Chemists use expensive tools called spectrometers (there are several kinds) to analyze unknown solid or liquid samples. We are working on a cheap version which we hope to use to identify oil contamination in water and soil, as well as a range of other possible toxins.
Spectrometers can also be used to identify species of plants or crop diseases, assess plumes from smokestacks, and have many other applications.
What we perceive as a single color consists of multiple blended colors- just as green paint can be made from mixing yellow and blue paint. A spectrometer is a device that splits light into the various colors it is composed of, which we otherwise cannot distinguish with the naked eye. By viewing a substance through a spectrometer, one can distinguish the exact mixture of colors, which correspond to specific wavelengths of light, that make up the perceived color of the sample.
Make a spectrometer
The PLOTS spectrometer is a Do-it-Yourself tool made from simple materials:
- 4 1/8" x 8 3/8" stiff black card paper
- a clean DVD-R
- a webcam
- velcro, dark tape, a box cutter/x-acto knife
The DVD's tightly packed grooves act as a diffraction grating -- basically a prism. When light enters, the different wavelengths of light are bent to different degrees, forming a rainbow -- a spectrum.
The above link offers step-by-step instructions on making your own spectrometer. There is also a short tutorial on how to take out the filter on the webcam (optional). This design is released under the CERN Open Hardware License 1.1 (read agreement here). It features:
- around 400-900 nanometer range, maybe wider (what you can see with the naked eye, plus some infrared)
- 5-10 nm spectral resolution
- 20-30 samples per second
- ~ $10 in materials
- < 1 hour construction time
- open-source software
Though these specs look pretty good, they still need to be compared rigorously with a traditional laboratory spectrometer. Are you interested in trying it?
Using your spectrometer
As we ship to the different Kickstarter backers, we'll post notes on how people plan to use their spectrometer:
One group of toxins common to fossil fuel contamination are PAHs, polycyclic aromatic hydrocarbons, which are generally carcinogenic. We're trying to develop a step-by-step experimental procedure to prepare a soil or water sample, shine a full-spectrum light (like a halogen lamp) through it, and detect the missing wavelengths.
If you're interested, please chip in to develop and document a consistent way to read samples here:
We're also putting together a list of research (some of it our own) to draw upon in developing spectral analysis techniques for anything from soil to grapes to coffee:
Online spectral analysis
Along with the physical tool itself, the PLOTS team has also developed a software suite and online spectrum sharing website which allows anyone to upload their data and work with others to try to interpret it. These tools are early prototypes and we're looking for help developing them.
Finally, a FAQ with some insights about actually using your spectrometer can be found here:
This is an early-stage, speculative project, but our goals include:
- Identify a contaminant in a sample, like a polycyclic aromatic hydrocarbon -- i.e. naphthalene, anthracene or tetracene. Tetracene has absorption bands well into the visible range.
- Identify a plant species by its spectrum. (see this helpful paper by Zomer et al) Or perhaps a mineral, using the ASTER spectral library
- Try to identify something in a smokestack plume, like a refinery plume
Several older designs have been documented on this site. Guides have been made showing you how to make some of these; they include: