Nanoscale tipped microwire arrays enhance electrical trap and depth injection of nanoparticles

Nanoscale devices have the potential to measure biological tissues as well as individual cells/neurons. However, three-dimensional (3D) multi-site probing remains problematic because only planar-type device designs are applicable to sample surfaces. Herein we report 3D nanoscale electrode tipped microwire arrays with high aspect ratios. A nanoscale tipped wire is formed by isotropic silicon etching to the tip of a vapor-liquid-solid grown silicon microwire. After coating the wire with a metal (e.g., Pt and Au), only the nanotip section can be exposed from the surrounding outer shell (e.g., SiO(2) and parylene) by photoresist spray coating and subsequent cycled photoresist etchings. As a promising device application, we demonstrate the trapping of polystyrene nanoparticles in a solution using a fabricated Au-nanotip wire array. The sharpened nanotip has a 150 nm curvature radius and a 4.2 μm(2) electrode area. The nanotip wires exhibit a locally enhanced trapping performance with a low trapping voltage of 20 mV. Moreover, these trapped nanoparticles can be injected into a soft material (gelatin), demonstrating a multi-site wide-area batch depth injection and an assembly of nanoparticles. Such nanotip wire arrays should be applicable to trap numerous particles, including DNA/molecules attached to Au particles, and may realize injection into biological tissues and individual cells/neurons.