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Metal nanoparticles coated with an organic monolayer, so-called monolayer protected clusters (MPCs), can show quantised charging at room temperature due to their sub-attofarad capacitance arising from the core size and the nature of the protecting monolayer. In this tutorial review, we examine the factors affecting the energetics of MPC charging. In the first section, the underlying physics of quantised charging is outlined and we give an overview of the various methods that can be used to measure single electron transfer to nanoparticles. In the subsequent sections, we discuss how electrochemical measurements can be used to give information on the quantised charging of freely diffusing and films of immobilised MPCs. The predictions of models used to determine MPC capacitance are compared with experimental data from the literature.

The article throws light on the time-resolved electrochemical detection of discrete adsorption events. It reports the amperometric detection of single carboxylated micro and nanospheres adsorbing on electrodes as well-resolved, discrete steps in the current-time response. Detection at the single-event level is a necessary requirement for a range of single-molecule experiments and can greatly enhance existing sensor technologies. Electrochemical detection of micron-sized latex beads at arrays of microelectrodes has also been proposed as a sensing technique for use in sandwich-type immunoassays, and it was deduced that single-bead detection could be realized.

Thiol-protected gold nanoparticles, so-called monolayer protected clusters (MPCs), are unique in that they can be repeatedly isolated and dispersed without irreversible aggregation. This extraordinary stability is due to the strength of the gold-thiol bond. From extensive research on 2D self-assembled thiol monolayers on Au (SAMs), the gold-sulfur bond is broken only under extreme oxidative conditions, at high temperatures or by electrochemical reduction. MPCs are essentially 3D SAMs and have been termed freely diffusing nanoelectrodes.

Describes the preparation of hexanethiol-capped Au (C6S-Au) particles by the Brust method using the modification proposed by Murray and colleagues to obtain particles of small core radius and improved monodispersity. Methods used to investigate the monolayer protected clusters (MPC) redox properties; Current response; Differential pulse voltammetry response; Oxidation states for monolayer protected gold nanoparticles.

This article reports on the ion permeability of self-assembled monolayers (SAMs) formed on the surface of charged alkanethiol-protected gold nanoparticles, so-called monolayer-protected clusters (MPCs). The capacitance and thus the charging energy required to add/remove an electron from the metal core are extremely sensitive to ions entering the monolayer, and the extent of ion penetration can be tuned by the charge and size of the ions and the permittivity of the solvent. Experimentally, this effect is comparable to ion association with conventional redox molecules, indicating that MPCs despite their large size and the fundamentally differing nature of the electron transfer process can be treated analogously to redox molecules. [ABSTRACT FROM AUTHOR]