Size Purification of Phosphonium-Stabilized Gold Nanoclusters Monitored by Anodic Stripping Voltammetry (ASV)

Here we describe the size purification of chemically-synthesized tetrakis(hydroxymethyl)phosphonium chloride (THPC)-stabilized Au nanoclusters (NCs). The as-synthesized product contains Au NCs with an average size of 1.6 nm in diameter and contains a significant fraction of ∼4 nm diameter Au nanoparticles (NPs). Solvent fractionation allows isolation of the smaller size Au NCs from the size disperse population. Use of methanol, ethanol and 1-propanol mixed with water-soluble THPC Au NCs leads to selective isolation of the ∼1.6 nm Au NCs, resulting in a more pure and uniform solution in terms of size. Anodic stripping voltammetry (ASV) following purification and attachment to (aminopropyl)triethoxysilane (APTES)-functionalized indium tin oxide-coated glass (glass/ITO/APTES) electrodes provide a simple, fast, and low-cost method for monitoring the size compared to transmission electron microscopy (TEM) or mass spectrometry. This is necessary as a rapid screening tool for optimization of the fractionation and purification conditions as TEM and mass spectrometry would be cost prohibited. Importantly, TEM confirmed the ASV results for the optimized conditions, showing the validity of ASV for rapid size screening for purification. The purification of 1.6 nm diameter THPC Au NCs and attachment to electrode surfaces is important for studying their electrochemical stability for applications in catalysis and sensing in the future.