Open source spectrophotometer

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Desire is to create a spectrophotometer for general use, as part of an open-source biotech hardware toolkit.



An absorbance spectrophotometer is a devices used to shine a specific wavelength of light through a sample, in order to divine the type and concentration of chemical species within the sample.

How to get specific wavelengths of light? First, use a light source which contains many wavelengths, then filter the light or diffract the wavelengths spatially. Although fluorescence (ex: phosphors) can be used to increase the number of wavelengths, a mere filter or prism can only separate the types of light already within the source.

More detail and extra notes in Light sources and Diffraction Gratings

Because we want to use this for biotechnology applications, we can come up with some desired wavelengths: Proteins, for example, are quantifiable by the absorbance and/or fluorescence of tyrosine and tryptophan, which absorb ~280 nm and emit from 300-350 nm. Other interesting wavelengths include DNA (260 nm) NADH (460 nm), chlorophyll (680 / 700 nm) and a variety of chromogenic reagents which can indicate very low concentrations of heavy metals.


Found an excellent low-cost project already written up by a brazilian group1, using a white LED, cd-rom diffraction grating, stepper motor, and phototransistor. First goal: implement using Arduino!


Need more wavelengths and less moving parts for successful low-cost biotechnology laboratory.

Stanford group2 uses 0.5 and 1 um amplitude gratings directly above a CCD, they get 1.7 nm bandwidth / pixel. We could use a digital SLR CCD, which we've heard have smaller elements (the paper's CCDs were ~10 um squares). There are a wide variety of amplitude (AKA transmission) gratings available, but a few things still need to be figured out:

1: UV is absorbed by glass and plastic, so we can't build a UV-sensitive devices with a transmission grating unless it is quartz / fused silica.

2: Need to understand the equation relating the grating distance and blaze angle to the zero and first order characteristics of the diffraction.


fused silica transmission grating

1. Germano Veras et al. 2009 "A portable, inexpensive and microcontrolled spectrophotometer based on white LED as light source and CD media as diffraction grid" Talanta 77(3), 1155-115

2. Gaylin M. Lee et al. 1997 "Miniature spectrometers for biochemical analysis" Sensors and Actuators A 58 p. 61-66