Actuation and tracking of a single magnetic particle on a chip

We present the defined actuation of a single magnetic particle on a crossbar array chip. Two orthogonal layers of parallel microwires are used to generate highly localized magnetic field gradients for particle trapping and movement. We introduce an analytical model to simulate the actuation of the particle, which is in precise agreement with the experimentally observed trajectory. The single-particle approach allows us to resolve subtle features of the induced magnetic field distribution. We demonstrate that the actuation strongly depends on the applied current sequence and introduce switching patterns for reliable control of an individual particle. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3673909

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 oxidization rate of individual silver nanoparticles to silver chloride at the chosen electrode potential