# Adsorption-Coupled Oxidation of Single Ag Nanoparticles as Resolved by Stochastic Scanning Electrochemical Microscopy

## TL;DR

This study uses scanning electrochemical microscopy to understand how silver nanoparticles adsorb and oxidize on a platinum electrode, improving electrochemical detection methods.

## Contribution

A new method combining stochastic amperometry and SECM to quantify Ag nanoparticle adsorption kinetics on a Pt UME tip.

## Key findings

- Citrate caps on Ag nanoparticles accelerate adsorption through oxidative chemisorption on the Pt tip.
- SECM enables determination of adsorption rate constants and diffusion coefficients of nanoparticles.
- Maximum collision frequency requires a large contact area between the Pt tip and nanoparticles.

## Abstract

The oxidation of Ag nanoparticles at the ultramicroelectrode
(UME)
has been extensively studied at the single-particle level for fundamental
electrochemistry and electroanalytical sensing. The fast oxidation
of a Ag nanoparticle is preceded by the adsorption of the nanoparticle,
which can kinetically lower the frequency of amperometric spikes as
an important analytical measure. Herein, we combine stochastic amperometry
with scanning electrochemical microscopy (SECM) to quantitatively
assess the adsorption kinetics of Ag nanoparticles on the Pt UME tip.
We developed a theoretical model to simulate the dependence of the
collision frequency on the adsorption rate constant and the distance
between the tip and an insulating substrate. Experimentally, we confirm
the advantage of SECM to determine the adsorption rate constant and
diffusion coefficient (or concentration) of nanoparticles when the
concentration (or diffusion coefficient) is known. We find that the
maximum collision frequency based on the diffusion-limited adsorption
of Ag nanoparticles requires a large contact area of a polished and
cleaned tip with the nanoparticles. The adsorption of Ag nanoparticles
is accelerated by citrate caps, which can be oxidatively chemisorbed
on the Pt tip to enable a new covalent mode of nanoparticle–electrode
interactions. SECM provides useful mechanistic insights into a deeper
understanding of nanoparticle–electrode interactions for superior
electrochemical detection.