A novel hybridization indicator for the low-background detection of short DNA fragments based on an electrically neutral cobalt(II) complex

An electrically neutral cobalt complex, Co(Eim)4(NCS)2 (Eim = 1-ethylimidazole, NCS = isothiocyanate) was synthesized and its interaction with double-stranded DNA (dsDNA) was comprehensively studied by electrochemical methods on a glassy carbon electrode (GCE). The experimental results revealed that the cobalt complex could interact with dsDNA via a specific groove-binding mode with an affinity constant of 3.6 × 105 M−1. The surface-based studies showed that Co(Eim)4(NCS)2 could electrochemically accumulate within the immobilized dsDNA layer rather than single-stranded DNA (ssDNA) layer. Based on this fact, the cobalt complex was utilized as an electrochemical hybridization indicator for the detection of oligonucleotides related to CaMV35S promoter gene. The results showed that the developed biosensor presented very low background interference due to the negligible affinity of the Co(Eim)4(NCS)2 complex with ssDNA. The hybridization specificity experiments further indicated that the biosensor could well discriminate the complementary sequence from the base-mismatched and the non-complementary sequences. The complementary target sequence could be quantified over the range from 5.0 × 10−9 M to 2.0 × 10−6 M with a detection limit of 2.0 × 10−10 M.

► An electrically neutral cobalt complex was synthesized and used as a novel electrochemical DNA hybridization indicator. ► The complex shows specific interaction with double-stranded DNA rather than with single-stranded DNA. ► The cobalt complex-based biosensor presents very low background interference due to the negligible affinity of the cobalt complex with single-stranded DNA.