The development of sensor for Hg2+ detection has constantly come into a spotlight due to its high impact for human health care. Surface-enhanced Raman scattering (SERS), which can provides single molecule sensitivity, molecular specificity, and facile detection, have rarely been applied to the detection of Hg2+ because of difficulties in quantitative analysis. This study reports novel single-nanowire-on-film (SNOF) SERS sensor for the detection of Hg2+ based on a structure-switching aptamer which provides ultrasensitivity, selectivity, and reusability. We expect that this sensor can be applied for multiplex detection of metal ions.