By Madeleine Eaton
At this point in the pandemic, we’ve all become familiar with the COVID-19 test – shoving a swab down one’s nose or throat until they sneeze or paying exorbitant amounts for PCR certificates. But what if there were a different way – something user friendly and low cost that could be adapted to test for many different pathogens? Through synthetic biology, a team at the Wyss Institute is aiming to do just that.
The overall aim of synthetic biology is to re-engineer organisms to give them new biological abilities able to be exploited for use.1 A core component of many current developments is synthetic gene circuits. These are similar to normal electrical circuits, except using cellular parts (instead of wires) engineered in a way that they perform certain outputs or functions.1 They are typically composed of a sensor detecting nucleic acids or small molecules combined with a transducer producing a detectable output1. While several recent advancements in the synthetic biology field have exploited the design of synthetic circuits, their potential incorporation into wearable materials has been limited by one major problem: they require the use of live organisms in the devices.2 The organisms require environmental regulation of nutrients, temperature, and waste. They can also pose a biohazard problem for the wearer if they contain genetically engineered cells contained within the system.2 As a result, although these networks have great potential, their use has been limited to in vivo systems within laboratory environments.1 Fortunately, this is changing. Over the past three years, researchers at the Wyss Institute at Harvard, as well as those at MIT, have been working on incorporating synthetic biosensor technology into wearable materials able to detect certain bacteria and viruses.
The approach used by those at the Wyss Institute is based on what is called wearable freeze-dried cell-free technology.3 This approach combines transcriptional/translational machinery combined with synthetic gene circuits and freeze-dried for preservation.2 Upon rehydration, the system acts as a biosensor for certain molecules, for example viral RNA, and produces a measurable output such as color change.2 By integrating this technology into textiles, the team could create wearable biosensors.
Their first demonstration of the usefulness and principle of this technology was in the Zika outbreak in 2015. Standard diagnostic methods are typically cross-reactive in patients who have been infected by related viruses, requiring the use of costly nucleic acid-based methods like PCR testing in order to distinguish between strains which have similar genetic makeup.1 Researchers created a two-step paper-based biosensor containing freeze-dried biological components that upon detecting viral RNA sequences change color from yellow to purple.4 The second part of the test uses another color changing reaction relying on CRISPR-Cas9 aided sequence recognition at the single base level to identify a patient’s specific viral strain.5 This makes it easy to distinguish closely related viruses such as Zika from Dengue virus.
With the emergence of the pandemic, they took the next step and made the technology wearable by integrating it into facemasks for COVID diagnosis. Detection uses respiratory droplets accumulating on the inside of the mask from normal talking or coughing. The mask itself is formed from four components: a hydration reservoir, a sample collection pad, a paper analytic device containing three core reaction circuits, and a lateral flow test.3 By pressing a button on the outside of the mask, the user hydrates the three freeze-dried reactions.2 Any captured viral particles are transported from the sample collection pad to the analytical device, where each of the three reactions occurs sequentially. Firstly, lysis reagents lyse the viral membrane to expose RNA before an amplification step via a reverse transcriptase polymerase reaction.2 Finally, CRISPR based technology cleaves a probe upon detection of the amplified double-stranded spike protein DNA.2 The results are reported in a lateral flow assay format similar to those taken at home2, which is easily interpretable by the user.
The total reaction from activation to detection is around 90 minutes and it has a detection limit comparable to WHO (World Health Organization) endorsed RT-PCR tests.3 Another major benefit of the technology is that it can operate at room temperature and is shelf-stable, so that patients can be diagnosed outside of a lab with just the press of a button.3 The potential applications of wearable biosensor technology are near endless. They can be incorporated into different textiles and materials or adapted to detect different pathogens, even closely related strains, making it a useful tool against new emerging pandemic agents.3 First responders, medical professionals in hospitals, front-line soldiers, or anyone working in areas with elevated risks of chemical or biological agent exposure could all benefit.3
With all these elements in mind, it is evident how synthetic biology has enabled the design of freeze-dried synthetic gene circuits incorporated first into paper and now into textiles. The pressing threat of novel pathogens highlights our need for cheap and quick diagnostic tools, and this highly accurate and shelf-stable technology represents a promising development in fighting them on a global scale.
References:
- Pardee K. Paper-based diagnostics using synthetic Gene Networks. Cell. 2014Nov6;7(45):1327–.
- Nguyen PQ, Soenksen LR, Donghia NM, Angenent-Mari NM, de Puig H, Huang A, et al. Wearable materials with embedded synthetic biology sensors for biomolecule detection. Nature Biotechnology. 2021;39(11):1366–74.
- Brownell L. Face masks that can diagnose COVID-19 [Internet]. Wyss Institute. Harvard University; 2022 [cited 2022Oct15]. Available from: https://wyss.harvard.edu/news/face-masks-that-can-diagnose-covid-19/
- Finding zika one paper disc at a time [Internet]. Wyss Institute. Harvard University; 2020 [cited 2022Oct15]. Available from: https://wyss.harvard.edu/news/finding-zika-one-paper-disc-at-a-time/
- Pardee K, Green AA, Takahashi MK, Braff D, Lambert G, Lee JW, et al. Rapid, low-cost detection of zika virus using programmable biomolecular components. Cell. 2016May19;165(5):1255–66.
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