In-situ galvanic replacement reaction assisted preparation of porous Cu–Au composites as highly sensitive SERS substrates

Background

Surface-enhanced Raman spectroscopy (SERS) substrates have undergone extensive development over the years, yet the challenge of significantly enhancing their sensitivity persists. Most existing substrates face considerable difficulties in obtaining the strongest electromagnetic coupling to maximize SERS signal intensity, i.e., it is hard to achieve optimal structural parameters such as the gap width and particle size, and to fabricate surfaces that are free from contamination such as surfactants. Therefore, there is a pressing need for a substrate optimization approach that allows for in-situ monitoring and real-time dynamic adjustments to precisely achieve the ideal substrate characteristics for superior performance.

Results

In this study, a highly sensitive porous copper-gold (Cu–Au) SERS substrate was fabricated using the galvanic replacement reaction (GRR), coupled with in-situ SERS monitoring to optimize substrate preparation. The Cu–Au nanoparticles formed and grew on sacrificial templates while noble metal ions were reduced by the sacrificial metal during GRR. The substrate preparation process revealed that the optimal preparation time was 200 ± 20 s. The SERS performance with crystal violet (CV) as a probe molecule demonstrated the substrate's remarkable sensitivity with detecting concentrations as low as 10⁻¹⁶ M, which surpasses most literature reports. The optimized SERS substrate was further tested for detecting malachite green (MG), yielding an ultra-high enhancement factor (EF) of 8.96 × 10¹⁴. The entire optimization process did not involve the addition of aggregation or surfactant agents, ensuring a clean substrate surface.

Significance and novelty

This study is a further proof of the significance of the in-situ optimization of SERS substrates via GRR which allows real-time adjustment of nanoparticle size and gap width to enhance sensitivity. This approach has enabled us to develop substrates with exceptional sensitivity and reproducibility. These significant contributions may open up new avenues for the facile fabrication of ultrasensitive SERS substrates.