Hemoglobin polymerization in sickle cells studied by circular polarized light scattering

Measurement of circular intensity differential scattering (CIDS) from single airborne aerosol particles for bioaerosol detection and identification

The circular intensity differential scattering (CIDS), i.e. the normalized Mueller matrix element -S₁₄/S₁₁, can be used to detect the helical structures of DNA molecules in biological systems, however, no CIDS measurement from single particles has been reported to date. We report an innovative method for measuring CIDS phase functions from single particles individually flowing through a scattering laser beam. CIDS signals were obtained from polystyrene latex (PSL) microspheres with or without coating of DNA molecules, tryptophan particles, and aggregates of B. subtilis spores, at the size of 3 μm in diameter. Preliminary results show that this method is able to measure CIDS phase function in tens of microseconds from single particles, and has the ability to identify particles containing biological molecules.

Polarized light interaction with tissues

This tutorial-review introduces the fundamentals of polarized light interaction with biological tissues and presents some of the recent key polarization optical methods that have made possible the quantitative studies essential for biomedical diagnostics. Tissue structures and the corresponding models showing linear and circular birefringence, dichroism, and chirality are analyzed. As the basis for a quantitative description of the interaction of polarized light with tissues, the theory of polarization transfer in a random medium is used. This theory employs the modified transfer equation for Stokes parameters to predict the polarization properties of single- and multiple-scattered optical fields. The near-order of scatterers in tissues is accounted for to provide an adequate description of tissue polarization properties. Biomedical diagnostic techniques based on polarized light detection, including polarization imaging and spectroscopy, amplitude and intensity light scattering matrix measurements, and polarization-sensitive optical coherence tomography are described. Examples of biomedical applications of these techniques for early diagnostics of cataracts, detection of precancer, and prediction of skin disease are presented. The substantial reduction of light scattering multiplicity at tissue optical clearing that leads to a lesser influence of scattering on the measured intrinsic polarization properties of the tissue and allows for more precise quantification of these properties is demonstrated.

Mueller matrix measurements on absorbing turbid medium

Polarization parameters of diffuse backscattered light from a turbid sample are sensitive to its structural properties and can, therefore, be used to probe morphological features of tissue and, thus, monitor changes that arise due to a disease. Extraction of morphological information from measured polarization parameters, however, requires a careful understanding of the dependence of these on factors such as size, size distribution, shape, and dielectric constant of the scatterers, which are often quite involved. In particular, the presence of absorption complicates the dependence of polarization parameters on tissue morphological features. We have found that, while for medium comprising small size scatterers (Rayleigh scatterers), the depolarization shows the expected decrease with an increase in the absorption of the scattering medium, a counterintuitive behavior was observed for larger size (>lambda) scatterers. Further analysis of the results suggests that the observed behavior might arise due to the relative contribution of two depolarizing processes, one resulting from a series of out-of-plane scattering and the other due to the angular variation of the state of polarization in a single scattering event.

Myocardial revascularization in a sickle-cell trait patient

A 56-year-old man with confirmed sickle-cell trait AS underwent successful triple-vessel myocardial revascularization with internal mammary artery and vein conduits. Variations in routine technique included limitation in hypothermia (32 degrees C), avoidance of intraoperative autologous salvage, hypoxia, severe anemia (< 25% hematocrit), acidosis and postoperative reinfusion of mediastinal drainage.

Carbon monoxide religation kinetics to hemoglobin S polymers following ligand photolysis

The re-equilibration rate of carbon monoxide binding to hemoglobin S polymers is determined by time-resolved measurements of linear dichroism spectra. Linear dichroism is used to detect religation to hemoglobin in the polymer in the presence of rebinding to free hemoglobin S tetramers. Measurement of the linear dichroism resulting from photolysis of the small percentage of ligand bound to the polymer is accomplished through the use of an ultrasensitive, ellipsometric linear dichroism technique developed for this purpose. The major finding is that the return of the polymer phase to its equilibrium ligation state is much slower than that of the solution phase hemoglobin tetramers. Assuming all hemes in the polymer are equally likely to participate in rebinding, the re-equilibration rate for carbon monoxide religation to hemoglobin S polymers is found to be 0.14 +/- 0.07 (s-1 mM-1), about 1000 times slower than the rebinding rate of carbon monoxide to T-state monomer hemoglobin. Several interpretations of this result are discussed. An understanding of the ligand binding kinetics to hemoglobin S polymers could have pathophysiological significance in its relevance to polymer formation and melting during red blood cell circulation.