Ultraviolet Pulsed Laser-Induced Fluorescence Nonlinearity in Optically Thick Organic Samples.

A simple two-component model is worked out to investigate pulsed laser-induced fluorescence in complex organic samples, like biological tissues, optically thick at the excitation wavelength. Expression for emitted fluorescence signal is obtained. Saturation process is shown to be determined not only by fluorophores excited by the laser, but non-fluorescent chromophores with overlapping absorption band as well. For homogeneous samples the forms of saturation curves are determined by fluorophore's features. Experimental saturation curves of bulk paper and mice tissues ultraviolet pulsed laser-induced fluorescence are discussed considering this model. For the ns and shorter laser pulse durations with wavelength in 200-300 nm region, pulse energy density should be less than 200 µJ/cm2 for correct quantitative comparison of fluorescence spectra of biological tissues with primarily tryptophan fluorescence.

Laser-induced fluorescence and X-ray spectral analysis of carious process in hard dental tissues.

Morphological and spectral X-ray analysis of carious and noncarious extracted teeth showed the patterns of dentin ossification in caries of different degree. Parietal ectopic ossification of the canal and cavity lumens in stages III and IV dental caries is regarded as a specific structural marker of pathological regeneration. The X-ray spectral analysis showed that the progress of carious process is paralleled by loss of mineral components. Laser-induced fluorescent study of tissues in extracted teeth showed 4 spectral bands corresponding to mineral and protein components of the tooth. The progress of carious process was associated with reduction of the fluorescence intensities of the spectral bands characteristic of dental collagen and mineral components.

Morphological evaluation of cytoarchitectonics of aortic graft at the biotechnological stage with analysis of changes in laser-induced fluorescence spectra.

We performed a fluorescent microscopic examination of human and animal aortic grafts at different stages of decellularization. Treatment of aortic grafts with trypsin/EDTA solution for 48 h leads to their complete decellularization and preserved the connective tissue fiber backbone, which gains a netlike structure. The use of this protocol of decellularization leads to disappearance of subintimal calcium deposits in human aortic grafts. Differences in laser-induced fluorescence spectra of aortas before decellularization and at different stages of this process were revealed. Our findings suggest that the use of fluorescence induced by excimer lasers is promising for identification of the composition of biological tissues, analysis of their state, and the presence of changes.

Influence of mineral components on laser-induced fluorescence spectra of calcified human heart-valve tissues.

Laser-induced fluorescence (LIF) spectra of calcified human heart-valve tissue and LIF spectra of macroscopic calcinosis fragments dissected from human heart valves were compared with LIF spectra of pig myocardium tissues. Excitation was provided by an excimer laser with wavelength lambda = 248 nm. Fluorescence bands that were due to mineral and organic tissue components were identified by measurement of LIF spectra of macroscopic fragments of calcified tissues that had been heat treated at 700 degrees C. The studies showed that LIF spectra of calcified tissues include fluorescence emission from tryptophan, collagen, elastin, and a mineral component of tissue, hydroxylapatite. The observed differences in LIF spectra of normal and calcified tissues with different pathologies may result not only from calcification-induced changes in relative collagen and elastin concentrations but also from additional (absent in normal heart tissue) fluorescence of hydroxylapatite. The calcification-induced changes in the LIF spectra of human heart-valve tissues, characterized by a 330/450 nm ratio, were found to be quite appreciable, which suggests that this ratio can be used with LIF measurements to evaluate the degree of heart-tissue calcification.