Method for Low Nanomolar Concentration Analyte Sensing Using Electrochemical Enzymatic Biosensors.

We introduce a new electrochemical measurement method compatible with an enzymatic biosensor that is capable of analyte sensing down to the low nanomolar concentration regime. This method is termed accumulation mode sensing and utilizes an immobilized redox polymer mediator wired to an oxidoreductase enzyme to store charge during a premeasurement charge concentration step, followed by a measurement step in which this accumulated charge is quantified. We demonstrate this new method using a model glucose sensor and show how the sensitivity of a sensor can be modified simply by adjusting the time duration of the charge concentration step.

Collision Dynamics during the Electrooxidation of Individual Silver Nanoparticles.

Recent high-bandwidth recordings of the oxidation and dissolution of 35 nm radius Ag nanoparticles at a Au microelectrode show that these nanoparticles undergo multiple collisions with the electrode, generating multiple electrochemical current peaks. In the time interval between observed current peaks, the nanoparticles diffuse in the solution near the electrolyte/electrode interface. Here, we demonstrate that simulations of random nanoparticle motion, coupled with electrochemical kinetic parameters, quantitatively reproduce the experimentally observed multicurrent peak behavior.

Observation of Multipeak Collision Behavior during the Electro-Oxidation of Single Ag Nanoparticles.

The dynamic collision behavior of the electro-oxidation of single Ag nanoparticles is observed at Au microelectrodes using stochastic single-nanoparticle collision amperometry. Results show that an Ag nanoparticle collision/oxidation event typically consists of a series of 1 to ∼10 discrete "sub-events" over an ∼20 ms interval. Results also show that the Ag nanoparticles typically undergo only partial oxidation prior to diffusing away from the Au electrode into the bulk solution.

Electrogenerated Chemiluminescence Reporting on Closed Bipolar Microelectrodes and the Influence of Electrode Size.

We report a fundamental study of the use of Ru(bpy)-based electrogenerated chemiluminescence (ECL) as an optical reporting system for the detection of redox-active analyte on closed bipolar microelectrodes, focused on gaining an in-depth understanding of the correlation between ECL emission intensity and electrochemical current. We demonstrate the significant effect that the size of the anodic and cathodic poles has on the resulting ECL signal and show how this influences the quantitative detection of analyte on a closed bipolar electrode. By carefully designing the geometry of the bipolar electrode, the detection performance of the system can be tuned to different analyte concentration ranges.

Imaging transient formation of diffusion layers with fluorescence-enabled electrochemical microscopy.

Fluorescence-enabled electrochemical microscopy (FEEM) is demonstrated as a new technique to image transient concentration profiles of redox species generated on ultramicroelectrodes (UMEs). FEEM converts an electrical signal into an optical signal by electrically coupling a conventional redox reaction to a fluorogenic reporter reaction on a closed bipolar electrode. We describe the implementation of FEEM for diffusion layer imaging and use an array of thousands of parallel bipolar electrodes to image the diffusion layers of UMEs in two and three dimensions.

Fluorescence-enabled electrochemical microscopy with dihydroresorufin as a fluorogenic indicator.

Recently, we introduced a new electrochemical imaging technique called fluorescence-enabled electrochemical microscopy (FFEM). The central idea of FEEM is that a closed bipolar electrode is utilized to electrically couple a redox reaction of interest to a complementary fluorogenic reaction converting an electrochemical signal into a fluorescent signal. This simple strategy enables one to use fluorescence microscopy to observe conventional electrochemical processes on very large electrochemical arrays.

Coupled electrochemical reactions at bipolar microelectrodes and nanoelectrodes.

Here we report the voltammetric study of coupled electrochemical reactions on microelectrodes and nanoelectrodes in a closed bipolar cell. We use steady-state cyclic voltammetry to discuss the overall voltammetric response of closed bipolar electrodes (BPEs) and understand its dependence on the concentration of redox species and electrode size. Much of the previous work in bipolar electroanalytical chemistry has focused on the use of an "open" cell with the BPE located in an open microchannel.