Biosensors Using Micromachined Polyimide Probes

This paper explores the electrochemical patterning of thin metal films using a scanning probe tip as an electrode. In particular, a masking nickel film is etched to reveal a gold pattern to which biomolecules like liposomes and proteins can be attached after treatment with functionalized self assembled monolayers (SAMs) of gold-thiolate. The machining is performed by ultracomplaint polyimide micromachined probes (with tip diameter <200 nm) as the machining tool in NaCl:HCl electrolyte. These probes provide an embedded electrical lead as well as high mechanical compliance that eliminates the need for servo control, which is typically needed to maintain the proximity between the workpiece and the tool. By applying 500 ns, 2 V pulses, 3 μm wide patterns were fabricated. Experiments suggest that they can be scaled down to tens of nanometers by using 5 ns pulses. Selective adsorption of undecanethiol SAMs to the patterned gold was confirmed using XPS spectroscopy.