Nanoparticle-antibody conjugates and procedures for producing and using said conjugates

A method of detecting a target molecule in a sample, comprising: contacting a sample with a first antibody that binds to the target molecule; contacting the sample with a second antibody conjugated with one or more enzyme molecules, in which the enzyme molecules are capable of producing at least one product capable of reducing metal ions to metal in a state of zero oxidation and in the that the second antibody specifically binds to the first antibody; contacting the sample with a third antibody, in which the third antibody is an antibody-conjugated particle conjugate that comprises two or more nanoparticles directly linked to an antibody through a metal-thiol bond and specifically binds to the second antibody; contacting the sample with a substrate of the enzyme molecules and a metal ion, so that a metal precipitate forms and is placed with the target molecule; and detect the metal precipitate, thereby detecting the target molecule.