Single-Molecule Electrochemical Analysis of Per- and Polyfluoroalkyl Carboxylic Acid Isomers
Per- and polyfluoroalkyl carboxylic acids (PFCAs) are persistent organic pollutants whose isomers exhibit distinct environmental behaviors, bioaccumulation potentials, and toxic effects due to structural variations. Accurate identification of PFCA isomers is critical for risk assessment and pollution control, yet existing detection methods predominantly rely on standard references, posing challenges for precise analysis of isomers with subtle structural differences. Single-molecule electrochemical sensing via nanopores offers a standard-free approach by correlating molecular volume with current blockade, but its capability to distinguish PFCA isomers remained unverified. This study targeted three sets of PFCA isomers: 4,5,5-trifluoropent-4-enoic acid vs. 4,4,4-trifluoro-3-methylbut-2-enoic acid; 3,3,3-trifluoro-2-methylpropanoic acid vs. 4,4,4-trifluorobutanoic acid; and 2-(trifluoromethoxy)acetic acid, 3,3,3-trifluorolactic acid, and (2R)-3,3,3-trifluoro-2-hydroxypropanoic acid. By engineering nanopore interfaces (WT, R220N, R220Q Aerolysin) and extracting multi-dimensional characteristic parameters, the method achieved near 100% accuracy in identifying all seven isomers. Feature selection further enabled high classification accuracy with low data volumes, laying the foundation for rapid single-molecule detection of PFAS and other emerging contaminants.