Murat Canpolat

Light scattering from cells: the contribution of the nucleus and the effects of proliferative status.

As part of our ongoing efforts to understand the fundamental nature of light scattering from cells and tissues, we present data on elastic light scattering from isolated mammalian tumor cells and nuclei. The contribution of scattering from internal structures and in particular from the nuclei was compared to scattering from whole cells. Roughly 55% of the elastic light scattering at high-angles (> 40 degrees) comes from intracellular structures. An upper limit of 40% on the fractional contribution of nuclei to scattering from cells in tissue was determined. Using cell suspensions isolated from monolayer cultures at different stages of growth, we have also found that scattering at angles greater than about 110 degrees was correlated with the DNA content of the cells. Based on model calculations and the relative size difference of nuclei from cells in different stages of growth, we argue that this difference in scattering results from changes in the internal structures of the nucleus. This interpretation is consistent with our estimate of 0.2 micron as the mean size of the scattering centers in cells. Additionally, we find that while scattering from the nucleus accounts for a majority of internal scattering, a significant portion must result from scattering off of cytoplasmic structures such as mitochondria.

Particle size analysis of turbid media with a single optical fiber in contact with the medium to deliver and detect white light

Wavelength-dependent elastic-scattering spectra of highly scattering media measured with only a single fiber for both light delivery and collection are presented. White light is used as a source, and oscillations of the detected light intensities are seen as a function of wavelength. The maximum and minimum of the oscillations can be used to determine scatterer size for monodisperse distributions of spheres when the refractive indices are known. In addition, several properties of the probe relevant to tissue diagnosis are examined and discussed including the effects of absorption, a broad distribution of scatterers, and the depth probed.

The puzzling behavior of water at very low temperature

Although H2O has been the topic of considerable research since the beginning of the century, most of its anomalous physical properties are still not well understood. First we discuss some of the anomalies of this ‘‘complex fluid. ’’ Then we describe a qualitative interpretation in terms of percolation concepts. Finally, we discuss recent experiments and simulations relating to the liquid–liquid phase transition hypothesis that, in addition to the known critical point in water, there may exist a ‘‘second ’’ critical point at low temperatures. In particular, we discuss very recent measurements at Tsukuba of the compression-induced melting and decompression-induced melting lines of high-pressure forms of ice. We show how knowledge of these lines enables one to obtain an approximation for the Gibbs potential G(P,T) and the equation of state V(P,T) for water, both of which are consistent with the possible continuity of liquid water and the amorphous forms of solid water.

Healing and interdiffusion processes at particle-particle junction during film formation from high-T latex particles

Abstract When amorphous polymers of same type are brought into contact at temperatures above the glass transition, the interface gradually heals and junction boundaries eventually disappear. Here we used a steady-state fluorescence technique to examine the healing and interdiffusion of polymer molecules during annealing of latex film above the glass transition. The film was prepared from a mixture of naphthalene-(donor) and pyrene-(acceptor) labelled poly(methyl methacrylate) latex particles. We report that during the annealing processes the transparency of the film changed considerably. Healing temperature (TH) and time (τH) were measured when the latex film became almost transparent. Above TH interdiffusion of polymer chains was observed by detecting the energy transfer from excited naphthalene to pyrene molecules. Healing and diffusion activation energies were calculated and found to be 9.84 kcal mol−1 and 30 kcal mol−1, respectively, for the annealed latex film samples.

Photon diffusion study in films formed from high-T latex particles

Abstract The steady-state fluorescence technique was used to study the evolution of transparency during film formation from high-T latex particles. The latex films were prepared from pyrene-labelled poly(methyl methacrylate) particles and annealed in 10 min time intervals above the glass transition temperature (Tg). Scanning electron microscopy was used to detect the variation in physical structure of annealed films. Monte Carlo simulations were performed for photons diffusing the latex films and the number of emitted and scattered photons was calculated. The crossing density of polymer chains at the particle-particle interface was found to depend linearly on ( time ) 1 2 . The activation energy for back-and-forth motion of a reptating polymer chain was measured and found to be 29 kcal mol−1. The corresponding frequencies of a reptating chain were between 1.5 and 42 s−1 above Tg.

