Probe-assisted detection of Fe³⁺ ions in a multi-functionalized nanopore

Iron is an essential element that plays critical roles in many biological/metabolic processes, ranging from oxygen transport, mitochondrial respiration, to host defense and cell signaling. Maintaining an appropriate iron level in the body is vital to the human health. Iron deficiency or overload can cause life-threatening conditions. Thus, developing a new, rapid, cost-effective, and easy to use method for iron detection is significant not only for environmental monitoring but also for disease prevention. In this study, we report an innovative Fe³⁺ detection strategy by using both a ligand probe and an engineered nanopore with two binding sites. In our design, one binding site of the nanopore has a strong interaction with the ligand probe, while the other is more selective toward interfering species. Based on the difference in the number of ligand DTPMPA events in the absence and presence of ferric ions, micromolar concentrations of Fe³⁺ could be detected within minutes. Our method is selective: micromolar concentrations of Mg²⁺, Ca²⁺, Cd²⁺, Zn²⁺, Ni²⁺, Co²⁺, Mn²⁺, and Cu²⁺ would not interfere with the detection of ferric ions. Furthermore, Cu²⁺, Ni²⁺, Co²⁺, Zn²⁺, and Mn²⁺ produced current blockage events with quite different signatures from each other, enabling their simultaneous detection. In addition, simulated water and serum samples were successfully analyzed. The nanopore sensing strategy developed in this work should find useful application in the development of stochastic sensors for other substances, especially in situations where multi-analyte concurrent detection is desired.