Dielectrophoretic Assembly of Gold Nanoparticles in Nanoscale Junctions for Rapid, Miniature Chemiresistor Vapor Sensors

Abstract

A method for fabricating integrated arrays of nanoscale chemiresistor vapor sensors using functionalized gold nanoparticles is presented. Controlled placement of nanoparticles was accomplished with dielectrophoresis, achieving localized nanoparticle assembly between 50-nm-thick, 100-nm-wide nanofabricated electrodes with 50 nm spacing. Each individual sensor comprises an assembly of thiol-functionalized 10-nm-diameter gold nanoparticles, making a total active sensing volume with thickness of 30 to 40 nm and area dimension 50 nm × 50 nm. The small electrode spacing enables contiguous films of just 3 to 4 layers of nanoparticles. Combination of top-down lithographic fabrication and bottom-up directed assembly allows multiple sensors spaced by 200 μm to be fabricated on a single chip. A second set of chemiresistor sensors with larger 20 μm electrode spacing and 200–300 nm film thickness were fabricated for comparison. Nanoscale sensors fabricated using 4 different types of thiolated capping ligands exhibited response sensitivity and selectivity similar to the larger chemiresistor sensors, but with a signal-to-noise degradation to 25% of the micron scale devices. The results demonstrate that nanofabricated sensors with dense arrays of many different types of functionalized nanoparticles can be integrated on a single chip, and it should be possible to create integrated, independent nanoscale sensors separated by only hundreds of nanometers.