Abstract
Nanogap sensors have a wide range of applications as they can provide accurate direct detection of biomolecules through impedimetric or amperometric signals. Signal response from nanogap sensors is dependent on both the electrode spacing and surface area. However, creating large surface area nanogap sensors presents several challenges during fabrication. We show two different approaches to achieve both horizontal and vertical coplanar nanogap geometries. In the first method we use electron-beam lithography (EBL) to pattern an 11 mm long serpentine nanogap (215 nm) between two electrodes. For the second method we use inductively-coupled plasma (ICP) reactive ion etching (RIE) to create a channel in a silicon substrate, optically pattern a buried 1.0 mm × 1.5 mm electrode before anodically bonding a second identical electrode, patterned on glass, directly above. The devices have a wide range of applicability in different sensing techniques with the large area nanogaps presenting advantages over other devices of the same family. As a case study we explore the detection of peptide nucleic acid (PNA)−DNA binding events using dielectric spectroscopy with the horizontal coplanar device.
Highlights
There is increasing motivation to develop low-cost parallel assays for point-of-care devices for disease diagnostics and environmental monitoring
The device is comprised of a central ~200 nm nanogap consisting of twenty 400 μm straight sections connected with twenty arcs of 50 μm radius to form an 11 mm long serpentine, maximising the length of the nanogap in the writeable area of the electron-beam lithography (EBL) system
In order to demonstrate a direct electrical detection application using a nanogap sensor, the horizontal coplanar nanogap device described in Section 2.1 was used to perform dielectric spectroscopy sensing of single-stranded DNA hybridisation with a ssPNA probe layer in phosphate-buffered saline (PBS)
Summary
There is increasing motivation to develop low-cost parallel assays for point-of-care devices for disease diagnostics and environmental monitoring. These often consist of triangular point-like electrodes with minute interelectrode distances to match that of the target molecule and minimal contact area for improved selectivity The second are those used for electrochemical sensing applications, where both reduced interelectrode distance and large surface area can lead to improved performance. Redox cycling involves polarising two closely-spaced electrodes so that an analyte can be repeatedly cycled between a reduced and oxidised state This leads to a single molecule contributing to the current response on each reaction, effectively amplifying the sensor response. The second method uses very simple optical lithography and a dry anisotropic etch to form a well-controlled sub-micron depth channel This channel allows a large lower electrode to be buried before an identical upper electrode patterned on glass is anodically bonded directly above, forming a ~500 nm nanogap.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
