An Electrochemical Study of the Surface Hybridization Process of Morpholino-DNA: Thermodynamics and Kinetics

Morpholino (MO) is a neutral analogue of DNA, which shows promise in the development of DNA biosensors and diagnostic devices. The present study explores the hybridization process of a surface-attached MO 22-mer with 10-mer and 20-mer DNA targets on a gold electrode. The melting process of the MO-DNA duplex at the electrode/buffer interface is recorded using cyclic voltammetry. These results show that the length of target DNA, the binding location of the target DNA on the surface-immobilized MO chain, and electrostatic forces from neighbouring duplexes all modulate the stability and hybridization kinetics of the DNA targets with the MO probes. Melting temperatures for immobilized MO-DNA duplexes are found to be insensitive to ionic strength, provided the duplexes do not have a linker. Although the melting temperature does not shift appreciably with ionic strength, the maximum hybridization yield does. This somewhat surprising observation is considered to originate from an electrostatic limit on the extent of attainable hybridization. It is also reported that hybridization tends to initiate at the upper half of MO probes.