How a new test could help curb the spread of Ebola

New technology uses magnetic nanoparticles for simpler, cheaper diagnosis

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The Ebola virus has claimed the lives of more than 11,000 people in West Africa since March 2014. With more than 27,000 confirmed and suspected cases of Ebola virus disease in Guinea, Liberia and Sierra Leone since the outbreak began, detection is key to controlling the spread of the disease. However, current tests are either too expensive to be useful where they are most needed, or not sensitive enough to provide an accurate diagnosis.

A new test that uses magnetic nanoparticles could help curb the spread of Ebola, enabling healthcare workers to identify and isolate patients more quickly and easily. Research published in Biosensors and Bioelectronics shows that the new test is 100 times more sensitive than the current test, and easier to use.

TProfessor Xiyun Yan, PhDhe Ebola virus causes an acute illness that is deadly in half of all cases, on average. The current outbreak of Ebola affects countries in West Africa. In the most severely affected countries, like Guinea, Liberia and Sierra Leone, resources are limited, making control of the outbreak challenging. There is no vaccine for Ebola, so detecting the virus is key to controlling the outbreak: with an accurate diagnosis, patients can be isolated and treated properly, reducing the risk of spread.

“In West Africa, resources are under pressure, so complicated, expensive tests are not very helpful,” said Professor Xiyun Yan, one of the authors of the study, from the Chinese Academy of Sciences. “Our new strip test is a simple, one-step test that is cheap and easy to use, and provides a visible signal, which means people don’t need training to use it. We think it will be especially helpful in rural areas, where technical equipment and skills are not available.”

Improving a popular diagnostic test

Currently there are two main ways to test for the Ebola virus: using a method called polymerase chain reaction (PCR), which makes copies of the molecules for detection, and with antibody-capture enzyme-linked immunosorbent assay (ELISA), which gives a visual indication when a given molecule is in a sample. PCR is very sensitive but expensive and complicated, requiring special skills and technical equipment. The ELISA – or gold strip test – is cheaper, but sensitivity is very low, which means it often gives the wrong results.

The new test, called the nanozyme test, is similar to the gold strip test. It uses magnetic nanoparticles, which work like enzymes to make the signal stronger, giving a clearer result you can see with the naked eye. The test can detect much smaller amounts of the virus and is 100 times more sensitive than the gold strip test.

“People have loved the strip test for many years, but it has a major weakness: it’s not sensitive enough,” said Dr. Yan. “We’re very excited about our new nanozyme test, as it is much more sensitive and you don’t need any specialist equipment to get a quick, accurate result.”

Strip tests work by attaching molecules called antibodies to gold particles to look for a particular molecule in a sample. When they attach to the molecule you’re looking for, in this case a virus, they produce a signal, such as a color change. In order to find the virus, the particles need to be labelled with enzymes, which speed up detection and signalling.

The magnetic properties of the nanozymes make the detection sensitivity 10 times higher, and the catalytic properties make the signal 100 times stronger, generating a deep color reaction that can be seen by the naked eye. (Image credit: Demin Duan et al)

With the new nanozyme test, the researchers applied magnetic nanoparticles as a nanozyme probe in place of gold nanoparticles. After labeling with an antibody that attaches to the Ebola virus, this novel probe is able to recognize and separate the virus in a sample. The nanoparticles are magnetic, so to concentrate the virus particles in a sample, all you need to do is hold the sample against a magnet; no expensive lab equipment is needed.

Results of testing using (A) the nanozyme strip and (B) a standard gold strip. The asterisk (*) indicates the limit of visual detection, showing that the nanozyme strip is more sensitive. (Image appears as figure 3 in the study. Credit: Demin Duan et al)The nanozyme test is 100 times more sensitive than the gold strip test, detecting molecules called glycoproteins on the surface of the Ebola virus at concentrations as low as 1 nanogram per milliliter.

“Nobody believed that nanoparticles had enzyme activity; it seems unbelievable,” said Dr. Yan. “Being magnetic, the nanoparticles can physically collect virus particles together when you hold a magnet against the sample. It can work the same way with other biological molecules: nanozymes can detect any molecules in a sample in just one step. That’s why we’re so excited by this – it’s simple!”

The team is now developing automatic equipment to avoid contamination. Any test that comes into contact with a person’s hands can be contaminated, so making the test automatic would reduce the risk of contamination, therefore increasing the accuracy of the results.

Nanozyme as a powerful detection technology

The new nanozyme test is the result of an interdisciplinary collaboration that is also leading to new applications for the technology. The underlying discovery – that the magnetic nanoparticles can function as enzymes – can be used in many other areas. The researchers have applied for a patent for the new nanozyme test and are excited about its potential.

“We had an idea and talked to many people about it, and the result is a test that will overcome a problem,” said Dr. Yan. “We have built strong collaborations that have finally made this method successful, and we’re looking forward to applying it to many other areas.”

Dr. Yan and her colleagues had the original idea for the technology, and developed the platform. They worked with Professor George Fu Gao, Deputy Director-General of the Chinese Center for Disease Control and Prevention (CDC), to access the pseudo-virus and detection molecule to create the Ebola test, with colleagues in Canada to get the antibody. Clinicians helped them test the accuracy of the technology, and the CDC is now taking the test to West Africa to try out in the field.

Now that the researchers have shown the technology is robust, they are collaborating with other colleagues and companies to develop it further. The technology can be applied to the detection of any biological molecules, making it useful to diagnose other infectious diseases, like flu, and potentially detect tumors. The researchers are working with clinical teams to apply the technology to other viruses and tumors.

They are also working with a company that treats wastewater to see if it can help remove environmental contamination. A large volume of wastewater is produced during paper manufacture. This wastewater contains a phenol that can cause cancer. The nanozymes can break down this phenol into water and carbon dioxide, so they could be used to decontaminate the water.

Read the article

This study is freely available until October 2, 2015: 

Demin Duan et al: “Nanozyme-strip for rapid local diagnosis of Ebola,” Biosensors and Bioelectronics (December 2015)

Corresponding author

Dr. Xiyun Yan is Professor and Director of the key Laboratory of Protein & Peptide Pharmaceutical at the Institute of Biophysics, Chinese Academy of Sciences. She is President of the Asian Biophysical Association (ABA) and Vice President & Secretary-General of the Biophysical Society of China. Dr. Yan made groundbreaking contributions to our knowledge of nanozymes, showing that they have intrinsic enzyme-like activity. Dr. Yan’s lab is developing the technology in the areas of tumor and water treatment. Dr. Yan has 125 publications and 28 patents.

The journal

Biosensors & Bioelectronics is the principal international journal devoted to research, design, development and application of biosensors and bioelectronics. It is an interdisciplinary journal serving professionals with an interest in the exploitation of biological materials and designs in novel diagnostic and electronic devices including sensors, DNA chips, electronic noses, lab-on-a-chip and μ-TAS. Read more.

Related resources

The latest on the Ebola outbreak:

Elsevier's Ebola Information Center features free health and medical research, online tools and expert advice on Ebola

Elsevier Connect Contributor

Lucy Goodchild-van
  HiltenAfter a few accidents, Lucy Goodchild van Hilten discovered that she’s a much better writer than a scientist. Following an MSc in the History of   Science, Medicine and Technology at Imperial College London, she became Assistant Editor of Microbiology Today. A stint in the press office at Imperial saw her stories on the front pages, and she moved to Amsterdam to work at Elsevier as Senior Marketing   Communications Manager for Life Sciences.

 She’s now a freelance writer at Tell Lucy. Tweet her @LucyGoodchild.

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