Urchin-like gold microstructures with tunable length of nanothorns

In this paper, we exploited a unique reaction of silver ions to create and design urchin-like gold microstructures (UL-AuMSs) with controllable length of nanothorns. The UL-AuMSs were synthesized via a simple one-pot synthetic protocol without using any surface capping agents or polymeric stabilizers. The reactants consisted of tetrachloroauric (III) acid, silver nitrate, and hydrogen peroxide (H2O2). H2O2 functioned as the sole reducing agent while trace silver ions played an important role as the shape controlling agent. Without trace silver ions, quasi-sphere gold microstructures (QS-AuMSs) were obtained. The time-dependent SEM investigations corroborated that UL-AuMSs and QS-AuMSs grew from flower-like gold microstructures (FL-AuMSs). The added trace silver ions reacted with physically adsorbed chloride ions on gold surfaces and formed into solid silver chloride capable of altering the dendritic growth of QS-AuMSs to the dominated trunk-growth of UL-AuMSs. The cleaned UL-AuMSs with average thorn lengths of 166 and 187 nm expressed high SERS activity as 0.1 nM of Rhodamine 6G could be detected with a short 15-min incubation. The easily visualized UL-AuMSs under a microscope assisting the SERS detection at selected spots was demonstrated.