Using nanoparticle aggregation to give an ultrasensitive amperometric metal ion sensor

Herein we show an electrochemical sensor for the detection of copper ions that has a limit of detection below 1 pM. This extraordinarily low limit of detection is achieved in two ways. The first is to use SAM modified electrodes to give low background current where electron transfer to the underlying polycrystalline electrode is achieved through gold nanoparticles attached to the terminus of the SAM. The gold nanoparticles are modified with cysteine to allow copper accumulation. The second way the low detection limits are achieved is by the addition of cysteine-modified nanoparticles to the sample solution, as well as the SAM modified electrode. The complexation of copper with the nanoparticles in solution causes them to aggregate with these aggregates accumulating on the electrode. Thus a higher percentage of copper in the solution is collected at the electrode giving the enhanced detection limits. (C) 2009 Elsevier B.V. All rights reserved.