Salt-free in-solution surface-enhanced Raman spectroscopy substrates based on gold nanoparticle-decorated silica...

Area of Science:

• Nanotechnology
• Materials Science
• Analytical Chemistry

Background:

• Noble metal colloids (gold, silver) are crucial substrates for Surface-Enhanced Raman Spectroscopy (SERS).
• Narrowing interparticle distance enhances SERS signal magnitude, particularly in in-solution applications.
• Conventional salt-induced aggregation for distance reduction causes substrate instability and poor signal reproducibility.

Purpose of the Study:

• To develop stable and reproducible in-solution SERS substrates using gold nanoparticles on silica spheres.
• To avoid salt-induced aggregation issues in SERS analysis.
• To investigate the effect of nanoparticle shape (nanospheres vs. nanostars) on SERS performance.

Main Methods:

• Preparation of 100 nm silica spheres (SiO2) as water-dispersible substrates.
• Coating silica spheres with gold nanospheres (AuNPs) and gold nanostars (AuNSs).
• Utilizing 3-aminopropyltrimethoxysilane (APTMS) as a crosslinker to control gold-to-gold distance.
• Optimization of gold nanoparticle to SiO2 number ratios (NRs) using mercaptobenzonitrile (MBN) as a probe molecule.

Main Results:

• Successfully prepared stable gold nanoparticle-coated silica sphere SERS substrates.
• Achieved significant SERS signal enhancement compared to dispersed gold nanoparticles.
• Observed enhancement factors of 2.7 for AuNP-SiO2 and 6.0 for AuNS-SiO2.
• Demonstrated superior performance of non-spherical gold nanostars on silica for SERS.

Conclusions:

• Gold nanoparticle-coated silica spheres offer a stable and effective platform for in-solution SERS.
• This approach overcomes the limitations of salt-induced aggregation, improving reproducibility.
• Non-spherical nanoparticles, like gold nanostars, provide greater SERS signal enhancement on silica substrates.