Public Lab Research note

Mobile cuvette holder

by cfastie | February 25, 2014 18:27 25 Feb 18:27 | #10065 | #10065

At SNOWFEST we made great progress on the smartphone spectrometer cuvette holder thanks to Jeff's Sketchup skills. Jeff started from scratch and created a working design which we printed on the Public Lab MakerBot Replicator 1 stationed at SNOWFEST HQ.

Jeff's cardboard mockup, the first prototype (pink), and two versions I printed on Monday.

This device is an attachment for the Public Lab smartphone spectrometer, and its design is still evolving. The current version will allow fluorescence measurements by shining a blue/UV laser through the sample in a cuvette. This technique has great promise for detecting various hydrocarbons associated with petroleum. A cuvette with a control substance can be measured at the same time.

The laser shines through both cuvettes. Fish oil fluoresces with a wavelength longer than the laser light, and the control (baby oil) does not. The spectrometer can capture spectra of both colors simultaneously.

The hollow area in the attachment will be developed to hold a battery and electronics to control LEDs which can be used for calibration and as a full spectrum light source for absorption and transmission measurements. In its current state, it can be used for absorption by inserting a small bulb behind the cuvettes.

The Public Lab smartphone spectrometer with cuvette attachment holding two cuvettes. A laser is inserted in one of the laser ports.

The files for the current iteration are all at Thingiverse. This includes an x3g file that is ready to print on a MakerBot Replicator 1 with PLA. An stl file for slicing to print on other printers is also there, as is the Sketchup file if you want to continue adding features or make it fit the spectrometer better. The standard Public Lab smartphone spectrometer fits well and sort of snaps on firmly. But I am not sure exactly what vertical angle is best, and this might vary from phone to phone. It is designed to use standard 12.4 mm square x 45 mm tall plastic cuvettes.

Screen capture from Sketchup of MobileCuvette0.1.6.skp.

Changes that have been made since SNOWFEST include:

  • adding windows for transmission or absorption measurements
  • making it shorter so you can grab the cuvettes to remove them
  • adding side clips to hold the spectrometer in place
  • lots of modifications to reduce the need for support structures (interior laser ports are teardrop, exterior overhangs are angled)
  • Netfabb finds NOTHING TO FIX in the current Sketchup version

The current x3g file builds very little support, and may therefore print with saggy ceilings. The minimal support structures for exterior overhangs are rather fragile, so monitoring the first 15 minutes of printing is advised.

Here are the files that are at Thingiverse right now, but the Thingiverse versions will usually be the most current.


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Wow, amazing progress! I love the photoshoot.

Can you upload the sketchup files etc. in the research note as well?

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Nice! I'm going to go print one tomorrow.

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That is great. It's just like a double beam spectrophotometer. Any chance to post some results. For example a 10mg sodium nitrate aqueous solution, shine laser and get whole spectra including UV-visible. The 10mg/L nitrate concentration in water(mainly groundwater) would give "baby blue" symptoms to children. Is so incredible to see all these improvements in such a short time by people actions.

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