Schematic diagram and a photo of SAMERA.
Performance of SAMERA in precision and accuracy.
Design and Evaluation of a Semi-Automated Multi-endpoint ROS-activity Analyzer (SAMERA) System for Evaluating the Oxidative Potential of Ambient Aerosols
Timeline: August 2017 - November 2019
Brief intro: Many acellular assays have been developed for assessing the oxidative potential (OP) of ambient PM2.5, yet no consensus has been reached on the most appropriate method. Most of these methods are highly time- and labor-intensive, making it difficult to analyze a large sample-set. Here, we have developed a semi-automated multi-endpoint ROS-activity analyzer (SAMERA) for measuring the five most commonly used endpoints of OP: consumption rate of dithiothreitol (OPDTT), ascorbic acid (OPAA-SLF) and glutathione (OPGSH-SLF), and the generation rate of •OH in DTT (OPOH-DTT) and in surrogate lung fluid (OPOH-SLF). We used both ROS-active standard chemicals and real PM2.5 samples to evaluate SAMERA. A high analytical precision (CoV < 10% for chemicals and <15% for samples) was obtained for both chemicals and PM samples. The results generated from the automated SAMERA were in good agreement with those obtained from manual operation (R2 = 0.99 for chemicals and 0.86-0.97 for samples). Preliminary results demonstrate the stability and capability of SAMERA for providing a comprehensive OP dataset, which can be integrated into the epidemiological models in future studies.
This work has been published in Aerosol Science and Technology (Impact factor: 4.809 in 2021).
Five sampling sites located in Midwest US (Figure 1 of Randy's ACP paper)
A glance from the frozen Chicago site (by Randy Yu).
Major finding of the research: variations of different endpoints and PM mass show totally different pattern.
Spatiotemporal Variability of PM2.5 OP and mass concentrations in Midwest U.S.
Timeline: April 2019 – May 2021
Brief intro: Oxidative potential has been proposed as a better health metric over mass when considering the imbalance of toxicological effect and chemical composition of PM2.5. We assessed OP of ambient PM2.5 in Midwestern US (N = 241; five sites including urban, rural, and roadside environments) using five OP endpoints. The results indicated that PM2.5 mass concentrations are generally distributed highly homogeneously, while most OP endpoints showed significant spatiotemporal heterogeneity. Methanol-soluble OP had higher OP levels than corresponding water-soluble OP, indicating more ROS-active species extracted in methanol. Furthermore, we found a weak correlation and inconsistent slope values between PM2.5 mass and most OP endpoints. the poor-to-moderate intercorrelations among different OP endpoints infer different mechanisms of OP represented by these endpoints, and thus demonstrate the rationale for analyzing multiple acellular endpoints for a better and comprehensive assessment of OP.
This work has been published in Atmospheric Chemistry & Physics (Impact factor: 6.133 in 2023).
Schematic diagram and a photo of SAMERA.
Performance of SAMERA in precision and accuracy.
Design and Evaluation of a Semi-Automated Multi-endpoint ROS-activity Analyzer (SAMERA) System for Evaluating the Oxidative Potential of Ambient Aerosols
Timeline: August 2017 - November 2019
Brief intro: Many acellular assays have been developed for assessing the oxidative potential (OP) of ambient PM2.5, yet no consensus has been reached on the most appropriate method. Most of these methods are highly time- and labor-intensive, making it difficult to analyze a large sample-set. Here, we have developed a semi-automated multi-endpoint ROS-activity analyzer (SAMERA) for measuring the five most commonly used endpoints of OP: consumption rate of dithiothreitol (OPDTT), ascorbic acid (OPAA-SLF) and glutathione (OPGSH-SLF), and the generation rate of •OH in DTT (OPOH-DTT) and in surrogate lung fluid (OPOH-SLF). We used both ROS-active standard chemicals and real PM2.5 samples to evaluate SAMERA. A high analytical precision (CoV < 10% for chemicals and <15% for samples) was obtained for both chemicals and PM samples. The results generated from the automated SAMERA were in good agreement with those obtained from manual operation (R2 = 0.99 for chemicals and 0.86-0.97 for samples). Preliminary results demonstrate the stability and capability of SAMERA for providing a comprehensive OP dataset, which can be integrated into the epidemiological models in future studies.
This work has been published in Aerosol Science and Technology (Impact factor: 4.809 in 2021).
Different synergistic/antagonistic patterns were observed between metals and quinones.
The remixture of HULIS and hydrophilic fractions of PM2.5 extracts show different activities with the summation of their individual activities, indicating the existence of interactions among species.
DTT consumption can be well represented by three key metals + HULIS, while OH generation cannot.
Major finding of the research: both synergistic and antagonistic interactions exist between metals and organic species of PM2.5 in two OP endpoints (DTT consumption and OH generation in DTT).
The Interactions among Metals and Organic Species in Ambient Particulate Matter (PM) on ROS Generation
Timeline: June 2016 – August 2017
Brief intro: Conventional methods for evaluating the oxidative potential of PM species generally treat them individually, which might not reflect the actual mechanism because of the possible existence of interactions among these components. We assessed the interactions among the particulate matter (PM) components in generating the reactive oxygen species (ROS) based on a dithiothreitol (DTT) assay, by measuring both DTT consumption and hydroxyl radical ( ·OH) generation. The interactions of Fe were additive with quinones in DTT consumption but strongly synergistic in ·OH generation. Cu showed antagonistic interactions with quinones in both DTT consumption and ·OH generation. Mn interacted synergistically with quinones in DTT oxidation but antagonistically in ·OH generation. The nature of the interactions of these metals (Fe, Mn, and Cu) with ambient humic-like substances (HULIS) resembled that with quinones, although the intensity of interactions were weaker in DTT consumption than · OH generation. Finally, we demonstrated that the DTT consumption capability of ambient PM can be well explained by HULIS, three transition metals (Fe, Mn, and Cu), and their interactions, but ·OH generation involves a contribution ( ∼50%) from additional compounds (aliphatic species or metals other than Fe, Mn, and Cu) present in the hydrophilic PM fraction. The study highlights the need to account for the interactions between organic compounds and metals while apportioning the relative contributions of chemical components in the PM oxidative potential.
This work has been published in Environmental Science & Technology (Impact factor: 9.028 in 2023).