Ambient temperature and humidity strongly affect inactivation rates of enveloped viruses, but a mechanistic, quantitative theory of these effects has been elusive. We measure the stability of ...SARS-CoV-2 on an inert surface at nine temperature and humidity conditions and develop a mechanistic model to explain and predict how temperature and humidity alter virus inactivation. We find SARS-CoV-2 survives longest at low temperatures and extreme relative humidities (RH); median estimated virus half-life is >24 hours at 10C and 40% RH, but ~1.5 hours at 27C and 65% RH. Our mechanistic model uses fundamental chemistry to explain why inactivation rate increases with increased temperature and shows a U-shaped dependence on RH. The model accurately predicts existing measurements of five different human coronaviruses, suggesting that shared mechanisms may affect stability for many viruses. The results indicate scenarios of high transmission risk, point to mitigation strategies, and advance the mechanistic study of virus transmission.
Aerosol microdroplets exhibit a stable pH gradient Wei, Haoran; Vejerano, Eric P.; Leng, Weinan ...
Proceedings of the National Academy of Sciences - PNAS,
07/2018, Letnik:
115, Številka:
28
Journal Article
Recenzirano
Odprti dostop
Suspended aqueous aerosol droplets (<50 μm) are microreactors for many important atmospheric reactions. In droplets and other aquatic environments, pH is arguably the key parameter dictating chemical ...and biological processes. The nature of the droplet air/water interface has the potential to significantly alter droplet pH relative to bulk water. Historically, it has been challenging to measure the pH of individual droplets because of their inaccessibility to conventional pH probes. In this study, we scanned droplets containing 4-mercaptobenzoic acid–functionalized gold nanoparticle pH nanoprobes by 2D and 3D laser confocal Raman microscopy. Using surface-enhanced Raman scattering, we acquired the pH distribution inside approximately 20-μm-diameter phosphate-buffered aerosol droplets and found that the pH in the core of a droplet is higher than that of bulk solution by up to 3.6 pH units. This finding suggests the accumulation of protons at the air/water interface and is consistent with recent thermodynamic model results. The existence of this pH shift was corroborated by the observation that a catalytic reaction that occurs only under basic conditions (i.e., dimerization of 4-aminothiophenol to produce dimercaptoazobenzene) occurs within the high pH core of a droplet, but not in bulk solution. Our nanoparticle probe enables pH quantification through the cross-section of an aerosol droplet, revealing a spatial gradient that has implications for acid-base–catalyzed atmospheric chemistry.
Ammonium is an important atmospheric constituent that dictates many environmental processes. The impact of the ammonium ion concentration on 10-50 μm aerosol droplet pH was quantified using pH ...nanoprobes and surface-enhanced Raman spectroscopy (SERS). Sample solutions were prepared by mixing 1 M ammonium sulfate (AS), ammonium nitrate (AN), sodium sulfate (SS), or sodium nitrate (SN) solutions with 1 M phosphate buffer (PB) at different volume ratios. Stable pH values were measured for pure PB, AS, and AN droplets at different concentrations. The centroid pH of 1 M PB droplets was ∼11, but when PB was systematically replaced with ammonium (AS- or AN-PB), the centroid pH within the droplets decreased from ≈11 to 5.5. Such a decrease was not observed in sodium (SS- or SN-PB) droplets, and no pH differences were observed between sulfate and nitrate salts. Ammonia partitioning to the gas phase in ammonium-containing droplets was evaluated to be negligible. Raman sulfate peak (∼980 cm
) intensity measurements and surface tension measurements were conducted to investigate changes in ion distribution. The pH difference between ammonium-containing droplets and ammonium-free droplets is attributed to the alteration of the ion distribution in the presence of ammonium.
Nanoparticle surface coatings dictate their fate, transport, and bioavailability. We used a gold nanoparticle–bacterial cellulose substrate and “hot spot”-normalized surface-enhanced Raman scattering ...(HSNSERS) to achieve in situ and real-time monitoring of ligand exchange reactions on the gold surface. This approach enables semiquantitative determination of citrate surface coverage. Following exposure of the citrate-coated nanoparticles to a suite of guest ligands (thiolates, amines, carboxylates, inorganic ions, and proteins), the guest ligand signal exhibited first-order growth kinetics, while the desorption mediated decay of the citrate signal followed a first-order model. Guest ligand functional group chemistry dictated the kinetics of citrate desorption, while the guest ligand concentration played only a minor role. Thiolates and BSA were more efficient at ligand exchange than amine-containing chemicals, carboxylate-containing chemicals, and inorganic salts due to their higher binding energies with the AuNP surface. Amine-containing molecules overcoated rather than displaced the citrate layer via electrostatic interaction. Citrate exhibited low resistance to replacement at high surface coverages, but higher resistance at lower coverage, thus suggesting a transformation of the citrate-binding mode during desorption. High resistance to replacement in streamwater suggests that the role of surface-adsorbed citrate in nanomaterial fate and transport must be better understood.
