Organic Macrocycle as Highly Selective Adaptor for Nanopore Sensing of Aromatic Carboxylic Acids in Oilfield Produced Water

Aromatic carboxylic acids (ACAs) play a critical role in determining the disposal strategy of oilfield produced water (PW). In this work, we report a single-molecule nanopore sensor for the discrimination of six distinct ACAs. By employing an organic macrocycle as an adapter with the wild-type α-hemolysin nanopore, each ACA generates a characteristic current blockade, enabling clear discrimination based on the number of aromatic rings and carboxyl groups. The sensing signals remain unaffected by a 10-fold excess of phenols, metal ions, and polycyclic aromatic hydrocarbons. Furthermore, nuclear magnetic resonance, theoretical calculations, and nanopore experiments for carboxylic acid derivatives with varying hydrophilic and hydrophobic groups reveal that highly selective ACA recognition synergistically relies on size matching, hydrophilic interactions, and electrostatic effects. Notably, this strategy allows direct, label-free, and rapid quantification of 9-anthracenecarboxylic acid (9-AA) in authentic PW samples, demonstrating specific target detection within a complex matrix and highlighting the potential of nanopore technology for on-site environmental analysis.