We have developed a new method for Staphylococcus aureus (S. aureus) detection, which employs fluorescent silica nanoparticles (FSiNPs) modified with metal-dipicolylamine complex (M-dpa-HCC). Among the M-dpa-HCC/FSiNP complexes, Cu-dpa-HCC/FSiNP formed large aggregates with S. aureus in 10 min, which were easily observed by the naked eye. The antibacterial activity of Cu-dpa-HCC/FSiNP was also confirmed.