It is well known that atmospheric aerosol size and composition impact air quality, climate, and health. The aerosol composition is typically a mixture and consists of a wide range of organic and ...inorganic particles that interact with each other. Furthermore, water vapor is ubiquitous in the atmosphere, in indoor air, and within the human body’s respiratory system, and the presence of water can alter the aerosol morphology and propensity to form droplets. Specifically, aerosol mixtures can undergo liquid–liquid phase separation (LLPS) in the presence of water vapor. However, the experimental conditions for which LLPS impacts water uptake and the subsequent prediction of aerosol mixtures are poorly understood. To improve our understanding of aerosol mixtures and droplets, this study explores two ternary systems that undergo LLPS, namely, the 2MGA system (sucrose + ammonium sulfate + 2-methylglutaric acid) and the PEG1000 system (sucrose + ammonium sulfate + polyethylene glycol 1000). In this study, the ratio of species and the O:C ratios are systematically changed, and the hygroscopic properties of the resultant aerosol were investigated. Here, we show that the droplet activation above 100% RH of the 2MGA system was influenced by LLPS, while the droplet activation of the PEG1000 system was observed to be linearly additive regardless of chemical composition, O:C ratio, and LLPS. A theoretical model that accounts for LLPS with O:C ratios was developed and predicts the water uptake of internally mixed systems of different compositions and phase states. Hence, this study provides a computationally efficient algorithm to account for the LLPS and solubility parameterized by the O:C ratio for droplet activation at supersaturated relative humidity conditions and may thus be extended to mixed inorganic–organic aerosol populations with unspeciated organic composition found in the ambient environment.
The factors contributing to the survival of enveloped viruses (e.g., influenza and SARS-CoV-2) on fomite surfaces are of societal interest. The bacteriophage Phi6 is an enveloped viral surrogate ...commonly used to study viability. To investigate how viability changes during the evaporation of droplets on polypropylene, we conducted experiments using a fixed initial Phi6 concentration while systematically varying the culture concentration and composition (by amendment with 2% fetal bovine serum (FBS), 0.08 wt % BSA, or 0.5 wt % SDS). The results were consistent with the well-founded relative humidity (RH) effect on virus viability; however, the measured viability change was greater than that previously reported for droplets containing either inorganic salts or proteins alone, and the protein effects diverged in 1× Dulbecco’s modified Eagle’s medium (DMEM). We attribute this discrepancy to changes in virus distribution during droplet evaporation that arise due to the variable solute drying patterns (i.e., the “coffee-ring” effect) that are a function of the droplet biochemical composition. To test this hypothesis, we used surface-enhanced Raman spectroscopy (SERS) imaging and three types of gold nanoparticles (pH nanoprobe, positively charged (AuNPs(+)), and negatively charged (AuNPs(−))) as physical surrogates for Phi6 and determined that lower DMEM concentrations, as well as lower protein concentrations, suppressed the coffee-ring effect. This result was observed irrespective of particle surface charge. The trends in the coffee-ring effect correlate well with the measured changes in virus infectivity. The correlation suggests that conditions resulting in more concentrated coffee rings provide protective effects against inactivation when viruses and proteins aggregate.
•Bacterial cellular changes after inactivation contribute to SERS signal changes.•SERS peak changes for each method were extracted and illustrated using barcodes.•Nucleic acid peaks dominant ...following heat, UV254, and UV254/chlorine treatments.•Free chlorine mostly leads to the decrease in carbohydrate peaks.•The SERS results are verified using different bacterial species and water matrices.
