Abstract: Monodispersed metal nanoparticles are prepared by preparing a homogeneous metal complex solution by mixing metal salt with a complexing agent in solvent. A precipitating agent is added into the homogeneous metal complex solution to form a slurry. A homogeneous mixture of reducing agent and solvent is added to perform reducing reaction on the slurry to form metal nanoparticles in a controlled environment under gas purge. A capping agent is added to modify surface properties of metal nanoparticles. The metal nanoparticles are washed and the metal nanoparticles are recovered by phase extraction or centrifugation. The technique can be used to prepare conductive pastes with bimodal particle size distribution.

Abstract: The microneedle array includes a substrate having a central opening formed therethrough, and a plurality of microneedles positioned about a perimeter defining the central opening. At least one of the microneedles has a recess formed therein adjacent a tip thereof, and this recess is at least partially filled with a layer of active material. A sensor for detecting chemical analytes, biological analytes or the like may be constructed by providing two such microneedle arrays, with one serving as the working electrode and one serving as a reference electrode. The working electrode and the reference electrode may both be connected to a signal analyzer for detecting electrochemical signals. The working electrode and the reference electrode may be separate from one another or may be stacked together.