Writing Tiny Nanoclusters Using a Nanofountain Pen Operated by Spontaneous Evaporation

Tow-dimensional and 3-dimensional colloidal structures have been used to study surface-enhanced Raman scattering and localized surface plasmon resonance because of their regular stacking structures. However, freely controlling the number and size of the colloidal assemblies remains a challenge. In this study, we demonstrated the fabrication and mechanism of tiny nanoclusters using spontaneous evaporation-based nanofountain pens (NFPs). A micrometer-scale NFP nozzle was fabricated using a glass capillary. The gold nanoparticles (AuNPs) dispersed ink formed the pendant droplet at the NFP nozzle tip, where the AuNPs accumulated within the pendant droplet because of evaporation. The accumulated AuNPs were transferred onto the substrate via a stamp-like process to create nanoclusters. Using water evaporation analyzed by diffusion equations, we showed that reducing the AuNP accumulation to one hundred is possible. This precise adjustment enables fabrication until submicrometer-level nanoclusters. The fabrication method using NFPs can create 3D structures, and this operation is not significantly affected by the size or composition of the AuNPs. This could be expanded to metabolite-included nanocluster where metabolite can be located at the hot spot among AuNPs. Therefore, we expect that this will be utilized to create SERS signals and conduct disease diagnosis research using extremely small amounts of metabolites.