Reliable ferrocenyloligonucleotide-immobilized electrodes and their application to electrochemical DNase I assay Original Research Article

A ferrocenyloligonucleotide (FcODN) having contiguous cytosine bases was immobilized effectively and reproducibly on a gold electrode furnished with a self-assembled monolayer (SAM) having an N-hydroxysuccinimide-activated carboxylic acid. The resulting electrode was used as a sensor chip in DNase I assay. Thus, the current response of the modified electrode decreased upon addition of DNase I, demonstrating that the phosphodiester bonds of FcODN were cleaved. The DNase I activity assessed by Δi defined as (i0 − i)/i0, where i0 and i represent the current before and after DNase I treatment, respectively, was found to be reproducible with a standard deviation not greater than 9%. The DNase I can be quantitated in the range of 10−5 to 10−3 units μL−1 with a detection limit of 10−5 units μL−1 with this sensor chip. The current signal of the FcODN electrode was stable to storage in Biopak water up to 16 days with a 30% signal decrease over this period. DNase I activity in human sera was also determined successfully with this sensor chip.