Interface-Engineered Janus Au@CeO 2 Nanostructures for Ultrasensitive Ratiometric SERS Platforms

Monolayer noble metal nanoparticle (NP) arrays hold great promise as surface-enhanced Raman scattering (SERS) substrates due to their strong SERS performance and cost-effectiveness. However, precise regulation of hotspot intensity and density remains a critical challenge for practical applications. Here, we propose a SERS substrate based on Janus-structure NPs, which realizes accessible metal-semiconductor interface hotspots, as well as the regulation of interparticle nanogaps of ∼1 nm through a multifunctional surface ligand. By selectively depositing cerium oxide (CeO₂) onto one terminus of gold nanorods (Au NRs), we fabricate Janus nanostructures that generate highly accessible and intensified hotspots. Another key enabler of this advancement is 4-mercaptophenylboronic acid (MPBA), a multifunctional ligand that precisely regulates interparticle spacing, increases hotspot density, and simultaneously serves as both a Raman molecule and a bacterial recognition unit. The SERS enhancement effect of the Janus NP array can reach more than 11 times that of the conventional Au NR array. Based on this MPBA-functionalized Janus NP array substrate, a SERS sensor for Escherichia coli was constructed, which exhibited a robust linear detection response to bacterial concentrations ranging from 6 to 6 × 10⁴ CFU/μL, with an ultralow detection limit of approximately 1.1 CFU/μL. Our work introduces a versatile strategy for next-generation SERS substrates.