Plasmonic colloidal nanoparticles with open eccentric cavities via acid-induced chemical transformation

Abstract

Surface-enhanced Raman spectroscopy (SERS) has been considered a promising technique for the detection of trace molecules in biomedicine and environmental monitoring. The ideal metal nanoparticles for SERS must not only fulfill important requirements such as high near-field enhancement and a tunable far-field response but also overcome the diffusion limitation at extremely lower concentrations of a target material. Here, we introduce a novel method to produce gold nanoparticles with open eccentric cavities by selectively adapting the structure of non-plasmonic nanoparticles via acid-mediated surface replacement. Copper oxide nanoparticles with open eccentric cavities are first prepared using a microwave-irradiation-assisted surfactant-free hydrothermal reaction and are then transformed into gold nanoparticles by an acidic gold precursor while maintaining their original structure. Because of the strong near-field enhancement occurring at the mouth of the open cavities and the very rough surfaces resulting from the uniformly covered hyperbranched sharp multi-tips and the free access of SERS molecules inside of the nanoparticles without diffusion limitation, adenine, one of the four bases in DNA, in an extremely diluted aqueous solution (1.0 pM) was successfully detected with excellent reproducibility upon laser excitation with a 785-nm wavelength. The gold nanoparticles with open eccentric cavities provide a powerful platform for the detection of ultra-trace analytes in an aqueous solution within near-infrared wavelengths, which is essential for highly sensitive, reliable and direct in vivo analysis. Scientists have made colloidal gold nanoparticles with open cavities that have an intense surface-enhanced Raman spectroscopy (SERS) signal. The researchers, who are in Korea, prepared the nanoparticles by producing copper oxide nanoparticles having very rough surfaces and an open cavity through a microwave-assisted hydrothermal reaction. They then converted them into gold nanoparticles with the same structure by using an acidic gold precursor. As the rough surface and open cavity mouth greatly enhance the near field, the nanoparticles produce a very strong SERS signal. The researchers demonstrated the potential of the nanoparticles by using them to detect adenine, one of the four bases of DNA, in an extremely low concentration (1.0 picomolar) solution. They anticipate that the nanoparticles will be valuable for detecting very low concentrations of analytes in aqueous solutions using near-infrared excitation. Plasmonic gold nanoparticles with open eccentric cavity are fabricated by selectively adapting the structure of non-plasmonic nanoparticles via acid-induced chemical transformation. Because of strong near-field enhancement occurring at the mouth of the open cavity and very rough surfaces resulting from uniformly covered hyperbranched sharp multi-tips as well as free access of SERS molecules inside the nanoparticles without diffusion limitation, adenine, one of four bases in DNA, in an extremely diluted aqueous solution (1.0 pM) was successfully detected with excellent reproducibility at a laser excitation with 785 nm wavelength.