will discuss the possibilities of TLS for the characterization of optical, thermal, and size-based parameters of disperse solutions of proteins, nanoparticles, and engineered macromolecules with due account of measurement accuracy. A mode-mismatched thermal-lens spectrometer with simultaneous recording of transient and steady-state signals was built [1]. A protocol for handling transient curves based on changes in thermal diffusivity during the experiment was proposed. On the basis of optimization of the operating parameters of the spectrometer and developing some algorithms and adjustment procedures, the bias of most instrumental factors as well as most factors associated with the test sample can be reduced to values below 1%. The examples of errors introduced by sample absorbance, radiation sources, etc. and appropriate choices or adjustments of the experimental conditions will be discussed. The use of a thermal-lens signal normalized to both the excitation power and absorbance makes it possible to avoid a systematic error in thermal diffusivity, which may indicate the correctness of thermal-lens measurements for heterogeneous systems. One of the examples is aqueous graphene oxide (GO) dispersions. They have advantageous thermal and optical properties but complex surface morphology of nanoparticles, which requires special analysis approaches. TLS was used for a wide range of GO concentrations and sizes. Transient measurements showed thermal-insulation properties of GO at concentrations of ca. 0.1 mg/L and an increase in thermal diffusivity (at concentrations up to 10 mg/L) to a level higher than that of water (0.160 mm2/s). TLS also revealed previously undescribed simultaneous photochemical reduction and decomposition of GO into smaller clusters. Another example is phthalocyanines as metal-containing macromolecules with a complex structure that are promising as cytostatics. Such a use requires the knowledge of their forms of existence in solution at low concentrations (< 50 nmol/L), which has not been fully established yet. For various phthalocyanine species, a decrease in the thermal-lens signal was found for different times of irradiation and lifetime in the dark. TLS provides a way to distinguish photochemical transformations (photobleaching or photoinduced oxidation) and a decrease in thermal diffusivity probably due to disaggregation of phthalocyanine clusters. [1] V.R. Khabibullin, M. Franko, M.A. Proskurnin, Nanomaterials 13(3), 430 (2023). [2] V.R. Khabibullin, L.O. Usoltseva, P.A. Galkina, V.R. Galimova, D.S. Volkov, I.V. Mikheev, M.A. Proskurnin, Physchem 3(1), 156-197 (2023).