Poor reproducibility has long been one of the major limitations for quantitative surface-enhanced Raman scattering (SERS) analysis. Historically, plasmonic nanoparticles (NPs) have been assembled onto a certain solid support to address this limitation. Here, in this work, we report a highly reproducible and self-healing liquid SERS platform based on a three-dimensional liquid freestanding membrane. Briefly, the plasmonic NP suspension is mixed with an analyte and then transferred into the perforated mold to form an FSM, which not only improves signal reproducibility but also enables on-demand analysis. The FSM was characterized in situ with a confocal laser scanning microscope and small-angle X-ray scattering. It was found that even with the most common, wet chemistry-prepared nonuniform silver NPs (Ag NPs), the relative standard deviation (RSD) of a large-area (3.5 mm2) SERS mapping was only 8.80%. The RSDs of the 2500 point-mappings of FSMs formed with Au or Ag NPs of different shapes and sizes were all below 10%. Various samples were quantitatively analyzed with the FSM method and compared with high-performance liquid chromatography/UV–vis. Statistical analysis revealed no significant difference. It is worth mentioning that this general-purpose method with low cost is extremely simple, which may pave the way for universal SERS quantitative analysis on-demand at the point-of-use.

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Copper foam in situ loaded with precious metal nanoparticles as transmission SEIRAS substrate.