prerequisite for continuous monitoring. Optical signalling methods (such as fluorescence) are sensitive and selective, and provide a platform for real-time response, and local observation. As chemosensors are designed to be both targeting (i.e. can recognize and bind a specific species) and sensitive to various concentration ranges, they can be used to observed real-live events on the cellular level. As each molecule can give rise to a signal/readout, that can be selectively measured, chemosensors are often said to be non-invasive and consequently have attracted significant attentions for their applications within biological matter, such as within living cells. Many examples of chemosensors have been developed for observing cellular function and properties, including monitoring ion flux concentrations and transports within cells such as Ca(II), Zn(II), Cu(II) and other physiologically important cations and anions, as well as biomolecules. The design of ligands for the selective recognition of suitable guests such as metal cations and anions has been an important goal of supramolecular chemistry. The term supramolecular analytical chemistry has recently been coined to describe the application of molecular sensors to analytical chemistry. Small molecule sensors are related to chemosensors. However, these are traditionally considered as being structurally simple molecules and reflect the need to form chelating molecules for complexing ions in analytical chemistry. History While chemosensors were first defined in the 1980s, the first example of such a fluorescent chemosensor can be documented to be that of Friedrich Goppelsroder, who in 1867, developed a method for the determination/sensing of aluminium ion, using fluorescent ligand/chelate. This and subsequent work by others, gave birth to what is considered as modern analytical chemistry. In the 1980s the development of chemosensing was achieved by Anthony W. Czarnik, A. Prasanna de Silva and Roger Tsien, who developed various types of luminescent probes for ions and molecules in solutions and within biological cells, for real-time applications. Tsien went on to study and developing this area of research further by developing and studding fluorescent proteins for applications in biology, such as green fluorescent proteins (GFP) for which he was awarded the Nobel Prize in Chemistry in 2008. The work of Lynn Sousa in the late 1970s, on the detection of alkali metal ions, possibly resulting in one of the first examples of the use of supramolecular chemistry in fluorescent sensing design, as well as that of J.-M. Lehn, H. Bouas-Laurent and co-workers at Université Bordeaux I, France. The development of PET