Tuesday, 4 November 2014

Shrinking down chemical analysis - microTAS 2014

Just got back from microTAS conference 2014 (micro total analysis systems). The conference was all about miniaturised chemical detectors. A lot of what was shown was lab-on-a-chip devices which makes use of semiconductor chip technology to fabricate channels in plastics to automate lab work.

One of the questions I often get when I show off microfluidic chips is "What's so amazing about that?". Most people don't have a macroscale reference to see how amazing fluid moves in small channels. So the day before we had to leave for San Antonio we decided to do an experiment for the video competition (very quickly!!) where we went from a macrofluidic mixer to a microfluidic mixer. We ended up placing in the top 3 videos at microTAS the only educational video.

Just to give a taster as to what was at microTAS here are some of the amazing devices that were being shown off.

Digital microfluidics
A.H.C. Ng gave a presentation on a digital microfluidic system from the wheeler lab from the University of Toronto that automated the synthesis of gold nanoparticles with DNA bound only on one side of the nanoparticle which can then self assemble into structures.

I was surprised to find out that the digital microfluidics platform they developed is open source and is available online. All is needed is a high voltage power supply and some pcbs and an arduino. They also got a video into the top three videos at microTAS which shows off their open source digital microfluidic device Dropbot.

Droplet to digital microfluidics
Steve C. C. Shih presented a talk on his new droplet to digital system from the Joint Bioenergy Institute USA. A droplet maker was used to put single yeast cells into each drop. These were then transferred over to a digital microfluidic device that mixed the droplets with an ionic liquid. The idea was to see how ionic liquids damage the yeast. As ionic liquids can be used to help convert cellulose into sugars for biofuel production. However the ionic liquids can damage the yeast cells which are meant to eat the sugars.

Graphical abstract: A droplet-to-digital (D2D) microfluidic device for single cell assays

They designed and made the whole system using arduino's. The device really leveraged the best out of both technologies and has been published in lab on a chip last week

 image file: c4lc00794h-f3.tif

Inertial microfluidics
I went to a workshop run by Assoc. Prof. Di Carlo on inertial microfluidics. Two main forces dictate if a microfluidic flow will be laminar (Steady and predictable) or turbulent (unsteady and difficult to model); inertial forces, which relates to the momentum of the fluid and viscous forces, where the fluid resists being sheared. Often when modelling microfluidics we ignore inertia and arrive at Stokes flow. However a recent review by Assoc. Prof. Di Carlo looked at including these effects and the different phenomenon that can be observed.

You are also able to arrange particles in a flow due to the way the particles deform the flow. This deformation is felt by other particles and leads to nicely ordered particles in channels.

Di Carlo Inertial Microfluidics
You can use this to put individual particles or cells into single droplets which is super useful for doing lots of cell based analysis.

Dino Di Carlo
It can also be used to align particles along a channel.

As fluid moves around a corner or around a barrier you get vortices set up which allow you to more easily mix solutions. Which as I showed with the mixer at the beginning of this post is quite difficult.

 uFlow was demonstrated a program written in python that allows for calculation of the flow pattern at the outlet. If you were to do this with a finite element modelling program it would take hours to run each time. To reduce this time they calculated advection maps (transport map) for pillars at different places in the channel and operated on the concentration profile by these maps to make the simulation run in real time. This was a really interesting way to speed up simulations in microfluidics and I am thinking about what else could be simulated in this way.


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