Fold it: Origami kit simplifies testing

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  • Published: Jul 1, 2012
  • Author: David Bradley
  • Channels: UV/Vis Spectroscopy
thumbnail image: Fold it: Origami kit simplifies testing

Testing times out in the field

Aptamer-Based Origami Paper Analytical Device for Electrochemical Detection of Adenosine

An origami-style test kit needs only a voltmeter for diagnostics rather than sophisticated instrumentation and could facilitate much simpler point-of-care and environmental analytics.

Sophisticated laboratory analysis is usually the most reliable way to obtain data, but is by definition impossible to implement in point-of-care diagnostics or environmental testing in the field. This point is revealed in stark relief in the developing world, where such laboratories may not even exist. As such, simple, inexpensive test methods that work without complex instrumentation would be a boon to diagnosticians and scientists.

Researchers at the University of Texas at Austin and the University of Illinois at Urbana-Champaign have come up with a "back-of-an-envelope" solution based on folding paper sensors. Writing in the journal Angewandte Chemie, the team describes how they wax print the "sensor" on one side of a piece of chromatography paper, fold it in an origami-style, laminate it, and the test kit is ready. An inexpensive and widely available voltmeter is all that is then need to obtain a reading.

Wax printing of the chromatography paper produces a patterned hydrophobic, area, while the unprinted areas remain hydrophilic. Richard Crooks and Hong Liu and colleagues were able to print a sample inlet and two hydrophilic channels, each leading from the inlet to a small chamber. The two chambers are connected to each other through a narrow opening. They then "print" the required reagents on to the paper and then using screen-printing with conductive carbon ink, they can add two electrodes to the paper device. When the paper is folded down the middle, they produce a three-dimensional structure without the need for sticky tape or adhesives. The folding brings the electrodes into contact with the chambers. In a final step the device is laminated.

Now, when a drop of sample is added to the inlet, the liquid migrates through the two channels. One of the channels contains microspheres coated with a strand of DNA constructed to selectively bind to the target analyte, an aptamer. As a proof of principle, the team used an aptamer for adenosine. Any adenosine present in the sample then binds to the aptamer. This processes releases one of the other printed reagents, an enzyme coupled to the aptamer. The enzyme then diffuses through the channel, ultimately reaching the chamber, which contains glucose and iron hexacyanoferrate. Here, the enzyme catalyses the oxidation of the glucose, which reduces the iron(III) to the iron(II) form. Meanwhile, the sample has flowed through the second channel which contains the spheres but with no aptamer, which means no iron(III) is reduced. The oxidation state of the iron in one chamber is now different from that in the other chamber, which creates an electrical potential that can be quite easily measured by charging a capacitor and testing the voltage across it with a voltmeter.

The team suggests that the principle might be used to easily and inexpensively produce rapid tests for a broad spectrum of different analytes of medical and environmental importance. Presumably, the inclusion of a colour-changing dye in the system might preclude the need for the voltmeter aspect of the test allowing for a simple colour difference to be observed if the analyte is present in the sample.

Related Links

Angew Chem Int Edn, 2012, online: "Aptamer-Based Origami Paper Analytical Device for Electrochemical Detection of Adenosine"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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