Circumventing silver oxidation induced performance degradation of silver surface-enhanced Raman scattering substrates

Shape-Preserving Transformation of Electrodeposited Macroporous Microparticles for Single-Particle SERS Applications

Microparticles composed of bicontinuous and ordered macropores are important in many applications. However, rational integration of ordered macropores into a single crystalline microparticle remains a challenge. Here, we report a method to prepare three-dimensionally ordered macroporous (3DOM) Ag₇O₈NO₃ micropyramids via selectively cementing the colloidal crystal templates via an electrochemical method and their shape-preserving transformation into 3DOM Ag micropryamids formed by Ag nanoparticles via a chemical reduction process. The interconnected macropores facilitated the transportation and enrichment of the analyte molecules into the 3DOM Ag micropyramids. The dense Ag nanoparticles on the skeletons of the 3DOM Ag micropyramids provided strong electromagnetic fields. Taken together, a 3DOM Ag micropyramid as a kind of single-particle surface-enhanced Raman scattering (SERS) sensing substrate demonstrated high SERS sensitivity and outstanding SERS signal reproducibility. We explored the application of 3DOM Ag micropyramids in SERS detection of biomolecules (e.g., adenosine, adenine, hemoglobin bovine, and lysozyme) and proved their potentials in distinguishing exosomes from tumor and non-tumor cells. The method can be extended to prepared 3DOM structures of other materials with promising applications in sensing, separation, and catalytic fields.

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.