Surfactant size effect on surface-enhanced Raman scattering intensity from silver nanoparticles

Area of Science:

• Nanotechnology
• Surface Chemistry
• Spectroscopy

Background:

• Surface-enhanced Raman scattering (SERS) is a powerful technique for detecting molecules at low concentrations.
• The efficiency of SERS is highly dependent on the properties of the metal nanoparticles (NPs) used as substrates.
• Surface modifiers, such as surfactants, play a crucial role in NP synthesis and SERS performance.

Purpose of the Study:

• To investigate the influence of adsorbed surfactant size on silver nanoparticles (AgNPs) for SERS applications.
• To correlate surfactant size with the SERS signal intensity and elemental composition of AgNPs.

Main Methods:

• Synthesis of AgNPs stabilized with surfactants of different molecular weights (sodium citrate vs. sodium polyacrylate).
• Immobilization of Raman-active dyes (4-mercaptobenzoic acid and 4-naphthalene thiol) onto AgNP surfaces.
• SERS measurements to quantify signal intensity.
• Elemental analysis (EA) to determine sulfur content.

Main Results:

• AgNPs stabilized with smaller sodium citrate (MW: 258) exhibited a 10-fold higher SERS signal intensity compared to those stabilized with larger sodium polyacrylate (MW: 2100).
• Elemental analysis showed significantly higher sulfur content (0.94 wt%) in citrate-stabilized AgNPs versus polyacrylate-stabilized AgNPs (0.12 wt%).
• Steric hindrance from larger surfactants was identified as a factor affecting ligand exchange and sulfur incorporation.

Conclusions:

• The size of the initial surfactant is a critical parameter influencing SERS signal enhancement in AgNPs.
• Smaller surfactants facilitate better ligand exchange, leading to higher sulfur content and improved SERS performance.
• Consideration of surfactant size is essential for designing effective AgNP substrates for SERS.