Abstract
Raman spectroscopy represents a widely used analytical spectroscopic technique providing unique information about the vibrational motion of molecules. In the Raman study of biological molecules and their interaction including biomembrane models, markers or probes that could have undesirable effects are not needed.
The applicability of the conventional Raman spectroscopy to liquid samples is generally limited by a weak Raman scattering cross-section to the highly concentrated samples. This can be overcome by drop coating deposition Raman Spectroscopy (DCDRS) which is based on the drying of a small deposited droplet of liquid sample on the hydrophobic substrate.
Evaporation of solvent from droplet lead to the preconcentration of a studied analyte into dried patterns from which normal Raman spectra can be acquired. The sensitivity of the spectra and the dried patterns are influenced not only by the properties of the solution but also depends on the substrate characteristic such as wettability and roughness that governs the droplet drying dynamics.
We focused our attention on the spherical membrane structures, liposomes, which are often used as real membrane models. Liposome suspensions, dried on smooth and nanostructured hydrophobic substrates with different roughness, were studied by DCDRS.
Evaporation of solvent from droplets of liposome suspension led to the accumulation of solute in the ring-shaped pattern. Used substrates were prepared by a method based on the deposition of arrays of nanoparticles (Cu or Ag) fusing a gas aggregation source and subsequent overcoating these substrates by sputter-deposited thin C:F film.
The nanoroughness and with it connected wettability of produced coatings is controlled by the number of nanoparticles in the base layer including an option of a gradient surface coverage. It was shown that in the case of liposome suspension, the nanoroughness leads to stronger preconcentration as well as to the reduction of the ring diameter, i.e. two parameters crucial for the DCDR measurements.