Advancing the science of dynamic airborne nanosized particles using Nano-DIHM

In situ and real-time characterization of aerosols is vital to several fundamental and applied research domains including atmospheric chemistry, air quality monitoring, or climate change studies. To date, digital holographic microscopy is commonly used to characterize dynamic nanosized particles, but optical traps are required. In this study, a novel integrated digital in-line holographic microscope coupled with a flow tube (Nano-DIHM) is demonstrated to characterize particle phase, shape, morphology, 4D dynamic trajectories, and 3D dimensions of airborne particles ranging from the nanoscale to the microscale. We demonstrate the application of Nano-DIHM for nanosized particles (≤200 nm) in dynamic systems without optical traps. The Nano-DIHM allows observation of moving particles in 3D space and simultaneous measurement of each particle’s three dimensions. As a proof of concept, we report the real-time observation of 100 nm and 200 nm particles, i.e. polystyrene latex spheres and the mixture of metal oxide nanoparticles, in air and aqueous/solid/heterogeneous phases in stationary and dynamic modes. Our observations are validated by high-resolution scanning/transmission electron microscopy and aerosol sizers. The complete automation of software (Octopus/Stingray) with Nano-DIHM permits the reconstruction of thousands of holograms within an hour with 62.5 millisecond time resolution for each hologram, allowing to explore the complex physical and chemical processes of aerosols.

Effects of Air Purifiers on the Spread of Simulated Respiratory Droplet Nuclei and Virus Aggregates

The present study was performed to quantitatively evaluate the effects of air purifiers on the spread of COVID-19 and to suggest guidelines for their safe use. To simulate respiratory droplet nuclei and nano-sized virus aggregates, deionized water containing 100 nm of polystyrene latex (PSL) particles was sprayed using a vibrating mesh nebulizer, and the changes in the particle number concentration were measured for various locations of the particle source and air purifier in a standard 30 m3 test chamber. The spread of the simulated respiratory droplet nuclei by the air purifier was not significant, but the nano-sized aggregates were significantly affected by the airflow generated by the air purifier. However, due to the removal of the airborne particles by the HEPA filter contained in the air purifier, continuous operation of the air purifier reduced the number concentration of both the simulated respiratory droplet nuclei and nano-sized aggregates in comparison to the experiment without operation of the air purifier. The effect of the airflow generated by the air purifier on the spread of simulated respiratory droplet nuclei and nano-sized aggregates was negligible when the distance between the air purifier and the nebulizer exceeded 1 m.

Technical note: Measurement of chemically resolved volume equivalent diameter and effective density of particles by AAC-SPAMS

Size and effective density (ρe) are important properties of aerosol particles and are related to their influences on human health and the global climate. The volume equivalent diameter (Dve) is an intrinsic property that is used to evaluate particle size. Three definitions of ρe are generally used to characterize the physical property of a particle as an alternative to particle density, in which only the ρeII, defined as the ratio of particle density (ρp) to a dynamic shape factor (χ), has the characteristic of being independent of particle size. However, it is still challenging to simultaneously characterize the Dve and ρeII of aspherical particles. Here, we present a novel system that classifies particles with their aerodynamic diameter (Da) by aerodynamic aerosol classifier (AAC) and determines their vacuum aerodynamic diameter (Dva) by single-particle aerosol mass spectrometry (SPAMS) to achieve a measurement of Dve and ρeII. The reliability of the AAC-SPAMS system for accurately obtaining Dve and ρeII is verified based on the result that the deviation between the measured and theoretical values is less than 6 % for the size-resolved spherical polystyrene latex (PSL). The AAC-SPAMS system was applied to characterize the Dve and ρeII of (NH4)2SO4 and NaNO3 particles, suggesting that these particles are aspherical and their ρeII is independent of particle size. Finally, the AAC-SPAMS system was deployed in a field measurement, showing that it is a powerful technique to characterize the chemically resolved Dve and ρeII of particles in real time.

Phagocytosis of microparticles increases responsiveness of macrophage-like cell lines U937 and THP-1 to bacterial lipopolysaccharide and lipopeptide

