This protocol allows you to do surprisingly sophisticated at home ‘spectrophotometer’ experiments by turning your mobile phone into a colorimeter. I’m impressed by the quality of the data you can get using these methods, which allow students to do quantitative experiments at home. The protocol is based on this excellent video from Tommy Technetium, but I’ve tweaked the method a bit and suggested some other biological experiments that could be done in this way.
Link to experimental protocols (GoogleDoc)
The protocol relies on you downloading a colour picker app to a smart phone. You need an app that will report numerical RGB values, not just suggest paint colours for you! I use ColorPicker as an iPhone app, Android users are recommended to use ColorGrab.
My protocol relies on using 1 cm cuvettes that you would use in a spectrophotometer. I posted these out to students when we were doing the experiments remotely. If you are able to order from scientific suppliers they are easy to get hold of. If you are doing the experiment at home you can get them from Amazon. If you can’t get hold of cuvettes then TicTac packets are a good alternative!
I have designed a simple cuvette holder for you to make out of card/cardboard. I found that my data was much more reliable having a consistent place to put the cuvettes into. A template for this is below.
Before measuring your experimental samples I recommend constructing a calibration curve. This teaches students about dilutions, and gets them to pick the best colour channel to use for data collection. I’m really impressed how smooth the calibration curves can be! It also helps to optimise the method by finding the dynamic range of the colorimeter – the RGB values saturate out reasonably quickly, so finding an appropriate dilution to use in the methods will result in better experimental data. Videos demonstrating setting up a calibration curve for two different experiments are at the bottom of this page.
Once you have the colorimeter working there are a variety of different experiments you can do. Suggestions marked with an * require you to obtain some acetone based nail polish remover, which you can buy for about £1.
- Compare the colour of tea/coffee made by different brands
- Compare the colour of tea made by boiling a tea bag for different lengths of time
- Compare the solubility of spices (e.g. paprika) in water vs alcohol (e.g. vodka) or water vs acetone*
- Compare the chlorophyll content of leaves from the sunny and shady side of a plant*
- Compare the chlorophyll content of two different species*
I hope this protocol is useful to you – it is really flexible and I think is a nice way to introduce students to some important concepts in biology/biochemistry. I am going to use it as a pre-lab exercise before students meet spectrophotometers, as hopefully this ‘at home’ protocol makes the concepts more accessible.
If you have any comments about the protocol, or ideas for other experiments that could be done using it please do get in touch!
Dr Katharine Hubbard 