Nano-porous hydroxyapatite (HAp) was prepared with sol-gel method to modify glassy carbon electrode (GCE) due to its excellent biocompatibility and particular adsorbability. Double-stranded (ds) DNA was immobilized by effective adsorption on the nano-porous hydroxyapatite modified GCE surface. The interactions of DNA immobilized on the HAp film with methylene blue (MB) were investigated by means of cyclic voltammetry (CV). The results show that the redox currents of MB at DNA modified electrode had linear relationship with scan rate from 20 to 200 mV•s^－1, as expected for a surface-controlled process. The anodic and cathodic peak potentials both shifted negatively with increasing pH from 6.0 to 7.4. The results show that the interaction of DNA with MB was an electrostatic mode when ionic strength of PBS was smaller than 59 mmol•L^－1, while there was not only electrostatic but also intercalative mode between them when the ionic strength of PBS was more than 59 mmol•L^－1. The binding constant of MB to DNA was calculated to be 4.2×10⁴ mol^－1•L according to Langmuir adsorption formula.

Key words: DNA, nano hydroxyapatite, methylene blue, glassy carbon electrode