Following bacterial infection, macrophages produce pro-inflammatory cytokines in response to bacterial cell components, including lipopolysaccharide (LPS) and lipopeptide, and simultaneously phagocytize and digest the invading bacteria. To study the effects of phagocytosis on pro-inflammatory responses, we determined if phagocytosis of polystyrene latex beads with ~ 1 µm diameter increases pro-inflammatory cytokine expression by human macrophage-like U937 and THP-1 cells stimulated with LPS. Treating macrophage-like cells with beads coated with IgG to facilitate Fcγ receptor-mediated phagocytosis increased LPS-induced expression of pro-inflammatory cytokines, including tumor necrosis factor-alpha, interleukin-1 beta, and interleukin-6. Treatment with beads coated with poly-l-lysine to facilitate Fcγ receptor–independent phagocytosis also increased LPS-induced cytokine expression. Our results indicate that LPS-induced pro-inflammatory responses are enhanced by bead phagocytosis regardless of the uptake mechanism. Additionally, phagocytosis enhanced LPS-induced NF-κB activation, suggesting that Toll-like receptor (TLR) 4 signaling is enhanced by phagocytosis. Furthermore, bead phagocytosis enhanced pro-inflammatory responses in U937 cells stimulated with lipopeptide, a ligand for the TLR2/TLR6 heterodimeric receptor. In conclusion, microparticle phagocytosis by macrophage-like U937 and THP-1 cells enhances the innate immune response induced by bacterial components.

Development and creation of zeta potential reference material of the particles in a liquid medium

A comprehensive study to develop and create standard samples of the zeta potential unit of particles in a liquid in accordance with the requirements of GOST ISO 13099-2-2016 in the range of measured values from minus 150 mV to plus 150 mV was carried out. The existing standard samples of zeta potential in Russia and the world have been investigated; the analysis of the applicability of the starting materials and components for the creation of new standard samples has done. Samples based on modified polystyrene latex microspheres, bovine serum albumin and supramolecular systems based on aqueous solutions of L-cysteine, N-acetylcysteine, and silver acetate were considered as promising standard samples of the zeta potential of particles. All studies were carried out on equipment from the State Primary Standard of Dispersed Parameters of Aerosols, Suspensions and Powder Materials GET 163-2020 using the method of electrophoretic light scattering and measuring the pH value. It was found that polystyrene latex microspheres do not correspond to the requirements of the work in terms of developing a set of standard samples. Samples based on suspensions of bovine serum albumin do not correspond to the requirements of GOST ISO 13099-2-2016. Supramolecular systems based on aqueous solutions of L-cysteine, N-acetylcysteine, and silver acetate were proposed as standard samples. Such systems are characterized by the ability to modify the initial potential-determining layer of particles without changing their aggregate stability. Studies of the long-term stability of the developed standard samples of the zeta-potential unit of particles in a liquid have been carried out.

Changes in nanoparticles uptake and distribution caused by an intramacrophagic parasitic infection

This study investigates if visceral leishmaniasis infection has effect in the organ and cellular uptake and distribution of 100-200 nm near-infrared fluorescently-labelled non-biodegradable polystyrene latex beads (PS NP) or biodegradable...

Design of hybrid biocatalysts by controlled heteroaggregation of manganese oxide and sulfate latex particles to combat reactive oxygen species

The preparation of an antioxidant hybrid material by controlled heteroaggregation of manganese oxide nanoparticles (MnO2 NPs) and sulfate-functionalized polystyrene latex (SL) beads was accomplished. Negatively charged MnO2 NPs were prepared...

Aqueous particle generation with a 3D printed nebulizer

In this study, we describe the design and testing of a high-output-stability, constant-liquid-feed nebulizer using the Venturi principle to generate liquid particles from solutions. This atomizer, the PRinted drOpleT Generator (PROTeGE), was manufactured using stereolithography (SLA) printing. Different concentrations of ammonium sulfate solutions were used to characterize the size and number concentration of the generated particles. A comparison of a 3D printed 0.5 mm orifice against a commercially available 0.5 mm brass orifice using the same ammonium sulfate solution was also performed. The particle number concentration generated with the printed orifice was higher, by ∼×2, than the particle number concentration generated with the brass orifice. PROTeGE is also capable of dispersing polystyrene latex (PSL) spheres for calibration purposes. The particle number concentrations obtained in this study ranged from ∼ 10 000 cm−3 for 0.75 µm to ∼ 100 cm−3 for 5.0 µm PSL particles with a dependence on the concentration of the dispersed solution. For the different concentrated ammonium sulfate solutions particle number concentrations from ∼ 14 000 cm−3 for 0.1 g L−1 to 7600 cm−3 for 5.0 g L−1 were measured. An additional measurement with a scanning electrical mobility system (SEMS) was performed for the 0.6 g L−1 solution to measure particles in the size range of 10 to 1000 nm. The generated particle number size distributions (PNSDs) showed a maximum at 50 nm with particle number concentrations of ∼ 40 000 cm−3. PROTeGE is easy to manufacture and operate, low in maintenance, and cost-effective for laboratory and field generation of particles from aqueous media in a size range of 10 to 5000 nm.