In vitro and in vivo bioimaging by Quinoline conjugated probes and dyes

Abstract

Bioimaging has emerged as an admirable technique for the early-stage detection of diseases that are difficult to drive backwards in the advanced stages, such as cancer and Alzheimer's disease. It provides a non-invasive approach for gathering information on the progress or reoccurrence of these diseases. However, smart fluorescent dyes are essential for bioimaging, allowing real-time visualization and tracking of biological processes. Fluorescent dyes or fluorophores absorb and emit light at two different wavelengths to generate fluorescence. They predominantly belong to small organic molecules and remain indispensable tools in scientific research. The most widely employed organic dyes in bioimaging applications are rhodamine, coumarin, fluorescein, cyanine, resorufin, BODIPY, quinoline, and Alexa Fluor dyes. Among them, quinoline-conjugated probes and dyes offer several advantages for bioimaging due to their unique structural and photophysical properties. Their tunable fluorescence properties, environmental sensitivity, enhanced photostability, NIR emission, high quantum yields, selective targeting, binding ability, minimal cytotoxicity, and versatility in sensing mechanisms provide unique advantages in multiplex imaging. Besides, fluorescent labelling with several traditional dyes significantly impacts the parent biological properties. However, such adverse effects are less experienced with quinoline dyes due to their excellent biocompatibility. In addition, cationic quinoline conjugates have been found to improve water solubility and mitochondria targeting ability. Therefore, they become excellent choices for imaging purposes. Moreover, quinoline-based probes show excellent molecular recognition properties. Scientists have highlighted their sensing abilities recently but have not adequately emphasized their imaging capabilities. Herein, we have comprehensively discussed almost 170 quinoline-conjugated molecules for their in vitro and in vivo imaging applications. We have confined our discussion to quinoline conjugates that are capable of bioimaging. Significantly, quinoline moiety plays an important role in these conjugates to improve their bioimaging performance. Appropriately, we have carefully classified these probes and dyes according to the role played by the quinoline unit. This will provide an important vision of using quinoline moiety to improve the performance of newly designed molecules for bioimaging applications. We hope this review will encourage researchers and young scientists to develop new generation quinoline conjugated dyes with superior bioimaging ability in the future.