Electrochemical synthesis of ultra-compact gold hexagonal nanostar substrate for enhanced and stable SERS detection

Surface-enhanced Raman spectroscopy (SERS) amplifies Raman signals via localized fields on nanostructured metallic substrates. The fabrication of efficient substrates remains challenging, as nanolithography and templating are complex, while chemical reduction and self-assembly often suffer from low reproducibility and limited stability.

A rapid electrochemical deposition strategy is reported to synthesize gold hexagonal nanostar by precise modulation of particle size and spacing. The formation process is governed by a voltage-dependent balance between Au⁺ ion reduction kinetics and diffusion. Low overpotentials limit growth to small tip-localized features, while moderate potentials (-0.60 to -0.65 V) accelerate lateral expansion, increasing diameter and reducing spacing. At higher overpotentials (-0.70 to -0.75 V), diffusion-consumption imbalance drives vertical growth, widening spacing despite limited diameter gain. By programming deposition voltages and intervals, the gold hexagonal nanostars were tuned to an optimal diameter of 141.22 nm and an interparticle spacing of 14.72 nm. The resulting three-dimensional nanostructures generated abundant electromagnetic "hot spots," with a 44-fold SERS improvement over conventional counterparts. The substrates exhibited excellent signal uniformity with a relative standard deviation as low as 4.27 %. The electrochemically active surface area via gold oxide stripping reaction, absorption rate and theoretical simulations were also computed.

The engineered SERS substrate was successfully administered for direct ultrasensitive detection of malachite green and levofloxacin with high recovery rates in real fish and aquaculture samples. This template-free, programmable approach provides a scalable pathway for constructing high-performance SERS substrates, offering significant potential for applications in food safety monitoring and environmental analysis.