Fun with PhotosynQ: Cuvette Holder

So while I had some down time (we are going through a slight board re-design to decrease noise and cross-talk) I worked on the ability of the PhotosynQ platform to gather non-plant data. I present to in all its glory, the MultispeQ cuvette holder attachment!

Here is the obligatory “action shot”. In reality the light pulses are so fast/short you can’t see anything.

Since a cuvette holder is basically useless without established methods that use it, I decided to adapt an assay designed to measure active soil carbon (carbon that is readily available for use by microbes) to the PhotosynQ platform. This assay is already in use by the USDA & many Universities ( Ohio, Missouri, etc).

The cuvette holder and PhotosynQ platform can (with a little work) be used for any of your standard absorbance assays that use wavelengths close to what the MultispeQ has available. For example, you could do Bradfords assay, or OD590 (the MultispeQ’s version of OD600). I am also working on a right angle cuvette holder for turbidity and fluorescence measurements.

The method is described here (it is pretty close to what I did) and I’ve got my own procedure that I will put out shortly (once I make a how to guide).

The MultispeQ in its natural habitat (the MSU Horticulture Gardens

The basic idea is that you can go outside, collect a soil sample, oxidize it with permanganate for 10 minutes, find the absorbance of the sample, compare it to a standard curve/plug some numbers into a formula, and then get a mg/kg amount of active carbon in your soil.

Here is a picture of my standard solutions (in the falcon tubes) and my soil sample (in the cuvette). Don’t worry, even though it looks like my soil sample will fall outside of the standard curve it doesn’t.

So after some troubleshooting I developed a protocol that works pretty well with the MultispeQ as it is now (once the new boards are in I might have to redo it, but its only going to get better).

Sadly as of now you have to calculate the absorbance manually (we are working on fixing that).

As you can see the standard deviation for the MultispeQ is higher than the labs spectrophotometer, but we expect that to go down significantly with the new boards.

This is a graph of the stand curve as done on the MultispeQ and the standard curve produced by the labs spectrophotometer.

Once the new boards are in I will work on optimizing this protocol so that the MultispeQ reports values that are closer to the labs spectrophotometer. I also have grand plans to integrate this assay into the PhotosynQ app, so you won’t need to plug anything into formulas or excel. As shown above, the deviation between the two becomes greater as adsorption rises. This will cause the MultispeQ to report values that can be ~30% greater than our control spectrophotometer. However, absorbances this large only occur in very poor soils, and as soil quality increases the error between the MultispeQ and the control spectrophotometer goes down considerably (in laymans terms we are able to very accurately calculate the absorbance of dilute solutions, even with the cross-talk and noise problems that we are correcting).


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