Negative differential electrolyte resistance in a solid-state nanopore resulting from electroosmotic flow bistability

Area of Science:

• Nanotechnology
• Physical Chemistry
• Electrochemistry

Background:

• Solid-state nanopores are crucial for single-molecule analysis and ion transport studies.
• Negative differential resistance (NDR) is an uncommon electrical phenomenon with potential applications in electronic devices.
• Understanding ion and fluid dynamics within nanopores is key to controlling their electrical properties.

Purpose of the Study:

• To demonstrate and investigate negative differential resistance (NDR) in a solid-state nanopore system.
• To elucidate the underlying physical mechanisms responsible for NDR, focusing on the interplay of ion distribution and fluid flow.
• To explore the sensitivity of NDR to surface charge density and its implications for chemical sensing.

Main Methods:

• Experimental setup using a solid-state nanopore separating KCl solutions under constant applied pressure.
• Electrical measurements to observe NDR by varying applied voltage.
• Finite element simulations solving Navier-Stokes, Poisson, and Nernst-Planck equations to model ion and fluid dynamics.
• Chemical stimuli (pH and Ca2+) used to modulate nanopore surface charge density.

Main Results:

• A solid-state nanopore exhibited negative differential resistance (NDR) under applied pressure, characterized by a switch between high and low conductivity states.
• NDR arises from a positive feedback loop between ion concentration polarization and electroosmotic flow, leading to bistability.
• The NDR switching potential is highly sensitive to nanopore surface charge density, influenced by pH and divalent cations like Ca2+.

Conclusions:

• The observed NDR in solid-state nanopores is a result of coupled electrokinetic and ion distribution phenomena.
• The sensitivity of NDR to surface charge density suggests that nanopore devices can be engineered for sensitive detection of chemical species.
• This work highlights the potential of nanopore systems for developing novel chemical sensors and tunable electronic components.