Recent progress and outlooks in rhodamine-based fluorescent probes for detection and imaging of reactive oxygen, nitrogen, and sulfur species.

Reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species (RSS) serve as vital mediators essential for preserving intracellular redox homeostasis within the human body, thereby possessing significant implications across physiological and pathological domains. Nevertheless, deviations from normal levels of ROS, RNS, and RSS disturb redox homeostasis, leading to detrimental consequences that compromise bodily integrity. This disruption is closely linked to the onset of various human diseases, thereby posing a substantial threat to human health and survival. Small-molecule fluorescent probes exhibit considerable potential as analytical instruments for the monitoring of ROS, RNS, and RSS due to their exceptional sensitivity and selectivity, operational simplicity, non-invasiveness, localization capabilities, and ability to facilitate in situ optical signal generation for real-time dynamic analyte monitoring. Due to their distinctive transition from their spirocyclic form (non-fluorescent) to their ring-opened form (fluorescent), along with their exceptional light stability, broad wavelength range, high fluorescence quantum yield, and high extinction coefficient, rhodamine fluorophores have been extensively employed in the development of fluorescent probes. This review primarily concentrates on the investigation of fluorescent probes utilizing rhodamine dyes for ROS, RNS, and RSS detection from the perspective of different response groups since 2016. The scope of this review encompasses the design of probe structures, elucidation of response mechanisms, and exploration of biological applications.

Rhodamine-based fluorescent sensors for the rapid and selective off-on detection of salicylic acid and their use in plant cell imaging.

Salicylic acid (SA) is a key hormone that regulates plant growth and immunity, and understanding the physiologic processes induced by SA enables the development of highly pathogen-resistant crops. Here, we report the synthesis of three new SA-sensors (R1-R3) from hydroxyphenol derivatives of a rhodamine-acylhydrazone scaffold and their characterization by NMR and HRMS. Spectroscopic analyses revealed that structural variations in R1-R3 resulted in sensors with different sensitivities for SA. Sensor R2 (with the 3-hydroxyphenyl modification) outperformed R1 (2-hydroxyphenyl) and R3 (4-hydroxyphenyl). The SA-detection limit of R2 is 0.9 µM with an ultra-fast response time (<60 s). In addition, their plant imaging indicated that designed sensor R2 is useful for the further study of SA biology and the discovery and development of new inducers of plant immunity.