A More Practical DNA Sensor

Early disease detection and personalized medicine have the potential to save countless lives, and due to recent advances in the biological sciences, they are more accessible than ever before. However, existing diagnostic tests are still expensive or otherwise impractical for real-world use in many cases. To make a big impact on human health, diagnostic tests need to be inexpensive, easy to use, and available at the point of care.

DNA-based sensors have risen in popularity lately because they meet all of these criteria. These electrochemical sensors, which cost around 50 cents, have thin electrodes coated with an engineered sequence of DNA bound to an enzyme that is capable of shredding nucleic acids. When a target DNA sequence — from a cancerous cell, or an infectious disease like influenza, for instance — binds to the engineered DNA, it activates the enzyme, causing the DNA coating the electrode to be cut to shreds. The destruction of the sequence alters how electrical current flows through the sensor, indicating that the target molecule has been detected.

This might be the perfect solution to the problem, if not for the fact that the DNA coating the sensors has a very short shelf life, and must be stored under highly-controlled conditions. This makes DNA sensors difficult to work with under real-world conditions, especially in regions with limited resources. But now, a team of engineers at MIT has developed a simple strategy to significantly extend the shelf life of DNA sensors. Using their approach, the sensors are able to stay viable for months, and even under unfavorable conditions, like high heat levels.

The researchers started by laminating inexpensive gold‑leaf electrodes onto plastic film and tethering diagnostic DNA strands to them through gold-sulfur bonds. They then discovered that brushing a solution of an ordinary polymer called polyvinyl alcohol (PVA) over the device and letting it dry formed an ultrathin barrier that shields the fragile biomolecules from heat, moisture, and reactive oxygen species. These are the primary forces that normally strip the DNA from the surface.

Stress tests revealed that PVA‑protected sensors stored for two months at temperatures as high as 150 degrees Fahrenheit performed as well as freshly fabricated devices. After simply rinsing off the polymer, the team used the very same sensors to spot PCA3, a biomarker for prostate cancer. The platform can be re‑tuned in a matter of days to detect virtually any pathogen or genetic mutation.

The protective coating adds less than a penny to the cost of the sensor. The low cost, combined with shelf‑stability at tropical temperatures and the ability to read results with a phone‑sized potentiostat, could bring molecular diagnostics to rural clinics, or even a patient’s own living room. Next up, the team is planning to conduct field trials of the system to move toward ultimately making it available for real-world use.