A　novel　squaraine-based　chemosensor　SQ-1　has　been　synthesized,　and　its　sensing　behavior　toward　various　metal　ions　was　investigated　by　UV-　vis　and　fluorescence　spectroscopies.　In　AcOH-H2O　(40:60,　v/v)　solution,　Hg2+　ions　coordinate　with　SQ-1　causing　a　deaggregation　which　induces　a　visual　color　and　absorption　spectral　changes　as　well　as　strong　fluorescence.　In　contrast,　the　addition　of　other　metals　(e.g.,　Pb2+,　Cd2+,　Cu2+,　Zn2+,　Al3+,　Ni2+,　Co2+,　Fe3+,　Ca2+,　K+,　Mg2+,　Na+,　and　Ag+)　does　not　induce　these　changes　at　all.　Thus　SQ-1　is　a　specific　Hg2+　sensing　agent　due　to　the　inducing　deaggregation　of　the　dye　molecule　by　Hg2+.