Plasmonic Dual-Gap Nanodumbbells for Label-Free On-Particle Raman DNA Assays.

Metal nanostructures with a tunable plasmonic gap are useful for photonics, surface-enhanced spectroscopy, biosensing and bioimaging applications. The use of these structures as chemical and biological sensing/imaging probes typically requires an ultra-precise synthesis of the targeted nanostructure in a high yield, Raman dye-labeling and complex assay components and procedures. Here, we designed and synthesized a plasmonic nanostructure with tunable dual nanogaps, Au dual-gap nanodumbbells (AuDGNs), via the anisotropic adsorption of polyethyleneimine on Au nanorods to facilitate tip-selective Au growths on nanorod tips for forming mushroom-shaped dumbbell-head structures at both tips and result in dual gaps (intra-head and inter-head gaps) within a single particle. AuDGNs were synthesized in a high yield (>90%) while controlling the inter-head gap size, and the average surface-enhanced Raman scattering (SERS) enhancement factor (EF) value is 7.5×10 8 with a very narrow EF distribution from 1.5×10 8 to 1.5×10 9 for >90% of analyzed particles. Importantly, AuDGNs enabled label-free on-particle SERS detection assays through the diffusion of target molecules into the intraparticle dumbbell gap for different DNA sequences with varying ATGC combinations in a highly specific and sensitive manner without a need for Raman dyes. This article is protected by copyright. All rights reserved.