Abstract: There is provided a novel method for amplifying mass spectrometric signals. More particularly, a novel method for detecting signals of a target molecule includes: i) allowing a test sample, in which it is required to determine whether or not a target molecule is present, to be contact with a gold particle whose surface is modified to selectively bind to the target molecule, ii) allowing a low molecular molecule engrafted to the gold particle to generate mass spectrometric signals after the interaction, such as binding, between the gold particle and the target molecule, and iii) amplifying the mass spectrometric signals by generating a great deal of mass spectrometric signals of the low molecular molecule even in the presence of a trace of the target molecule. Also, the assay system using the method and the gold particle prepared in the method are provided.