A while ago, we introduced our new Nano Channel >Trap< Chips, designed to simplify trapping particles precisely where we want them inside our Nano Channel Chips.
In all our other chips, we are depending on high concentration samples to make it statistically likely that we will find particles in a number of channel-volumes (which are just femto liters, meaning, normally we need particles per femtoliter!).
But with these trap-chips unusually high concentrations are no longer needed as the traps act as a filter and even low-concentration samples will eventually have particles in the traps if enough liquid flow through the channels.
This time, we're showcasing our new innovation in collaboration with Prof. Qian Chen from the University of Illinois Urbana-Champaign where we conducted a product demo. The images and movie below are collected by PhD candidate Oliver Lin from her group.
Any Nano Channel Chip - with or without traps - has 4 inlets and 2 large bypass channels. The two bypass channels are enormous (relatively speaking) and allow for filling or exchange of up to two liquids at once, within seconds.
These two bypass channels are connected via the nano channels between them - a large pressure in one bypass channel drives the liquid through the nano channels into the other bypass channel, and vice versa. This is how we obtain flow control in the chips.
Only the nano channels are visible in the TEM and the larger micro-bypass channels are inside the solid silicon in the chip and are therefore not seen.
In any experiment, the strongly hydrophilic chip will pull in the liquid as soon as it touches any of the 4 inlets. When we prepared the chip for the experiment showcased here, we simply put one droplet onto one inlet. The capillary forces pull the liquid into the nano channels and even into the bypass channel on the other side of the chip. This ensures that a large number of channel-volumes pass through the filter.
The filters are basically confinements in the channel. Specifically here, the channels are 90 nm deep almost everywhere, except in a small region where the depth is only 5-10 nm. That means liquid can flow through the entire channel but particles larger than 5-10 nm are trapped at the confinement.
Various channel designs exist, and in this case, we use a highly condensed channel pattern for optimizing the number of trapping sites in one chip. The particular design used in this case has 54 channels to trap particles! The traps can be seen in this image in between all the blue, broader channels, as the small horizontal brown channels (the color always corresponds to the depth of the channels!).
Sample preparation with these chips is always very straightforward, similar to using a traditional grid. The steps are simple and take just 5 minutes, even for people with no practice:
1) Liquid is added to the chip with a pipette - 0.5 µL is plenty!
2) The chip is placed in the holder
3) The lid is screwed on
4) Holder is inserted in the TEM
The sample used is ~80 nm gold particles with a thin polymer coating.
This first image outlines the different depths of the channels and the direction of the liquid flow. The 'deep' liquid region (~90 nm) in the middle is where the particles can flow - and they flow no further than the shallow (5-10 nm) channels that go off to the sides. The liquid freely travels through the shallow channels and therefore particles are continuously supplied to the channel.
In the following movie, interesting particle dynamics can be observed: In the top, all the particles have stacked together in seemingly robust assemblies, but closer to the bottom the assembling is still going on! In fact, throughout the movie the assembly can be seen growing and below the growing assembly the dynamics are so fast that just a dark blur of particles can be seen.
Interesting experiments can be made with our Nano Channel Chips and nanoparticle self-assembly. With these chips it will be possible to
- Heat up the liquid (which our new prototype can do to 150C)
- Flush in multiple liquids
- Break up the self-assembly by flowing backwards - only to watch it reassemble again (and again)
Thanks to Prof. Qian Chen and Oliver Lin from the University of Illinois Urbana-Champaign, for their time and interesting results to share.
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