Technical_description

#Technical_Description
This is a technical description of how the ion sensitive electordes (ISEs) are set up for the depolarization experiment.
Ion selective electrode senses a specific ion and converts changes in its activity into an electrical potential, the voltage being dependent on log of activity of ions in solution.
An ISE is immersed in aqueous solution containing the ions to be measured together with a separate external reference electrode in case it is not a combination electrode without a built-in reference electrode.
In our set up, Na+ ISE has a separate external reference electrode while Cl- ISE has an in-built reference electrode. 
The example given is only for sodium and chloride measurements. The experiment gives a real time measurement of these ions in parts per million. The arduino sketch should be modified based on calibration measurements with standard solutions. This should be performed for each batch of experiments.
Pictures of the measurement set up can be found in
setup_picture1.jpg
setup_picture2.jpg
This shows how the setup would look for a calibration sample of 100ml of buffered salt solution
These show the setup for measuring Sodium and Chloride at the same time. The chloride channel has a single electrode, the sodium channel has the detection electrode and a reference electrode combined into a single potential difference.
The two bread boards are for each "channel" one for sodium, one for chloride. The circuit diagram for these op-amp non-inverting circuits are
given in the file "cdi.pdf"
The setup uses an Arduino Uno. The sketch file for this is also given for this example setup: "Cl_Na_electrode.ino". The calibration parameters
are set at the top of the sketch.

In this example set up, the Chloride voltage is read at the A0 analogue channel of the Arduino and the sodium at the A1 channel. 
The final experiment requires the addition of a potassium ion-sensitive electrode which could be similarly amplified to the Cl- electrode
and attached to the A2 channel. The script would then need updating to include these values as well.

The sensitivity of all the three electrodes must be determined by measuring the voltage in solutions containing, for example, 10ppm and 100ppm of the target ion, and the Slope will be the slope of the (straight) calibration line drawn on a graph of mV versus Log Activity. i.e. S = [ mV(100ppm) - mV(10ppm) ] / [Log100 - Log10]
Once the sensitivity has been measured alterations in ionic concentrations in cell solutions before and after induction of apoptosis can then be determined by measuring the voltage and plotting the result on the calibration graph.
However, there are some limitations to the set up. Since these are resin based electrodes, quick changes in ionic concentrations in solutions are harder to measure as the exchange of ions with the resin takes time. Also, there is the problem of ionic intereference for simultaneous measurement of multiple monovalent ions.  

All material is available open source under Apache: https://www.apache.org/licenses/LICENSE-2.0