A novel water-soluble near-infrared fluorescent probe for monitoring viscosity fluctuations in plants and zebrafish under abiotic stresses.

Viscosity is one of the important microenvironmental parameters of abiotic stress. Abnormal changes in viscosity have been shown to be correlated with pathological activities and diseases of plants. However, current probes may not be suitable for sensing in plants due to their hydrophobicity and the phytochromes found in plants. With this research, we successfully constructed a structurally simple, water-soluble near-infrared fluorescent probe HJA-MQ-D, which can simultaneously monitor dynamic viscosity changes in plants and animal systems. The probe exhibits a relatively long emission wavelength (nearly 700 nm) and large Stokes shift (88 nm), and exceptional viscosity-responsive performances with 140-fold fluorescence intensity enhancement. More importantly, the HJA-MQ-D can image the viscosity fluctuation at the cellular level in plants (onion inner epidermis and mung bean sections) as well as at the whole-plant level (mung bean and peanut seedling). In addition, HJA-MQ-D was used to monitor the viscosity changes in a nystatin-induced zebrafish model. Based on these advanced characteristics, we anticipate that this probe will provide a powerful new tool for cross-species viscosity monitoring.