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One-Step Controlled Synthesis of Size-Tunable Toroidal Gold Particles for Biochemical Sensing

Controlling the size and shape of nanoparticles is a major goal in materials science. Here we show the fast, 30 min, controlled one-step synthesis of gold particles (tAUPs) with sizes tunable from 350 nm to 1.7 μm by using a mixture of surfactant scaffolds made from sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB). The as-synthesized tAUPs have nanospikes that protrude either inward or outward from the ring cavity. The number of nanospikes can be tuned by a two-step temperature change process to create so-called rough tAUPs. The toroidal gold particle structures exhibit surface plasmon extinction peaks in the near-infrared region and demonstrate a high surface-enhanced Raman scattering (SERS) sensitivity for the detection of 4-mercaptobenzoic acid (4-MBA) molecules. The protruding nanospikes significantly enhance the electromagnetic field oscillating inside the ring cavity. This is confirmed through sensitive detection of 4-MBA molecules as well as by simulation. Rough tAUP structure...