Nanoporous Ag Microparticles with Tailorable and Noncontaminated Nanopores for SERS Sensing Applications

Nanoporous metallic microarchitectures with noncontaminated surfaces hold significant promise in catalytic and sensing fields. Fabrication of nanoporous metal microparticles without using any organic ligands remains a significant challenge. Here, a green synthesis strategy is presented inspired by dealloying mechanisms. Ag7O8NO3 microparticles are first electrodeposited. Subsequent chemical reduction process selectively removes nitrogen and oxygen species from the Ag7O8NO3 microparticles while preserving the original morphology, giving rise to the formation of nanoporous Ag microparticles without using organic agents under room temperature within several minutes. Based on the ion diffusion limited growth mechanism, a quantitative correlation is established between the opening size of the nanopores and the concentration of the reductive agents, allowing to rationally prepare nanopores with opening size ranging from < 20 nm to > 110 nm. The ultraclean surface of the nanoporous Ag microparticles guarantees a clean surface-enhanced Raman spectroscopy (SERS) background. Reliable and sensitive SERS detection of proteins by unfolding the protein structure is further demonstrated to expose the otherwise concealed parts to the nanoporous Ag microparticles. A simple but powerful approach is developed to design ultraclean nanoporous metallic microarchitectures with promising applications in those fields requiring clean surfaces, such as in SERS sensing and catalytic fields.