ИСТИНА

Transient photothermal lens spectrometry was used for the estimation and evaluation of concentrational, size, and optical and thermooptical parameters of various homogenous and heterogeneous samples containing inorganic dispersions, proteins, polymers for the needs of chemical and biochemical analysis. These experiments are based on dual-beam thermal lensing with back-synchronized working mode. This mode features different and flexible measurement conditions for the blooming and dissipating of the photothermal element (thermal lens) unachieved in lock-in measurements. This was used for enhancing the reproducibility and sensitivity of thermal lensing. In this excitation/data-treatment mode, the advantages are (i) the possibility of detection under batch and flow conditions with no change in the optical-scheme design of the instrument; (ii) the possibility to switch between transient and steady-state thermal-lens measurements within a single set of experiments; and (iii) a wide linear dynamic range (more than five orders of magnitude of detectable absorbances) including strongly absorbing and scattering samples. In spite of a somewhat lower detection sensitivity compared to more commonly used lock-in schemes, the flexibility of this measurement mode provide a much larger volume of information, making it a powerful tool for studying complex formation at trace concentrations, and transient heat flow around light-absorbing dispersions. Low limits of detection (at the nanomolar level of target substances) both for biological and environmental samples result from both the optimum selection of parameters of photothermal measurements and methodology of analytical photometry, which is still is rather rarely used in biophotometry and photothermics and optoacoustics. For this photothermal measurement mode, a model for the approximation of transient and steady-state photothermal measurements was developed, which provides the possibility to estimate the main photothermal constants (thermal diffusivity, thermal conductivity, thermal-expansion coefficient). This was tested on water and organic solvents, aqueous polymers and surfactants, and inorganic precipitations. Among biological samples, we tested heme proteins and metal and carbon nanoparticle suspensions. We showed that even at low concentrations of proteins and relatively weak cw laser excitation, the thermal lensing in protein- and nanoparticle-containing solutions demonstrates a deviation from a behavior expected from homogenous solutions: the detection sensitivity decreases compared to theoretical estimations and the transient TLS signals show lower development times, which makes it possible to estimate with some a priori data various parameters. The examples of calculations will be discussed. These data were supported with the results from independent methods like optoacoustics, conventional absorption UV/vis and IR spectroscopy, and fluorescence spectroscopy. The use of photothermal spectroscopy for the estimation of thermal-diffusion coefficient and thermal conductivity can be used for more methodologically approved optimization of instrumental features and biomedical applications of photothermal lensing. This paper is supported by the 2010 grant program of the Presidium of the Russian Academy of Sciences «The development of improvement of the methods for chemical analysis and investigation of the structure of substances and materials» and the Russian Foundation for Basic Research, grant no. 10-03-01018-а.