Macrocyclic Complexes for Imaging

One constant problem for crown ether based sensors in vivo is the ubiquitous presence of chemical species that will compete with the target analyte for the sensor binding site. For sensors incorporating [18]crown-6 this especially problematic as sodium, potassium, ammonium and hydronium (H30+) cations are all attracted to the threefold symmetry of the crown s cavity. Protonated terminal amines, including amino acids and peptides, can also interfere with analyte detection. It is therefore all the more pleasing when a crown ether based sensor is developed that does not bind to biologically common cations. This is the case for a saxitoxin chemosensor reported by Gawley, LeBlanc and co-workers [24], 

Saxitoxin is a neurotoxin produced by certain species of dinoflagellates, cyanobacteria and, most famously, many species of both marine and freshwater pufferfish. The toxin is found throughout these fish, from internal organs through 

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