A method for detecting metal ions and chemical/biochemical molecules is provided. The method includes providing a probe, wherein the probe includes: a gold nanocluster; a reducing agent and a chelating agent partially capped on a surface of the gold nanocluster, wherein the probe is formed of reducing gold ions by the reducing agent, and the gold ions and the reducing agent have a molar ratio of 1:0.7 to 1:1.9. The probe may interact with several metal ions of an aqueous solution to produce different changes of fluorescent spectra. Chemical/biochemical molecules can be detected by the fluorescent spectra difference caused by the interaction between the metal ions and the chemical/biochemical molecules.