A disposable paper-based hydrophobic substrate for highly sensitive surface-enhanced Raman scattering detection

Detection of target analytes with high sensitivity and reproducibility remains a challenge for surface-enhanced Raman scattering (SERS) due to the lack of cost-effective and highly sensitive substrates. In this study, a hydrophobic SERS substrate capable of concentrating nanoparticles and analytes was prepared by spin-coating lubricating liquid onto commercial paper. The condensation effect of the paper-based hydrophobic substrate induced aggregation of gold nanoparticles (Au NPs) to generate ''hot spots'' for SERS and to drive analytes to the hot-spot areas for more sensitive detection. The obtained SERS signal intensity was 5-fold higher than that obtained using common paper, and a detection limit (LOD) of 4.3 × 10^-10 M for rhodamine 6G (R6G) was achieved. Randomly selected points on the substrate and different batches of substrates all exhibited high reproducibility, and the relative standard deviation (RSD) at 1362 cm^-1 is approximately 11%. A further application of the hydrophobic substrate was demonstrated by the detection of cytochrome C within a linear detection range of 3.90 × 10^-8 M-1.25 × 10^-6 M. In addition, the prepared substrate can obtain identifiable SERS spectra of cancer cells and non-cancer cells because a large number of AuNP or Au NPs clusters can adhere to cells, resulting in the construction of a 3D hotspot matrix. The disposable hydrophobic paper substrate eliminates the problem of solution diffusion, and also provides an effective platform for biomolecular screening detection.

Recyclable three-dimensional Ag nanorod arrays decorated with O-g-C3N4 for highly sensitive SERS sensing of organic pollutants

A three-dimensional (3D) substrate was developed by assembling a monolayer of graphitic carbon nitride (O-g-C₃N₄) on Ag nanorod arrays (Ag NRs) for sensitive and recyclable surface enhanced Raman scattering (SERS) detection. The prepared Ag NRs/O-g-C₃N₄ substrate not only generated a significant Raman enhancement effect as a result of the strong π-π stacking interaction between O-g-C₃N₄ and the analytes but also possessed excellent self-cleaning property via visible-light irradiation that was attributed to its outstanding catalytic performance. Highly sensitive SERS detection could be achieved with a LOD of 8.2 × 10^-10 M for R6 G, and the substrate could be used repeatedly for at least four cycles with tolerable intensity attenuation. In addition, the 3D substrate exhibited long-term stability originating from the electron-donor effect of O-g-C₃N₄ and high reproducibility due to the uniform decoration of O-g-C₃N₄ on the Ag NRs through the strong interaction. Furthermore, using Ag NRs/O-g-C₃N₄, the recyclable detection of antibiotics in a water sample was demonstrated with high sensitivity, which indicates that the 3D Ag NRs/O-g-C₃N₄ substrate is a promising candidate for eliminating the challenges of single-use SERS substrates and building a portable SERS platform to sense organic molecular species.