Healing and photon diffusion during sintering of high-T latex particles

A steady-state fluorescence technique was used to examine the annealing of films formed from high- T latex particles above the glass transition temperature. The films were prepared by sintering pyrene-labeled poly(methyl methacrylate) latex particles. During the annealing processes, the transparency of the film changed considerably. Direct fluorescence emission from excited pyrene was monitored as a function of annealing temperature to detect these changes. Scanning electron microscopy in conjunction with Monte Carlo simulations of photon diffusion in latex film were used to interpret the fluorescence results. Healing temperature and time were measured at the point where the fluorescence emission intensity becomes maximum. This was associated with the longest optical path of a photon in latex film during healing of particle-particle boundaries. Healing activation energy was measured and found to be 10 kcal/mol.

Direct fluorescence technique to study evolution in transparency and crossing density at polymer–polymer interface during film formation from high‐T latex particles

The Direct Fluorescence method was used to study the healing process during latex film formation above the glass transition temperature. The latex film was prepared from pyrene (P)-labeled poly(methyl methacrylate) (PMMA) particles. Heptane was used as a mixing agent. The steady-state fluorescence technique was employed to measure the density of polymer chains crossing the particle particle interface. Various latex films with different latex content were used to study the transparency below and above the healing temperature. Crossing density was found to depend linearly on (time) 1/2 , which was proposed by Prager and Tirrell.

Monitoring photosensitizer concentration by use of a fiber-optic probe with a small source–detector separation

We present a noninvasive method to track the concentration of photodynamic therapy drugs in real time. The method is based on measurements of backscattered and fluorescent light with a steady-state fluorescence spectrometer. The ratio of the fluorescent light to the scattered light is found to be linearly proportional to the absorption coefficient of the photosensitizer. The fiber-optic probe used for the measurements has a small source-detector separation; therefore the measurements could be performed through the working channel of an endoscope.

The puzzling statistical physics of liquid water

Although H2O has been the topic of considerable research since the beginning of the century, the peculiar physical properties are still not well understood. We discuss recent experiments and simulations relating to the hypothesis that, in addition to the known critical point in water, there exists a “second” critical point at low temperatures. In particular, we discuss very recent measurements of the compression-induced melting and decompression-induced melting lines of high-pressure forms of ice. We show how knowledge of these lines enables one to obtain an approximation for the Gibbs potential G(P,T) and the equation of state V(P,T) for water, both of which are consistent with the possible continuity of liquid water and the amorphous forms of solid water. We also comment on some of the evidence that is equally consistent with other scenarios for the behavior of liquid water.

Intra-operative brain tumor detection using elastic light single-scattering spectroscopy: a feasibility study

We have investigated the potential application of elastic light single-scattering spectroscopy (ELSSS) as an adjunctive tool for intraoperative rapid detection of brain tumors and demarcation of the tumor from the surrounding normal tissue. Measurements were performed on 29 excised tumor specimens from 29 patients. There were 21 instances of low-grade tumors and eight instances of high-grade tumors. Normal gray matter and white matter brain tissue specimens of four epilepsy patients were used as a control group. One low-grade and one high-grade tumor were misclassified as normal brain tissue. Of the low- and high-grade tumors, 20 out of 21 and 7 out of 8 were correctly classified by the ELSSS system, respectively. One normal white matter tissue margin was detected in a high-grade tumor, and three normal tissue margins were detected in three low-grade tumors using spectroscopic data analysis and confirmed by histopathology. The spectral slopes were shown to be positive for normal white matter brain tissue and negative for normal gray matter and tumor tissues. Our results indicate that signs of spectral slopes may enable the discrimination of brain tumors from surrounding normal white matter brain tissue with a sensitivity of 93% and specificity of 100%.