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I have to develop a sensor that can detect photosynthesis. So when the plants are exposed to sun I should get an indication that photosynthesis is happening inside the leaves.

I found many products on internet but these are very costly, except this one (must be cheaper since used for kids) which shows a video of a sensor.

Can somebody tell me what is the main sensor which has been used here?

Another link

This says that:

During photosynthesis, leaves soak up blue and red light but reflect invisible near-infrared light.

So may be there is an infrared sensor under the pcb.

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    \$\begingroup\$ Do you mean a sensor that detects if there is enough (and the right wavelength) of light to do photosynthesis, or do you actually mean something that is able to detect the chemical process (and if it has to work with both, C3 and C4 plants)? \$\endgroup\$ – PlasmaHH Jan 28 '15 at 13:59
  • \$\begingroup\$ @PlasmaHH Right now I need to get an indication that yes photosynthesis is actually happening when exposed in sun. But the complexity would gradually increase. Do you have any idea what the sensor is in the video ? \$\endgroup\$ – user3891236 Jan 28 '15 at 14:04
  • \$\begingroup\$ Weird, I have no idea what the sensor is. It looks to have two probes, so conductivity???? \$\endgroup\$ – George Herold Jan 28 '15 at 14:10
  • \$\begingroup\$ Can you post a link to the other sensors (hopefully one that describes how it works.) \$\endgroup\$ – George Herold Jan 28 '15 at 14:19
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    \$\begingroup\$ @user3891236: you mean the photosynthesis that is taking place in the shadowed part of the leaf? that part without light? \$\endgroup\$ – PlasmaHH Jan 28 '15 at 15:00
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Here, It looks like an LDR (light dependent resistor) and also some probes to tell when it is touching the leaf. So really just measuring the light level. (with no filters!) I'm guessing I could shine a green led on it and it would tell me the leaf is making sugar, while in fact green light doesn't work.

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  • \$\begingroup\$ Why you said green LED does not work ? \$\endgroup\$ – user3891236 Jan 28 '15 at 14:42
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    \$\begingroup\$ @user3891236: because most chlorophyll molecules ignore green light, which is evident, given most leaves appear green. \$\endgroup\$ – PlasmaHH Jan 28 '15 at 14:45
  • \$\begingroup\$ google.com/… \$\endgroup\$ – George Herold Jan 28 '15 at 14:47
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If you want to measure how much light is available for photosynthesis, the method shown in your video is fine. If you want to measure photosynthesis as it occurs, I think the easiest way is to use a water dwelling photosynthetic plant and measure the oxygen produced, as in http://biologycorner.com/worksheets/photosynthesis_rate.html.

enter image description here

You might be able to do this by just using an oxygen electrode in the water, or if you capture the gas, you can measure the gas volume, probably by an optical interruptor or float mechanism. The rate of gas production, or the derivative of Volume, is the speed of photosynthesis.

Other than that, the only other method I could think of would be to do research to determine if the electrochemistry of photosynthesis changed membrane potentials in plant cells, and if so, use techniques such as are mentioned in THIS QUESTION. Brief research shows that there are electrical potential changes associated w/ photosynthesis: http://www.annualreviews.org/doi/pdf/10.1146/annurev.pp.28.060177.002443. Between that and the electrical potentential in plants ref I provide in the linked question, you have a reasonable start.

An additional useful resource might be Noninvasive Measurement of Membrane Potential Modulation in Microorganisms: Photosynthesis in Green Algae.Eun-Hee Lee et al. ACS Nano (Impact Factor: 12.03). 12/2013; DOI: 10.1021/nn405437z PubMed

http://www.researchgate.net/publication/259392613_Noninvasive_Measurement_of_Membrane_Potential_Modulation_in_Microorganisms_Photosynthesis_in_Green_Algae

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