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Issue 11, 2008
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An electrochemical immunosensor using p-aminophenol redox cycling by NADH on a self-assembled monolayer and ferrocene-modified Au electrodes

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Abstract

Redox cycling of enzymatically amplified electroactive species has been widely employed for high signal amplification in electrochemical biosensors. However, gold (Au) electrodes are not generally suitable for redox cycling using a reducing (or oxidizing) agent because of the high background current caused by the redox reaction of the agent at highly electrocatalytic Au electrodes. Here we report a new redox cycling scheme, using nicotinamide adenine dinucleotide (NADH), which can be applied to Au electrodes. Importantly, p-aminophenol (AP) redox cycling by NADH is achieved in the absence of diaphorase enzyme. The Au electrodes are modified with a mixed self-assembled monolayer of mercaptododecanoic acid and mercaptoundecanol, and a partially ferrocenyl-tethered dendrimer layer. The self-assembled monolayer of long thiol molecules significantly decreases the background current of the modified Au electrodes, and the ferrocene modification facilitates easy oxidation of AP. The low amount of ferrocene on the Au electrodes minimizes ferrocene-mediated oxidation of NADH. In sandwich-type electrochemical immunosensors for mouse immunoglobulin G (IgG), an alkaline phosphatase label converts p-aminophenylphosphate (APP) into electroactive AP. The amplified AP is oxidized to p-quinoneimine (QI) by electrochemically generated ferrocenium ion. NADH reduces QI back to AP, which can be re-oxidized. This redox cycling enables a low detection limit for mouse IgG (1 pg mL−1) to be obtained.

Graphical abstract: An electrochemical immunosensor using p-aminophenol redox cycling by NADH on a self-assembled monolayer and ferrocene-modified Au electrodes

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Publication details

The article was received on 15 Apr 2008, accepted on 24 Jun 2008 and first published on 11 Aug 2008


Article type: Paper
DOI: 10.1039/B806302H
Citation: Analyst, 2008,133, 1599-1604
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    An electrochemical immunosensor using p-aminophenol redox cycling by NADH on a self-assembled monolayer and ferrocene-modified Au electrodes

    S. J. Kwon, H. Yang, K. Jo and J. Kwak, Analyst, 2008, 133, 1599
    DOI: 10.1039/B806302H

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