Temperature-controlled confocal Raman microscopy to detect phase transitions in phospholipid vesicles.
Optical-trapping confocal Raman microscopy enhances the capabilities of traditional Raman spectroscopy for the analysis of small particles by significantly reducing the sampling volume and minimizing background signal from the particle surroundings. Chemical composition and structural information can be obtained from optically trapped particles in aqueous solution without the need for labeling or extensive sample preparation. In this work, the challenges of measuring temperature dependent changes in suspended particles are addressed with the development of a small-volume, thermally conductive sample cell attached to a temperature-controlled microscope stage. To demonstrate its function, the gel to liquid-crystalline phase transitions of optically trapped lipid vesicles, composed of pure 1,2-ditridecanoyl-sn-glycero-3-phosphocholine (DTPC), 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), were detected by changes in Raman spectra of the lipid bilayer. The Raman scattering data were found to correlate well with differential scanning calorimetry (DSC) results.
Fox
Christopher B
CB
Department of Bioengineering, University of Utah, Salt Lake City, UT 84112-9202, USA.
Myers
Grant A
GA
Harris
Joel M
JM
D004867:Equipment Design; D008051:Lipid Bilayers / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry*; D008560:Membrane Fluidity; D018613:Microscopy, Confocal / Q000295:instrumentation / Q000379:methods*; D044367:Phase Transition; D010743:Phospholipids / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013059:Spectrum Analysis, Raman / Q000295:instrumentation / Q000379:methods*; D014159:Transducers
D008051:Lipid Bilayers; D008081:Liposomes; D010743:Phospholipids