Interface-Engineered Janus Au@CeO2 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.