Simple morphological control over functional diversity of SERS materials

Introduction. Nowadays, surface-enhanced Raman spectroscopy (SERS) becomes a promising universal low-cost and real-time tool in biomedical applications, medical screening or forensic analysis allowing for detection of... [ view full abstract ]

Introduction. Nowadays, surface-enhanced Raman spectroscopy (SERS) becomes a promising universal low-cost and real-time tool in biomedical applications, medical screening or forensic analysis allowing for detection of different molecules below nanomolar concentrations. Silver nanoparticles (AgNPs) and nanostructures (AgNSs) have proven to be a common choice for SERS measurements due to a tunable plasmon resonance, high stability and facile fabrication methods. However, a proper design of silver-based nanomaterials for highly sensitive SERS applications still remains a challenge. In this work, effective and simple preparation methods of various AgNSs is proposed and systematically developed using aqueous diamminesilver hydroxide as a precursor.

Methods. AgNPs and AgNSs were prepared using several novel routes based on transformation of [Ag(NH₃)₂]OH via formation of Ag₂O and pure silver under different conditions such as hydrolytic heating, aerosol pyrolysis or reduction by H₂O₂. The obtained AgNPs are comprehensively characterized by scanning and transmission electron microscopy; ultraviolet-visible, infrared and Raman spectroscopy; X-ray analysis; dynamic light scattering.

Results. The decomposition of aqueous diamminesilver hydroxide under heating or using aerosol spray pyrolysis results in formation of pure AgNPs and AgNSs with following morphologies: spheres, rings with hierarchical structures, porous spheroids, cuboids and more complex structures. The reduction of silver (I) oxide by hydrogen peroxide in the presence of polyvinylpyrrolidone leads to the formation of octahedral AgNSs with multiple hot spots. All described AgNPs and AgNSs demonstrate their high efficiency in SERS measurements with enhancement factors of about 10⁴ - 10⁸ and were used in a form of SERS active substrates for a study of different biomolecules and pollutants.

Discussion. The use of the aqueous diamminesilver hydroxide to prepare AgNSs gives a large benefit owing to the simplicity, promptness and low temperature conditions of the production process (typically lower than 250 ^oC). In particular, it demonstrates the formation of various nanoparticle morphologies highly suitable for different SERS measurements. It is shown that the best SERS active properties among the mentioned AgNSs are revealed for silver rings and octahedral silver skeleton particles.

This research is supported by the Grant of the President of Russian Federation for the governmental support of young scientists (#MK-1146.2017.3).