An improved understanding of bacterial inactivation mechanisms will provide useful insights for infectious disease control and prevention. We evaluated bacterial response to several inactivation methods using surface-enhanced Raman spectroscopy (SERS). The results indicate that changes in the SERS signal are highly related to cellular disruption and that cellular changes arising after cell inactivation cannot be ignored. The membrane integrity of heat and the combination of UV254 and free chlorine (UV254/chlorine) treated Pseudomonas syringae (P. syringae) cells were severely disrupted, leading to significantly increased peak intensities. Conversely, ethanol treated bacteria exhibited intact cell morphologies and the SERS spectra remained virtually unchanged. On the basis of time dependent SERS signals, we extracted dominant SERS patterns. Peaks related to nucleic acids accounted for the main changes observed during heat, UV254, and UV254/chlorine treatment, likely due to their outward diffusion from the cell cytoplasm. For free chlorine treated P. syringae, carbohydrates and proteins on the cell membrane were denatured or lost, resulting in a decrease in related peak intensities. The nucleobases were likely oxidized when treated with UV254 and chlorine, thus leading to shifts in the related peaks. The generality of the method was verified using two additional bacterial strains: Escherichia coli and Bacillus subtilis as well as in different water matrices. The results suggest that SERS spectral analysis is a promising means to examine bacterial stress response at the molecular level and has applicability in diverse environmental implementations.
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Characterization of single droplet pH is required to better understand differences in droplet and bulk water chemistries and the variability of individual atmospheric droplets. In this study, we ...demonstrate the use of flash-freeze surface-enhanced Raman spectroscopy (SERS) as a means to characterize the pH of micrometer-sized droplets generated from mixtures of low solute concentration environmental water samples and a pH nanoprobe. These samples included stream waters, rain, and snowmelt from areas surrounding Blacksburg, Virginia. Compared to room-temperature SERS, flash-freeze SERS preserves the initial droplet properties and minimizes water loss due to localized heat generation in the vicinity of SERS hot spots. Moreover, the flash-freeze SERS approach provides greater sensitivity relative to pH paper for low solute concentration droplets. We observed that pH values measured by flash-freeze SERS were generally comparable with those obtained at room temperature, but did not result in heating-induced droplet destabilization. Using flash-freeze SERS, we observed that droplet and bulk pH were comparable for most environmental samples. One rainwater sample showed a higher droplet pH compared to its bulk sample. Upon the basis of ICP-MS results, the ionic composition of this rainwater was significantly different from the other collected samples, thus suggesting the effect of droplet composition on droplet pH.
The phase state of aerosol particles can impact numerous atmospheric processes, including new particle growth, heterogeneous chemistry, cloud condensation nucleus formation, and ice nucleation. In ...this article, the phase transitions of inorganic, organic, and organic/inorganic aerosol particles are discussed, with particular focus on liquid-liquid phase separation (LLPS). The physical chemistry that determines whether LLPS occurs, at what relative humidity it occurs, and the resultant particle morphology is explained using both theoretical and experimental methods. The known impacts of LLPS on aerosol processes in the atmosphere are discussed. Finally, potential evidence for LLPS from field and chamber studies is presented. By understanding the physical chemistry of the phase transitions of aerosol particles, we will acquire a better understanding of aerosol processes, which in turn impact human health and climate. Expected final online publication date for the
, Volume 75 is April 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
Sulfate formation is arguably the most important chemical process during urban haze events in China; however, the complex mechanism of sulfate formation from SO2 remains unresolved. Recent studies ...showed regionally transported sea spray aerosols (SSAs) and transition-metal ions (TMI)-catalyzed SO2 oxidation are major contributors to sulfate in haze events near coastal regions. To better understand the role of SSA and TMI catalysis, we investigated the reaction kinetics of Mn2+-catalyzed SO2 oxidation in NaCl microdroplets using confocal Raman spectroscopy coupled with a relative humidity (RH) and trace gas control system. We demonstrated that the reaction occurred on the droplet surface according to the linear correlation between the reaction rate and the droplet radius. The saturation concentration for both Mn2+ (0.001 mol/L at 1 ppm SO2) and SO2 (2 ppm at 10–5 mol/L Mn2+) implies the existence of an upper limit of the SO2 uptake coefficient, which is intercorrelated with Mn2+ and SO2 concentrations. The uptake coefficient increased with high ionic strength, while it remained constant when the pH ranged from 5 to 8. The uptake coefficient was on the order of 10–5 to 10–4, which is 10 to 100 times larger than that of the uncatalyzed autoxidation of SO2 and is overall higher than other mineral dust oxidation pathways.
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