Abstract: The present disclosure relates to an oligonucleotide-immobilized microoscillator for detecting silver ions and a method for detecting silver ions using resonance of the same. A DNA including a thiol-terminated cytosine is immobilized on the surface of the microoscillator. In accordance with the present disclosure, silver nanoparticles detrimental to the human body and environment can be detected and quantified through a simple method based on the mechanical property of resonance frequency. Since trace silver nanoparticles below 1 nM can be detected with high sensitivity and selectivity, it may be usefully applied as a biosensor for detecting the toxic material.