Sep 12 2017
Engineered strands of DNA, nanoscale tools known as "nanoswitches", could be the key to cheaper, easier, faster and more sensitive tests capable of enabling high-fidelity detection of biomarkers that indicate the existence of different viral strains, diseases and also genetic variabilities as subtle as a single-gene mutation.
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One critical application in both basic research and clinical practice is the detection of biomarkers in our bodies, which convey vital information about our current health. However, current methods tend to be either cheap and easy or highly sensitive, but generally not both.
Wesley Wong, PhD and Senior Author on the paper
This is the reason why Wong and his team have adapted their DNA nanoswitch technology - earlier demonstrated to assist drug discovery and the measure of biochemical interactions – into a novel platform that they refer to as the nanoswitch-linked immunosorbent assay (NLISA) for sensitive, fast and specific protein detection, which they recently reported in a new paper in Proceedings of the National Academy of Sciences.
"It's a 'best of both worlds' approach," says Wong, Senior Author on the paper, who is a Key Investigator in the Boston Children's Hospital Program in Cellular and Molecular Medicine, an Assistant Professor at Harvard Medical School and an Associate Faculty Member at the Wyss Institute for Biologically Inspired Engineering at Harvard University. "This technology could translate into laboratory and point-of-care tests that are as affordable and easy to use as at-home pregnancy tests, but are much more sensitive and accurate."
A process called gel electrophoresis is used by the NLISA platform for screening synthesized, single strands of DNA "reagents" capable of changing their shape when a specific biomarker is present. They begin as linear, long strands of DNA, but are decorated with proteins that have the potential to bind a desired and matching protein biomarker. The proteins, after being exposed to that matching biomarker, bind to it and cause the strand of DNA to then bend into a loop.
When combined with gel electrophoresis, that shape change makes it very easy to detect whether or not the desired biomarker is present. An electric field pulls molecules via a porous gel in gel electrophoresis. Linear DNA nanoswitches travel much faster via the pores in the gel, while triggered nanoswitch loops travel much slower due to their clunkier shape.
Simply put, the distances the nanoswitches travel through the gel indicate whether a biomarker is present or not?
Clinton Hansen, PhD, First Author and a Postdoctoral Fellow, the Wong lab
'Run the gel'
Consider, for instance, prostate-specific antigen (PSA), which is a blood serum marker used for testing men for prostate cancer. In order to demonstrate their NLISA system, blood serum samples were spiked with varied levels of PSA by Wong and his team. They then integrated the nanoswitch reagents for PSA with the serum samples and carried out gel electrophoresis on the mixture. The team succeeded in detecting the existence of PSA with higher sensitivity in less volume than with comparable assays.
Additionally, during another proof-of-concept demonstration, Wong's team demonstrated that their NLISA platform was able to distinguish between highly-similar viral strains of Dengue fever in 45 minutes or less.
By running a gel, we perturb the nanoswitches with an electric field to reduce false positive results using a process called 'kinetic proofreading. Although similar proteins -- such as related viral strains -- might initially 'trip' the nanoswitches into loops, these close-but-not-quite-perfect bonds can be broken, leaving behind only true positive results. This allows us to discern between viral strains that may even be different by just a single gene mutation.
Wesley Wong, PhD and Senior Author on the paper
Wong suggests that the NLISA system is capable of becoming a standard for protein detection, and could also be developed into a handheld, portable device for clinical use.