Dielectrophoretic devices fabricated by proton beam writing for concentration, assembly, and detection of nanoparticles

Dielectrophoresis (DEP) is a phenomenon with the directional movement of microparticles due to the DEP force under an uneven AC electric field. We utilize polymer surfaces with microstructures such as μm-scale pit arrays for DEP devices to assemble or concentrate nanoparticles. For micro-structuring of the polymer such as PMMA with a thickness of 5-10 μm, we applied proton beam writing (PBW), a direct-write lithographic technique for high-aspect-ratio microstructures of polymeric materials such as PMMA and epoxy resin. Pit arrays such as 5×5 arrays of circular pits with a diameter of 5 μm on the 5-10 μm thick PMMA. We demonstrated the collection and assembly of Ag nanoparticles (diameter of 100 nm) on the PMMA pit arrays from the colloidal suspension of the metallic nanoparticles in water. The DEP experiments were performed with the amplitude (10-20 V) and frequency (1-100 kHz) of applied ac voltages with an additional dc offset voltage of less than 1 V. We also discuss the possible application of this technique to the detection of micro and nanoparticles such as plastics, dielectrics, and metals in environmental water.