A Signal Amplification Scheme for Ultrasensitive Amperometric Detection in Flowing Streams

Abstract

A new signal amplification scheme for ultrasensitive amperometric electrochemical detection of redox-active molecules in quiescent solution and in flowing streams is described. The method is based upon a continuous regeneration of electrochemically oxidized analytes by reaction with a sacrificial electron donor in solution. It utilizes a selective coating on the electrode that is chosen to have properties which allow for relatively facile electrooxidation of analyte but which also inhibit electrooxidation of the sacrificial electron donor. Ultrasensitive detection of hydroxymethylferrocene (HMFc) as a model analyte using ferrocyanide as the sacrificial electron donor is demonstrated at a dodecanethiol-coated gold electrode. Signal amplification factors of several hundred to several thousand are obtained in flow injection mode for analyte injections in a concentration range between 10-4 and 10-7 M where peaks can be discerned both with and without amplification. Even higher amplification factors are estimated for analyte concentrations below approximately 10-8 M, for which peaks without amplification are undetectable. Amperometric detection of 60 million injected HMFc analyte molecules (corresponding to either a 10-μL injection at 10-11 M or a 1.0-mL injection at 10-13 M) is demonstrated using the new method in flow injection mode.