Vibrational response of hydrogen-bonded interfacial water is dominated by intramolecular coupling.

Using the surface-specific vibrational technique of vibrational sum-frequency generation, we reveal that the double-peaked structure in the vibrational spectrum of hydrogen-bonded interfacial water molecules originates from vibrational coupling between the stretch and bending overtone, rather than from structural effects. This is demonstrated by isotopic dilution experiments, which reveal a smooth transition from two peaks to one peak, as D2O is converted into HDO. Our results show that the water interface is structurally more homogeneous than previously thought.

Chemical specificity in three-dimensional imaging with multiplex coherent anti-Stokes Raman scattering microscopy.

We demonstrate the three-dimensional (3D) imaging capabilities and chemical specificity of multiplex coherent anti-Stokes Raman scattering microscopy. The simultaneous acquisition of a significant part of the vibrational spectrum at each specimen position permits straightforward differentiation among chemical species. 3D imaging is illustrated with a lipid multilamellar vesicle, and lateral and axial resolutions are determined.

Measuring molecular order and orientation using coherent anti-stokes Raman scattering microscopy.

Coherent anti-Stokes Raman scattering microscopy develops rapidly into a powerful technique to image both the chemical composition and physical state in complex samples from biophysics, biology, and the material sciences. This nonlinear vibrational technique increases the signal relative to spontaneous Raman scattering and does not require labeling of the specimen. A theoretical description of the technique is provided and the two major modes of operation: picosecond- and multiplex coherent anti-Stokes Raman scattering are discussed.

Calcium-induced phospholipid ordering depends on surface pressure.

The effect of sodium and calcium ions on zwitterionic and anionic phospholipids monolayers is investigated using vibrational sum-frequency generation in conjunction with surface pressure measurements and fluorescence microscopy. Sodium ions only subtly affect the monolayer structure, while the effect of calcium is large and depends strongly on the surface pressure. At low surface pressures (approximately 5 mN/m), the presence on Ca2+ results in the unexpected appearance of ordered domains.