Capture of Single Silver Nanoparticles in Nanopore Arrays Detected by Simultaneous Amperometry and Surface-Enhanced Raman Scattering

• Published in: Analytical chemistry (Washington) Vol. 91; no. 7; pp. 4568 - 4576
• Main Authors: Kim, Ju-Young, Han, Donghoon, Crouch, Garrison M, Kwon, Seung-Ryong, Bohn, Paul W
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 02.04.2019; American Chemical Society (ACS)
• Subjects: Amperometry; Arrays; Benzene; Chemistry; Collision dynamics; Confined spaces; Electrical measurement; Electrodes; Gold; Nanoparticles; Oxidation; Porosity; Raman spectra; Silver
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/acs.analchem.8b05748

The attoliter volumes and confinement abilities of zero-dimensional nanopore-electrode arrays (NEAs) hold considerable promise for examining the behavior of single nanoparticles. In this work, we use surface-enhanced Raman scattering (SERS) in tandem with amperometry in order to monitor single Ag Raman-sentinel nanoparticles transported to and captured in single nanopores. To that end, highly ordered solid-state NEAs were fabricated to contain periodic arrays of nanopores, each housing a single recessed Au-ring electrode. These were used to electrostatically capture and trap single silver nanoparticles (AgNPs) functionalized with the electrochemically stable Raman reporter, 1,4-bis­(2-methylstyryl)­benzene (bis-MSB). Transport and capture of the bis-MSB-tagged AgNPs in the nanopores was followed by simultaneous amperometry and SERS signals characteristic of AgNP oxidation and enhanced Raman scattering by bis-MSB at silver–gold hot spots, respectively. The frequency and magnitude of oxidation-current spikes increased with stepwise increases in DC voltage, and characteristic bis-MSB SERS spectra were observed. Under AC excitation, on the other hand, two distinctly different types of SERS signals were observed, independent of frequency and amplitude: (1) strong, transient (<10 s) spectra and (2) slow (>100 s) monotonically diminishing spectra. We hypothesize that the former behavior results from AgNP aggregates, whereas the latter occurs as a result of multiple incomplete AgNP-oxidation events in succession. These results show that attoliter-volume NEAs are competent for acquiring concurrent SERS spectra and for amperometry of single nanoparticles and that together these measurements can illuminate the collision dynamics of nanoparticles in confined environments.