Mapping and Monitoring Toxicants Using Carbon Nanotube Sensors

By Maggie He
Jul 08, 2021

MIT Superfund Research Program scientists and engineers are studying N-nitrosodimethylamine (NDMA) and polycyclic aromatic hydrocarbons (PAHs), chemicals that can be harmful to the environment and also to our health. Both NDMA and PAHs undergo secondary chemical reactions to produce alkylating agents that damage DNA, and consequently they have the potential to cause cancer. NDMA arises in the environment as a result of reactions among legacy contaminants that were released to the environment by previous industrial processes. It is also a contaminant with emerging importance, since it is produced by chlorination of water and by carbon capture. As a result, the contamination of NDMA in drinking water is a significant health concern. PAHs are intrinsic products of combustion. The chemical structure of PAHs varies in their polycyclic skeleton as well as their exocyclic functional groups. PAHs and their breakdown products by atmospheric oxidation have different levels of carcinogenicity.

NDMA and PAHs are conventionally detected and monitored by in-lab analysis using high-performance liquid chromatography (HPLC) and gas chromatography (GC) coupled to mass spectrometry (MS). Although these analyses can detect environmentally relevant concentrations, they are slow, expensive, require sample preparation/pre-concentration, and necessitate sophisticated, expensive, and bulky instrumentation. Additionally, laborious analyses with extensive field sampling and transport cannot provide real-time monitoring of contamination levels. Considering the limitations of conventional analyses, portable sensors with the capability of real-time monitoring that can be distributed to contaminated sites for an extended period are needed. In addition to portable sensors, online and positional tracking of contaminants will modernize our technologies and improve human health by enabling steps for minimizing exposure.

Carbon nanotube sensors are ideal active elements that enable portable deployment in the field. They require little power, are inexpensive, and provide real-time response to analytes. Carbon nanotubes derive much of their behavior from their one-dimension (1-D), tube-shaped nanomaterial structures. These unique nanomaterials have very high surface area and outstanding electrical and mechanical properties essential to sensor applications. Most importantly, the properties of carbon nanotubes can be tailored by functionalization, wherein chemical groups can be anchored to the material’s surface, to impart sensitivity and selectivity to specific analytes.

Carbon nanotubes are readily incorporated into chemiresistive sensor chips and passive radio frequency identification (RFID) tags (Figure 1). Chemiresistive sensors are readable by a direct electrical connection and RFID tags can be wirelessly powered and read by a smartphone’s near-field communication (NFC). The response of these sensors can provide quantitative information about the analyte’s concentration.

At the MIT-SRP Center, graduate student Shao-Xiong Luo and postdoctoral fellow Maggie He from the Swager laboratory are developing portable carbon nanotube sensors for the mapping and monitoring of carcinogenic NDMA and PAHs in air and water. The team is currently developing methods for the functionalization of carbon nanotubes, incorporating selectors to tailor the carbon nanotubes to selectively interact with NDMA and PAHs and fabricating sensors with these materials to test device performance.

The team anticipates realization of portable sensors that can be used in the field to detect these toxicants in the Mystic River Watershed near three Massachusetts Superfund sites in the near future. Densely distributing sensors at contaminated sites will allow SRP to dynamically and efficiently track contamination levels. The collected spatiotemporal data on the actual concentration of NDMA and PAHs will be shared with the public, so that communities there can make well-informed actions to minimize harmful exposure, and will also be shared with the EPA in order to optimize efforts for site remediation.

Reference:

Zhu, R.; Desroches, M.; Yoon, B.; Swager, T. M. Wireless Oxygen Sensors Enabled by Fe(II)-Polymer Wrapped Carbon Nanotubes. ACS Sensors 2017, 2 (7), 1044–1050.