Optical properties of living organisms

Zhou, Yuming (1999). Optical properties of living organisms. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000ff6a


Part One: Biophoton Emission in Synchronously Developing Populations of Early Developing Drosophila Embryos

Intense and often prolonged biophoton bursts are emitted from synchronously developing Drosophila embryos minutes to hours after a brief light exposure. Statistical analysis revealed strong correlations among some of the parameters, suggesting that there are physiological constraints on total light output and coherent correlations among the embryos.

Two models are presented to account for the phenomenon. The first model follows Strogatz and Mirillo (1988), in which synchronisation is achieved in a system of N locally interacting oscillators. Each embryo is modelled as a non-linear oscillator with a collective phase. Synchronous photon emission patterns similar to that observed in the experiment were found in the simulation once the coupling intensity K is increased over a threshold. In a system of 200 oscillators in a two-dimensional lattice, typically, about 10% to 15% oscillators is involved in a burst of photon emission.

Biophoton emission is formally reminiscent of the phenomena of superradiance and superfluorescence in physical systems. In a second model system based on a freelaser hamiltonian, each embryo is described with three collective operators summed over all the atoms involved in the biophoton process within the embryo. A simple number-phase-angle (NPA) description of time averages can be used to simplify the mathematical treatment in the limit of small population inversion (Bonifacio, et al, 1984). This model gives a better description of the experiment data.

Part Two: Optical Properties of Liquid Crystalline of Collagenous Tissues

This part of the thesis involves research on collagenous tissues, pig skin and rat tail tendon, by using polarized microscopy and X-ray diffraction.

It has long been widely noted that biological molecules such as lipids and proteins possess properties of liquid crystals at physiological temperatures. Supermolecular assemblies of collagenous tissues follow liquid crystalline mesophase geometries, so that molecular orientational order can be analysed by liquid crystal theory. In this way, the observed optical properties of collagenous tissues can be linked to their molecular structures.

The intensity of the light transmitted through birefringent collagenous tissues viewed between crossed polars is determined by intrinsic molecular orientational order as well as the degree of coherent alignment of supermolecular assembles. The light intensity is a linear function of relative sample retardations R, where R is small (Ross S., et al, 1997). It is proven that both intrinsic and form birefringences are linear functions of the molecular orientational order parameter S in the case of small sample retardation.

The order parameter is of different magnitudes at different scales because of hierarchical structures of collagenous tissues. It has been observed in the retardation measurement of a pork skin sample that retardation is large whereas angle distribution of collagen fibrils is wide under a higher magnification as molecular alignment is more ordered in a small area. A two-scale fibril network model is proposed to interpret the experiment results.

Water and hydrogen bonding are crucial in maintaining the structures and functions of biological materials. Water is capable of forming three dimensional hydrogen bonded network both in bulk state and in biological system (Pimental, 1960). Changing this hydrogen bonding networks of protein-solution complex will greatly affect the biological structure and function.

It is observed that sample retardation of a fixed tendon section are different immersed at solutions with the same refractive index but with different hydrogen bonding abilities. This cannot be accounted for by the conventional theory of form birefringence. It is suggested that collagen conformation is solvent dependent, so that the different conformations lead to different retardations of the collagen-solvent complex.

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