Are Colouring Pencils the Newest Tool For Doctors?

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Slightly different to the usual Doctors’ toolkit… Image by Michael Randall on Flickr: https://www.flickr.com/photos/pigpogm/146858542/

In a recent paper, a group of scientists have investigated a new technique for clinical testing, which seems to largely revolve around using colouring pencils and paper, very similar to the toolkit we (hopefully, if the digital age hasn’t gone too far) all possess for writing, colouring and drawing – but with a few differences of course. The technique is suggested as having the potential to be used by doctors as a diagnostic tool, for example, being able to test blood sugar levels in an individual. The “colouring pencils” also combat a problem often faced when designing new tools for diagnosis, as the diagnostic kit would be portable, and have a long shelf-life.

But these colouring pencils aren’t just ordinary colouring pencils. While they look like the very same ones we would use to complete a colour-by-numbers picture as a child (or even now), what’s inside them is slightly different. These pencils still contain the usual pencil ingredient of graphite, but inside the pencil core or “lead” as it is often wrongly named, are chemical reagents, chemicals which when combined with another chemical, will cause a reaction, while other pencils contain combinations of enzymes, proteins which will significantly speed up the chemical reaction. The pencils can be used to draw the chemicals onto the paper, and then have a blood sample dotted nearby, so that the spots move towards each other and combine. When substances in the blood react with the reagents in the pencil core, they produce a different colour. This can allow us to see whether a certain chemical is present in the blood sample, or even how much of a certain substance is present, quickly and simply.

In this diagram from the published paper, we can see that the reagent (ABTS) was added to the first, and biggest circle, then the enzyme mixture to the second. These then moved towards the third, where they reacted with the glucose sample, producing the blue colour we can see in the lower two test papers. We can also see that when a greater concentration of glucose was used, the blue is deeper.
In this diagram from the published paper, we can  see in A and B that the reagent (ABTS) was added via a pencil, to the first, circle (the sample zone), then the enzyme mixture (HRP ad GOx) to the second (the reagent zone). In C and D, a sample containing glucose was added to the sample zone and left for 30 minutes, producing the blue colour we can see in these. We can also see that when a greater concentration of glucose was used (0.8mM instead of 0.25mM), the blue is deeper, and when no glucose was added, no blue colour is produced.

When used to measure blood glucose levels, one pencil contains two enzymes, and another contains a reagent. When glucose is added to a mixture of these, they make a product which is coloured blue, so shows up on the “paper” as a blue dot or shape. The more prominent the blue colour, the more glucose is present in the blood.

As weird as it sounds, this “special” colouring pencil kit may have potential as a much easier way of testing diabetics, or testing for other conditions, which can be identified by the presence of certain chemicals in the blood. Just imagine one day, your doctor sketching away to tell you what’s wrong, instead of having to wait for your blood test results! Another use that comes to mind is a little primary-school aged me, playing with these chemistry pencils to learn about chemical reactions. Either way, this is an exciting new possibility, and shows us that new techniques for clinical diagnosis might not look the way we expect. I’m looking forward to hearing more about this in the future!

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