Chemistry set pencils can turn life-saving tests into ...

Chemistry set pencils can turn life-savingtests into child's play16 April 2015, by Mark Lorch

The new chemistry lab - just add water. Credit: stux

If you've ever sat opposite a doctor and wonderedwhat she was scribbling on her notepad, theanswer may soon not only be medical notes onyour condition, but real-time chemical preparationsfor an instant diagnostic test.

Thanks to the work of a team of researchers fromCalifornia Polytechnic State University, recently published in the journal Lab on a Chip, chemicalsformed into pencils can be made to react with oneanother by simply drawing with them on paper. Theteam may have taken inspiration from colouringbooks for their take on a chemical toolkit, but theirapproach could make carrying out simple butcommon diagnostic tests based on chemicalreactions – for example diabetes, HIV, or tests for environmental pollutants – much easier.

The project started with an established techniquecalled paper-based microfluidics. This uses thecapillary effect of paper to carefully mix togetherwhat are called reagents – those chemicals mixedto form a reaction, or to measure the presence orabsence of a substance. The capillary effect inaction is easily seen by dropping two inks of

different colours onto a piece of tissue paper. As theliquid is absorbed by the paper the colour dropsspread out until they merge with one another andform a colour blend. In the same way two or morereagents can be mixed with water on a strip ofpaper.

In this case, the difference is that the reagentsaren't added to the paper via droplets. Insteadthey're applied via pencils, meaning that withoutspecialist equipment anyone can set about creatingchemical reactions by simply using them on thepaper.

Colouring-in chemistry. Credit: Lab on a Chip/RSC

The team made the reagent pencils by pulverisinga mixture of graphite (just as you'd find in normalpencils), test reagents and polyethylene glycol,which helps to keep the reagent dispersedthroughout the mixture, as is used for the samereason in toothpaste. They compressed the mixtureinto pellets and mounted them into mechanicalpencil holders bought from the high street stores.

The reaction paper pad was created by using awaxy ink to print small connected enclosures ontofilter paper. The reagent pencils could be used tocolour in these areas within the enclosures – whenwater was added to the paper, the reagentsdissolved and, confined by the waxy ink, were

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forced to diffuse towards one another and react.

Real world uses for real world problems

The team demonstrated a potential use of thereagent pencil technique by using it in place of acommon test used by diabetics to check their bloodglucose levels, which involves reacting a pinprickblood sample with a chemical solution andexamining the result.

An example of how chemical reactions using pencils canprovide instant results. Credit: Lab on a Chip/RSC

One pencil was constructed with a mixture ofenzymes, one called horseradish peroxidase (HRP)and the other glucose oxidase (GOx). A secondpencil contained a reagent called ABTS. Whencombined in the presence of glucose these reacttogether to give a blue-coloured product.Comparing the results from their pencils on the padwith the more traditional dropper method used bydiabetics the team found the results were identical.

The image shows, on the left, the reagents appliedvia droplets of solution. On the right, the reagentpencils were used. The top row shows the paper atthe beginning of the test, the bottom row the result.Applied to the left enclosure, the sample solutioncarries the two reagents together which react. Thecoloured product produced is, as shown on thegraph, identical between the two methods.

This is of course extremely easy to set up.Traditional diagnostic tests require training, whilethis pad and pencil system requires no more thanskill than required to colour within the lines. Thereagents are extremely stable once made intopencils – usually they would degrade in a matter ofdays as liquids, limiting how and where the testscan be made. However the reagent pencils showedno sign of degrading after two months.

So this pencil tool kit has obvious advantages: a kitof reagent pencils, much like a box of colouringpencils, is easily transported, without the chemicalsdegrading. Kits could be designed with particulartests in mind – and the reaction mix can beadjusted by applying more or less, without the needor equipment to make-up complex solutions.There's scope to monitor environmental pollutants,carry out diagnostic tests in remote locations – notto mention teach chemistry in primary schools.

This story is published courtesy of TheConversation (under Creative Commons-Attribution/No derivatives).

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Source: The ConversationAPA citation: Chemistry set pencils can turn life-saving tests into child's play (2015, April 16) retrieved 28May 2022 from https://phys.org/news/2015-04-chemistry-pencils-life-saving-child.html

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