Silica-encapsulated DNA tracers for measuring aerosol distribution dynamics in real-world settings

Abstract

Aerosolized particles play a significant role in human health and environmental risk management. The global importance of aerosol-related hazards, such as the circulation of pathogens and high levels of air pollutants, have led to a surging demand for suitable surrogate tracers to investigate the complex dynamics of airborne particles in real-world scenarios. In this study, we propose a novel approach using silica particles with encapsulated DNA (SPED) as a tracing agent for measuring aerosol distribution indoors. In a series of experiments with a portable setup, SPED were successfully aerosolized, recaptured, and quantified using quantitative polymerase chain reaction (qPCR). Position dependency and ventilation effects within a confined space could be shown in a quantitative fashion achieving detection limits below 0.1 ng particles per m³ of sampled air. In conclusion, SPED show promise for a flexible, cost-effective, and low-impact characterization of aerosol dynamics in a wide range of settings.

Keywords: DNA; aerosol; nanoparticles; silica; tracing; ventilation.

FIGURE 1

Schematic description of the tracing method using SPED. DNA is encapsulated in silica particles to form SPED, which are then aerosolized using an airbrush gun. The air is sampled using glass biosamplers. DNA is released from the collected SPED and quantified by qPCR

FIGURE 2

(A) Scanning electron microscopy (SEM) image of SPED species S2. Scale bar is 500 nm. (B) Hydrodynamic size distribution of two batches of SPED (S1 and S2) by analytical photocentrifugation. For S1, the median is at 133.5 nm, for S2 at 160.6 nm. (C) Diameter of droplets generated by the airbrush gun, as measured by phase Doppler anemometry. The arithmetic mean droplet size is 10.8 ± 4.4 µm

FIGURE 3

Schematic representation of exposure scenarios with evaporating droplets, comparing (A) virus‐carrying aerosols as produced by a human cough with (B) the laboratory setup used in this study

FIGURE 4

(A) Schematic representation of room characterization experiments. SPED are dispersed in an indoor environment, recollected using one or several sampling devices and analyzed using quantitative PCR. (B) Room layout of the laboratory used for the experiments, schematically showing benchtops, sinks, fume hoods, and hallways. Distances of the sampling device locations from the source of dispersion are indicated

FIGURE 5

Time‐, position‐, and ventilation‐dependent effects as measured by air sampling after dispersion of SPED aerosols. Error bars are calculated from standard deviations of PCR triplicates. Position numbers refer to sampler location in the room as depicted in Figure 4b. (A) Time‐dependent measurement using two air samplers. The y‐axis indicates the integrated amount of collected SPED (in mg) over a total time of 120 min. The measurement point at 0 min was taken immediately before dispersion as a zero control. The first five measurements are zoomed in for clarity. (B) Measurement of position‐dependent relative exposure of 4 impingers. Two experiments were performed with particles S1 and a third using particles S2. The values reflect the total amount of particles collected after a 2‐h sampling time. The data are normalized to the first position in each set. (C) Total load relative to position 1 per impinger with (data from S1 experiment 2) and without ventilation under equal conditions as in (C). (D) Same as (C) but comparing position 1 to an additional position in the adjacent atrium (position 5), which is additionally zoomed in for clarity