PlasmonicNanocrevice-Gap Nanosnowman Particles EnablingColocalization of Raman Reporters with Super-Localized Electric Fieldsfor Highly Sensitive, Specific, and Quantitative Surface-EnhancedRaman Scattering Biosensing

Surface-enhanced Raman scattering (SERS) is based on a highly localized electric field (E-field), i.e., hotspot, on plasmonic nanostructures and enables a wide variety of ultrasensitive molecular-fingerprint sensing applications. However, reliably forming and controlling hotspots, and positioning molecules within them to reproducibly obtain maximal and quantitative Raman signals, remains challenging. Here, we designed and synthesized gold nanocrevice-gap nanosnowman particles (AuNCNSs) that feature a superlocalized E-field inside the nanocrevice gap via surface-modified DNA-directed nanostructure growth chemistry. AuNCNSs facilitate a capacitive plasmon mode with an intense, broadly distributed near-field enhancement, yielding a 157-fold amplification (analytical SERS enhancement factor = ∼3.1 × 1010). Remarkably, ∼10% of Raman dyes confined within the nanocrevice gap contribute to ∼90% of the total SERS intensity, effectively dividing SERS signal generation and target-sensing regions. Further, the Raman dyes adsorbed outside the nanocrevice gap region can be washed away with minimal signal loss, freeing the non-nanocrevice-gap nanoparticle surface for reliable and efficient functional ligand modification such as antibodies or DNA. The SERS tag-linked immunosorbent assay (SLISA) with antibody-modified AuNCNSs can detect as low as 10 fM viral targets, which is a 100-fold better sensitivity than conventional ELISA results for the same target, and the dynamic range is >5 orders of magnitude, ranging from 10 fM to >1 nM. Importantly, the specificity of the AuNCNS immunoassay is extraordinary, with almost undetectable SERS signals for nonspecific influenza targets, suggesting that AuNCNSs can be promising bioprobe platforms with high sensitivity and reliable target quantification capability by super-colocalizing Raman dyes and E-field inside the nanocrevice gap along with highly reliable and stable ligand modification on open non-NCG particle surfaces.