Recent advances in colorimetric and fluorometric sensing of neurotransmitters by organic scaffolds

Neurotransmitters are chemical compounds released by neurons acting as messengers that transmit signals to other neurons, called postsynaptic neurons, or other types of cells. These neurotransmitters play a crucial role in the nervous system, and abnormalities in their levels have been associated with physical, psychotic, and neurodegenerative diseases such as Alzheimer's, Parkinson's, dementia, addiction, depression, and schizophrenia. This makes it necessary to develop sensitive and reliable techniques for their detection and monitoring in order to screen diseases. Meanwhile, neurotransmitters' detection remains a challenge and continues to attract considerable attention. Fluorescent and colorimetric organic probes were and still efficient tools for rapid, selective and low-cost detection of a large scale of analytes. Neurotransmitters can interact with the sensing molecule leading to the formation of complexes or new molecules displaying photophysical properties different from the starting fluorophore or/and chromophore and thus through different sensing mechanisms. Diverse applications of the sensors like live cell imaging are being reported. This review is a collection of recent development in the design of new organic receptors utilized for the detection of neurotransmitters including monoamines (catecholamines, serotonin and histamine), amino acids (glutamate, aspartate and glycine), gasotransmitters, and acetylcholine.