Conductive Gold Thin Film Prepared by the Two-Dimensional Assembly of Gold Nanoparticles on a Plastic Surface

Gold thin films are useful as conductive materials for electrical devices and sensors, owing to their high conductivity and inertness. In the present study, we propose a novel alternative to conventional gold-coating techniques (i.e., gold-vapor deposition and gold plating) to prepare a gold thin film on a plastic surface using a gold colloidal solution. Gold nanoparticles (AuNPs) were immobilized on a plastic surface with a high density of amino groups (two-dimensional assembly of AuNPs) and subsequently grew to form a gold thin film. The growth of the AuNPs was induced using an amino acid as the reducing agent. The selection of the amino acid significantly influenced the growth of the AuNPs and the morphology of the gold thin film. Microscopic observations and absorbance measurements demonstrated the growth and connection of the AuNPs on the surface. The thickness of the gold thin film was limited to between 50 nm and 0.5 μm by varying the growth conditions. The formed film was lustrous and exhibited electrical conductivity comparable to that of a gold-vapor deposited surface. Moreover, we successfully micropatterned the gold thin film on the plastic substrate using the present method combined with a microcontact printing method. The results indicate that our approach has significant potential for use in the manufacture of electrical devices and biosensors.