Droplet biosensing method opens the door for faster identification of
COVID-19

Date:
July 21, 2020
Source:
Virginia Tech
Summary:
Researchers have developed an ultrasensitive biosensing method
that could dramatically shorten the amount of time required to
verify the presence of the COVID-19 virus in a sample.



FULL STORY ========================================================================== Mechanical engineering associate professor Jiangtao Cheng and electrical
and computer engineering assistant professor Wei Zhou have developed
an ultrasensitive biosensing method that could dramatically shorten the
amount of time required to verify the presence of the COVID-19 virus in a sample. Their peer-reviewed research was published in ACS Nano on June 29.


========================================================================== There's significant room to improve the pace of coronavirus testing,
Cheng and Zhou have found. Current COVID-19 verification tests require
a few hours to complete, as verification of the presence of the virus
requires the extraction and comparison of viral genetic material, a time-intensive process requiring a series of steps. The amount of virus
in a sampling is also subject to error, and patients who have had the
virus for a shorter period of time may test negative because there is
not enough of the virus present to trigger a positive result.

In Cheng and Zhou's method, all of the contents of a sampling droplet can
be detected, and there is no extraction or other tedious procedures. The contents of a microdroplet are condensed and characterized in minutes, drastically reducing the error margin and giving a clear picture of the materials present.

The key to this method is in creating a surface over which water
containing the sample travels in different ways. On surfaces where
drops of water may "stick" or "glide," the determining factor is
friction. Surfaces that introduce more friction cause water droplets
to stop, whereas less friction causes water droplets to glide over the
surface uninhibited.

The method starts by placing a collected sample into liquid. The liquid is
then introduced into an engineered substrate surface with both high and
low friction regions. Droplets containing sample will move more quickly
in some areas but anchor in other locations thanks to a nanoantenna
coating that introduces more friction. These stop-and-go waterslides
allow water droplets to be directed and transported in a programmable and reconfigurable fashion. The "stopped" locations are very small because of
an intricately placed coating of carbon nanotubes on etched micropillars.

These prescribed spots with nanoantennae are established as active
sensors.

Cheng and Zhou's group heats the substrate surface so that the anchored
water droplet starts to evaporate. In comparison with natural evaporation,
this so- called partial Leidenfrost-assisted evaporation provides a
levitating force which causes the contents of the droplet to float
toward the nanoantenna as the liquid evaporates. The bundle of sample
particles shrinks toward the constrained center of the droplet base,
resulting in a rapidly-produced package of analyte molecules.

For fast sensing and analysis of these molecules, a laser beam is
directed onto the spot with the packed-in molecules to generate their vibrational fingerprint light signals, a description of the molecules
expressed in waveforms. This method of laser-enabled feedback is called surface-enhanced Raman spectroscopy.

All of this happens in just a few minutes, and the fingerprint spectrum
and frequency of the coronavirus can be quickly picked out of a lineup
of the returned data.

Professor Cheng and Zhou's team is pursuing a patent on the method,
and are also pursuing funding from the National Institutes for Health
to deliver the method for widespread use.

A full summary and description of this research is available in the June
26, 2020, publication of ACS Nano.


========================================================================== Story Source: Materials provided by Virginia_Tech. Original written by
Alex Parrish. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Junyeob Song, Weifeng Cheng, Meitong Nie, Xukun He, Wonil Nam,
Jiangtao
Cheng, Wei Zhou. Partial Leidenfrost Evaporation-Assisted
Ultrasensitive Surface-Enhanced Raman Spectroscopy in a Janus Water
Droplet on Hierarchical Plasmonic Micro-/Nanostructures. ACS Nano,
2020; DOI: 10.1021/acsnano.0c04239 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200721114718.htm

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