Laser-irradiated synthesis of gold nanoworms with tunable near-infrared absorption for enhanced catalytic activity

Abstract

The synthesis of anisotropic nanoparticles with the ability to absorb light in the near-infrared region is of great interest due to their applications in nanotherapy and nanodiagnostics. Here, we describe the fabrication process of gold nanoworms (Au NWs) through laser irradiation of gold nanospheres (Au NSs) dispersed in a liquid medium. The resulting Au NWs exhibit a broadband plasmon absorption across the visible to near-infrared spectrum. The entire formation process is conducted in the presence of ethanol without the use of any templating agent, thereby yielding surfactant-free Au NWs. This feature enhances their surface reactivity and ensures biocompatibility. The formation process of Au NWs is intricately dependent on laser parameters; the extent of Au NWs formation escalated with increasing laser energy and irradiation time. The optimal conditions for the Au NWs formation are 120 mJ laser energy and 4 min of laser exposure time. Furthermore, varying the concentration of ethanol in the growth medium enables control over the length of nano-worms. To investigate their catalytic activity, the Au NWs with varying aspect ratios are used to reduce azo dyes such as methyl orange (MO) and rhodamine-b (RhB). Au NWs are found to have far superior catalytic activity than their spherical counterparts. Moreover, high aspect ratio Au NWs are more efficient catalysts than those with low aspect ratios. The long Au NWs demonstrated 5.5-fold and 2.2-fold higher catalytic activity than the Au NSs for MO and RhB, respectively.