Efficiently shape-selective synthesis of single crystal silver nanocube with the combination of HNO3/NaCl and reaction time for developing surface enhanced Raman scattering (SERS) substrate

Abstract

Shape control of noble nanomaterials has garnered significant attention in the past decade because niche applications rely on the relationship between the nanoparticle morphology and optical properties. Although many chemical methods have been reported, there is still a need for improvement in terms of uniformity, yields, and synthesis scale. This work exploited the novel modification approach based on the polyol method to control synthesis to obtain a high amount of single-crystal silver nanocubes (AgNCs) with relatively homogeneous sizes and edge lengths of approximately 100 nm. Furthermore, we have discovered the high effectiveness of controlling temperature conditions to examine the conversion from silver nanocubes to tetrahedron nanoparticles, which had been rarely studied before. These as-prepared AgNCs colloidal solutions were further used to develop the SERS substrate on the glass slide through the facile drop cast method. Additionally, through synthesis using ethylene glycol and redispersed in the ethanol solvent, the obtained AgNCs have a high probability coverage on the glass slide once natural evaporation technique to achieve a remarkable amplification effect and reproducibility behavior. It was explored that these substrates could significantly enhance the Raman signal of 4-mercaptobenzoic acid (4-MBA), which is utilized as the probe molecule to assess the SERS behaviors. The enhancement factor (EF) of the SERS substrates prepared using AgNCs was approximately 3.6 × 106. The presence of 4-MBA could be detected with AgNCs in concentrations ranging from 0.01 to 10 mM, with a limit of detection (LOD) of 8.40 μM and a limit of quantification (LOQ) of 25.46 μM. Through analyzing over 20 different spots on various AgNC substrates, synthesized with similar methods and conditions, the Raman signals of 4-MBA were almost unchanged, with a relative standard deviation (RSD) value of 5.81%, indicating that the SERS signal produced by AgNC substrates was highly reproducible. Based on the results, the SERS nanosubstrates developed with AgNCs could potentially be used to detect trace amounts of other harmful organic compounds.