Protein-enabled detection of ibuprofen and sulfamethoxazole using solid-state nanopores

Enabled by proteins, we present an all-electrical method for rapid detection of small pharmaceuticals (ibuprofen and sulfamethoxazole [SMZ]) in aqueous media using silicon nitride pores. Specifically, we use carrier proteins, bovine serum albumin (BSA), and take advantage of their interactions with two small drug molecules to form BSA-drug complexes which can be detected by nm-diameter pores, thereby confirming the presence of small pharmaceuticals. We demonstrate detection of ibuprofen and SMZ at concentrations down to 100 nM (similar to 21 mu g/L) and 48.5 nM (12 mu g/L), respectively. We observe changes in electrical signal characteristics (reflected in event durations, rates, current magnitudes, and estimated particle diameters) of BSA-drug complexes compared to BSA-only, and differences between these two small pharmaceuticals, possibly paving a path toward developing selective sensors by identifying "electrical fingerprints" of these molecules in the future. These distinct electrical signals are likely a combined result of diffusion, electrophoretic and electroosmotic effects, interactions between the pore and particles, which depend on pore diameters, pH, and the resulting surface charges. The use of single-molecule-counting nanopores allows sensing of small pharmaceuticals, studies of protein conformational changes, and may aid in efforts to evaluate the impact of small drug molecules on aquatic and human life.