Micro-macro SERS strategy for highly sensitive paper cartridge with trace-level molecular detection.

Surface-enhanced Raman Scattering (SERS) has become a powerful spectroscopic technology for highly sensitive detection. However, SERS is still limited in the lab because it either requires complicated preparation or is limited to specific compounds, causing poor applicability for practical applications. Herein, a micro-macro SERS strategy, synergizing polymer-assisted printed process with paper-tip enrichment process, is proposed to fabricate highly sensitive paper cartridges for sensitive practical applications. The polymer-assisted printed process finely aggregates nanoparticles with a discrete degree of 1.77, and SERS results are matched with theoretical enhancement, indicating small cluster-dominated hotspots at the micro-scale and thus 41-fold SERS increase compared to other aggregation methods. The paper-tip enrichment process moves molecules in a fluid into small tips filled with plasmonic clusters, and molecular localization at hotspots is achieved by the simulation and optimization of fluidic velocity at the macro-scale, generating a 39.5-fold SERS sensibility increase in comparison with other flow methods. A highly sensitive paper cartridge contains a paper-tip and a 3D-printed cartridge, which is simple, easy-to-operate, and costs around 2 US dollars. With a detection limit of 10  M for probe molecules, the application of real samples and multiple analytes achieves single-molecule level sensitivity and reliable repeatability with a 30-min standardized procedure. The micro-macro SERS strategy demonstrates its potential in practical applications that require point-of-care detection.