Nanogap Devices for Analytical Applications

Micro- and nanogap devices are becoming increasingly popular for a wide range of sensing applications due to their potential for low-concentration label-free detection of targetanalytes as well as the ability to use minute sample volumes.Such devices can be operated in generator-collector configuration for the amperometric detection of nitrates, thiolates, chlorides and sulfides. The devices offer a widerange of advantages such as: rapid and mainly planar interelectrode diffusion; feedback amplification for redox processes; discrimination of chemically reversible targets fromirreversible interferences, such as oxygen; and improved specificity due to the two applied potentials.When the interelectrode spacing is reduced into the ‘nano’ regime the effect of the electric double layer formed at the electrode surface is pronounced. In low-ionic-strengthelectrolytes, the Debye length becomes comparable with that of the nanogap itself, forming a uniform electric field across the sample medium. Surface-bound biomoleculesoccupy a significant fraction of the interelectrode spacing, making dielectric spectroscopy measurements more feasible.One of the key difficulties with fabricating these devices is maintaining a sufficiently large sensor surface area whilst minimising the interelectrode spacing. Here two novelfabrication methods for horizontal and vertical coplanar devices are presented to demonstrate how larger sensing areas can be achieved.