Self-Assembled Gold Nanoparticles as Reusable SERS Substrates for Polyphenolic Compound Detection.

Area of Science:

• Analytical Chemistry
• Materials Science
• Biochemistry

Background:

• Polyphenolic compounds, like chlorogenic acid, are crucial in biological processes and widely used in food, pharmaceutical, and cosmetic industries.
• Accurate detection of chlorogenic acid is essential for quality control of raw materials and final products.
• Raman spectroscopy offers sensitive, versatile qualitative and quantitative analysis, especially for field applications.

Purpose of the Study:

• To develop a facile, inexpensive, and reproducible method for fabricating enhanced substrates for surface-enhanced Raman spectroscopy (SERS).
• To implement SERS for accurate and sensitive detection of chlorogenic acid.
• To establish a reliable benchmarking procedure for SERS substrate validation.

Main Methods:

• Fabrication of SERS substrates using self-assembled gold nanoparticles at liquid-liquid interfaces via an "aqua-print" process.
• Benchmarking of substrates using rhodamine 6G dye to determine enhancement factors.
• Detection of chlorogenic acid using the optimized SERS substrates across a concentration range.
• Raman mapping for signal uniformity assessment and DFT calculations for spectral analysis.

Main Results:

• The optimized SERS substrates, particularly those with 72 nm gold nanoparticles, achieved a high enhancement factor of 4 × 10⁴.
• Accurate detection of chlorogenic acid was demonstrated in the concentration range of 10 μM to 350 μM with high linearity (R² > 99%).
• Uniform signal distribution was confirmed by Raman mapping (standard deviation < 15%), and DFT calculations supported the formation of chlorogenic acid dimers.

Conclusions:

• The proposed "aqua-print" method provides a reproducible and cost-effective route to high-performance SERS substrates.
• The developed SERS approach enables sensitive and accurate in-field detection of chlorogenic acid.
• This work is significant for developing field-deployable methods for polyphenol analysis in raw materials and extracted products.