Platinum Nanoelectrodes Research Articles

A nanofluidic channel with embedded transverse nanoelectrodes

In this paper, we demonstrate fabrication and characterization of a nanofluidicchannel with embedded transverse nanoelectrodes using a combinationof conventional photolithography and focused ion beam technologies.Glass-capped silicon dioxide nanochannels having 20 nm depth, 50 nm width, and2 µm length with embedded platinum nanoelectrodes were fabricated. Channel patency wasverified through measurements of the resistivity in phosphate buffered saline andelectrostatic action on charged fluorescent nanospheres. Platinum nanoelectrodefunctionality was also tested using transverse resistance measurements in nanochannelsfilled with air, deionized water, and saline solution.

Electrochemistry of Individual Molecules in Zeptoliter Volumes

Electrochemical experiments were carried out in a nanometer-sized cylindrical thin layer cell (TLC) formed by etching the surface of a disk-type platinum nanoelectrode (5- to 150-nm radius). Using high frequency ac voltage, the surface of such an electrode was etched to remove a very thin (> or = 1-nm-thick) layer of Pt. The resulting zeptoliter-scale cavity inside the glass sheath was filled with aqueous solution containing redox species, and the etched electrode was immersed in a dry (no external solution) pool of mercury to produce a TLC. Several approaches based on steady-state voltammetry and scanning electrochemical microscopy (SECM) were developed to independently evaluate the electrode radius and the etched volume. The number of redox molecules in the TLC could be varied between one and a few hundred by changing its volume and solution concentration. In this way, the transition between a random and deterministic number of trapped molecules was observed. High quality steady-state voltammograms of > or = 1 molecules were obtained for different neutral and charged redox species and different concentrations of supporting electrolyte. The analysis of such voltammograms yields information about mass transfer, adsorption, electron transfer kinetics, and double-layer effects on the nanoscale.

Feedback-Independent Pt Nanoelectrodes for Shear Force-Based Constant-Distance Mode Scanning Electrochemical Microscopy

A new generation of platinum nanoelectrodes for constant-distance mode scanning electrochemical microscopy (CD-SECM) has been prepared, characterized, and used for high spatial resolution electrochemical measurements and visualization of electrochemically induced concentration gradients in microcavities. The probes have long (1-2 cm), narrow quartz tips that were conically polished and have a Pt nanoelectrode that is slightly offset from center. Because of the size and location of the electrode on the probe, it does not exhibit SECM feedback while approaching the analyzed sample surfaces even to distances within a few hundred nanometers. The probe was positioned near the surface while scanning and performing electrochemical measurements through use of nonoptical shear force control of the tip-to-sample distance. Test structures consisted of cylindrically shaped microcavities that are 50 microm in diameter with three individually addressable electrodes: a gold disk at 8-microm depth, a crescent-shaped gold ring at 4-microm depth along the wall, and a top gold electrode at the rim. Different electrodes within the microcavity were used to reduce and oxidize redox species in 250 microL of a solution of 5 mM hexaamineruthenium(III) chloride and 0.1 M potassium chloride, protected from evaporation by mineral oil, while the SECM tip followed the topography of the structures and monitored the current from the oxidation of [Ru(NH3)6]2+. Electrochemically generated concentration profiles were obtained from these complex test structures that are not possible with any other SECM technology at this time.

Conductivity measurements of individual poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) nanowires on nanoelectrodes using manipulation with an atomic force microscope

We have prepared conducting polymer nanowires of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) with diameters under 10 nm by a molecular combing method, and have measured the conductivity of the individual PEDOT nanowires on platinum nanoelectrodes using manipulation with an atomic force microscope (AFM). The temperature dependence of the conductance was explained well by a quasi-one-dimensional variable range hopping model. The conductivity of two single nanowires was determined to be 0.6 and 0.09S∕cm, which is of the same order as that of PEDOT/PSS films. After all the nanowires crossed over the nanoelectrodes were cut off with AFM manipulation, the current was drastically decreased down to the background level. These results directly indicate that the conductivity was derived from the PEDOT nanowires on the nanoelectrodes.

Platinum Nanoelectrodes Embedded in an Insulating Alumina Matrix: An Innovative Approach

A novel strategy, based on MOCVD, has been employed for preparation of ensembles of platinum nanoelectrodes. Pt/Al2O3 films with different Pt loading were deposited in just one step on glass capillaries. Nanocomposite films with varying Pt/Al atomic ratios were investigated by both cyclic voltammetry and TEM. Ensembles of nanoelectrodes with either overlap or no overlap of the diffusion layers of each nanoelectrode are obtained, depending on the Pt loading. From TEM measurements average Pt particle size of 3 – 7 nm was determined (Figure).