Correlated Electrochemical and Optical Detection Reveals the Chemical Reactivity of Individual Silver Nanoparticles

Abstract

Electrochemical (EC) impacts of single nanoparticles (NPs) on an ultramicroelectrode are coupled with optics to identify chemical processes at the level of individual NPs. While the EC signals characterize the charge transfer process, the optical monitoring gives a complementary picture of the transport and chemical transformation of the NPs. This is illustrated in the case of electrodissolution of Ag NPs. In the simplest case, the optically monitored dissolution of individual NPs is synchronized with individual EC spikes. Optics then validates in situ the concept of EC nanoimpacts for sizing and counting of NPs. Chemical complexity is introduced by using a precipitating agent, SCN(-), which tunes the overall electrodissolution kinetics. Particularly, the charge transfer and dissolution steps occur sequentially as the synchronicity between the EC and optical signals is lost. This demonstrates the level of complexity that can be revealed from such electrochemistry/optics coupling.

Time-Resolved Detection of Surface Oxide Formation at Individual Gold Nanoparticles: Role in Electrocatalysis and New Approach for Sizing by Electrochemical Impacts

“…NP aggregation is increasingly recognized as important in NP impact studies. 8,19,20 This was confirmed by performing dynamic light scattering (DLS, see the inset of SI, Figure S6), where the average size of the NPs (aggregates) increased continuously with time, after mixing. Furthermore, the influence of aggregation on the SNEI experiments was investigated by performing a measurement 1 hour after solution preparation; as shown in SI, Figure S6, the observed current spikes are, on average, much larger than those seen in Figure 3c, which was recorded in a 'fresh' solution.…”

“…This typically involves monitoring the current-time (I-t) transients associated with the stochastic collision of NPs from a (dilute) colloidal solution with a collector electrode, with the detected current arising from either: (i) a heterogeneous electron-transfer reaction taking place at the NP surface (e.g., electrocatalytic amplification [3][4][5][6] ); or (ii) the electro-dissolution of the NP itself. 7,8 In this contribution, we introduce a third approach to investigate the dynamic interaction between metal NPs and a collector electrode, in which the detected current arises from NP surface oxidation, as is shown schematically in Figure 1a for the case of an Au NP. This measurement is much more challenging than the (volumetric) anodic oxidation of metal NPs 7,8 , due to the smaller charges involved and much faster timescale of the process, but opens up new prospects for detecting noble metals and analyzing the formation of surface oxides, which can greatly influence (retard or accelerate) electrocatalysis.…”

Impact and oxidation of single silver nanoparticles at electrode surfaces: one shot versus multiple events

“…Most importantly, in none of these cases does the charge consumed during single events account for the stripping of entire NPs and hence represents only a partial stripping process. 27–29 It should be noted that when the NP diameter increases from 20 to 60 nm, the occurrence of such bundles of low current (green and brown) events is more frequent (28% and 58% of the total charge for d = 20 nm and d = 60 nm, respectively). Furthermore, contrary to the cases of d = 10 nm and d = 20 nm, for d = 40 and d = 60 nm, very long saw-tooth events are also present (Fig.…”

“…Citrate capped Ag NPs were chosen for this study, since they have been used in most previous single NP electrodissolution studies. 16–21,26,27,29,31 Likewise, most previous studies have been carried out with citrate present in solutions (ESI, Section S1 and Table S1†). …”

The role of the food matrix and gastrointestinal tract in the assessment of biological properties of ingested engineered nanomaterials (iENMs): State of the science and knowledge gaps

“…The chemical reactivity and toxicity of inorganic ENMs is also closely related to their composition, e.g. , gold nanoparticles tend to have a relatively low chemical reactivity and toxicity (Khalili Fard et al , 2015; Pradeep and Anshup, 2009), whereas silver nanoparticles tend to be relatively highly reactive and toxic due to the release of ions (Brasiliense et al , 2016; Khalili Fard et al , 2015). …”