Single-molecule porphyrin-metal ion interaction and sensing application.

It remains a significant challenge to study the interactions between metal ions and porphyrin molecules at single ion level. Here, we constructed a nanopore-based sensing for label-free and real-time analysis of the interaction between Cu2+ and 5,10,15,20-tetrakis(4-sulfonatophenyl)-porphyrin (TPPS). The results demonstrate that emerging electronic signatures of the Cu2+-TPPS complex that is completely different form the original free TPPS were observed in the α-hemolysin (α-HL) nanopore. Based on the distinctive electronic signal patterns between TPPS and Cu2+-TPPS complex, the unique nanopore sensor can achieve a highly sensitive detection of Cu2+ in aqueous media. The frequency of signature events showed a linear response toward the concentration of Cu2+ in the range of 0.03 µM - 1.0 μM, with a detection limit of 16 nM (S/N = 3). The sensing system also exhibited high selectivity against other metal ions, and the feasibility of this approach for practical applications was demonstrated with the determination of Cu2+ in running water.