Team:Newcastle/Notebook/Lab/Microfluidics

Lab Notes: Microfluidics

This page documents the wet lab experiments relating to our microfluidic devices. Be sure to look at our library of frequently used protocols that are referenced from this page with any amendments.

26/07/16

Ollie and Jake spent the morning with Dr Lucy Eland from the ICOS research group, who showed them how to manufacture microfluidic devices from polydimethylsiloxane (PDMS) gel . These would be useful in achieving the required temperature change to activate our heat-mediated devices in a more controlled manner, due to the very small volume of bacterial culture in the internal chamber.

28/07/16

We spent the morning testing the heating effect of varying electrical current on LB broth, determining how the time taken to achieve a 15 °C increase changed depending on the amount of current (ampere) supplied. This experiment demonstrated a large change in heating over a very small range of currents, and informed our future designs by providing the optimum current for a steady increase in temperature without boiling the broth in the chamber or failing to achieve the required temperature within a reasonable amount of time (12 mA).

02/08/16

Lucy showed us how to properly prepare the PDMS gel devices for lab use, refining their shape using scalpels and punching holes for electrode insertion. We then bonded the chambers to glass slides for later integration into the breadboard kit. Ollie then began work on a mounting piece to receive the slide and consulted with Dr John Hedley to see if there were any cheaper alternatives to the lab standard platinum wire, which there were not. Jake and Josh conducted conductivity experiments with salt solutions of varying concentration, which unfortunately did not provide replicable results due to copper buildup at the anode. We also calculated that 0.03g of chlorine gas could potentially be produced due to electrolysis of the LB broth inside the chamber, but observed no negative effects on cell growth during plate counts.

03/08/16

Ollie began research on sources of platinum wire, seeking sponsorship from corporate groups for the project, as well as examining the electrochemistry of other metals typically used as electrodes outside of biological applications. The main issue concerning these substances was the leaching of biologically active ions (e.g. Cu²⁺) into solution due to electrolysis which would interfere with the activity of the E. coli we were examining.

15/08/16

Ollie met with electrochemist Professor Ulrich Stimming and Dr Jochen Friedl to discuss our microfluidic devices and enquire as to ways in which our electrical heating experiment protocols could be improved, as they had so far provided inconsistent results. They very kindly agreed to let use their impedance spectrometry equipment to determine conductivity and resistivity of fluids inside our microfluidic chambers.

25/08/16

We wrote up finalised versions of our electrical heat testing protocols using the feedback gained from the discussion with Professor Stimmer and Dr Friedl.

05/09/16

The University of Reading's Microbial fuel cell kit inspired us to try and design our own microfluidic version, which we could not only integrate into our breadboard but investigate its electrical output relative to the larger version. Ollie created a 3D model which was sent to Jekaterina Maksimova in OpenLab, but unfortunately made a mistake with the sizing of the model and the resulting 3D prints were far too small to be used.

06/09/16

We finished soldering the electrical cables to the breadboard receptor piece and were successfully able to attach the microfluidic device and integrate it into our kit.

09/09/16

After some improved mathemetics, Ollie was able to correctly size the 3D prints for the microfluidic microbial fuel cell. He then attempted to mould a gel construct around the print, but did not fill the mould to a high enough level for the gel to completely cover the chamber-forming parts of the mould, which resulted in tearing of the device when the mould was removed.

19/08/16

Once again Ollie attempted to make a microfluidic fuel cell, this time allowing plenty of spare PDMS mix to fill the mould well above the chamber forming components of the print. Thankfully it worked, and upon bonding to a glass slide we had successfully built our design. At this point, any further designs were suspended to allow time to work on other areas of the project.

05/10/16

Ollie tested the output of the microfluidic fuel cell using the same reagents used in the experiments with the Reading Fuel Cell kit, preparing them via the same protocol He made up 10 ml of potassium hexacyanoferrate (III) solution in one universal tube, and mixed 3 ml methylene blue + potassium phosphate buffer, 3 ml glucose + arabinose solution and 4 ml lysogeny broth (LB) with chloramphenicol containing the K101 large porin construct in another tube. A small piece of cationic exchange membrane was placed in the moulded receptacle, then one chamber of the microfluidic device was filled with potassium hexacyanoferrate (III) and the other with the mixed solution following low-speed vortexing. The microfluidic fuel cell behaved very similarly to the larger University of Reading's microbial fuel cell device, showing a small increase in output voltage over time, but with a much lower base output of approximately 20 mV, reaching 35 mV after 60 minutes.