Detection of gastrointestinal cancer by elastic scattering and absorption spectroscopies with the Los Alamos Optical Biopsy System

The Los Alamos National Laboratory has continued the development of the Optical Biopsy System (OBS) for noninvasive, real-time in situ diagnosis of tissue pathologies. In proceedings of earlier SPIE conferences we reported on clinical measurements in the bladder, and we report here on recent results of clinical tests in the gastrointestinal tract. With the OBS, tissue pathologies are detected/diagnosed using spectral measurements of the elastic optical transport properties (scattering and absorption) of the tissue over a wide range of wavelengths. The use of elastic scattering as the key to optical tissue diagnostics in the OBS is based on the fact that many tissue pathologies, including a majority of cancer forms, exhibit significant architectural changes at the cellular and sub-cellular level. Since the cellular components that cause elastic scattering have dimensions typically on the order of visible to near-IR wavelengths, the elastic (Mie) scattering properties will be wavelength dependent. Thus, morphology and size changes can be expected to cause significant changes m an optical signature that is derived from the wavelength-dependence of elastic scattering. Additionally, the optical geometry of the OBS beneficially enhances its sensitivity for measuring absorption bands. The OBS employs a small fiber-optic probe that is amenable to use with any endoscope or catheter, or to direct surface examination, as well as interstitial needle insertion. Data acquistion/display time is <1 second

Near-field photothermal microspectroscopy for adult stem-cell identification and characterization.

The identification of stem cells in adult tissue is a challenging problem in biomedicine. Currently, stem cells are identified by individual epitopes, which are generally tissue-specific. The discovery of a stem cell marker common to other adult tissue types could open avenues in the development of therapeutic stem cell strategies. We report the use of the novel technique of Fourier transform infrared near-field photothermal micro-spectroscopy (FTIR-PTMS) for the characterization of stem cells, transit amplifying (TA) cells and terminally differentiated (TD) cells in the corneal epithelium. Principal component analysis (PCA) data demonstrates excellent discrimination of cell type by spectra. PCA in combination with linear discriminant analysis (PCA-LDA) shows that FTIR-PTMS very effectively discriminates between the three cell populations. Statistically significant differences above the 99% confidence level between infrared (IR) spectra from stem cells and TA cells suggest that nucleic acid conformational changes are an important component of the differences between spectral data from the two cell types. FTIR-PTMS is a new addition to existing spectroscopy methods based on the concept of interfacing a conventional FTIR spectrometer with an atomic force microscope equipped with a near-field thermal sensing probe. FTIR spectroscopy currently has a spatial resolution which is similar to that of diffraction-limited optical detection FTIR spectroscopy techniques, but as a near-field technique has considerable potential for further improvement. Our work also suggests that FTIR-PTMS is potentially more sensitive than synchrotron radiation FTIR spectroscopy for some applications. Micro-spectroscopy techniques like FTIR-PTMS provide information about the entire molecular composition of cells, in contrast to epitope recognition which only considers the presence or absence of individual molecules. Our results with FTIR-PTMS on corneal stem cells are promising for the potential development of an IR spectral fingerprint for stem cells

Conformational substates and motions in myoglobin. External influences on structure and dynamics

Myoglobin, a simppe dioxygen-storage protein, is a good laboratory for the investigation of the connection between protein structure, dynamics, and function. Fourier-transform infrared spectroscopy on carbon-monoxymyoglobin (MbCO) shows three major CO bands. These bands are excellent probes for the investigation of the structure-function relationship. They have different CO binding kinetics and their CO dipoles form different angles with respect to the heme normal, implying that MbCO exists in three major conformational substates, A0, A1, and A3. The entropies and enthalpies of these substates depend on temperature above approximately 180 K and are influenced by pH, solvent, and pressure. These results suggest that even a protein as simple as Mb can assume a small number of clearly different structures that perform the same function, but with different rates. Moreover, protein structure and dynamics depend strongly on the interaction of the protein with its environment