Conference papers

Collagen Matrices as an Improved Model for In Vitro Study of Live Cells Using Raman Microspectroscopy

Franck Bonnier et al. — Wed, 16 Nov 2011 04:36:30 PST

Due to its high lateral resolution, Raman microspectrsocopy is rapidly becoming an accepted technique for the subcellular imaging of single cells. Although the potential of the technique has frequently been demonstrated, many improvements have still to be realised to enhance the relevancy of the data collected. Although often employed, chemical fixation of cells can cause modifications to the molecular composition and therefore influence the observations made. However, the weak contribution of water to Raman spectra offers the potential to study live cells cultured in vitro using an immersion lens, giving the possibility to record highly specific spectra from cells in their original state. Unfortunately, in common 2-D culture models, the contribution of the substrates to the spectra recorded requires significant data pre-processing causing difficulties in developing automated methods for the correction of the spectra. Moreover, the 2-D in vitro cell model is not ideal and dissimilarities between different optical substrates within in vitro cell cultures results in morphological and functional changes to the cells. The interaction between the cells and their microenvironment is crucial to their behavior but also their response to different external agents such as radiation or anticancer drugs. In order to create an experimental model closer to the real conditions encountered by the cell in vivo, 3-D collagen gels have been evaluated as a substrate for the spectroscopic study of live cells. It is demonstrated that neither the medium used for cell culture nor the collagen gels themselves contribute to the spectra collected. Thus the background contributions are reduced to that of the water. Spectral measurements can be made in full cell culture medium, allowing prolonged measurement times. Optimizations made in the use of collagen gels for live cells analysis by Raman spectroscopy are encouraging and studying live cells within a collagenous microenvironment seems perfectly accessible.

Linear Electronic and Optical Processes in Fullerene Thin Films

Jonathan Moghal et al. — Mon, 27 Apr 2009 08:23:52 PDT

The electrical properties of C60 have been extensively studied in both the solid and solution phases. The vibrational spectroscopy of C60 is predominantly molecular in character. However electronic spectroscopy reveals features, which are specific to the solid. These features have been attributed to intermolecular charge transfer states. The relative importance of these inter – and intramolecular processes in terms of their contribution to the electronic transport is discussed. Cyclic voltammetry is employed to generate charged molecular species, which also contribute to the conduction process and comparisons to optical excited states species are drawn. The cyclic voltammetry was monitored in situ with vibrational spectroscopy so as to observe any shifts in the C60 spectrum due to charging. The current voltage characteristics of thin film sandwich structures fabricated by vacuum are then presented and discussed. A strongly non-linear behaviour is observed, a sharp increase in the device conductance being observed at relatively low voltages at both room temperature and at 20K. The room temperature IV curves confirm a lattice collapse upon charging. The high conductivity state is however observed to be stable at low temperature.

Vibrational Coupling in Conjugated π Systems with a view to Optimization of Fluorescence Yield through Phonon Confinement

Luke O'Neill et al. — Wed, 15 Apr 2009 07:33:53 PDT

A series of π conjugated systems were studied by absorption, photoluminescence and vibrational spectroscopy. As is common for these systems, a linear relationship between the positioning of the absorption and photoluminescence maxima plotted against inverse conjugation length is observed. The relationships are in good agreement with the simple particle in a box method, one of the earliest descriptions of the properties of one-dimensional organic molecules. In addition to the electronic transition energies, it was observed that the Stokes shift also exhibited a well-defined relationship with increasing conjugation length, implying a correlation between the electron-vibrational coupling and chain length. This correlation is further examined using Raman spectroscopy, whereby the integrated Raman scattering is seen to behave superlinearly with chain length. There is a clear indication that the vibrational activity and thus nonradiative decay processes are controllable through molecular structure. The correlations between the Stokes energies and the vibrational structure are also observed in a selection of PPV based polymers and a clear trend of increasing luminescence efficiency with decreasing vibrational activity and Stokes shift is observable. The implications of such structure property relationships in terms of materials design are discussed.

