Structural Change of a Single Ag Nanoparticle Observed by Dark‐field Microspectroscopy

Abstract

Silver nanoparticles (AgNPs) have been widely used as photocatalysts and nanosensors. Observation of the spectroscopy of a single AgNP greatly helps us understand the catalytic characteristics and morphology change of the AgNP during reactions. In the present study, AgNPs physically adsorbed on indium tin oxide (ITO) conductive glass were electrochemically reduced and oxidized, and the plasmonic resonance Rayleigh scattering (PRRS) spectrum of an individual AgNP was observed under a dark-field microscopy (DFM) equipped with a spectrometer. The electrochemical oxidization of the AgNP under constant potential caused a redshift of the PRRS peak for 30±5 nm. However, electrochemical reduction of the AgNP could not make the PRRS peak completely shift back to the initial position. In situ AFM and SEM characterization confirmed that very small Ag fragments (<10 nm) formed around the AgNP core during electrochemical oxidization. Results showed that dark-field microspectroscopy could be used as a sensitive tool for estimating the morphology/structural changes of nanoparticles that can hardly be observed through the cyclic voltammograms of multiple AgNPs.

Colorimetric detection of Cu2+ based on the formation of peptide–copper complexes on silver nanoparticle surfaces

“…The first spin–orbit pair of small intensity at higher BE values is due to the oxidized Ag surface atoms bonding with the peptide molecule. The main signal, the Ag 3d 5/2 component, centered at 367.6 eV BE, corresponds to metallic Ag atoms in the bulk of AgNPs [ 19 ].…”

Emerging Optical Microscopy Techniques for Electrochemistry

“…The conversion of Ag-based metallic NPs into Ag + salt nanocrystals is evidenced under dark-field microscopy by a decrease in the intensity of the light they scatter without, however, reaching total signal extinction. A spectrometer inserted at the end of the optical path, or a hyperspectral camera, completed the pure optical imaging with their UV-vis spectrum, providing information on the composition and conversion mechanisms in solutions of Ag + precipitating agents (77,78,(86)(87)(88).…”

Dark-Field Microscopy: Recent Advances in Accurate Analysis and Emerging Applications

“…(B) Schematic of the structural change of silver nanoparticles monitored by DFM. Adapted from Pang, J.; Liu, H.-L.; Li, J.; Zhai, T.-T.; Wang, K.; Xia, X.-H. ChemPhysChem 2018 , 19 , 954–958 (ref ). Copyright 2018 Wiley.…”

“…It was determined that the electrochemical detection of silver nanoparticles could be inhibited at the electrode surface at high electrode potentials . During the iDFM of the electrochemical redox of silver nanoparticles, Wang et al discovered that electrochemical reduction could not completely lead to recovery of the wavelength shift after electrochemical oxidization, which was attributed to the newly formed small silver nanoparticles (Figure B) . Tschulik and co-workers also investigated the electrochemical dissolution of silver nanoparticles in different systems with hyperspectral DFM and found that the dissolution process could be regulated by the coexisting anions. , …”

“…80 During the iDFM of the electrochemical redox of silver nanoparticles, Wang et al discovered that electrochemical reduction could not completely lead to recovery of the wavelength shift after electrochemical oxidization, which was attributed to the newly formed small silver nanoparticles (Figure 7B). 81 Tschulik and co-workers also investigated the electrochemical dissolution of silver nanoparticles in different systems with hyperspectral DFM and found that the dissolution process could be regulated by the coexisting anions. 82,83 The deposition of copper on plasmonic nanoprobes, which has been widely used for the accurate analysis as discussed above, could also be imaged under DFM.…”