Scientists from the prestigious Massachusetts Institute of Technology (MIT) have made a significant breakthrough in the development of diagnostic tools that could revolutionize healthcare access worldwide. These are inexpensive, single-use DNA-coated electrochemical sensors that promise rapid and affordable detection of a wide range of diseases, from cancer to infectious diseases like the flu and HIV. This innovation opens the door to diagnostics that can be performed directly in a doctor's office or even in the comfort of one's own home, eliminating the need for expensive and complex laboratory equipment.

Innovative approach to diagnostics: DNA sensors and CRISPR technology

The core of this revolutionary technology lies in the use of a cheap electrode coated with specific DNA strands. These electrochemical sensors use a DNA-cutting enzyme, which is an integral part of the CRISPR gene-editing system. When the sensor detects a target molecule, such as a cancer-associated gene or a viral sequence, the enzyme Cas12 is activated. This enzyme, known for its ability to non-specifically cut DNA, begins to "mow down" the DNA strands from the electrode's surface, similar to a lawnmower cutting grass. This change in the DNA structure on the electrode results in a measurable change in the electrical signal, which is a clear indicator of the presence of the target molecule.

Professor Ariel Furst, an assistant professor of chemical engineering at MIT and senior author of the study, points out that her team's focus is on diagnostics that are currently of limited availability to many people. "Our goal is to create a sensor for point-of-care use. People shouldn't have to use it only in a clinic. They could also use it at home," explains Furst. This vision of decentralized diagnostics is key to improving global health, especially in resource-limited regions where traditional laboratories are rare or inaccessible.

Overcoming challenges: DNA stability and polymer coating

One of the main limitations of previous DNA-based sensor technologies was the instability of the DNA coating on the electrode. DNA degrades quickly, which significantly shortened the sensor's shelf life and required strictly controlled storage conditions, such as refrigeration. This greatly limited their application, especially in remote or warmer climates.

In a recent study, published late last month in the journal ACS Sensors, MIT researchers found an elegant solution to this problem. They stabilized the DNA with a coating of a polymer called polyvinyl alcohol (PVA). This polymer, which costs less than one cent per coating, acts like a protective tarp that shields the DNA underneath. After being applied to the electrode, the polymer dries and forms a thin, protective film.

Professor Furst explains the protection mechanism: "Once it's dried, it seems to create a very strong barrier against the main things that can harm DNA, such as reactive oxygen species that can damage the DNA itself or break the thiol bond to the gold and strip the DNA from the electrode." Thanks to this innovative coating, the sensors can now be stored for up to two months, even at high temperatures up to approximately 65 degrees Celsius (150 degrees Fahrenheit). After storage, the sensors successfully detected the PCA3 gene, a marker for prostate cancer that is often used in the diagnosis of this disease.

Accessibility and wide application

The cost of making these DNA-based sensors is only about 50 cents, making them extremely affordable. This low cost, combined with an extended shelf life and resistance to environmental conditions, paves the way for mass application in resource-limited regions where traditional diagnostic methods are often too expensive or logistically unfeasible. Imagine the possibility of rapid testing for HIV or HPV in rural areas of Africa or Asia, without the need for complex infrastructure or a cold chain.

Electrochemical sensors work by measuring changes in the flow of electric current when a target molecule interacts with an enzyme. This is the same technology used by glucometers to detect the concentration of glucose in a blood sample, which indicates their reliability and ease of use. The sensors developed in Professor Furst's lab consist of DNA attached to a cheap gold foil electrode, which is laminated onto a plastic sheet. The DNA is attached to the electrode using a sulfur-containing molecule known as a thiol.

In a 2021 study, Professor Furst's lab showed that these sensors could be used to detect the genetic material of HIV and human papillomavirus (HPV). The sensors detect their targets using a guide RNA strand, which can be designed to bind to almost any DNA or RNA sequence. The guide RNA is associated with the enzyme Cas12, which non-specifically cleaves DNA when activated and belongs to the same family of proteins as the Cas9 enzyme used for CRISPR genome editing.

If the target is present, it binds to the guide RNA and activates Cas12, which then cuts the DNA attached to the electrode. This changes the current produced by the electrode, which can be measured using a potentiostat (the same technology used in handheld glucometers). "If Cas12 is turned on, it's like a lawnmower that cuts all the DNA on your electrode, and that turns your signal off," explains Furst.

Potential applications and future steps

This type of test could be used with various types of samples, including urine, saliva, or nasal swabs, which further expands its applicability. The researchers hope to use this approach to develop cheaper diagnostic tests for infectious diseases, such as HPV or HIV, that could be used in a doctor's office or at home. In addition, this method could also be applied to develop tests for emerging infectious diseases, which is of utmost importance in the context of global pandemics.

The team of researchers from Professor Furst's lab was recently accepted into delta v, a student enterprise accelerator at MIT, where they hope to launch a startup to further develop this technology. Now that they can create tests with a much longer shelf life, they plan to start sending them to locations where they can be tested with patient samples in real-world conditions.

"Our goal is to continue testing with patient samples against different diseases in real-world settings," says Furst. "Our limitation before was that we had to make the sensors on-site, but now that we can protect them, we can ship them. We don't have to use refrigeration. This allows us to access much more robust or non-ideal testing environments."

This research, partly funded by the MIT Committee on Research Support and the MathWorks Fellowship, represents a significant step forward in the democratization of diagnostics. The ability to create cheap, stable, and easily portable diagnostic tools has the potential to transform public health, enabling faster disease detection, more effective epidemic monitoring, and improved access to healthcare for millions of people worldwide.

Source: Massachusetts Institute of Technology