In recent times, we have all experienced the value of diagnostics used in the comfort and ease of our own homes. Imagine if we could look for other infectious diseases just as easily, with less invasive, self-administered, highly accurate, and reliable tests. Such tests would be highly valuable for patients where privacy is a concern, for patients in rural regions, and for rapidly screening large groups at venues and events. With the convergence of advances in telehealth and biotechnology, this is the direction that the diagnostics industry is heading towards.
By far the most challenging issue for diagnostics developers is the issue of sample preparation. For NAATs to run, nucleic acids must be isolated from the sample’s debris of cell material. In blood samples, there is extra debris from red blood cells and platelets. Lab-based PCR fractions off the nucleic acids from debris using large centrifuge machinery. However, at-home diagnostic devices cannot afford to be so generous with equipment. One popular approach several diagnostic players have turned to is the use of magnetic beads to isolate the nucleic acid. These magnetic beads are biofunctionalized with antibodies on their surfaces that will bind to all nucleic acids. The isolated nucleic acid can then be immobilized temporarily by a magnet, and the remaining debris in the sample can be washed away. Magnetic beads are very effective for small devices designed for the home, but they are expensive. Alternative sample preparation solutions exist, such as sonication methods, but these trade off with other limitations, such as a need for a power source.
Conventional PCR relies on a heating system that rapidly cycles through high and low temperatures to denature nucleic acids, opening them up for the amplification reaction to take place. In recent decades, players have turned to using isothermal NAATs, techniques that only use one temperature, to eliminate this constraint. There are many types of isothermal techniques, with the most used being loop-mediated isothermal amplification (LAMP), yet many industry players will use their own patented amplification chemistries. What these isothermal techniques have in common is the use of a polymerase with strand-displacement properties to replace the role of temperature in opening the nucleic acids. LAMP and other isothermal techniques are fast to amplify and eliminate the design issues of high temperatures. These technologies still have some challenges to solve, like issues with non-specific amplification (the amplification of unwanted DNA), which increases the risk of false positives in the test. These isothermal techniques also still require a small heating element (LAMP, for instance, runs at 60 degrees Celsius). Nevertheless, players are already optimizing their chemistries for room temperature.