Low melting point metal-based flexible 3D biomedical microelectrode array by phase transition method.

In this study, we present a dimension-controllable 3D biomedical microelectrode based on low melting point metals (Bi/In/Sn/Zn alloy) applied using the phase transition method. We have established a process, in which the liquid metal is pumped through a syringe needle of the dispensing system to form a needle shape after cooling at room temperature. PDMS (polydimethylsiloxane) was chosen as the substrate of the electrode as it is amenable to micro-molding and has excellent flexibility. Several key factors, including lifting velocity of the syringe needle and sample temperature were examined as to how they would affect the height, width and depth-width ratio of the electrode, to realize size control of the electrode. Afterwards, the skin-electrode impedance was tested and the results were compared with those of an Ag/AgCl (wet) electrode. The impedance at 10 Hz is 2.357 ± 0.198 MΩ for the 3D microelectrode. From data, the impedance of 3D microelectrode is found to be at the same level as the Ag/AgCl electrode at the frequency of 10 Hz. By increasing the size of the array, the impedance of the low melting point metal electrode and the wet electrode converge. The resistance of the electrode was also measured to describe its stretchability. The electrode can be stretched to a maximum of 42% before it becomes non-conducting. In addition to acquisition of bio-electric signals, our method has strong prospects in the field of bio-sensing.