Trapping of hyaluronic acid molecules on sharp nano-electrodes of various metals

This paper reports on the trapping of hyaluronic acid (HA) molecule from an aqueous solution by using a pair of sharp thin film nano-electrodes with a gap of 3 μm on an SiO2 surface which is hydrophobic due to hexamethyl-disilazane (HMDS) treatment. By applying high frequency AC voltage with a sine wave, the HA molecule (about 10 μm long) can be trapped between the Al nano-electrode tips. A frequency of 500 kHz or higher and peak-to-peak voltage of 20 V or higher were necessary to trap the HA molecular string. The width and height of the trapped HA molecule were 45–60 nm and 5–10 nm, respectively, indicating that the trapped string was a bundle of molecules. In addition to the Al electrode, HA molecules can be trapped to both Au and Pt electrodes subject to HMDS post-treatment to ensure the substrate surface is sufficiently hydrophobic. The results suggest that the trapping of the HA molecule is caused not by a chemical reaction with the metal surface but by physical adhesion to the metal surface.