Structural Analysis by Enhanced Raman Scattering

Area of Science:

• Surface science
• Nanotechnology
• Spectroscopy
• Computational chemistry

Background:

• Gold nanostructures concentrate light, enabling molecular-level surface visualization.
• Surface-enhanced Raman scattering (SERS) provides molecular orientation and position data but is challenging to interpret quantitatively.
• Understanding interfacial molecular structure is crucial in fields like materials science and biochemistry.

Purpose of the Study:

• To develop a ratiometric analysis method for quantitative interpretation of SERS data.
• To determine the precise interfacial structure of molecules on gold nanostructures.
• To apply the method to surfactant layers and phospholipid bilayers.

Main Methods:

• Combined surface-enhanced Raman scattering (SERS) and unenhanced Raman spectroscopy.
• Integrated theoretical calculations of optical fields and molecular polarizability.
• Applied a ratiometric analysis approach to experimental spectral data.

Main Results:

• Determined surfactant alkane chain tilt angle (25°) on gold nanorods, consistent with layer thickness.
• Mapped lipid double bond orientation (normal to bilayer) and position (13 Å from nitrogen) in phospholipid bilayers.
• Characterized tryptophan orientation (indole ring 43° from bilayer normal) near glycerol headgroups.

Conclusions:

• The developed ratiometric analysis method enables quantitative determination of interfacial molecular structure.
• This technique provides precise structural information under ambient conditions using minimal material and no labels.
• The method is applicable to various interfacial systems, including surfactants and biological membranes.