Acid Test

Nucleic acid testing is a vital part of many diagnostic assays – and not only human diagnostics; it can also be used to detect microorganisms in the environment, spot animal diseases, and even save crops from plant pathogens. But generally, the process is complicated and involves specialized equipment that requires transportation of the sample to a laboratory; there is no practical way to perform these tests in the field – and in settings where access to expensive equipment is limited, there may be no testing options at all. To address this problem specifically in the agricultural sector, we developed specialized dipstick technology to purify DNA from plants – but then we realized that there were many more potential applications for our discovery, including a wide range of human infectious disease diagnostics.

Our new dipstick takes advantage of the intrinsic absorbent nature of cellulose filters (or other materials) to draw up a set volume of the sample, which contains nucleic acids that rapidly adsorb to the filter surface. The volume of sample assayed is determined by the size of the nucleic acid binding zone of the dipstick, so the dipsticks can be customized for specific sample or assay types. Because nucleic acids are large molecules (giving them lots of contact points with the cellulose), they remain attached to the filter during the brief washing step; however, smaller molecules, including those that inhibit downstream applications, are rapidly released. After washing, we then place the dipsticks into the DNA amplification reaction, at which point the nucleic acids are rapidly eluted – likely due to displacement by dNTPs, which are abundant in the amplification solution.

After the DNA has been purified, it can be tested in the laboratory using standard practices. But the exciting thing about the dipstick technology is that it opens the door to conducting the entire process (from sample to result) in the field with the right supporting technology. To that end, I developed a small portable device that takes the tube containing the dipstick-purified DNA, runs the reaction, automatically analyzes the results, and sends the data to the user’s mobile phone. It may sound a little like science fiction, but we’ve already tested the system in a project we are running in the jungles of Papua New Guinea, where we are using it to detect a pathogen that is devastating coconut plantations. Science fiction is rapidly becoming reality!

Making a difference with simplicity

Our research into nucleic acid extraction dipsticks was inspired by the philosophy that we share in our lab. We aim to make complete diagnostic systems that are simple, cheap, and robust, so that they can be used by anyone, including people without scientific training. We also want our systems to be used in places with limited resources (such as remote field sites, developing countries, or schools). Ultimately, we want to see our diagnostic tools make a real difference in the world – and in particular, we want to help developing countries by making diagnostic testing affordable and accessible to people who might not have other health care options.

But human health concerns aren’t limited only to disease diagnostics. To give an alternative example, food-borne diseases are a leading cause of illness and death in many developing countries. As a result, there is a real need to develop affordable and practical diagnostic technologies that can help improve food safety – ideally without requiring equipment and resources that aren’t easily available. We have already successfully tested a complete food-pathogen detection system in Cambodia and Laos in a pilot project aimed at developing a safe, robust, low-cost, and easy-to-use method of detecting known food pathogens on fresh produce. We managed to create a system that costs less than US$1 and requires only a few steps, with which we were able to successfully detect the presence of a dangerous food pathogen on samples collected from produce markets. The dipstick technology was developed just after the completion of the pilot project, so although it was not part of the original study, it will certainly be included in any future developments. The technology has so many potential applications to improve lives that we are always on the lookout for new projects!

Putting the tech to work

We’ve tested a wide variety of samples, including human blood, farm animal samples and crop plants (1). The dipsticks have worked on everything we have tried to date – so I believe that, with some optimization, they are likely to work on any sample type. As such, dipsticks could potentially be incorporated into any diagnostic system that detects disease based on specific nucleic acid sequences – including cancer, viruses, and bacterial diseases.

The dipstick’s speed and simplicity certainly make in-lab diagnostic tests faster and more streamlined, but the best thing is the potential to perform diagnostic assays at the point of need. For example, we have now combined the dipstick technology with other user-friendly tools that we have developed to create complete “sample-to-result” diagnostic systems that greatly simplify and speed up disease identification. The combination hides the complex science away from the user, meaning that no scientific training is required to perform diagnostic tests and obtain useful information. And that makes it feasible to perform molecular diagnostic assays in remote field sites, in the GP’s office, or even at the patient’s bedside. No matter where the test is needed, its user can rapidly identify a disease and then prescribe the correct treatment.

It’s our hope that such simple testing systems will help to reduce misdiagnosis and the prescription of incorrect treatments (for instance, antibiotics in the case of a viral disease). Another exciting possibility is that the technology may, in the not-too-distant future, enable patients to perform molecular assays in their own home and automatically transmit the results to their doctors for remote diagnosis and monitoring. However, it is important to note that our technology is just a tool. It is not designed to replace the trained pathologists and laboratory medicine professionals who will always be required to interpret the data our diagnostics obtain. These systems aren’t designed to allow people without medical training to self-diagnose – we’re well aware of the problems that would likely create for patients and doctors alike...

Making perfect cents

A key feature of our dipstick technology, especially for users with limited resources, is that it’s not only simple to use, but also inexpensive. Each test costs only a few cents, which makes diagnostic testing affordable and accessible to those in developing countries or less economically stable areas. As such, we really feel that the dipstick and other technologies we are developing will make a real difference to many people around the world – our first and most important goal.

We have filed a provisional patent on the dipstick technology and a number of companies have already expressed an interest in helping to make it commercially available. At this stage, though, we are still very much interested in hearing from others who can help us enhance the technology’s availability. So to any researchers or institutions who might have a proposal for us in terms of new applications or new opportunities to share the benefits of the dipstick: please do get in touch!