Week 5

            I have chosen to go ahead with the fluorometer for my sensor. I am working with Dana on the sensor and we have made good progress this week. We started out by building a light detector using the photo resistor provided in the RadioShack kit. The circuit design was very simple and is connected to a potentiometer so we can adjust the sensitivity. The light intensity is displayed on the led readout on the RadioShack kit. That was the easy part.

            Next we set up a system of clamps so we can arrange a place for our light source, photo resistor, and our sample. We used a small test tube to hold our sample and a blue led light from the lab as the light source. We narrowed the beam of the light by pointing it at a small aperture. Our sample is located behind the aperture where the restricted beam of light will hit it. Perpendicular to the blue beam of light is our photo resistor. It is placed about a centimeter away from the sample. Over the photo resistor we have placed five layers of thin red transparent plastic. This stops the majority of scattered blue light from entering the photo resistor.

            The third step was obtaining a sample of known concentration to calibrate the fluorometer. This did not go so well, because we could not find any fluorometer to measure a sample. Neither Jim nor Bob Kirk (head of the chemistry laboratories) knew of a fluorometer we could use. So we decided to make a stock solution of unknown chlorophyll concentration and make our calibration in reference to this stock solution. We did this by using a quick and dirty chlorophyll extraction procedure. We boiled a few spinach leaves then mashed them into a paste and allowed the paste to sit overnight in rubbing alcohol. The next day we sieved the remaining chunks of spinach out of the mixture. It worked very well, the solution lights up bright red under blue light.

            We then started making dilutions of this stock solution in rubbing alcohol. We tried MANY different dilutions but did not find any correlation between concentration and the led readout. The next day we rearranged our set up and made sure every piece of the layout was very steady. Most importantly we made a new holder for the samples, so the samples would be in exactly the same position every time. We finally found good results by making dilutions using only drops from the stock solutions in six milliliters of rubbing alcohol. We blanked our fluorometer system by putting in a sample of only rubbing alcohol and adjusting the potentiometer so the led readout was zero. We increased the concentration by five-drop intervals until we reached 55 drops and the led readout was 10. We made a calibration curve from these measurements. Our curve is linear from 0 to 20 drops, and then follows another linear trend with a lesser slope from 20 to 55 drops. I don’t quite understand this, but it seems to work.

            I hope everything works for us on Tuesday although I am a little worried. We really struggled with making a calibration curve for our fluorometer because our results were not consistent. Also I am not sure how much our stock solution of chlorophyll will degrade over the weekend. Perhaps on Tuesday our stock solution will have lost some of its chlorophyll content. As of now it is in a jar in my fridge and I have my fingers crossed. Overall, I had fun making it and even more fun watching different solutions fluoresce under blue light. The picture below is our fluorometer while a sample is being read.