Abstract: Provided is a metal colloid having higher visibility and higher sensitivity than a gold colloid and a Au-core Pt-shell composite colloid and suitable as a labeling agent for use in a test such as an immunoassay. An alloyed Au/Pt composite colloid formed by mixing a gold salt and a platinum salt with at least one reducing agent selected from the group consisting of an amino acid and a derivative thereof, an oligopeptide and a derivative thereof, and an amino sugar in the presence of an alkali, thereby reducing the gold salt and platinum salt.

Abstract: To provide a precious metal colloid enabling a production in simply and in low cost, a long-term storage, and a formation of a thin film having a high conductivity, a precious metal fine-particle, a composition including the same, and a method for producing a precious metal fine-particle for forming such precious metal colloid, which is a precious metal colloid in which a protection component protects a precious metal fine-particle selected from gold, silver, platinum, and palladium, a precious metal colloid in which the maximum peak of 13C-NMR spectrum of the protection component separated from the precious metal colloid by ultracentrifugation treatment presents in 160 to 190 ppm other than peaks of a primary carbon and an aromatic carbon, or a precious metal colloid in which peaks of 13C-NMR spectrum present in 20 to 90 ppm and 160 to 190 ppm.

Abstract: To provide a precious metal colloid enabling a production in simply and in low cost, a long-term storage, and a formation of a thin film having a high conductivity, a precious metal fine-particle, a composition including the same, and a method for producing a precious metal fine-particle for forming such precious metal colloid, which is a precious metal colloid in which a protection component protects a precious metal fine-particle selected from gold, silver, platinum, and palladium, a precious metal colloid in which the maximum peak of 13C-NMR spectrum of the protection component separated from the precious metal colloid by ultracentrifugation treatment presents in 160 to 190 ppm other than peaks of a primary carbon and an aromatic carbon, or a precious metal colloid in which peaks of 13C-NMR spectrum present in 20 to 90 ppm and 160 to 190 ppm.