Simple, Cheap Nitrate Tester Is Open Source

Too much of a good thing can be a bad thing, and nitrate pollution due to agricultural fertilizer runoff is a major problem for both lakes and coastal waters. Assessing nitrate levels commercially is an expensive process that uses proprietary instruments and toxic reagents such as cadmium. But [Joshua Pearce] has recently developed an open-source photometer for nitrate field measurement that uses an enzyme from spinach and costs a mere $65USD to build.

The device itself is incredibly simple – a 3D printed enclosure houses an LED light source and a light sensor. The sample to be tested is mixed with a commercially available reagent kit based on the enzyme nitrate reductase, resulting in a characteristic color change proportional to the amount of nitrate present. The instrument reads the amount of light absorbed by the sample, and communicates the results to an Android device over a Bluetooth link.

Open-source instruments like this can really open up educational opportunities for STEM groups to get out into the real world and start making measurements that can make a difference. Not only can this enable citizen scientists and activists, but it also opens the door for getting farmers involved in controlling nitrate pollution at its source – knowing when a field has been fertilized enough can save a farmer unnecessary expense and reduce nitrate runoff.

There are a lot of other ways to put an open-source instrument like this to use in biohacking – photometery is a very common measuring modality in the life sciences, after all. We’ve seen similar instruments before, like a DIY spectrophotometer, or this 2015 Hackaday Prize entry medical tricorder with a built-in spectrophotometer. Still, for simplicity of build and potential impact, it’s hard to beat this instrument.

19 thoughts on “Simple, Cheap Nitrate Tester Is Open Source

    1. Yeah it would be then but its more or less unreliable then. Making reagents that always show the same result for same concentrations of nitrate isn’t that easy…

      I think thats a small trade off here…

    2. Do you make your own steel, wire, sponges, soap, integrated chips, silicon boules, cd players, screwdrivers etc. Likely not, because some of us while we could do so, choose to invest our time and energy for a better return on that time investment. In addition while all the proper steps could be taken by one’s self the yield and quality of such endeavors is usually substantially less then commercial solutions with a much higher investment in quality control then the average kitchen lab.

  1. At first I wasn’t sure what the advantage of the instrument was over just looking at the color of the reagent, but the article makes the point that using a sensor device like this leads to a much higher accuracy.

    Today I Learned and that makes it a good day. Cool beans!

  2. If you install a couple LEDs of specific wavelengths (easier than a diffraction grating) you’d vastly improve the usability of this device. Many assays use absorptivity to determine concentration, as the article pointed out, but they rarely use the same wavelength. Pick your LEDs based on the assays you preform most often and save yourself from building multiple testing boxes.
    The ideal case is a variable wavelength source, but those cost big bucks and can be finicky to maintain. Not worth the hassle or $$ for most DIY folk.

    1. This! I have used LEDs reverse biased for sensing applications and they work surprisingly well. My favorite is a red LED used to see when the red light comes on in an arcade prize machine and a solenoid to hit the button. I got a PS Vita and an iPod before I was banned from the bowling alley :)

  3. So if we have thousands of these set up remotely to monitor background nitrates in a specific populated area could we not ascertain if there was a threat of explosives in that area?

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