Shape- and Size-Controlled Fabrication of Gold Nano-Urchins via Use of a Mixed Sodium Borohydride and Ascorbic Acid Reductant System

Urchin-shaped gold nanoparticles (AuNUs) are anisotropic nanomaterials with unique chemical and physical properties of interest for a variety of applications. However, synthesizing AuNUs with controlled sizes and shapes remains challenging. We demonstrate that a combination of sodium borohydride (NaBH4) and ascorbic acid (AA) as reducing agents can produce an aqueous dispersion of AuNUs after just 9 min at room temperature (25 degrees C). The AuNUs were size- and shapecontrolled using a molar ratio for NaBH4/AA/HAuCl4 = 1:1:1 at pH 3. The added aurate was almost entirely (98.8%) consumed in the formation of AuNUs. The resultant AuNU concentration was 1.1 x 10(10) particles/mL. The diameters observed in transmission electron microscopy were 145.1 +/- 37.4 nm. The AuNUs had an average of 12 spikes and an average volume of 3.7 x 10(5) nm(3). The partition volume between the spikes and the core of particles was 3:2. The AuNUs had a pink color and exhibited an absorption wavelength maximum at 540 nm. It is assumed that the AuNUs originate from icosahedral seeds and urchin shapes emerge from connecting smaller-sized seeds and larger-sized core particles.

Automated summary

The study demonstrates that a combination of sodium borohydride and ascorbic acid can synthesize urchn-shaped gold nanoparticles with controlled sizes and shapes in a short period of time, providing a new approach for the preparation of nanomaterials.