Chuanbo delivered an invited talk in 252nd ACS National Meeting, Philadelphia.

Symposium: COLL

Title: Controlled synthesis of plasmonic noble metal nanoparticles

Abstract: Plasmonic noble metal (Au, Ag) nanoparticles are widely applicable in surface-enhanced Raman spectroscopy (SERS) due to their outstanding optical properties. Controlled synthesis of the noble metal nanoparticles are of great significance for their enhanced activity in these applications. 

Conventional wet-chemistry synthesis of plasmonic noble metal nanoparticles usually suffers from poor yield, reproducibility and scalability. Toward solving this problem, we proposed a coordination-based synthesis by introducing a proper ligand to reduce the reduction potential of the noble metal salt such that self-nucleation events are effectively suppressed. By this means, a series of plasmonic noble metal nanoparticles, such as Au and Ag nanospheres and triangular nanoplates, have been synthesized on a large scale in high yield from a one-pot seeded growth system, with their size well tunable and stoichiometrically predictable in a broad range of 10-200 nm or a few microns. On the other hand, with appropriate ligands, galvanic replacement can be prevented when Au is depositing onto various Ag nanoparticles, giving rise to an unconventional class of Ag@Au core/shell nanocrystals. These novel nanocrystals show excellent Ag-like plasmonic property and Au-like chemical stability, and thus are particularly useful in biosensing or SERS applications under many harsh conditions.

The SERS activity of plasmonic nanoparticles also relies on availability of high-density hotspots for enhanced sensitivity, which can be achieved by rational design of nanostructures with inherent nanogaps. To this end, we successfully synthesized Au nanoframes with inherent nanogaps of < 7 nm by templating of Au against non-metallic AgI nanoparticles. In another demonstration, the nanogap structures can be obtained by dealloying Au-Ag alloy nanocrystals, leading to highly porous Au-Ag colloids. The ultrasmall nanogaps represent the hotspots, and thus enable superior activity in SERS applications.

In summary, we report controlled synthesis of plasmonic noble metal nanoparticles and unique strategies for constructing unconventional nanostructures, which opens up new opportunities in achieving significantly enhanced activity in many SERS-based applications.