The extraordinary properties of size-tunable nanoparticles (NPs) have given rise to their widespread applications in Nanophotonics, Biomedicine, Plasmonics etc. Semiconductor and metal NPs have found a number of significant applications in the modern biomedicine due to ultrasmall sizes (1-10 nm) and the size-dependent flexibility of their optical properties. In the present work passive Q-switched Nd:YAG pulsed laser was used to synthesize NPs by method of laser ablation in different liquids. For cases of hybrid metal NPs we have demonstrated that plasmon resonance can be modified and tuned from the plasmon resonances of pure metal NPs. The shifted plasmon resonance frequency at 437 nm for Au–Ag hybrid NPs, and 545 nm for Au–Cu hybrid NPs have been observed. Effectiveness of biotissue ablation in the case of the tissue sample that colored with metal NPs was approximately on 4-5 times larger than for the sample with non-colored area. Laser welding for deep-located biotissue layers colored by metal NPs has been realized. The luminescence properties of the colloidal hybrid Si–Ni nanoparticles’ system fabricated by pulsed laser ablation are also considered. The red-shifted photoluminescence of this system has been registered in the blue range of the spectrum because of the Stark effect in the Coulomb field of the charged Ni nanoparticles. Summarizing, the knowledge of peculiarities of optical properties of hybrid NPs is very important for biomedical applications. More complex nanoassemblies can be easily constructed by the presented technique of laser synthesis of colloidal QDs including complexes of NPs of different materials.
The luminescence properties of the colloidal hybrid Si–Ni nanoparticles system fabricated in pure water by pulsed laser ablation is considered. The red-shifted photoluminescence of this system has been registered in the blue range of the spectrum because of the Stark effect in the Coulomb field of the charged Ni nanoparticles.
Tissue nonlinear spectroscopy has been investigated as potential method for the monitoring of the laser ablation process of skin tissues. Nonlinear optical phenomenon of second harmonic generation that effectively occurs when femtosecond-picosecond duration pulses of laser irradiation passed through collagen contained layer is used to monitor photothermal processes. The samples of skin tissues were irradiated by continuous wave Nd:YAG laser and then were tested by probing picosecond beam. The change in amplitude of nonlinear optical response at ablated area of sample has been revealed. As result of laser ablation in 2mm of diameter area the SHG nonlinear signal was increased approximately two times. Polarization dependence of second harmonic generation has been studied, comparing with another nonlinear process - two-photon fluorescence in samples of ordered biotissue.
The knowledge of the peculiarities of nonlinear optical phenomena in different types of tissue is important for the development of new techniques for optical biomedical diagnostics. In this work, two-photon fluorescence (TPF) and second harmonic generation (SHG) have been studied simultaneously in ordered native tissue under the picosecond laser irradiation. For excitation of TFP with signal level in order of SHG the samples of tendon tissue were colored by Rhodamine 6G. The colored samples were irradiated by the laser beam in the direction, which was perpendicular to biofibers. SHG and TPF exhibited the different polarization dependence. Magnitude of SHG signal was about 2.5 times larger in case when polarization of the laser beam was parallel to the collagen fibers than in the perpendicular case. In contrast to SHG, the TPF signal was not show the polarization dependence. Since TPF and SHG both quadratically depend on intensity, the changing of irradiation intensity due to scattering would have the same impact on these phenomena. Influence of the light scattering was revealed using the weak linear polarized beam. The strong polarization dependence of SHG can be explained by the low propagation of the linear polarized light in the ordered tissue.
The spectral peculiarities of normal and tumor human tissues of different localization after sensitization by sodium fluorescein has been studied with help of multifrequency YAG:Nd laser. Fluorescence spectra of normal human tissue and breast, stomach, intestine, skin cancer at 355, 440 nm laser excitation were registered. The pharmacokinetic behavior of sodium fluorescein in normal and different tumor tissues has been investigated. The optimal time for diagnosis (12 - 18 hours after drug injection) was determined. The intensification of tumor tissue autofluorescence decreasing after sensitization of organisms by tumor seeking dye was observed. The electron excitation energy transfer from NAD(P)H to endogen chromophores or dyes localized in tumor has been discussed as possible reason of the observed phenomenon.
Determination of the tumor's penetration into the tissue is actual task of optical biopsy. For this aim the depth resolved fluorescence of the second generation sensitizer's molecules has been studied in tissue's phantom at different excitation wavelength. Fluorescence spectra from the superficially and deeply (up to 10 mm) located Chlorin e6 sensitizer's molecules at 355, 532, 660 nm laser excitation were registered. The comparison of the fluorescence signals registered at the different values of penetration into tissues of the probing radiation gives opportunity to define the presence of the sensitizer's molecules in different depth of tissue and to reveal such important clinical parameter as tumor's penetration into depth.
The possibility of laser fluorescence diagnosis of malignant tumors with the aid of multifrequency (355, 440, 446, 532, 660, 670 nm) solid state YAG:Nd laser and the rise in accuracy of this method were discussed. Permitted for clinical employment sodium fluorescein has been used as human tumor-localizing dye. The fluorescence spectra of sodium fluorescein containing human normal tissue and breast, stomach, intestine, skin cancer during excitation with the third harmonics of YAG:Nd and with help of multichannel fiber-optic spectrofluorometer were studied. The contrast accumulation of the dye in tumors of different localization was investigated. The fluorescence spectra of chlorine e6, containing animal tissues at different excitation wavelength (355, 532 and 660 nm) were obtained. The pharmacokinetic behavior of chlorine e6, containing different organs and tumor tissues of rats, infected with Sarcoma-45 has been investigated.
Generation of reactive photoproducts from the chromophores and destruction of biomolecules can be realized with high efficiency if the irradiation of the solutionis carried out by an intensive laser radiation, when two-step light absorption and photoreactions from highly excited electronic states of molecules are taken place. We have observed nonlinear decomposition of sensitizers in tissues upon picosecond laser radiation by fluorescence method. The subsequent change of the autofluorescence spectra of sensitized tissues has ben observed. Fluorescence spectra of tissues sensitized by tumor-localizing sensitizers hematoporphyrin derivative (HpD) chlorin e6 was registered using fiber-optic laser spectrofluorometer. It has been shown that initial rate of photobleaching is depended quadratically on the irradiation intensity. Two- photon excited fluorescence from tissues, sensitized by chlorin e(subscript 6$., and HpD has ben registered during excitation by picosecond YAG:Nd laser. These spectra coincided with that at one photon excitation, however, the background autofluorescence was absent. Red and near infrared radiation allows to increase the light penetration depth and as a result one can enhance the sensitivity of fluorescence diagnosis and the efficiency of photochemical treatment of tumors.