The development of optical methods in modern medicine in the areas of diagnostics, therapy, and surgery has stimulated the investigation of optical properties of various biological tissues, since the efficacy of laser treatment depends on the photon propagation and fluence rate distribution within irradiated tissues. In this work, an overview of published absorption and scattering properties of skin and subcutaneous tissues measured in wide wavelength range is presented. Basic principles of measurements of the tissue optical properties and techniques used for processing of the measured data are outlined.

In this article, we discuss the optical immersion method based on refractive index matching of scatterers (e.g., collagen, elastin fibers, cells and cell compartments) and the ground material (interstitial fluid and/or cytoplasm) of tissue and blood under the action of exogenous optical clearing agents. We analyze the optical clearing of fibrous and cell-structured tissues and blood from the point of view of receiving more valuable, normally hidden, information from spectroscopic and polarization measurements, confocal microscopy, optical coherence and optical projection tomography, as well as from nonlinear spectroscopies, such as two-photon fluorescence and second-harmonic generation techniques. Some important applications of the immersion technique to glucose sensing, drug delivery monitoring, improvements of image contrast and imaging depth, nondistortive delivery of laser radiation and precision tissue laser photodisruption, among others, are also described.

Water is the most important biological liquid. On the basis of literature data we present a simple approximation of water refractive index in dependence on temperature and wavelength in the spectral range from 200 to 1000 nm. The approximation is important for different applications in biomedical optics and optics of tissues.

Nanocomposites (NCs) consisting of a gold nanorod core and a mesoporous silica shell doped with hematoporphyrin (HP) have been fabricated in order to improve the efficiency of cancer treatment by combining photothermal and photodynamic therapies (PDT + PTT) in vivo. In addition to the long-wavelength plasmon resonance near 810–830 nm, the fabricated NCs exhibited a 400-nm absorbance peak corresponding to bound HP, generated singlet oxygen under 633-nm excitation near the 632.5-nm Q-band, and produced heat under a 808-nm near-infrared (NIR) laser irradiation. These modalities were used for a combined PDT + PTT treatment of large (about 3 cm³) solid tumors in vivo with a xenorafted tumor rat model. NCs were directly injected into tumors and irradiated simultaneously with 633-nm and 808-nm lasers to stimulate the combined photodynamic and photothermal activities of NCs. The efficiency of the combined therapy was evaluated by optical coherence tomography, histological analysis, and by measurements of the tumor volume growth during a 21-day period. The NC-mediated PDT led to weak changes in tissue histology and to a moderate 20% decrease in the tumor volume. In contrast, the combined PDT + PTT treatment resulted in the large-area tumor necrosis and led to dramatic decrease in the tumor volume.