Multiplex quantification of metals in airborne particulate matter via smartphone and paper-based microfluidics

On-site spatial variation study of airborne trace metals has been known to be the key to providing a comprehensive evaluation of air pollution information at any targeted location. However, the existing portable approaches either do not allow sample analysis in the longitudinal direction or is not yet practically applicable due to due to the lack of a portable detection method. In this paper, by integrating paper based colorimetric detection via cellphone and unmanned aerial vehicle (UAV) in-air sampling, we present an approach for on-site multiaxial quantification of airborne trace metals in an arrayed format. Using a self-built sampler mounting on a UAV, our approach enables automatic, multiaxial air PM sampling. In addition, by relying only on a cellphone and a custom-made field reaction kit, samples collected in-air can be readily processed, detected in an arrayed format and interpreted on-site within 30 min. Finally, an ultrafast batch-to-batch paper microfluidic chip fabrication protocol enables 48 chips to be fabricated under 30 s at a cost of 1.92 $, making the approach well-suited for disposable on-site use. Our system was first calibrated for 6 metals commonly found in airborne PM (i.e. Co, Cu, Fe, Mn, Cr and Ni), and the corresponding metals detection limits were found to be 8.16, 45.84, 1.86 × 10², 10.08, 1.52 × 10² and 80.40 ng. The validity of our approach was then demonstrated by characterizing 6 metals commonly found in air PM using a certified ash sample, and the experimentally determined metal weight percentage showed a good agreement with the manufacture certified value. Finally, the approach was used for on-site airborne trace metals spatial variation study at 4 difference locations in Fuzhou City (China), thus demonstrating the significance of our approach in supplementing air pollution information gathering and progressing rapid, on-site air toxicity assessment research.