The role of quinoline in the development of near-infrared fluorescent probes for diagnosis of Alzheimer's disease

Alzheimer's disease (AD) is a common neurodegenerative disorder, having some negative impacts, affecting memory and other cognitive abilities, caused by injuries in brain cells. It is widely accepted that early diagnosis is essential for the successful management of AD. Since the current diagnosing strategies for imaging Aβ and tau proteins face limitations, near-infrared fluorescence (NIRF) has been pursued as alternative for in vivo applications. As described in recent dedicated literature, quinoline (and its analogues) is a valuable scaffold for creating new fluorescent probes due to its compact molecular size, the presence of a nitrogen atom in its ring which enhances coordination properties, and its capacity to form hydrogen bonds, as well as the easy chemical manipulation to tune several properties. In recent years, numerous fluorescent probes incorporating this moiety have been developed. This review focuses on the quinoline moiety as key component of several fluorescent probes, highlighting their design strategies, optical characteristics, and in vitro and in vivo performance, based on their distinct detection mode such as aggregation induced emission (AIE), intramolecular charge transfer (ICT) and twisted intramolecular charge transfer (TICT).