Growth occurs along the straight-line path from a user selected electrode to a second electrode lying within a ~140° angular range and a ~100 µm radius of the initial electrode (see image). The applied voltage defines a ridge of electric field maxima that extends between the selected electrodes. This ridge serves as an electrochemical growth channel for the wires, analogous to the mechanical channels of templated nanowire-growth techniques. However, this template can be removed by simply switching off the voltage.

By readily attaching nanowires to macroscopic electrode pairs, this technology provides a convenient means of characterizing nanowire-transport properties. Alternatively, targets such as living cells may be located along the growth path prior to growth. DENA may then be used to grow a nanowire into contact with the cell for electrophysiological applications.

DENA is executed by depositing a ~10 µl aliquot of aqueous solution containing the growth material onto lithographically prepared electrode arrays. Growth is induced by applying a square-wave voltage across an electrode-pair and proceeds until the wire bridges the gap or the user terminates the voltage signal. The wire material is changed by swapping growth solutions: a 50 mM In(CH3COO)3 solution was used to grow In wires whereas a 10 mM ethylenedioxy-thiophene was used to grow polythiophene wires.

Electrode kits available by 2010

The range of known DENA-active materials is almost certainly incomplete, so an important future direction is the identification interesting wire-types. The on-chip production of biological filaments, like f-actin or sickle hemoglobin, are current goals. We have recently started the company NanoGenix to fabricate nanoelectrode growth-kits for sale to researchers and educators who require nanowire-growth capabilities. We expect these kits to be available by 2010.

The group published its research in Nanotechnology.