A Novel DNA Electrochemical Sensor Based on Grafting of L-Aspartic Acid and Cu2+ Ions on the Terminal of Molecule Beacons

A novel electrochemical DNA biosensor based on in-situ labeling of L -Aspartic acid-copper ion (Asp-Cu 2+ ) complex on the terminal of molecule beacons (MBs) was constructed. The MB with bifunctional groups of 3’–SH and 5’–COOH was first anchored on a gold electrode surface through Au-S assembly chemistry, then L -Aspartic acid (Asp) was grafted with the 5’–COOH of MB via succinimide coupling, which was used as a platform molecule for the following coordination assembly of copper ions (Cu 2+ ). Therefore an electroactive MBs probe with the copper complex (Asp-Cu 2+ ) as a signal source was obtained. The hybridization between the loop sequence and the target DNA transferred the hairpin-like MBs to the linear form, and the electroactive moiety of Asp-Cu 2+ was forced to leave away from the electrode surface, resulting in the reduction of the electrochemical response of the biosensor. The hybridization experiment results showed that the oxidation peak currents of developed biosensor attenuated linearly with the logarithmic values of the target DNA concentrations in the kinetic range from 1.0×10 -15 ~1.0×10 -10 M. The detection limit was estimated to be 0.17 fM. Moreover, the biosensor showed excellent selectivity for discriminating the complementary sequences from the mismatched and noncomplementary sequences.