Metal nanoparticle composite and production method thereof

A production method of a metal nanoparticle composite, wherein metal nanoparticles interacting with light of a wavelength greater than and equal to 380 nm for generating a local surface plasmon resonance, and metal nanoparticles with a mean particle diameter in a polyimide resin in a range of 20 nm to 30 nm do not contact with each other, and are independently dispersed in the metal nanoparticle composite, the metal nanoparticles are formed by metals selected from the group consist of gold (Au), silver (Ag), copper (Cu), palladium (Pd), platinum (Pt), tin (Sn), rhodium (Rh), andiridium (Ir), the production method of a metal nanoparticle composite comprising following Step A and Step B:

• A) performing a step of coating a coating liquid containing polyamic acid resin and a metal compound on a substrate, wherein a content of a metal component is in a range of 1 μg/cm2 to 30 μg/cm2, and drying to form a dried coating film with a thickness in a range of 30 nm to 1.7 μm;
• and
• B) performing a step of heat treatment on the coating film at a temperature in the range of 200° C. to 450° C., precipitating the metal nanoparticles by reducing metal ions (or metal salts) in the coating film to disperse the metal nanoparticles in the coating film, and imidizing the polyamic acid resin in the coating film to form a polyimide resin layer with a thickness in a range of 25 nm to 1 μm.