Development of methods for assessing oxidative stress caused by atmospheric aerosols

2012 Fall.Includes bibliographical references.Extensive epidemiological studies show strong associations between the exposure to atmospheric aerosol particulate matter (PM) in the size range of 0.1- 10 µm and health problems, including respiratory, atherosclerosis and cardiovascular diseases. However, the mechanisms of PM-induced toxicity are poorly understood. A leading hypothesis states that airborne PM induces harm by generating reactive oxygen species in and around human tissues, leading to oxidative stress. To improve understanding of this effect, methods including biological assays and chemical assays for assessing oxidative stress caused by atmospheric aerosols have been developed and are described in this dissertation. For biological assays, a cleavable tag immunoassay (CTI) was developed with an ultimate goal of measuring multiple oxidative stress biomarkers in a single run. As a proof-of-concept, the multianalyte analysis system CTI was performed in competitive, non-competitive, and mixed formats for detection of small molecules and protein biomarkers simultaneously. For chemical assays, a microfluidic electrochemical sensor and a microfluidic paper-based analytical device (µPAD) have been developed for assessing aerosol oxidative stress in an area-based exposure study and a personal exposure study, respectively. The microfluidic electrochemical sensor was used for assessing aerosol oxidative stress by measuring the oxidative activity. The sensor was coupled directly to a Particle-into-Liquid-Sampler (PILS) to create an on-line aerosol sampling/analysis system. The system offers analysis with 3 minute temporal resolution, making it the best available temporal resolution for aerosol oxidative activity. The sensor was also used to analyze the ability of aerosols to generate hydroxyl radicals as another parameter for assessing aerosol oxidative stress. The ultimate goal of this system is to create an on-line monitoring system using a similar approach for oxidative activity analysis. As a first step toward this goal, assay optimization and system characterization in an off-line format employing flow injection analysis and amperometric detection, were carried out and presented in this dissertation. A microfluidic paper-based analytical device (µPAD) was developed for measuring oxidative activity of aerosol collected by a personal sampler. The system allows analysis with minimal sample preparation and requires 100-fold less particulate matter mass than existing analysis methods

User-friendly diameter-based measurement paper sensor for chloride detection in water

Chloride (Cl−) is an anion widely distributed in nature. It is also an essential parameter to consider when assessing the water quality for ensuring drinking water safety, preventing infrastructure damage, mitigating environmental impact, identifying groundwater contamination. This work presents the first development of a diameter-based measurement paper sensor for chloride analysis using the reaction based on a Mohr's precipitation titration. The paper sensor that has a circular shape with 3-cm diameter was pre-coated with AgNO3 and CrO42− forming brown precipitates of the Ag2CrO4. The sensor was sealed using lamination films with 3-mm diameter hole-punched inlets on the top of the lamination film for sample delivery. To detect chloride, the sensor was simply immersed into the sample. The chloride solution flows into the central sample inlet and spreads radially to undergo the displacement reaction with Ag2CrO4 precipitate, forming AgCl white precipitate whose diameter proportional to the chloride that can be observed within 3 min. Concentration of AgNO3 used was found to impact the analytical figures of merit. The lower AgNO3 concentration yields lower limit of detection, narrower linear range but higher sensitivity. The sensor was applied for chloride analysis in tap water, drinking water and industrial water and the chloride concentration obtained from the developed sensors are not significant differences from those obtained from the standard titration method at 95% confidence interval (two tailed P = 0.08) indicating that the developed sensor provides accurate analysis of chloride in water samples from various sources. The developed sensor was used by the untrained staffs for on-site of analysis chloride in tap water collected at 26 locations in SaenSuk Municipality area, Chonburi, Thailand. The results showed that the chloride level in all samples is in range of 52.2–84.7 mg L−1 which is far below the acceptable range set by the Provincial Waterwork Authority of Thailand (< 250 mg L−1) indicating that the tap water used in this area is safe for consumers

Laboratory Evaluation of a Microfluidic Electrochemical Sensor for Aerosol Oxidative Load

