Optically-Monitored Nanopore Fabrication Using a Focused Laser Beam

Abstract

Solid-state nanopores (ssNPs) are extremely versatile single-molecule sensors and their potential have been established in numerous biomedical applications. However, the fabrication of ssNPs remains the main bottleneck to their widespread use. Herein, we introduce a rapid and localizable ssNPs fabrication method based on feedback-controlled optical etching. We show that a focused blue laser beam irreversibly etches silicon nitride (SiNx) membranes in solution. Furthermore, photoluminescence (PL) emitted from the SiNx is used to monitor the etching process in real-time, hence permitting rate adjustment. Transmission electron microscopy (TEM) images of the etched area reveal an inverted Gaussian thickness profile, corresponding to the intensity point spread function of the laser beam. Continued laser exposure leads to the opening of a nanopore, which can be controlled to reproducibly fabricate nanopores of different sizes. The optically-formed ssNPs exhibit electrical noise on par with TEM-drilled pores, and translocate DNA and proteins readily. Notably, due to the localized thinning, the laser-drilled ssNPs exhibit highly suppressed background PL and improved spatial resolution. Given the total control over the nanopore position, this easily implemented method is ideally suited for electro-optical sensing and opens up the possibility of fabricating large nanopore arrays in situ.

Automated, Ultra‐Fast Laser‐Drilling of Nanometer Scale Pores and Nanopore Arrays in Aqueous Solutions

“…Our results point to a highly Si:N composition‐ and pH‐dependent mechanism that is clearly photo‐activated. Importantly, we show that at high Si:N ratios and alkaline conditions, we can drill functional nanopores in <10 s at laser excitation powers that are roughly an order of magnitude smaller than those employed in previous reports . This enables controlled in situ laser fabrication of nanopore arrays with arbitrary patterns within minutes.…”

“…We recently reported on a method for direct, in situ laser‐based membrane‐thinning and fabrication of ssNPs in the range of just a few nanometers in freestanding silicon nitride (Si x N) membranes ( x = 0.75 for stoichiometric Si 3 N 4 ) . Requiring just a mW‐intensity laser and a confocal microscope, nanopores could be fabricated at any arbitrary position and in any quantity.…”

Comparing current noise in biological and solid-state nanopores

“…Nanopores can be drilled into the membrane in a variety of ways, e.g. by using a transmission electron microscope (TEM) 78,79 , focused ion beam milling (FIB) 80,81 , reactive ion etching (RIE) 82 , laser-etching 83,84 , or by dielectric breakdown 85,86 , resulting in pore diameters from sub-1nm to tens of nanometers. In a standard solid-state-nanopore experiment, the chip is sandwiched between two rubber O-rings that seal two compartments containing the electrolyte solution ( Fig.3f).…”

Nanopore Formation via Tip‐Controlled Local Breakdown Using an Atomic Force Microscope

“…Thus, not only can TCLB drive novel nanopore sensing applications, TCLB can simultaneously drive the industrial scaling of these applications. As an example, consider combining TCLB with photothermally assisted thinning . In a photothermally assisted thinning process, a laser beam is focused on a silicon nitride membrane, leading to formation of a locally thinned out region, with thinning achieved down to a few nanometers .…”

“…As an example, consider combining TCLB with photothermally assisted thinning. [27,42,48] In a photothermally Figure 6. a) Semilog plot of the mean breakdown time (〈t BD 〉) versus voltage for 12-14 nm thick silicon nitride membrane with an exponential fit.…”