Applications of fluorescence-assisted infrared microspectroscopy to the study of osteoporosis

Novel Use of Fluorescence Illumination with an Infrared Microscope

It has become increasingly obvious that infrared microspectroscopy can be the analysis tool of choice when determining the chemical composition of biological and biomedical samples. Frequently, fluorescence illumination is required for sample characterization, which previously required the use of a separate optical microscope. There has also been a need in the semiconductor manufacturing industry for a single tool for visualizing particle contaminants on integrated wafers as well as the ability to chemically determine their nature. There is now a single microscope platform for conducting rapid Nomarski differential interference contrast and fluorescence illumination sample visualization as well as infrared analysis. This novel infrared microscope has applicability to many fields of investigation, including pharmacology, forensics, cell biology, histology, gemology, and geology.

Dynamic photophysical processes in laser-irradiated human cortical skull bone measured by means of modulated diffuse luminescence

The technique of modulated luminescence of bones was developed experimentally and theoretically and was subsequently used to interpret measurements performed on the cortical layer of human skull bones. The photophysical theory is based on the optical excitation and decay rate equations of the fluorescent endogenous chromophore and on the molecular interaction parameter with the photon field density in the matrix of the bone. An effective mean relaxation lifetime, tau(M), of skull cortical bone was derived theoretically and was found to depend on the endogenous chromophore decay lifetime, tau(2), in the upper energy state, on the generated luminescence field density through its dependence on the incident photon field density and on the thickness of the bone. A linear dependence of tau(M) on laser beam intensity, I0, was found and sensitivity of the value of tau(M) to bone thickness, L, was observed for L < or = 6.2 mm. Both experimental dependencies of tau(M) on I0 and L were in excellent agreement with the theoretical model. The unusually long relaxation luminescence lifetime was accounted for theoretically by means of an excited-state manifold invoking intersystem crossing to a forbidden state followed by decay to the ground state of the chromophore. Best fits to the data were able to yield measurements of the following chromophore and photon field parameters: tau(2)=19.7 ms , optical scattering coefficient mu(s)(659 nm)=44,340 m(-1), optical absorption coefficient mu(a)(659 nm)=13 m(-1), and coupling coefficient B(21)= 1.6 x 10(4) m(3) J(-1) s(-1), the decay coupling coefficient of the endogenous chromophore participating in the optical interaction in the form of stimulated luminescence emission mediated by the luminescence photon field between the long-lived excited state E2 and the lower (ground) state E1. The method of modulated luminescence can be used to measure photophysical properties of the chromophore in cortical skull bones, being a sensitive marker of bone diseases, namely, osteoporosis and cancer.

Chemical makeup of microdamaged bone differs from undamaged bone

Microdamage naturally occurs in bone tissue as a result of cyclic loading placed on the body from normal daily activities. While it is usually repaired through the bone turnover process, accumulation of microdamage may result in reduced bone quality and increased fracture risk. It is unclear whether certain areas of bone are more susceptible to microdamage than others due to compositional differences. This study examines whether areas of microdamaged bone are chemically different than undamaged areas of bone. Bone samples (L3 vertebrae) were harvested from 15 dogs. Samples were stained with basic fuchsin, embedded in poly-methylmethacrylate, and cut into 5-microm-thick sections. Fuchsin staining was used to identify regions of microdamage, and synchrotron infrared microspectroscopic imaging was used to determine the local bone composition. Results showed that microdamaged areas of bone were chemically different than the surrounding undamaged areas. Specifically, the mineral stoichiometry was altered in microdamaged bone, where the carbonate/protein ratio and carbonate/phosphate ratio were significantly lower in areas of microdamage, and the acid phosphate content was higher. No differences were observed in tissue mineralization (phosphate/protein ratio) or crystallinity between the microdamaged and undamaged bone, indicating that the microdamaged regions of bone were not over-mineralized. The collagen cross-linking structure was also significantly different in microdamaged areas of bone, consistent with ruptured cross-links and reduced fracture resistance. All differences in composition had well-defined boundaries in the microcrack region, strongly suggesting that they occurred after microcrack formation. Even so, because microdamage results in an altered bone composition, an accumulation of microdamage might result in a long-term reduction in bone quality.