Brown: Team Resistance/1 July 2008

1 July 2008
Run tests with pBAD+arabinose to see if lysis works tube 1: 0.333 tube 2: 0.239
 * culture of pVJ4 plasmid
 * incubated 15hrs
 * OD after incubation:
 * Create 1/100 dilution (0.5mL culture in 49.5mL LB) and incubate approximately 1 hour so culture is in mid-log phase (Jain/Mekalanos paper saw optimal lysis when cells in this phase)

We created a new resistance measurement apparatus that uses gold plated terminals (gold is an inert metal and thus prevent redox chemistry from occurring in the solution of cells). Also, with the previous apparatus we saw that when wires were stuck through the cardboard, it was difficult to prevent them from moving around in the holes and thus it was difficult to obtain consistent resistance readings. The new version of the apparatus features two wires, each soldered at one end to a gold electrode, hot-glued to either side of a strip of wood (created by gluing 2 wooden stakes to each other). Therefore, as long as the width of this wooden strip stays constant, so should the distance between the electrodes.

Salt tests to test consistency of new apparatus: We compared the resistance measurements of salt solutions via the multimeter and the labview program/circuit.

NaCl concentration	Multimeter reading (Ω)	Apparatus reading .001M 	                              41.81kΩ, 220.3kΩ	<0kΩ, 30.719kΩ .005M	                                   225.1kΩ, <0kΩ	--

The first reading corresponds to when the positive and negative electrodes were in the first orientation. The second reading in each box corresponds to when the poles of the electrodes were switched. Additionally, it was observed that when the resistance was in the range of 30-40kΩ the resistance reading continuously increased. When the resistance was in the range of 220-230kΩ the resistance reading continuously decreased. These results indicate that ions are migrating from one electrode to the other and are affecting resistance measurements. This problem may be solved with the use of an alternating current as opposed to a direct current.

Because the labview program/circuit can only output a constant voltage, Dan helped us implement a sinusoidal alternating voltage into our program