Recent advances in the development and application of nanoelectrodes

Abstract

Nanoelectrodes have key advantages compared to electrodes of conventional size and are the tool of choice for numerous applications in both fundamental electrochemistry research and bioelectrochemical analysis. This Minireview summarizes recent advances in the development, characterization, and use of nanoelectrodes in nanoscale electroanalytical chemistry. Methods of nanoelectrode preparation include laser-pulled glass-sealed metal nanoelectrodes, mass-produced nanoelectrodes, carbon nanotube based and carbon-filled nanopipettes, and tunneling nanoelectrodes. Several new topics of their recent application are covered, which include the use of nanoelectrodes for electrochemical imaging at ultrahigh spatial resolution, imaging with nanoelectrodes and nanopipettes, electrochemical analysis of single cells, single enzymes, and single nanoparticles, and the use of nanoelectrodes to understand single nanobubbles.

Fig. 1

Scanning electron microscopy (SEM) images of template-stripped Au pyramidal tips. (A) Massively produced uniform Au pyramids. (B) A single Au pyramidal tip plucked from the mold using epoxy and a short piece of tungsten wire. Adapted with permission from Johnson et al. Copyright 2012 American Chemical Society.

Fig. 2

A) Schematic representation of a conventional glass pipette (left) and a nanotube endoscope (right) for intracellular probing. The nanotube endoscope could penetrate the membrane of a cell without greatly disrupting the cell. B) A 1 μm glass pipette in a HeLa cell (left) and a 100 nm nanotube endoscope interrogating a primary rat hepatocyte nucleus. C) SEM image of a nanotube endoscope with a 100 nm tip. The inset shows that the end of the nanotube remain open for fluid transfer. Adapted with permission from Singhal et al. Copyright 2010 Nature Publishing Group.

Fig. 3

A) Schematic illustration of the fabrication of a double-barrel carbon nanoprobe (DBCNP) using CVD method. A quartz theta capillary was pulled and one barrel was blocked while carbon deposition inside another barrel. B) Field emission scanning electron microscopy (FESEM) images of the side (left) and the top (right) of the DBCNP. Adapted with permission from Takahashi et al. Copyright 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fig. 4

Schematic illustration of the preparation of a Pt UME/TiO₂/Pt NP nanoelectrode (T-UME). A thin layer of TiO₂ was electrodeposited on a Pt UME to block electron transfer. When a single Pt NP collided and stuck to the UME, electron transfer to the solution species was restored. CVs could then be obtained using this T-UME in a new solution. Adapted with permission from Kim et al. Copyright 2014 American Chemical Society.

Fig. 5

A) Schematic illustration of the formation and self-assembly of Ag NPs at the liquid/liquid interface at the nanopipette tip. A disk-shape nanoelectrode could be produced. Adapted with permission from Zhu et al. Copyright 2014 American Chemical Society. B) Nanopipette-based electroplated nanoelectrodes. Left: Schematic illustration for fabricating nanopipette-based electroplated nanoelectrodes. A quartz nanopipette tip was immersed in a liquid gallium/indium alloy electrode to electrochemically deposit metal inside the pipette. FIB milling was then used to expose the metal. Right: SEM image of a RG 2 gold nanoelectrode prepared using this method. Adapted with permission from Hao et al. Copyright 2016 American Chemical Society.

Fig. 6

A) Schematic illustration for the electrochemically sensitive high-resolution imaging of EGFR proteins using a double barrel SECM–SICM probe with deposited Pt. B) Topographic (left) and electrochemical (right) images of A431 cells obtained using Pt deposited probes. The scanned area is 75 × 75 μm. Adapted with permission from Sen et al. Copyright 2015 American Chemical Society.

Fig. 7

Schematic illustration of electrochemical detection of the alkaline phosphatase (ALP) activity of a cell in a single droplet using a carbon-Ag/AgCl probe. ALP catalyzed the hydrolysis of p-aminophenyl phosphate (PAPP) to p-aminophenol (PAP) that could be oxidized at the probe. Adapted with permission from Ino et al. Copyright 2013 American Chemical Society.

Fig. 8

(A) TEM image of a pulled quartz nanopipette filled with carbon. B) TEM image of a 20 nm AuNP attached to a carbon nanoelectrode tip. A) and B) are adapted with permission from Yu et al. Copyright 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. C) Schematic illustration of the collision of a carbon nanotube (CNT)-modified Au NP at a Pt nanoelectrode (left). Upon CNT-modified Au NP attachment, an increase in current could be observed in the amperometric curve due to the increase in electrode area (right). C) and D) are adapted with permission from Park et al. Copyright 2013 American Chemical Society.

Fig. 9

A) Cyclic voltammogram of a 27-nm-radius Pt electrode in a 0.5 M H₂SO₄ solution at a scan rate of 100 mV/s. As the potential is scanned cathodically, the current firstly increased due to proton reduction and then suddenly dropped at ~−0.4 V due to the nucleation and quick growth of a hydrogen bubble at the electrode surface. The peak current is labeled as i^p_nb. The inset shows ~−0.4 nA of a residual current after the formation of a nanobubble. B) Cyclic voltammograms of the same 27-nm-radius Pt electrode recorded in the same H₂SO₄ solution at different scan rates. Adapted with permission from Luo et al. Copyright 2013 American Chemical Society.