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

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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 modi. cation 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.
Publisher
ROYAL SOC CHEMISTRY
Issue Date
2008
Language
English
Article Type
Article
Keywords

FLOW-INJECTION ANALYSIS; ULTRASENSITIVE DETECTION; ALKALINE-PHOSPHATASE; ENZYME-IMMUNOASSAY; TETHERED DENDRIMER; SULFITE OXIDASE; DNA; AMPLIFICATION; GOLD; ASSAY

Citation

ANALYST, v.133, no.11, pp.1599 - 1604

ISSN
0003-2654
DOI
10.1039/b806302h
URI
http://hdl.handle.net/10203/24811
Appears in Collection
CH-Journal Papers(저널논문)
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