<div><p>Human exposure to particulate matter (PM) air pollution is associated with human morbidity and mortality. The mechanisms by which PM impacts human health are unresolved, but evidence suggests that PM intake leads to cellular oxidative stress through the generation of reactive oxygen species (ROS). Therefore, reliable tools are needed for estimating the oxidant generating capacity, or oxidative load, of PM at high temporal resolution (minutes to hours). One of the most widely reported methods for assessing PM oxidative load is the dithiothreitol (DTT) assay. The traditional DTT assay utilizes filter-based PM collection in conjunction with chemical analysis to determine the oxidation rate of reduced DTT in solution with PM. However, the traditional DTT assay suffers from poor time resolution, loss of reactive species during sampling, and high limit of detection. Recently, a new DTT assay was developed that couples a particle-into-liquid-sampler with microfluidic-electrochemical detection. This “on-line” system allows high temporal resolution monitoring of PM reactivity with improved detection limits. This study reports on a laboratory comparison of the traditional and on-line DTT approaches. An urban dust sample was aerosolized in a laboratory test chamber at three atmospherically relevant concentrations. The on-line system gave a stronger correlation between DTT consumption rate and PM mass (<i>R</i>² = 0.69) than the traditional method (<i>R</i>² = 0.40) and increased precision at high temporal resolution, compared to the traditional method.</p> <p>Copyright 2014 American Association for Aerosol Research</p> </div

Microfluidic Paper-Based Analytical Device for Aerosol Oxidative Activity

Human exposure to particulate matter (PM) air pollution has been linked with respiratory, cardiovascular, and neurodegenerative diseases, in addition to various cancers. Consistent among all of these associations is the hypothesis that PM induces inflammation and oxidative stress in the affected tissue. Consequently, a variety of assays have been developed to quantify the oxidative activity of PM as a means to characterize its ability to induced oxidative stress. The vast majority of these assays rely on high-volume, fixed-location sampling methods due to limitations in assay sensitivity and detection limit. As a result, our understanding of how personal exposure contributes to the intake of oxidative air pollution is limited. To further this understanding, we present a microfluidic paper-based analytical device (μPAD) for measuring PM oxidative activity on filters collected by personal sampling. The μPAD is inexpensive to fabricate and provides fast and sensitive analysis of aerosol oxidative activity. The oxidative activity measurement is based on the dithiothreitol assay (DTT assay), uses colorimetric detection, and can be completed in the field within 30 min following sample collection. The μPAD assay was validated against the traditional DTT assay using 13 extracted aerosol samples including urban aerosols, biomass burning PM, cigarette smoke, and incense smoke. The results showed no significant differences in DTT consumption rate measured by the two methods. To demonstrate the utility of the approach, personal samples were collected to estimate human exposures to PM from indoor air, outdoor air on a clean day, and outdoor air on a wildfire-impacted day in Fort Collins, CO. Filter samples collected on the wildfire day gave the highest oxidative activity on a mass normalized basis, whereas typical ambient background air showed the lowest oxidative activity

Microfluidic Electrochemical Sensor for On-Line Monitoring of Aerosol Oxidative Activity

Particulate matter (PM) air pollution has a significant impact on human morbidity and mortality; however, the mechanisms of PM-induced toxicity are poorly defined. A leading hypothesis states that airborne PM induces harm by generating reactive oxygen species in and around human tissues, leading to oxidative stress. We report here a system employing a microfluidic electrochemical sensor coupled directly to a particle-into-liquid sampler (PILS) system to measure aerosol oxidative activity in an on-line format. The oxidative activity measurement is based on the dithiothreitol (DTT) assay, where, after being oxidized by PM, the remaining reduced DTT is analyzed by the microfluidic sensor. The sensor consists of an array of working, reference, and auxiliary electrodes fabricated in a poly­(dimethylsiloxane)-based microfluidic device. Cobalt­(II) phthalocyanine-modified carbon paste was used as the working electrode material, allowing selective detection of reduced DTT. The electrochemical sensor was validated off-line against the traditional DTT assay using filter samples taken from urban environments and biomass burning events. After off-line characterization, the sensor was coupled to a PILS to enable on-line sampling/analysis of aerosol oxidative activity. Urban dust and industrial incinerator ash samples were aerosolized in an aerosol chamber and analyzed for their oxidative activity. The on-line sensor reported DTT consumption rates (oxidative activity) in good correlation with aerosol concentration (<i>R</i>² from 0.86 to 0.97) with a time resolution of approximately 3 min