One of the best chemists alive today is George Whitesides at Harvard University. He has the highest Hirsch index of any living chemist, which means that he has written some of the most influential and powerful science publications and – more importantly – other people have cited his work as the inspiration for their own research. I recently saw a presentation he gave for the “Technology, Entertainment, and Design” conference, and decided to read through some of his published work in the area of water analysis. I found a fantastic article in the journal Lab Chip which outlined how his group of chemists at Harvard succeeded in making a low-cost analytical test out of simple paper that can test the purity of drinking water.
One of the major points of concern for Prof. Whitesides is the need to not only develop new analytical methods, but to have these methods be extremely low cost and simple to use. If sensing technology to detect lead or other contaminants is ever going to be distributed over the entire planet, including in the poorest countries which have the highest need for these analytical tests, the tests need to be only cost pennies and they need to be foolproof. Can scientists develop a sensitive test for the presence of lead in drinking water? Of course they can – they’ve already done it, decades ago. The ingenuity of chemists must now be applied to simplifying these tests and reducing the cost of analysis. Contaminated drinking water is an enormous problem overseas, with many families having zero access to a pure source. Being able to rapidly disseminate a reliable test for lead and other toxins would improve the health of millions of human beings.
The journal article I read went on to describe the actual design of the analytical device for lead in drinking water. The chemists chose to use paper for the bulk of the device, for the simple reason that it’s cheap. They wanted electrochemistry to be the technology behind the analysis, as electrochemisty is famous for being ridiculously sensitive and accurate when detecting metal ions. In order to accomplish this, they needed to have some rudimentary circuity and test chambers for the water to flow in and out of – the equivalent of a handful of glass beakers, but located on a slip of paper the size of a thumbnail. They settled on the use of a waxy plastic which could be printed onto the paper using standard thermal printing technology. The wax repels water, and so a “U” shape printed on the paper would be able to contain a droplet of water long enough for the analysis to take place.
As for the needed circuity, Prof. Whitesides settled on the use of electrically conductive ink made out of silver particles and other metallic components. This allowed the electrodes to be printed directly onto the paper, forming the various channels and patterns that were necessary. The result was a slip of paper that, as a result of microfluidic technology, was the microscopic equivalent of a sophisticated large-scale electrochemical cell. By clipping on a battery to the printed conductive lines, the disposable one-shot device as able to detect lead levels down to one part per billion. This means the device could detect the presence of as little as one lead atom floating in an ocean of a billion water molecules. This level of detection is ten times lower than the acceptable cutoff point for acceptable drinking water as published by the World Health Organization.
When you consider that this device requires absolutely minimal training, runs on a cheap disposable battery, is virtually foolproof, and – perhaps most important – only costs two cents to make, you begin to understand the implications of this new technology. Children and elderly alike are extremely vulnerable to lead poisoning, and ingestion through drinking water (whether it be lead pipes, or faulty plumbing joints) is one of the leading routes of exposure. A quick, accurate, cheap as dirt test that anyone can learn to carry out with about 20 seconds of training is technology poised to radically improve the health of patients formerly at risk for exposure to lead. The group of Prof. Whitesides is not stopping with lead detection, either – they are busy developing similar small-scale “disposable labs” that could test for other heavy metals such as mercury as well as test for the levels of important biological molecules (glucose, creatine) in blood and urine samples. I’m excited to see what is going to come out of the labs of this amazing chemist in the months ahead.
The source of this article can be found at: http://www.rsc.org/Publishing/Journals/LC/article.asp?doi=b917150a