A method for manufacturing a test paper is disclosed in the present invention, and at least comprises the following steps. First, a chemical precursor comprising at least a reducing agent is coated onto a substrate. The substrate is then dipped into a metal salt solution comprising a plurality of metal ions for a predetermined time to reduce the metal ions to form metal particles on the substrate. Finally, the substrate is taken out and dried to complete a manufacture of at least a test paper. In the meantime a method for using the test paper, and a chemical composition used in the abovementioned for manufacturing the test paper are also disclosed in the present invention.