Polymer‐Protected Sub‐2‐nm‐Nanogap Fabrication for Biological Sensing in Near‐Physiological Conditions

Abstract

Polymer‐protected sub‐2‐nm nanogaps that are fabricated via a novel electrical stressing approach exhibit substantial ionic‐current reduction in near‐physiological conditions. These devices enable direct DNA detection in aqueous solution by utilizing assembly of oligonucleotide‐modified gold nanoparticles to the nanogap (see image).

Parallel fabrication of polymer-protected nanogaps

“…Next, a simple voltage sweep at 1 mV per 7 s was applied to the bowtie structures at room temperature using a Keithley 4200 parameter analyzer to electrically stress the connected electrodes until nanogaps have formed in all the electrodes (figure 1(a)). Sub-2 nm nanogaps and selfaligned PMMA hole structures of 200 nm diameter were simultaneously formed at the constriction sites, similar to what we achieved in [25] for a single constriction. The formation of the sub-2 nm nanogaps was due to thermally assisted electromigration of the gold atoms, while Joule heating caused a rapid temperature rise at the constriction site leading to a local ablation of the PMMA, which resulted in a hole structure right on top of the nanogap (figure 1(b)).…”

“…We previously reported the realization of protected sub-2 nm nanogaps through a process of electromigration and concurrent self-aligned polymer ablation in a polymethylmethacrylate (PMMA)-coated constricted electrode structure, using a simple slow voltage sweep [25]. In the present work, we demonstrate that an array of such protected nanogaps can be fabricated by carrying out the electromigration process using a parallel connection of multiple constricted electrode structures.…”

“…The temperature increases rapidly by Joule heating during electrical stressing at the constriction site, and therefore the polymer layer experiences a local expansion and gradually reflows. A dome-shaped structure is then formed due to buckling and eventually the polymer is locally ablated, resulting in the formation of a hole located precisely at the final breakdown point of the electrode where the temperature is highest [25].…”

“…Furthermore, if nanogap devices are used for sensing in an aqueous environment, they are faced with the problem of high extraneous current due to parallel conduction paths through the ionic solution if the latter is in contact with the electrodes leading to the nanogap. To overcome this, a few techniques have been reported to selectively passivate the nanogap device, including local polymer ablation by an electric field [24] or Joule heating [25], as well as traditional lithographic patterning of a protective film [26]. The principle underlying these techniques is to insulate the electrodes from the solution with a polymer layer except for an opening at the nanogap position.…”

Capturing a DNA duplex under near-physiological conditions

“…32,33 In a typical experiment, we first patterned electrodes with a constriction by electron beam lithography. 32,33 In a typical experiment, we first patterned electrodes with a constriction by electron beam lithography.…”