Report on Monolith Devices

I’ve now made 18 pores in monolith devices, with only 1 real success, which was the first one that I report on already. All of the rest have failed for various reasons, mainly relating to the silicon nitride membrane in which the sensing pore is fabricated.

The first issue is fabrication time. Fabricating a pore in these membranes requires ~5 hours at 16 V, which is ~100 times longer than the previous batch. I suspect the reason for this is the low exposed membrane area provided by a 3×3 grid of wells in the spacer. Future iterations of this device would ideally have many more holes and/or larger membranes to expose as much sensing membrane as possible while maintaining integrity. This timescale means I can really only make 1 pore a day, so progress has been slow.

The most common cause of failure after pore fabrication so far is instability of the sensing membrane. Many of the pores I have made are >30 nm immediately after fabrication, which is unusual. Among pores that are initially small enough to be useful, many grow quite quickly in real time, and become unusably large before I am able to condition their electrical properties into a useful state. I saw instability issues in the previous batch of membranes on which I assembled our filter devices, but not to this extent.

Finally, for the handful of pores that were stable, I only saw a significant number of DNA translocations through the very first one, and nothing I could confidently call DNA since then.

All of the failure modes point the finger squarely at the sensing membrane. For the next batch of monolith devices I would suggest the following changes:

1 – more holes in the spacer to speed up pore formation

2 – a different source of nitride for the sensing membrane, if possible

Let me know if there are any questions.