text: Metal ions are essential to virtually all biological systems and hence studying their concentrations with effective probes is highly advantageous. Since metal ions are key to the causes of cancer, diabetes, and other diseases, monitoring them with probes that can provide insight into their concentrations with spatial and temporal resolution is of great interest to the scientific community. There are many applications that one can envision for small molecule sensors. It has been shown that one can use them to differentiate effectively between acceptable and harmful concentrations of mercury in fish. Further, since some types of neurons uptake zinc during their operation, these probes can be used as a way to track activity in the brain and could serve as an effective alternative to functional MRI. One can also track and quantify the growth of a cell, such as a fibroblast, that uptakes metal ions as it constructs itself. Numerous other biological processes can be tracked using small molecule sensors as many change metal concentrations as they occur, which can then be monitored. Still, the sensor must be tailored for its specific environment and sensing requirements. Depending on the application, the metal sensor should be selective for a certain type of metal, and especially needs to be able to bind its target metal with greater affinity than metals that naturally exist at high concentrations within the cell . Further, they should provide a response with a strong modulation in fluorescent spectrum and hence provide a high signal-to-noise ratio. Finally, it is essential that a sensor is not toxic to the biological system in which it is used.