Study of nonlinear optical phenomena in silicone films encapsulated with SiO2 and Si/SiO2 spherical particles

Infrared converters to visible range are in demand for creation of optoelectronic devices, infrared visualizers and other non-linear optical devices. In this work we study nonlinear optical properties of monodisperse SiO2 and Si/SiO2 spheres encapsulated into silicone films. The fabricated silicone films containing SiO2 spheres demonstrated a bright third harmonic generation signal, and films with Si/SiO2 spheres demonstrated a significant second harmonic generation signal in the whole visible range. The developed materials and methods provide a platform for future infrared to visible converters based on silicon.

Multiphoton microscopy for label-free multicolor imaging of peripheral nerve

Conventional histomorphometry of peripheral nerve entails lengthy chemical processing, ultrathin sectioning in resin, and imaging by light or electron microscopy. Multiphoton microscopy techniques exist enabling label-free and in vivo imaging of histological samples. Third-harmonic-generation microscopy has recently been demonstrated effective for imaging the myelin sheath of peripheral nerve axons in animal models. Herein, we characterize use of second and third harmonic generation microscopy for label-free imaging of murine and human peripheral nerve via a novel multicolor multiphoton microscope based on a single excitation wavelength at 1300 nm. Second harmonic generation signal from collagen centered about 650 nm delineates neural connective tissue, while third harmonic general signal centered about 433 nm delineates myelin and other lipids. In transgenic mice expressing yellow fluorescent protein linked to the thy1 promoter, three-photon-excitation with emission peak at 527 nm delineates axoplasm. We compare label-free multiphoton imaging of murine and human peripheral nerve against conventional chemical stains and discuss clinical implications of this approach in guiding intraoperative decision making in nerve transfer procedures.

Optical coherence tomography and multiphoton microscopy offer new options for the quantification of fibrotic aortic valve disease in ApoE−/− mice

Aortic valve sclerosis is characterized as the thickening of the aortic valve without obstruction of the left ventricular outflow. It has a prevalence of 30% in people over 65 years old. Aortic valve sclerosis represents a cardiovascular risk marker because it may progress to moderate or severe aortic valve stenosis. Thus, the early recognition and management of aortic valve sclerosis are of cardinal importance. We examined the aortic valve geometry and structure from healthy C57Bl6 wild type and age-matched hyperlipidemic ApoE−/− mice with aortic valve sclerosis using optical coherence tomography (OCT) and multiphoton microscopy (MPM) and compared results with histological analyses. Early fibrotic thickening, especially in the tip region of the native aortic valve leaflets from the ApoE−/− mice, was detectable in a precise spatial resolution using OCT. Evaluation of the second harmonic generation signal using MPM demonstrated that collagen content decreased in all aortic valve leaflet regions in the ApoE−/− mice. Lipid droplets and cholesterol crystals were detected using coherent anti-Stokes Raman scattering in the tissue from the ApoE−/− mice. Here, we demonstrated that OCT and MPM, which are fast and precise contactless imaging approaches, are suitable for defining early morphological and structural alterations of sclerotic murine aortic valves.