A signal amplification scheme for ultrasensitive amperometric detection inflowing streams

A new signal amplification scheme for ultrasensitive amperometric electroch emical detection of redox-active molecules in quiescent solution and in flo wing streams is described. The method is based upon a continuous regenerati on of electrochemically oxidized analytes by reaction with a sacrificial el ectron donor in solution. It utilizes a selective coating on the electrode that is chosen to have properties which allow for relatively facile electro oxidation of analyte but which also inhibit electrooxidation of the sacrifi cial electron donor. Ultrasensitive detection of hydroxymethylferrocene (HM Fc) as a model analyte using ferrocyanide as the sacrificial electron donor is demonstrated at a dodecanethiol-coated gold electrode. Signal amplifica tion factors of several hundred to several thousand are obtained in now inj ection mode for analyte injections in a concentration range between 10(-4) and 10(-7) M where peaks can be discerned both with and without amplificati on. Even higher amplification factors are estimated for analyte concentrati ons below approximately 10(-8) M, for which peaks without amplification are undetectable. Amperometric detection of 60 million injected HMFc analyte m olecules (corresponding to either a 10-mu L injection at 10(-11) M or a 1.0 -mL injection at 10(-13) M) is demonstrated using the new method in now inj ection mode.