Patent Application
20220107258
The search for, detection, capture, and identification of certain classes of airborne particles, whose presence within a variety of local environments may be life threatening, represent tasks of continuing importance. Among the most dangerous and difficult to find, detect, and identify in situ are the causative viruses of the COVID-19 pandemic affecting most communities in the world. In addition to the COVID-19 viruses, it is expected that there would appear in the near-time future other viral, and even bacterial, airborne threats whose real time detection and localization will become of comparable importance.
A variety of collection devices exist, that may be used to collect a large fraction of the particles present within relatively large selected volumes of ambient air and transfer them into very small volumes of liquids such as water. Many are described, for example, in the recent 2019 article “Collection, particle sizing and detection of airborne viruses” on pages 1596 to 1611 of Journal of Applied Microbiology volume 127. An earlier article providing similar and some additional techniques is “Methods for Sampling Airborne Viruses” on pages 413 to 444 of Microbiology and Molecular Biology Reviews September 2008. Although such collection techniques will provide samples rich in particulates, the means by which the COVID-90-containing fractions therein may be isolated and identified rapidly are not currently available.
Although light scattering techniques are always useful in identifying small particulates, the most difficult problem associated with attempts to detect such dangerous viruses by these techniques is the fact that they are so small (relative the wavelength of traditional scattered light measurement systems). Thus, irrespective of their numbers present, the amount of light scattered by them (relative to that scattered by traditionally present airborne particulates) is negligible.
Therein lays the basic problem: If one could collect all particles, including viruses, contained within a reasonable volume of the accessible ambient air, the significant problem of distinguishing light scattered by the COVID-19 viruses content from that scattered by the larger quantities of their unimportant companion particles would remain.
The particulate contents of a selected region of the air, in which the COVID-19 virus may be present, is collected within a very small volume of water or similar buffered fluid by means of one or more of the virus collection methods described in the two above-cited articles. An aliquot of this collected sample-bearing solution is injected into the buffered aqueous fluid flowing through an asymmetric flow field flow fractionation (A4F) system that separates and elutes the particulate contents of the injected sample by size, from the smallest to the largest. The thus-fractionated particles, in order of elution, would begin with the COVID-19 viruses if present followed by aggregates thereof, fragments of cellular debris perhaps also containing residual virus aggregates, and finally other particulate content in ascending order by size. The particles then pass through a fine laser beam, scattering some of the light incident on them into an array of scattered light detectors. Traditionally, the detectors collect scattered light at a set of angles spanning a range between 0 and 180 degrees. The sizes of the scattering particles are derived from the variation of intensity with angle of the light they scatter. If the shape of the eluting particle is known, this size result may be used to derive further details of its shape. The diameter of the near-spherical COVID-19 virus, for example, is 125 nm. If present in sufficient quantity, the presence of the COVID-19 viruses in the sample injected is confirmed. A 2013 article by Bousse, et al. in volume 193, pages 589 to 596, of the Journal of Virological Methods confirms the ability of A4F to detect and quantitate the specific types of viruses present as elements of a fractionated supernatant solution. In addition to the presence of viral particles, larger aggregates as well as aggregates of other aerosol particulates present will elute in order of increasing size. The distributions of such viral aggregates may be used to confirm further the COVID-19 light scattering and, thereby, its presence.
The outbreaks of COVID-19 infections have continued within a variety of regions, often associated with earlier events such as holiday celebrations, political rallies, religious gatherings, bars, etc. A significant fraction of the population continues to attend such events with no protective masking nor interest in maintaining safe spacing. Additionally, such safety regulations and requirements are often difficult to monitor and enforce within confined areas such as senior retirement centers, professional meetings, some hospitals, treatment centers, etc. The presence of airborne COVID-19 viruses within such regions cannot be confirmed in real-time. However, such viral content is detectable and, within reasonably short time periods, quantified by means of the inventive process disclosed herein.
The search for COVID-19, or similar viruses, begins with the collection of all the particulate contents of a specified spatial region and its transfer into a small volume of water or similar buffered fluid. This collection is by means of one or more of the virus collection methods described in the two cited reviews in the BACKGROUND section above. Following such a collection process, a solution of a few milliliters containing the constituents of the airborne region sampled is ready for processing in order to classify and identify its contents with particular attention to its COVID-19 fraction if present. In order to find the COVID-19 constituents of the collected sample, the injected aqueous sample must be separated into its constituent parts by means of the asymmetric flow field flow fractionation (A4F) process to be described.
The typical A4F channel, shown in
Most of the flow through the permeable plate 4 is controlled by a valve and exits at 7. The channel flow containing the fractionating sample, leaving the channel at 6, is just the difference between the inlet flow 2 and exit flow 7. The particle-containing sample is injected at 5. By controlling the transverse membrane flow exiting at 7, the flow perpendicular to the channel and leaving through the membrane is thus controlled. The injected particles are subject to two flow fields as they move through the channel: The flow through the channel from injection at 2 to exit at 6, and the perpendicular flow that leaves through the rigid permeable plate 4 through 7. The channel structure is generally tapered from entrance to exit to compensate somewhat for the net flow per unit area through 7. During the flow down the channel, the particles are fractionated because of their different sizes and structures.
The fractionated samples leaving the
There are other, more traditional, types of scattered light detection systems. These include an array of detectors surrounding a cylindrical flow cell illuminated by a laser beam perpendicular to the direction of flow there through, with each set at a different angle with respect to the direction of the incident beam of illumination.
The thus-fractionated particles, in order of elution, would begin with the COVID-19 viruses (the smallest) followed by aggregates thereof, fragments of cellular debris perhaps also containing residual virus aggregates, and finally other particulate content in ascending order by size. This solution may contain particulate debris, traces of virus-cell complexes, virus aggregates of various combinations, in addition to the single virus constituents themselves, if present. The size of the members of each such fraction may now calculated from the measurement of light it scatters as a function of scattering angle. The initial slope of said scattered light intensity is directly proportional to the square of particles' size. For example,
There are other forms of field flow fractionation by which means samples may be fractionated depending upon their composition. These include electrical, thermal, and gravitational. Details may be found in the text “Field-flow Fractionation Handbook” by M. Schimpf, K Caldwell, and J. C. Giddings.
It is obvious that detection of other health-threatening airborne particles and molecules by the same inventive means described may be achieved using the same sequence of collection, fractionation, and measurement. Among them are the many viruses that affect farm animals such as swine virus. Such airborne health-threatening airborne particles also include bacteria such as those responsible for airborne hospital-acquired infections, seasonal flu viruses whose physical locations relative to those stricken with the disease is rarely considered, asbestos particles, etc. It is of particular interest to note that the common, almost yearly, viruses that cause annual flu epidemics do not receive the attention that the COVID-19 viruses have received. Yet in 2018, for example, 80,000 Americans died of flu infections and their complications; about half of the number killed by COVID-19 virus to date.