Use of Raman Spectroscopy in the Investigation of Debundling of Single Walled Carbon Nanotubes

Elizabeth Gregan et al. — Wed, 15 Apr 2009 07:33:51 PDT

Samples of raw nanotubes are compared to those deposited from solutions to examine separation of nanotube bundles. Single wall nanotubes bundles produced by the arc-discharge and HiPco methods were solubilised in toluene, DMF and 1,2 dichloroethane. Resonant Raman spectroscopy was used to determine if debundling of the tubes sample occurred. The results showed some degree of debundling, best for the 1,2 dichloroethane solvent, which also shows long term solubility.

The Potential of Vibrational Spectroscopy in the Early Detection of Cervical Cancer: an Exciting Emerging Field

Eoghan O Faolain et al. — Wed, 15 Apr 2009 07:33:49 PDT

The application of vibrational spectroscopy to disease diagnosis is a relatively new, rapidly evolving scientific field. Techniques such as Raman and infrared spectroscopy have shown great promise in this regard over the past number of years. This study directly compared Raman spectroscopy and synchrotron infrared (SR-IR) spectroscopy on parallel cervical cancer samples. Both frozen and dewaxed formalin fixed paraffin preserved tissue sections were examined. Both tissue types produced good quality Raman and SR-IR spectra, although the lesser processed, frozen tissue sections displayed the most detailed spectra. Spectroscopy was shown capable of discriminating between different cell types in normal cervical tissue. Spectra recorded from invasive carcinoma showed a marked difference from those recorded from normal cervical epithelial cells. Spectral differences identified with the onset of carcinogenesis include increased nucleic acid contributions and decreased glycogen levels. These investigations pave the way for an enlarged study into this exciting new diagnostic field.

Electroabsorption Studies of Structurally Modified Fullerene Thin Films

Gerald Farrell et al. — Wed, 15 Apr 2009 07:33:48 PDT

Ultraviolet (UV/Vis) and Electroabsorption (EA) spectroscopy is used to examine and differentiate between intermolecular and intra molecular excited state species in fullerene films. Charge Transfer (CT) states are identified at 2.4 eV and 2.7 eV and dipole moments are calculated. Thermal annealing of C60 films is monitored in situ using absorption spectroscopy and electroabsorption spectroscopy. Recorded spectra display both some temperature dependent and partially irreversible effects, indicating the occurrence of an annealing process. EA shows that the CT states associated with the transferring an electron from the HOMO of one molecule located at the (0,0,0) position to the LUMO of its nearest neighbour in the (½,½,0) have been modified as a result of the annealing process. Confirmation of this structural change due to the annealing process is provided by previously reported X-Ray crystallographic work.

Interaction of Single Walled Carbon Nanotubes with Starch-based Systems

Alan Casey et al. — Wed, 15 Apr 2009 05:53:45 PDT

The interaction of carbon nanotubes with soft organic molecules such as cyclodextrins and other saccharides has recently been shown to produce water-soluble composites. Such systems offer considerable advantages over polymer based composites due to their biocompatibility and noncovalent coupling which can potentially preserve the unique properties of the tubes. The mechanism of interaction of such systems has been proposed to be dominated by hydrophobic and hydrophilic interactions along the surface of the tube. In this study a number of composite systems have been formed with HiPco carbon nanotubes using starch and starch based polymers. The first composite formed with starch was characterised using a range of spectroscopic, imaging and thermal techniques which showed clear evidence of an intermolecular interaction. The second and third composite systems formed utilised biodegradable starch based polymers namely starch cellulose acetate (SCA) and starch polycrapolactone (SPCL). The characterisation of these systems will be presented. Finally the potential for enzyme immobilisation into the composite matrix was investigated.

Correlation of Spectroscopic and Biochemical Assays Postionising Radiation Exposure in Human Skin Cell Analogues

Aidan Meade et al. — Wed, 15 Apr 2009 05:53:42 PDT

Raman spectroscopy, as an evaluation of the products of ionising radiation exposure in biological systems, has been utilised mainly in the evaluation of the impact of exposure in tissue, cellular constituents and live animals. It has also been recently demonstrated that Raman spectroscopy can demonstrate key spectroscopic changes in the live cell associated with significant apoptotic and necrotic chemical damage. The present preliminary work utilises Raman spectroscopy at 514.5 nm to evaluate the results of exposure to -rays in HaCaT cells from a Co-60 therapy source, in tandem with other biological assays. The results demonstrate that a number of spectral changes may be correlated with changes in the cell also identified in parallel biochemical assays.