Surface enhanced Raman correlation spectroscopy of particles in solution.

Area of Science:

• Analytical Chemistry
• Surface Science
• Spectroscopy

Background:

• Monitoring particle interactions with surfaces is crucial in various scientific fields.
• Label-free and chemically specific methods are needed for real-time analysis.
• Surface-enhanced Raman spectroscopy (SERS) offers high sensitivity for molecular detection.

Purpose of the Study:

• To demonstrate Surface-enhanced Raman correlation spectroscopy (SERCS) as a label-free method for monitoring particle-surface interactions.
• To measure diffusion constants of individual polymer beads and lipid vesicles near a SERS substrate.
• To investigate hindered diffusion and adsorption phenomena at the nanoscale.

Main Methods:

• Utilized a 2-D planar SERS substrate for enhanced signal acquisition.
• Acquired spectral data at high rates (31–83 Hz) using SERCS.
• Applied auto- and cross-correlation analysis to spectral data for diffusion measurements.

Main Results:

• Measured diffusion coefficients of 10(-10)-10(-11) cm(2)/s for particles (50–500 nm radius).
• Observed diffusion approximately 40 times slower than predicted by Stokes-Einstein equation, indicating hindered diffusion.
• Determined that enhanced signals originate from particles within 5 nm of the SERS substrate, suggesting surface adsorption.

Conclusions:

• SERCS is a viable label-free technique for studying particle-surface dynamics in solution.
• Hindered diffusion and adsorption are significant factors for particles near SERS substrates.
• This work highlights the utility and limitations of SERS for monitoring interactions on planar substrates.