A Fluorescent Assay to Quantitatively Evaluate Carbon Nanotube Contaminants

Y. Xu
Luna Innovations Inc,
United States

Keywords: carbon nanotubes, fluorescence, quantification, contaminants

Summary:

Carbon-based nanomaterials such as carbon nanotubes (CNTs), are widely used in numerous products (capacitors, water/oil purifiers, composites and thin films). The global market for all CNTs generated was nearly $239 million in 2012 revenues and is projected to reach over $900 million by 2016.The enormous potential of CNTs and their successful incorporation in commercial products have dramatically increased their production worldwide to more than 10,000 metric tons per year. As with many new materials, toxicology concerns are being raised with CNTs regarding their interactions with humans and any safety hazards and environmental health risks CNTs may pose. Results from recent animal studies indicate that CNT and carbon nanofibers (CNF) may pose a respiratory hazard. CNT exposure levels (inhalation and respiration) and occupational health for workers in large scale manufacturing and subsequent handling facilities are of particular concern. Also, multiple studies have shown that CNTs can be released into the environment from polymer-CNT composites. For example, epoxy-MWCNT nanocomposites that are increasingly used in many large-volume industries are often exposed to severe mechanical and environmental stresses, such that, during a polymer-MWCNT composite’s life cycle, MWCNT incorporated in the matrix will be eventually released into the environment. As several federal agencies consider regulations on the exposure limits of CNTs and carbon materials, sensitive and quantitative detection can help not only better define exposure limits but also monitor the potential release of CNTs. However, the current technologies are inadequate for the quantitative detection of CNT contamination. In order to overcome the limitation of existing methods, Luna is developing an optical sensing system that can specifically detect and quantify CNTs and provide a rapid, sensitive, and easy-to-use assessment tool for environmental samples. Dye labelled polymer is used as the key capture reagent for the CNT concentration indicator. The fluorescent tag on the polymer indicates the fluorescence quenching once the polymer has strong interaction with the CNT. Limits of detection (LOD) are determined as low as 3.0 - 5.0 ppb with a broad dynamic range of ng-mg/mL using Luna developed method. Interference compounds, such as PAHs, detergents, pesticides, other carbon sources, and real samples (Dan River water, VA) are tested. Different sets of calibration curves were generated and applied for measurement of variable ranges of CNT concentrations in the samples. A variety of CNT (single-walled and multi-walled with or without surface functionalization) in various environmental mediums including soil, water, and air can be quantified. CNTs can be distinguished from other carbon sources such as carbon black, amorphous carbon, graphite or carbon fibers. The test turnaround time is less than 30 minutes and training requirement is minimal, so this system can readily provide toxicity level information for the nano-toxicology R&D community such as NIEHS.