4th Year Research Seminar:
Ambient particulate matter (PM) air pollution is associated with negative health effects, including respiratory and cardiovascular diseases, and is estimated to cause millions of deaths worldwide each year.1 The current hypothesis is that PM produces reactive oxygen species (ROS) in the body, which leads to oxidative stress.2 Dithiothreitol (DTT) is commonly used as a model antioxidant to measure oxidative potential from PM-containing samples.3 PM catalyzes DTT oxidation, and the DTT loss rate is correlated to the PM’s oxidative potential. The traditional DTT assay is an indirect spectroscopic method that requires addition of the chromophore 5,5-dithio-bis-(2-nitrobenzoic acid) (DTNB). DTT concentration can also be directly measured electrochemically without dilution and correlates 1:1 with the absorbance assay.4 Electrodes for DTT measurement are carbon based, modified with the catalyst cobalt(II) phthalocyanine (CoPC), to reduce oxidation overpotential and electrode fouling.4 Presented here is an electrochemical assay that uses commercially available equipment, for labs that do not have access to electrode fabrication tools, that validates an end-point assay instead of the traditional kinetic assay, enabling batch processing of four samples per hour. The electrochemical assay is then applied to a large (>100) set of PM filter samples, collected as part of a cookstove replacement project in Honduras, for the first time. The commercial electrode system is compared to homemade graphite-thermoplastic electrodes (TPEs), which are easily modified with CoPC for DTT detection. Since large-scale PM health studies are hindered by the lack of sample analysis automation,5 the DTT assay is further improved to six samples per hour with a developed semi-automated system. The semi-automated system can use either electrochemical or absorbance detection, and the two detection motifs are compared. The semi-automated assay is validated with a model oxidant and then tested on real PM filter samples from chamber experiments.
- Cohen, A. J.; Brauer, M.; Burnett, R.; Anderson, H. R.; Frostad, J.; Estep, K.; Balakrishnan, K.; Brunekreef, B.; Dandona, L.; Dandona, R.; Feigin, V.; Freedman, G.; Hubbell, B.; Jobling, A.; Kan, H.; Knibbs, L.; Liu, Y.; Martin, R.; Morawska, L.; Pope, C. A., III; Shin, H.; Straif, K.; Shaddick, G.; Thomas, M.; van Dingenen, R.; van Donkelaar, A.; Vos, T.; Murray, C. J. L.; Forouzanfar, M. H., Estimates and 25-year trends of the global burden of disease attributable to ambient air pollution: an analysis of data from the Global Burden of Diseases Study 2015. The Lancet 2017, 389 (10082), 1907-1918.
- Chung, M. Y.; Lazaro, R. A.; Lim, D.; Jackson, J.; Lyon, J.; Rendulic, D.; Hasson, A. S., Aerosol-Borne Quinones and Reactive Oxygen Species Generation by Particulate Matter Extracts. Environmental Science & Technology 2006, 40 (16), 4880-4886.
- Crobeddu, B.; Aragao-Santiago, L.; Bui, L.-C.; Boland, S.; Baeza Squiban, A., Oxidative potential of particulate matter 2.5 as predictive indicator of cellular stress. Environ. Pollut. 2017, 230, 125-133.
- Sameenoi, Y.; Koehler, K.; Shapiro, J.; Boonsong, K.; Sun, Y.; Collett, J.; Volckens, J.; Henry, C. S., Microfluidic Electrochemical Sensor for On-Line Monitoring of Aerosol Oxidative Activity. J. Am. Chem. Soc. 2012, 134 (25), 10562-10568.
- Fang, T.; Verma, V.; Guo, H.; King, L.; Edgerton, E.; Weber, R., A semi-automated system for quantifying the oxidative potential of ambient particles in aqueous extracts using the dithiothreitol (DTT) assay: results from the Southeastern Center for Air Pollution and Epidemiology (SCAPE). Atmospheric Measurement Techniques 2015, 8 (1), 471.