DI-lambda is an open source spectrophotometer (video 1). In 2014, members of our team began working with high school students through the Open Science School association. Very soon, we were wishing for cheap and easy-to-understand lab equipment. We realized that a basic spectrophotometer, with open documentation, could teach both lab methods and the principles behind them, all at a price low enough for students to use, share and break as often as learning requires.

A spectrophotometer measures the absorbance of light at a certain wavelength. Our device achieves this with open hardware and source code freely available on github. DI-lamba features accuracy equalling top commercial models at a very low price, and is also capable of fluorescence measurements.

There have been many attempts to build open source spectrophotometers, but most are not available to the public. Our work includes key features not found in earlier efforts: Extensive documentation about design and building. A troubleshooting guide. Accuracy comparable to existing devices or industry standards. Design for cheap assembly and mass production

1/ One mass production success is the desktop spectrometry kit 3.0 from PublicLab (Fig. 1). (It is actually a spectrometer, not a spectrophotometer!) It looks simple and elegant, produces quality results, and has attracted a community of users.

3/ Another DIY solution came to us in the Journal of Marine Biology. It has a double channel, and it intended to measure pH with an indicator. The data looks great, but we weren’t able to access the source files. Source: Yang et al. (2014). "Seawater pH measurements in the field: A DIY photometer with 0.01 unit pH accuracy". Marine Chemistry. Volume 160, Pages 75–81.

4/ The last example here comes from another fellow iGEM team: iGEM Aachen 2014. Its design is somewhat similar to DI-lambda. They also measured fluorescence. We believe that our design can improve the overall accuracy.

Overall, while there are very promising projects, it looks like they most of them have been abandoned at early stages, after the initial limited success. The PublicLab spectrometer stands out here, has build instructions, is open-source, and can be purchased as a kit.

DI-lambda is an ​Open Hardware spectrophotometer, designed to be accurate, easy to modify, and extremely cheap. We achieve this by using LEDs instead of an optical refraction system.

This design choice (Fig. 5) means that the device is limited to one or a few pre-selected wavelengths, but most biological applications only use a few. It is also possible to select a different wavelength by populating a spare LED board, but since it's so cheap, it might be easier to just buy one for each task. Another disadvantage is large spectral width of LEDs, typically 15-25nm, compared to 1-5 nm for traditional spectrophotometers.

All this means that DI-lambda is not always able to replace a traditional spectrophotometer, but works great for a majority of biological applications.

We put a lot of time into calibrating our spectrophotometer. After tuning parameters, such as the distance between the LED, the sensor, and the cuvette, and the diameter of the pinhole through which the light has to pass, we achieve results that are virtually identical to our most reliable laboratory spectrophotometer.

We keep in mind the importance of interacting with the public and getting feedback from them, at at the same time communicate about science, synthetic biology and citizen science. We collaborated with several institutions and teams to organize events and workshops where participants could test spectrophotometer units… or even build their own units!

NightScience conference at the Center for Research and Interdisciplinarity in Paris was an opportunity in early July to meet 10 testers that built a simplified 1-channel version called DI-lambda Luna (Fig. 6). They had a high interest in electronics and synbio but low knowledge.

We took some time to cross the English channel and visit our friends at UCL. We spent a few days in London in the iGEM bootcamp organized by the students of UCL with the participation of synbio enthusiastics, high school students from UCL academy, and UCL, Birkbeck and London Hackerspace iGEM teams (Fig. 7). The pictures are just beautiful!

We are planning to make this tool available to more people and be able to mass produce it, keeping a cheap price and simple design. The interesting features of this tool are the low price and the ease to hack it, tune it to a specific need.

In order to do this tool and many more, this tool will continue integrated in the project Open Science School, at the Center for Research and Interdisciplinarity of Paris.

Please, do not hesitate to contact us if you want further information.