Grantee Research Project Results
Final Report: A smartphone-based colorimetric sensor for household lead detection
EPA Grant Number: SU840409Title: A smartphone-based colorimetric sensor for household lead detection
Investigators: Wei, Haoran , Cho, Seo Won , Butler, Craig , Wang, Hanwei
Institution: University of Wisconsin - Madison
EPA Project Officer: Harper, Jacquelyn
Phase: I
Project Period: July 1, 2022 through June 30, 2023
Project Amount: $25,000
RFA: 18th Annual P3 Awards: A National Student Design Competition Focusing on People, Prosperity and the Planet (2021) RFA Text | Recipients Lists
Research Category: P3 Challenge Area - Safe and Sustainable Water Resources , P3 Awards
Objective:
The overall goal of this research is to develop an affordable and easy-to-use sensor for highly selective and sensitive detection of lead in tap water. Lead poisoning has severe implications for brain function and the nervous system, particularly affecting the growth and development of children. One of the major sources of lead exposure stems from the corrosion of lead service lines (LSLs) in aging drinking water distribution infrastructures. The Flint Water Crisis serves as a stark reminder that lead poisoning often disproportionately affects underserved communities, who have limited economic and political influence to identify and address such issues. The initial crucial step in determining the magnitude and scope of lead pollution in tap water is rapid and cost-effective testing, which, unfortunately, is not currently available. Hence, there is a significant need for affordable household sensors that can offer regular monitoring of lead levels in drinking water.
To achieve this overall goal, we have developed a detailed research plan that consists of four interconnected objectives: 1) optimize the recognition elements for lead detection based on the selectivity and sensitivity of the Janus gold nanorod (AuJNR)-based colorimetric sensors, 2) quantify the influence of water chemistry, e.g., ionic strength, pH, and dissolved organic matter, on sensor performance, 3) validate the performance of AuJNR-based colorimetric sensors for lead detection in real drinking water samples using standard methods, and 4) educate children from low-income families in South Side, Chicago about the use of our lead sensor and health hazards of lead. This project aligns with the P3 approach in that it emphasizes the protection of the environment and public health from lead contamination.
Summary/Accomplishments (Outputs/Outcomes):
We employed a novel structure of AuNPs, namely, Janus gold nanorods (AuJNRs), for lead sensor development. Compared with gold nanospheres (AuNSs) that possess only one LSPR band at ⁓520 nm, AuJNRs exhibit a transverse and a longitudinal LSPR band at ⁓520 and ⁓810 nm, respectively. This dual-band nature provides an additional dimension that can be harnessed for effective lead sensing.
We used the tap water collected in Madison, WI to test the stability of AuNSs and AuJNRs because of its high ionic strength (conductivity: ⁓750 μS/cm). AuNSs exhibited severe and continuous aggregation, which was induced by high ionic strength. In contrast, AuJNRs did not aggregate in high ionic strength environments, which underscored the remarkable stability of AuJNRs, making them an ideal candidate for the development of colorimetric sensors that are effective in tap water. Furthermore, we engineered an innovative etching-based approach. When the surface of the AuJNRs is coated with thiosulfate, the addition of 2-mercaptoethanol and Pb2+ results in a selective etching at the tips of the AuJNRs and a substantial reduction of the longitudinal LSPR band. This unique optical response was harnessed for accurate Pb2+ quantification.
To test the sensor’s sensitivity, different volumes of a Pb2+ standard solution were spiked into tap water samples to create a concentration gradient (2-10,000 ppb). Our results showed that light extinction around the longitudinal LSPR band at 765 and 810 nm exhibited a linear decrease as the concentration of Pb2+ increased from 0.01-50 µM (2 to 10,000 ppb) at 0 min. At 15 min, this linear decrease was markedly accentuated, providing a distinct dynamic range for lead quantification. Our data demonstrated the exceptional sensitivity (an LOQ < 2 ppb) and quantitative performance (R2 > 0.98) of the AuJNR-based colorimetric sensors for lead detection in Madison tap water.
To learn about lead pollution in disadvantaged communities, we collected 22 tap water samples from South Chicago, including households and public places, such as water fountains in libraries and parks and analyzed lead using inductively coupled plasma mass spectrometry (ICP-MS). The results revealed a significant discrepancy between the average lead levels in the first-draw samples (2.44 ppb) and samples after 3-min flushing (0.60 ppb). This disparity suggests that water stagnation increases the lead concentration in tap water. Furthermore, we created an informative pamphlet for the participants detailing key factors regarding lead toxicity, lead service lines, and the process through which lead contaminates tap water. We also conducted a survey amongst sampling attendees who expressed interest. This survey measured their existing knowledge about lead pollution in tap water, their household's concern about tap water quality, the presence of any point-of-use treatments, and their willingness to have their tap water regularly tested.
Conclusions:
AuJNRs demonstrate remarkable stability in water environments with high ionic strength, attributed to their distinct structures. Using an innovative etching approach, the AuJNR-based lead sensor showed remarkable sensitivity to lead ions. Analysis of tap water samples from Chicago's south side revealed a distinct spatial pattern in lead concentrations. Notably, the Summit, IL area, characterized by a predominantly low-income demographic with 76.1% Hispanic and 8.7% Black or African American populations, recorded the highest lead levels. The survey indicated residents' limited awareness of Lead Service Lines (LSLs) and the government's LSL replacement initiative. Distributing informational brochures enhanced their understanding of lead contamination and increased their inclination to get their water tested and treated.
Supplemental Keywords:
Drinking water, Plasmonic colorimetric sensing, Citizen Science, Smartphone sensor, Machine Learning
Relevant Websites:
2023 P3 Expo - A Smartphone-based Colorimetric Sensor for Household Lead Detection
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.