Plasmonic Porous Multicore@shell Silver@zeolitic Imidazolate Framework-8 Nanoparticles as Synergistically Enhanced Surface-Enhanced Raman Scattering Platforms for Nanomolar-Trace Detection of Diverse Analytes

Surface-enhanced Raman scattering (SERS) is among the most sensitive molecular detection techniques, capable of reaching the single-molecule level. However, extending its utility beyond a narrow sensitive class of molecules is hampered by the difficulty of probing species with intrinsically weak Raman responses and poor affinity for noble metal substrates. Metal-organic frameworks (MOFs), with their high porosity and large surface area, are widely used to adsorb and enrich diverse molecules. Herein, we combine the high molecular capture capability of zeolitic imidazolate framework-8 (ZIF-8) with the localized surface plasmon resonances (LSPRs) of Ag nanoparticles (NPs), and successfully develop a plasmonic porous multicore@shell Ag@ZIF-8 nanostructure via a simple solvent-induced self-assembly approach, where AgNPs formed in methanol directly guide ZIF-8 growth, avoiding solvent-exchange steps and enabling scalable synthesis under ambient conditions. This hybrid architecture integrates the strong plasmonic response of multicore AgNPs with the highly porous ZIF-8 shell matrix capable of concentrating molecular analytes, thereby yielding a great enhancement in the SERS signal. Such a unique SERS substrate delivers consistent and superior detection performance for analytes of different sizes and metal affinities. By trapping analyte molecules within the porous three-dimensional ZIF-8 shell, the multicore@shell Ag@ZIF-8 platforms synergistically couple electromagnetic and adsorption-assisted chemical enhancement mechanisms. This design achieves SERS signal amplification of up to one, three, and even five orders of magnitude for methylene blue, thiram, and 4-nitrophenol, respectively, compared with bare-metal substrates, and enables ultrasensitive detection limits down to 10, 1, and 0.1 nM. Our study thus paves the way for the development of ultrasensitive, reliable, and scalable SERS substrates for a broad spectrum of molecular targets through rational design and facile synthesis.