In the current situation where COVID is drastically elevating the number of cases and death toll, most people are aware of the testing protocols. Even though it is not an invasive technique, but collecting nasal swabs is quite exasperating. In most countries, saliva is considered, but antigen count in the saliva is very less as compared to nasal swabs. These rapid tests are not 100% reliable. But in this era, recent development in technology now provides improved and much reliable versions for testing and diagnostics. Wearable electronic
devices are getting wide popularity by the usage of embedded biosensors which make it possible for visible on-the-spot detection.
Some of the reported flexible and lightweight wearables that detect airborne pathogens are freeze-dried, cell-free (FDCF)-based synthetic circuits. One of the FDCF type is a colorimetric-based, structure of layer-by-layer assembly of silicone elastomer on cellulose-based substrate. It is designed as cellulose matrix chambers on bottom layers, having fluid wicking ability, which is connected to top portal layer, having inflow pores. The chamber contains a freeze-dried reaction insert. These functionalized pores get activated by rehydration and show color change when exposed or encountered with a specific molecular target. This flexible module can be used as bracelets. The working environment needs to be taken into consideration such as temperature: skin-surface or ambient-temperature; humidity: not suitable in a highly humid environment or underwater, and the fluid intake volume: as little as in microlitres. The results are displayed within 40-60 minutes after exposure.
Another type uses fibre optics in which, the activated FDCF are immobilized in thread-form or woven into fabrics. Like explained above, the fabric wicks the fluid through the portals in the top layer. The hydrophilic threads made of polyester: polyamide (17:3) immobilized with cell-free reagent, then patterned to reaction compartments, and interweaved polymeric optic fibres for signal probing, which is monitored using mobile apps. The fabric wicks the fluid splashes, which activates the sensor and exhibits visible fluorescent or luminescent response. The detection time varies from 5-20minutes after exposure. The testing conditions are somewhat like the colorimetric detection sensor.
For daily use purposes and ease of wearability, the same sensor can be integrated into our face masks. The design contains four modular components: a reservoir for hydration, a collection sample pad (inside the face mask), a μPAD and a lateral flow assay strip. The μPAD wicks the sample from the collection pad through capillary action. It contains an array of freeze-dried lysis and detection components. Detection through the different zone is a multistep process, each zone contains (i) lyophilized lysis reagents (lyses viral membrane) and (ii) the RT-RPA reaction zone (amplifies the viral gene), and (iii) SHERLOCK sensor (detects the amplicons). The LFA strip is conjugated with complimentary targets, which detects the probe cleavage and produces a colorimetric response as readout. Even though the face-mask sensor readout takes 1.5h for activation, the advantage of such sensor is no power consumption, operates on its own, is stable, rapid testing device, cost-effective, single-use and disposal friendly. This is as accurate, sensitive, and specific to the real-life tests conducted (RT-PCR).
Peter Nguyen, a research scientist at the Wyss Institute, Harvard claims it is possible to shrink an entire diagnostic laboratory down into a small by the usage of synthetic biology-based sensor that works with any face mask or other garments to provide on-the-go detection of dangerous substances including viruses, bacteria, toxins, and chemical agents.
Authors: Alex Dennis, Keerthi Chellat (Master’s Student & Researcher in Nanotechnology, Amity Institute of Nanotechnology)
Reviewer: Som Thomas, PhD Scholar, University of Cincinnati, USA