general chemistry

Reagent pencils, turning chemistry into child’s play

If you’ve ever sat opposite a doctor and wondered what she was scribbling on her notepad, the answer may soon not only be medical notes on your condition, but real-time chemical preparations for an instant diagnostic test.

Thanks to the work of a team of researchers from California Polytechnic State University, recently published in the journal Lab on a Chip, chemicals formed into pencils can be made to react with one another by simply drawing with them on paper. The team may have taken inspiration from colouring books for their take on a chemical toolkit, but their approach could make carrying out simple but common diagnostic tests based on chemical reactions – for example diabetes, HIV, or tests for environmental pollutants – much easier.

The project started with an established technique called paper-based microfluidics. This uses the capillary effect of paper to carefully mix together what are called reagents – those chemicals mixed to form a reaction, or to measure the presence or absence of a substance. The capillary effect in action is easily seen by dropping two inks of different colours onto a piece of tissue paper. As the liquid is absorbed by the paper the colour drops spread out until they merge with one another and form a colour blend. In the same way two or more reagents can be mixed with water on a strip of paper.

Colouring-in chemistry.
Lab on a Chip/RSC

In this case, the difference is that the reagents aren’t added to the paper via droplets. Instead they’re applied via pencils, meaning that without specialist equipment anyone can set about creating chemical reactions by simply using them on the paper.

The team made the reagent pencils by pulverising a mixture of graphite (just as you’d find in normal pencils), test reagents and polyethylene glycol, which helps to keep the reagent dispersed throughout the mixture, as is used for the same reason in toothpaste. They compressed the mixture into pellets and mounted them into mechanical pencil holders bought from the high street stores.

The reaction paper pad was created by using a waxy ink to print small connected enclosures onto filter paper. The reagent pencils could be used to colour in these areas within the enclosures – when water was added to the paper, the reagents dissolved and, confined by the waxy ink, were forced to diffuse towards one another and react.

Real world uses for real world problems

The team demonstrated a potential use of the reagent pencil technique by using it in place of a common test used by diabetics to check their blood glucose levels, which involves reacting a pinprick blood sample with a chemical solution and examining the result.

One pencil was constructed with a mixture of enzymes, one called horseradish peroxidase (HRP) and the other glucose oxidase (GOx). A second pencil contained a reagent called ABTS. When combined in the presence of glucose these react together to give a blue-coloured product. Comparing the results from their pencils on the pad with the more traditional dropper method used by diabetics the team found the results were identical.

An example of how chemical reactions using pencils can provide instant results.
Lab on a Chip/RSC

The image shows, on the left, the reagents applied via droplets of solution. On the right, the reagent pencils were used. The top row shows the paper at the beginning of the test, the bottom row the result. Applied to the left enclosure, the sample solution carries the two reagents together which react. The coloured product produced is, as shown on the graph, identical between the two methods.

This is of course extremely easy to set up. Traditional diagnostic tests require training, while this pad and pencil system requires no more than skill than required to colour within the lines. The reagents are extremely stable once made into pencils – usually they would degrade in a matter of days as liquids, limiting how and where the tests can be made. However the reagent pencils showed no sign of degrading after two months.

So this pencil tool kit has obvious advantages: a kit of reagent pencils, much like a box of colouring pencils, is easily transported, without the chemicals degrading. Kits could be designed with particular tests in mind – and the reaction mix can be adjusted by applying more or less, without the need or equipment to make-up complex solutions. There’s scope to monitor environmental pollutants, carry out diagnostic tests in remote locations – not to mention teach chemistry in primary schools.

The Conversation

This article was originally published on The Conversation.
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By April 30, 2015 4 comments general chemistry

23 Million Times Slower than Molasses

I have the pleasure of teaching general chemistry II for the first time ever this semester. It is fun to go back and revisit concepts that I have not spent time with since taking general chemistry ~13 years ago. Our first few classes will focus on intermolecular forces (dipole-dipole, London Dispersion, etc.) and some of their macroscopic manifestations. Some examples covered in the book include surface tension, capillary action and viscosity. Searching these topics online led me to my new favorite experiment: the Pitch Drop Experiment.
Pitch Drop

In 1927, Professor Thomas Parnell started the Pitch Drop experiment in which he sought to measure the viscosity of pitch. Pitch is a general term used to describe a highly viscous solid polymer, but this material is often a complex mixture of phenols, aromatic and long chain hydrocarbons. Unfortunately, I could not find the exact composition of the pitch used in this specific experiment, but needless to say this sample does meet the description of a highly viscous material.

The experiment was initiated when Prof. Parnell heated up a sample of pitch and poured it into a conical piece of glass. The pitch was then left to sit for three years, presumably the length of time it needed to cool and completely settle into the cone shape. Immediately after the bottom of the funnel was cut open the pitch came rushing out. Just kidding. The pitch ever so slowly began dripping out of the funnel. How slowly? At a rate of approximately one drop every 10 years. In fact, the most recent drop—the 9th drop ever– fell on April 17th 2014.

The first report on this experiment was published in the European Journal of Physics in 1984. In that manuscript they calculated the pitch (2.3 x 108 Pa s) to be 230 billion times more viscous than water (1.0 x 10-3 Pa s). That means it’s more than 23 million times slower than molasses (5-10 Pa s). The longevity and creativity of this experiment won Thomas Parnell and John Mainstone (the caretaker of the experiment for more than 50 years) an Ig Nobel Prize in 2005. The experiment has also been officially included in the Guinness World Records as the world’s longest continuously running laboratory experiment.

Despite this experiment’s epicness, or maybe because of it, no one has ever been in the room to watch one of the pitch drops fall. The closest anyone has come is a time-lapse video below.

The video is unfortunately anticlimactic. It shows the 9th drop making contact with the 8th drop in the beaker. It isn’t the spectacle of a full ‘drop’ event, but don’t worry. The next occurrence is right around the corner: about 14 years away. In anticipation of this event the University of Queensland has set up three webcams and a continuously streaming live feed on a website called The Tenth Watch. Regardless of where you find yourself, you can keep a constant eye on the experiment as it progresses. And even if you miss the 10th drop, don’t worry, it’s estimated that there is enough pitch in the funnel to produce several more drops over the next 100 years.

By January 24, 2015 3 comments fun, general chemistry

New manufacturer of NMR instruments to enter the market

With the exit of Agilent from the NMR instrument market there’s a gap that is in desperate need of filling. Now it looks like a rather unusual group is considering plugging the hole. The company, usual associated with construction but also happens to be the largest manufacture of tyres in the world, is conducting a poll to see whether NMR is a viable option for them.

If you think the chemistry community needs a new NMR instrument manufacturer then please pop over to their website and let your thoughts be known.





The lego NMR instrument now comes with mini figures!



By January 19, 2015 0 comments fun, general chemistry

A Year in the Life of a New Research Lab…in Less than One Minute

The Hanson Research Group’s first experiment—initiated my second day on the job—involved two strategically placed Brinno TLC200 time-lapse cameras programmed to take one photo per day. The video from our first camera that covered our less-trafficked support space was posted in March. Below is the video from our second camera, which was placed in the main lab and focused on one of our fume hoods.

By July 18, 2014 8 comments fun, general chemistry