One of the outcomes of our kick-off meetings from the 14th of September was to try and alternate the emission of the blue LED and the measurement of the light to frequency converter. The trick for this would be to try and play with the Pulse Width Modulation of the Arduino and use Interrupts to keep the LED on for a certain amount of time and then turn on the light to frequency converter.
To implement the blinking of the LED we had to investigate if the GFP would stay fluorescent long enough after its excitation was stopped. We researched the fluorescence of GFP and found in this paper “Application of fluorescence lifetime imaging of enhanced green fluorescent protein to intracellular pH measurements” by T. Nakabayashi (see here) which shows that in a solution of 7-8 pH the lifetime of 3 nanoseconds. That means that between the time at which we stop the LED and the time at which we turn on the sensor there has to be maximum 1 nanosecond (the time for the light to travel from the sample to the sensor) so that we measure it at it maximum intensity.
With our current hardware this will not be possible, the rate of the Arduino clock is of 16Mhz, this means that by setting the smallest timer possible, we can have a tick each 62.5 ns, which is too slow for the measurement we want to make. For a tick each nanosecond we would need a chip with a rate of 1 GHz.
This improvement can sadly not be done with our current hardware setup, maybe if we find a low cost microcontroller with a higher rate we could investigate the blinking again, for now we will go back to laboratory testing.