Science Buddies: "Ask an Expert"

I was wondering if the do it yourself photoresistor that you can make would detect the bioluminescence of algae. I did an experiment this year where I rated the bioluminescence myself on a scale of 1-10, but I would like to find something that would be less subjective. I have read that you can build a photoresistor that measures the luminescence of glow in the dark objects, but did not know if it would be sensitive enough to measure the algae. Thank you.

It is certainly possible to amplify the output of a phototransistor or possibly a photoresistor circuit to detect light from something as dim as bioluminescent algae. Noise might be a problem unless the circuit was designed and built carefully.

I'm not familiar with any methods of making your own photoresistor though - where did you read about that?

Howard

There is a science buddies project to measure luminescence in glow in the dark objects. It is talking about measuring the luminescence of glow sticks. You build a circuit and construct light-protected jars to hold the glow sticks. So I was wondering if I could build the jars where they could hold the algae. I have to agitate the algae to produce their luminescence so I would have to figure out how to do that. Thank you for your reply.

Pardon me - I misread your question and thought you were suggesting building an actual light sensor. You want to make a light reading circuit that can respond to extremely low light. Yes, that's certainly possible. A simple photoresistor in the configuration of most of the Science Buddies circuits probably won't do the trick. It's more likely that you'll need to use a phototransistor and an amplifier to pick up the low levels of light you'll get from the algae.

http://www.buildcircuit.com/experiments ... -amplifier has a circuit that could probably be tweaked for your purposes. I haven't tried it myself to see if it really handles low light, but the idea is sound: use a phototransistor and then amplify the output to better handle low light. I looked around on the internet a bit to see if i could find something preassembled or a kit you can build, but didn't find anything. Maybe you'll have better luck than I did. Perhaps that 741 experimental circuit will head you in the right direction.

Howard

Thank you. That directs me in the right direction!

am new to this ....please i need fast help ....anyone can help me how to measure luminescence produce by the bacteria in my research work whic decreases simultaneously by addition some of my sample to this bacteria ...i mean is it possibe to measure lowest intensity of luminiscent produced by bacteria in the dark by the above experimental sets and the circuits you have suggested.

Hi,

One thing before I answer your questions--please put ALL your posts on a SEPARATE thread. When two or more students post on one thread it is confusing to the experts who are trying to answer one student at a time.

You could try building the amplified photoresistor circuit suggested by Howard in the previous post but unless you have some skill and experience in building electronic circuits this could be too difficult. If you have a digital camera that allows you to set the shutter speed you could take a photo of the bioluminescence http://www.abdn.ac.uk/staffpages/upload ... size=16512

You will need to have the bacterial cultures in a perfectly dark room and set up the camera on a support aimed at the bacteria as close as possible. Focus the camera with the lights on then set the exposure time to about 10 seconds. Turn off the lights and when the bacteria are glowing take the picture. Make sure the camera does not move during the photo. I don't know how long you will need to do the exposure. That is something you will have to try with your individual camera.

Let us know what you want to do. If you want to build an electronic device to measure luminescence we can help you with that. With photography you can see differences between bacterial cultures but you don't get a quantitative measurement of light intensity. Photography is useful because you will have an image to show people what your glowing bacteria look like.

Sybee