An optical sensor that can be produced at a low cost from inexpensive silicon fine particles as raw materials and a method for making the optical sensor are provided.In an optical sensor 1, a layer of n-type silicon fine particles 24 coated with a coating film having a functional group is selectively fixed and bonded onto only a pattern portion of a surface of a transparent electrode 14 coated with a coating film having a first functional group, and a layer of p-type silicon fine particles 25 coated with a coating film having a third functional group is fixed and bonded thereon. The first and second functional groups and the second and third coupling groups are respectively fixed with each other via bonds formed between them and coupling reactive groups in a coupling agent.