Seed shape-controlled, facet-selective growth of superspiky gold nanocrystals for biosensing applications

Abstract

Spiky plasmonic Au nanostructures have sparked considerable interest in plasmonic sensing, plasmon-enhanced spectroscopic biosensing and solar energy harvesting, owing to their distinctive complex three-dimensional structures and remarkable optical properties. Seeded synthesis is the premier route toward these superspiky Au nanocrystals, but spike growth on different types of Au seeds has remained largely unexplored. Here, we report the seeded synthesis of superspiky Au nanocrystals using Au spherical, cubic and nanorod seeds. The use of Au spherical seeds with varying sizes produces superspiky Au nanocrystals where the central core and spike dimensions increase as the seed concentration is decreased. A growth process that involves the facet-selective deposition and surface diffusion of Au atoms is observed for spike growth on Au cubic and nanorod seeds. A decrease in the seed concentration causes a redshift of the plasmon resonance wavelength of superspiky Au nanocrystals for all types of Au seeds investigated. This method provides control over the growth regions and the number and dimensions of spikes on Au seeds. These superspiky Au nanocrystals exhibit excellent plasmonic sensing and surface-enhanced Raman scattering (SERS) sensing performances that are dependent on their morphologies, which are tailorable by seed size and shape. A further examination reveals that a large SERS enhancement factor is achieved mostly using a near-infrared laser, which is attributed to the better resonance overlap of the plasmon band with the near-infrared laser wavelength. This work demonstrates the great potential of superspiky Au nanocrystals for versatile biosensing applications with tailorable plasmonic properties.