Hyperbranched Au Nanocorals for SERS Detection of Dye Pollutants

Gold (Au) nanomaterials having branched mor-phologies are recently attracting interest as surface-enhanced Raman scattering (SERS) substrates due to the abundance of hot spot regions in their structures. However, they are typically prepared through laborious experimental protocols that often make use of hazardous and expensive chemical reagents. In this study, we explored the use of environmentally compatible and low-cost organic acids that are known to occur naturally in plants (e.g., ascorbic acid, oxalic acid, tartaric acid) as alternative reagents to render the process greener. Aside from being environmentally friendly, the methodology presented here is convenient, direct, rapid, and inexpensive. The synthesis can be carried out in aqueous media at ambient conditions, does not require complicated setups, and the entire experimental procedure can be completed in less than an hour. Different organic acid combinations were tested, and it was found that the combination of ascorbic acid and oxalic acid can lead to the formation of hyperbranched Au nanocorals with distinct and extensive branching. Investigation of the formation mechanism revealed that the nanocorals are formed through a series of aggregation stages that begins with a one-dimensional (1D) assembly of branched Au nanoparticles, followed by aggregative growth into more expanded branched structures, which further merge to produce a densely packed three-dimensional (3D) network of nanocorals. The numerous tips and junctions in these hyperbranched nanocorals are plasmonic hot spots that allow for the SERS-based detection of rhodamine 6G, a toxic organic dye pollutant.