Electrochemical detection of lead ions via the covalent attachment of human angiotensin I to mercaptopropionic acid and thioctic acid self-assembled monolayers

An electrochemical sensor for the detection of lead ions is described which is made by modifying a gold electrode substrate with self-assembled monolayers (SAMs) of 3-mercaptopropionic acid (MPA) or thioctic acid (TA) followed by covalent attachment of a lead binding peptide, human angiotensin I. Cyclic voltammetry of MPA-angiotensin modified gold electrodes complexed with lead displayed voltammograms with prominent lead peaks at E0′, −0.29 V. A detection limit of 1 nM was achieved using Osteryoung square wave voltammetry. However, the electrodes were not stable over repeated electrochemical cycles due to partial electrochemical desorption of the SAM. The TA-angiotensin modified gold electrode showed greater stability and were able to be regenerated several times. Using Osteryoung square wave voltammetry for TA-angiotensin modified electrodes, lead concentrations down to 1.9 nM were detected. Although the detection limit of the TA-angiotensin modified electrode is higher than achieved with MPA-angiotensin, it is still well below Australian drinking water guidelines. Studies of interference effects on the Pb2+ current showed Hg2+ as a significant interferent but only at levels significantly greater than those found in natural waters.