Pd Nanoreefs on Au Truncated Octahedra Nanoprobes for Label-Free Biomolecule Detection via Surface-Enhanced Raman Scattering

Surface-enhanced Raman spectroscopy (SERS) enables ultrasensitive molecular detection but faces significant challenges when applied to biologically relevant molecules, such as amino acids and carbohydrates, due to their weak surface adsorption and low Raman cross sections, which lead to poor signal reproducibility. To address these limitations, we present morphology-engineered hybrid nanostructures, termed Pd nanoreef on Au truncated octahedron (Au-Pd NRTO), which combine the strong plasmonic properties of Au with the high binding affinity of Pd for oxygen-containing biomolecules. In this architecture, Pd selectively grows into coral-like columnar pillars at high-energy sites on the Au surface, precisely where electromagnetic field enhancement is maximized, significantly improving SERS signals. By tuning the extent of Pd growth, we achieve an optimal balance between preserving plasmonic activity and enhancing molecular adsorption. Finite element simulations, corroborated by experimental SERS data, reveal that intermediate Pd coverage yields the best sensing performance by coupling efficient near-field enhancement with effective analyte capture. Using this platform, we successfully performed label-free detection of small biomolecules, including neurotransmitters, monosaccharides, and amino acids, with high sensitivity and demonstrated multiplexing capability. These findings demonstrate a morphology-driven strategy for developing multifunctional plasmonic sensors, underscoring the importance of embedding chemically interactive sites directly within SERS-active regions to maximize detection efficiency.