SERS-Based Sensor Using Subnanometric Copper-Silver Mixed Clusters Ag_(8-Cu (n = 0-8) for Pyridine: A DFT Study

Area of Science:

• Computational Chemistry
• Materials Science
• Spectroscopy

Background:

• Surface-enhanced Raman spectroscopy (SERS) offers high sensitivity and selectivity for molecular analysis.
• Noble metal nanomaterials like silver and gold are common SERS substrates, but copper offers superior enhancement despite oxidation issues.
• Mixed metal nanostructures present a potential strategy to combine the benefits of different metals for improved SERS performance.

Purpose of the Study:

• To investigate the influence of copper-silver (Ag/Cu) mixing ratios on SERS signal enhancement.
• To explore the adsorption behavior of pyridine (Py) on Ag-Cu mixed clusters.
• To provide insights for designing cost-effective SERS analytical sensors.

Main Methods:

• Density Functional Theory (DFT) calculations using the PBE functional and cc-pVDZ-PP basis sets for Ag/Cu and cc-pVDZ for C, N, H.
• Computation of geometrical and electronic structures for Ag-Cu clusters and Py adsorption configurations.
• Calculation and analysis of SERS spectra, including Time-Dependent DFT (TD-DFT) for chemical enhancement mechanisms.

Main Results:

• Copper atoms substituted into silver clusters act as favorable adsorption sites for pyridine.
• SERS enhancement of pyridine's ring stretching peak (1590 cm⁻¹) increased significantly from 20 to 120 au as Cu atoms increased from 0 to 5 in Ag₈₋ₓCuₓ clusters.
• The SERS enhancement saturated beyond five copper atoms and was observed for other ligands like pyrazine and 3H-pyrrole.

Conclusions:

• Ag-Cu mixed clusters demonstrate tunable SERS enhancement properties.
• Optimal SERS performance for pyridine is achieved with a specific Ag/Cu ratio (e.g., Ag₃Cu₅), mitigating copper's oxidation issues.
• These findings support the development of more economical and efficient SERS-based analytical sensors.