On-Chip Stochastic Detection of Silver Nanoparticles without a Reference Electrode.

We report the electrochemical detection of 20 nm silver nanoparticles at a chip-based microelectrode array (MEA) without the need for a conventional reference electrode. This is possible due to the system's open-circuit potential allowing the oxidation of silver nanoparticles in the presence of phosphate-buffered saline (PBS). The hypothesis is confirmed by modulating the open-circuit potential via addition of ascorbic acid in solution, effectively inhibiting the detection of silver nanoparticle events.

The Influence of Supporting Ions on the Electrochemical Detection of Individual Silver Nanoparticles: Understanding the Shape and Frequency of Current Transients in Nano-impacts.

We report the influence of electrolyte composition and concentration on the stochastic amperometric detection of individual silver nanoparticles at microelectrode arrays and show that the sensor response at certain electrode potentials is dependent on both the conductivity of the electrolyte and the concentration of chloride ions. We further demonstrate that the chloride concentration in solution heavily influences the characteristic current spike shape of recorded nanoparticle impacts: While typically too short to be resolved in the measured current, the spike widths are significantly broadened at low chloride concentrations below 10 mm and range into the millisecond regime. The analysis of more than 25 000 spikes reveals that this effect can be explained by the diffusive mass transport of chloride ions to the nanoparticle, which limits the oxidation rate of individual silver nanoparticles to silver chloride at the chosen electrode potential.

MEAs and 3D nanoelectrodes: electrodeposition as tool for a precisely controlled nanofabrication.

Microelectrode arrays (MEAs) are gaining increasing importance for the investigation of signaling processes between electrogenic cells. However, efficient cell-chip coupling for robust and long-term electrophysiological recording and stimulation still remains a challenge. A possible approach for the improvement of the cell-electrode contact is the utilization of three-dimensional structures.

Nanoscale Electrochemical Sensor Arrays: Redox Cycling Amplification in Dual-Electrode Systems.

Micro- and nanofabriation technologies have a tremendous potential for the development of powerful sensor array platforms for electrochemical detection. The ability to integrate electrochemical sensor arrays with microfluidic devices nowadays provides possibilities for advanced lab-on-a-chip technology for the detection or quantification of multiple targets in a high-throughput approach. In particular, this is interesting for applications outside of analytical laboratories, such as point-of-care (POC) or on-site water screening where cost, measurement time, and the size of individual sensor devices are important factors to be considered.

Influence of Self-Assembled Alkanethiol Monolayers on Stochastic Amperometric On-Chip Detection of Silver Nanoparticles.

We investigate the influence of self-assembled alkanethiol monolayers at the surface of platinum microelectrode arrays on the stochastic amperometric detection of citrate-stabilized silver nanoparticles in aqueous solutions. The measurements were performed using a microelectrode array featuring 64 individually addressable electrodes that are recorded in parallel with a sampling rate of 10 kHz for each channel. We show that both the functional end group and the total length of the alkanethiol influence the charge transfer.

Stochastic On-Chip Detection of Subpicomolar Concentrations of Silver Nanoparticles.

We introduce the stochastic amperometric detection of silver nanoparticles on-chip using a microelectrode array. The technique combines the advantages of parallel and low-noise recordings at individually addressable microelectrodes. We demonstrate the detection of subpicomolar concentrations of silver nanoparticles with a diameter of 10 nm at sampling rates in the kilohertz regime for each channel.

Sensing with nanopores--the influence of asymmetric blocking on electrochemical redox cycling current.

Nanoporous redox cycling devices are highly efficient tools for the electrochemical sensing of redox-active molecules. By using a redox-active mediator, this concept can be exploited for the detection of molecular binding events via blocking of the redox cycling current within the nanopores. Here, we investigate the influence of different blocking scenarios inside a nanopore on the resulting redox cycling current.

Noise phenomena caused by reversible adsorption in nanoscale electrochemical devices.

We theoretically investigate reversible adsorption in electrochemical devices on a molecular level. To this end, a computational framework is introduced, which is based on 3D random walks including probabilities for adsorption and desorption events at surfaces. We demonstrate that this approach can be used to investigate adsorption phenomena in electrochemical sensors by analyzing experimental noise spectra of a nanofluidic redox cycling device.

How many molecules are required to obtain a steady faradaic current from mediated electron transfer at a single nanoparticle on a supporting surface?

We investigate the chronoamperometric noise characteristics of electron-transfer reactions occurring on single nanoparticles (NPs) and assemblies of well-separated NPs on a supporting surface. To this end, we combine a formerly described expression for the steady-state current of a single particle with the shot-noise model and derive an expression for the signal-to-noise ratio as a function of bulk concentration and particle radius. Our findings are supported by random-walk simulations, which closely match the analytical results.

Noise characteristics of nanoscaled redox-cycling sensors: investigations based on random walks.

We investigate noise effects in nanoscaled electrochemical sensors using a three-dimensional simulation based on random walks. The presented approach allows the prediction of time-dependent signals and noise characteristics for redox cycling devices of arbitrary geometry. We demonstrate that the simulation results closely match experimental data as well as theoretical expectations with regard to measured currents and noise power spectra.