June 2008

A pinprick of blood drives this lab

Automation practitioners at the analysis division level and in the food and pharmaceutical industries note this update.

A new testing device that operates much like pH litmus paper, except it conducts more complicated analyses, is near.

Technology Review reported researchers at Harvard's Whitesides Research Group might have found a way to make micro fluidics technology much cheaper. They do it by taking advantage of the natural movement of liquid through paper.

The result could be disposable diagnostic tests simple and abundant enough for use in the developing world.

The field of micro fluidics deals with the precise manipulation of tiny quantities of liquid. One of its most promising applications is the so-called lab-on-a-chip, which can work with much smaller fluid samples than larger devices require, potentially allowing for more portable diagnostic tools.

However, existing micro fluidic chips are generally from comparatively expensive materials like silicon, glass, or plastic and have tiny pumps and valves that can be difficult to manufacture.

Now, Harvard's George Whitesides and his team have built a micro fluidic device on a square of paper the size of a pinky fingernail. "It's the first example I've heard of paper micro fluidics," said Albert Folch, a bioengineer at the University of Washington who works on micro fabrication. "It's really clever because it uses paper as a substrate, which is universally available."

While larger paper tests (like those for pregnancy) are common, shrinking the paper and minimizing the quantity of the required chemical reagents reduces manufacturing costs.

The ability to direct the sample to particular regions of the paper enables the simultaneous performance of several tests, to look for multiple symptoms of a condition, like kidney failure or infectious disease, said Whitesides.

In addition, reducing sample size is a particular advantage in developing countries, where noninvasively gathering small amounts of fluids avoids the need for syringes.

A pinprick of blood or drop of urine soaked up at the edge of the Whitesides device moves naturally through the paper, in much the way wine will spread through a paper napkin.

However, the paper has a hydrophobic polymer, which directs the liquid along prescribed channels. Once the liquid reaches the wells at the ends of the channels, it interacts with reagents, turning the paper different colors.

The colors can match to those on a color key, much as they are in a pH test.

One test design that looks like a miniature, three-branched, geometric tree might have wells at the end of two branches for a glucose assay and one at the end of the third for a protein assay.