Observing Transient Bipolar Electrochemical Coupling on Single Nanoparticles Translocating through a Nanopore

Area of Science:

• Electrochemistry
• Nanotechnology
• Physical Chemistry

Background:

• Bipolar electrochemistry typically requires a continuous electrolyte and a conductive object spanning the electrode gap.
• Observing transient bipolar electrochemistry on nanoparticles presents unique challenges due to their small size and dynamic motion.

Purpose of the Study:

• To investigate transient bipolar electrochemical coupling on freely moving, small silver nanoparticles (Ag NPs).
• To explore the formation of hydrogen nanobubbles on Ag NPs within an asymmetric nanoelectrochemical environment.
• To demonstrate the utility of nanopore resistive-pulse sensing for studying nanoparticle electrochemistry.

Main Methods:

• Utilized an asymmetric nanoelectrochemical environment within a nanopore, with acid inside the pipette and halide ions in the bulk solution.
• Employed resistive-pulse sensing to monitor current blockages caused by single Ag NPs translocating through the nanopore.
• Performed simultaneous fluorescence and electrical recordings to correlate nanoparticle behavior with electrochemical events.

Main Results:

• Observed unusually large current blockages for 40 nm Ag NPs, attributed to H2 nanobubble formation via coupled faradaic reactions (proton/water reduction coupled to Ag/water oxidation).
• Demonstrated that large current blockages were dependent on applied voltage and bulk solution anions.
• Confirmed the correlation between large current blockages, Ag NP oxidation, and nanopore translocation.

Conclusions:

• Transient bipolar electrochemistry can occur on metal nanoparticles (<50 nm) in highly localized electric fields within nanopores.
• Nanopore resistive-pulse sensing is a viable method for studying transient bipolar electrochemistry on nanoparticles.
• This approach offers potential for future research in ultrafast electrochemistry, nanocatalyst screening, and nanoparticle gas nucleation.