Template-Confined Site-Specific Electrodeposition of Nanoparticle Cluster-in-Bowl Arrays as Surface Enhanced Raman Spectroscopy Substrates

Nanoparticle clusters have important applications in plasmonics and optical sensing fields. Various methods have been used to construct nanoparticle clusters, represented by assembling preprepared nanoparticles using DNA. However, preparation of nanoparticle clusters using a one-step method is still challenging. Herein, by using prepatterned microscale bowls as individual reaction containers, clusters of Au nanoparticles with a homogeneous structure are electrodeposited at the bottom of each bowl. The structure of the nanoparticle clusters can be simply manipulated by varying electrodeposition parameters. After coating these Au nanoparticle cluster-in-bowl arrays with a thin layer of Ag film, they can be used as surface enhanced Raman spectroscopy (SERS) substrates with an SERS enhancement factor of ∼10⁸. Importantly, the concave bowl structures can facilitate delivery of the analytes into the crevices between the bowls and the nanoparticle clusters where SERS "hot spots" (or sensitive sites) are located. The crevices with a gradually changed gap distance between the concave bowl structure and the nanoparticle clusters are excellent traps for catching and SERS sensing of biospecies with varied sizes (e.g., viruses and proteins). We demonstrated sensitive SERS detection of viruses and proteins using the nanoparticle-cluster-in-bowl SERS substrates. This technique has the ability to control the resulting structure at specific locations with electrodeposited materials, which enables new opportunities for assembling complex surface patterns with diverse applications in optical and plasmonic fields.