text: Mercury is a toxic heavy metal, and as such it is important to be able to detect it in biological systems. Sensors include:
  *Mercury Sensors (MS), a family of sensors that comprise complexes of fluorescein and napthofluorescein. The MS1 probe increases its emission upon binding of Hg(II), while maintaining great affinity for mercury over other heavy metal ions.
  *The S3 sensor is based on a BODIPY complex which undergoes a significant increase in fluorescence upon the binding of Hg(II).
  *MF1 uses a soft thioether chelator for Hg(II) bound to a fluorescein-like xanthenone reporter. It has good contrast upon binding mercury and good selectivity. MF1 is sensitive enough that it has been proposed to be used to test fish for toxic levels of mercury.