Femtosecond-laser enabled hybrid manufacturing of scalable and disposable high-performance SERS substrates.

Surface-enhanced Raman spectroscopy (SERS) is a well-known label-free analytical technique for chemical and biological detection. Electromagnetic enhancement near the nanostructured surfaces contributes to the SERS performance. However, the substrate-based nanostructured SERS surfaces are conventionally fabricated using time- and resource-intensive techniques. A cost-effective and scalable process chain to fabricate disposable thermoplastic SERS substrates is investigated herewith. The surface design includes a multiscale topography that consists of single-tier laser-induced periodic surface structures (LIPSSs) encircled by two-tier hierarchical structures (HSs). Different types of LIPSS were investigated, generated by linear and circular polarisation of the laser. The process chain employed to produce high-performance SERS substrates includes, first, ultrashort laser-enabled fabrication of a textured metallic master and then replication of functional topographies on cyclic olefin copolymer (COC) using hot embossing and finally mask-coating the LIPSS 'hot spot' with gold for an electromagnetic enhancement. The HS topographies facilitated the superhydrophobic evaporation of samples to enrich the analytes onto the SERS 'hot spot' on the COC substrates. This multiscale design achieved a detection limit of up to 10-7M for methylene blue and 4-MBA analytes. Highly regular linear LIPSS produced consistent Raman signals with a relative standard deviation (RSD) of 6.7%, ensuring reproducibility. In contrast quasi-regular triangular LIPSS exhibited enhanced signal intensity but with a relatively higher RSD of 10.2%. This scalable and cost-efficient approach has potential for widespread use in food and agricultural sectors, advancing the practical applications of SERS technology.