*3.3.2 Dopamine*

A catecholamine compound dopamine is known as a neurotransmitter that regulates a wide range of cognitive functions such as behavior, learning, motivation, and memory [63–65]. The dopamine content in the human brain is an important factor that can cause various diseases that include Parkinson's disease, and in fact it is used as a marker in the diagnosis of several conditions related to neurotransmitters. Therefore, there is a strong quest for developing efficient and rapid methods that can selectively determine and continuously sense the dopamine levels on a real-time basis. The DCM fluorosensor (**DCM3-Fe2+**) was developed for selective detection of dopamine based on on–off sensing mechanism [66]. The electron-donor part of DCM fluorophore is modified with a ligand, diethyliminodiacetic acid, such that it selectively complexes with iron(II) ions. In the absence of dopamine, the sensor molecule **DCM3-Fe2+ is** weakly fluorescent due to inhibition of ICT because of Fe2+ complexation with the donor moiety (off-state fluorescence). However, a much stronger fluorescence emission was observed upon gradual addition of dopamine owing to the release of Fe2+ from DCM complex. A good linear relationship was

observed between the dopamine concentration and the fluorescence intensity. That means the observed fluorescence enhancement which is observed after addition of dopamine serves as an indicator to monitor dopamine content in a given sample. Besides, the fluorosensor does show any fluorescence response against other foreign substances, thereby allowing selective detection of dopamine.
