Iron is an essential element in the composition of living organisms and plays a crucial role in a wide range of biological activities. The human body primarily obtains essential iron through the consumption of food. Therefore, it is vital for the health of human body to maintain iron homeostasis. The reducing character of the cellular microenvironment enables Fe2+ to occupy a dominant position within the cell. Hence, there is an urgent need for a simple and sensitive tool that can detect a large amount of Fe2+ in organisms. In this work, a highly specific fluorescent chemodosimeter NPCO (\"NP\" represents the naphthalimide fluorophore, and \"CO\" represents the carbamoyl oxime structure) for the detection of Fe2+ with excellent sensitivity (LOD = 82 nM) was constructed by incorporating a novel carbamoyl oxime structure as the recognition group. NPCO can be effectively employed for the detection of Fe2+ in food samples, living cells, and zebrafish. Furthermore, by using soybean sprouts as a model plant, the application of NPCO was expanded to detect Fe2+ in plants. Therefore, NPCO could be used as an excellent assay tool for detecting Fe2+ in organisms and is expected to be an important aid in exploring the mechanism of iron regulation.

Iron-reducing microorganisms (FeRM) play key roles in many natural and engineering processes. Visualizing and isolating FeRM from multispecies samples are essential to understand the in situ location and geochemical role of FeRM. Here, we visualized FeRM by a \"turn-on\" Fe2+-specific fluorescent chemodosimeter (FSFC) with high sensitivity, selectivity, and stability. This FSFC could selectively identify and locate active FeRM from either pure culture, coculture of different bacteria, or sediment-containing samples. Fluorescent intensity of the FSFC could be used as an indicator of Fe2+ concentration in bacterial cultures. By combining the use of the FSFC with that of a single-cell sorter, we obtained three FSFC-labeled cells from an enriched consortium, and all of them were subsequently shown to be capable of iron reduction; two unlabeled cells were shown to have no iron-reducing capability, further confirming the feasibility of the FSFC.IMPORTANCE Visualization and isolation of FeRM from samples containing multiple species are commonly needed by researchers from different disciplines, such as environmental microbiology, environmental sciences, and geochemistry. However, no available method has been reported. In this study, we provide a method to visualize FeRM and evaluate their activity even at the single-cell level. When this approach is combined with use of a single-cell sorter, FeRM can also be isolated from samples containing multiple species. This method can be used as a powerful tool to uncover the in situ or ex situ role of FeRM and their interactions with ambient microbes or chemicals.

The precise cellular function of peroxynitrite (ONOO-) in biosystems remains elusive, primarily owing to being short of ultrasensitive techniques for monitoring its intracellular distribution. In this work, a novel rhodamine B cyclic 1,2-dimethylhydrazine fluorescent chemodosimeter RDMH-PN for highly specific and ultrasensitive monitoring of basal ONOO- in biosystems was rationally designed. The fluorescence titration experiments demonstrated that RDMH-PN was capable of quantitatively detecting 0-100 nM ONOO- (limit of detection = 0.68 nM). In addition, RDMH-PN has outstanding performances of ultrafast measurement, naked-eye detection, and preeminent selectivity toward ONOO- to accurately detect intracellular basal ONOO-. Finally, it has been confirmed that RDMH-PN could not only map the intracellular basal ONOO- level by inhibition tests but also trace the fluctuations of endogenous and exogenous ONOO- levels with diverse stimulations in live cells and zebrafish.

A new fluorometric chemodosimeter 2-amino-3-(((E)-3-(1-phenylimidazo[1,5-α]pyridin-3-yl)benzylidene)amino)maleonitrile (BPI-MAL) has been designed and synthesized for sensing hypochlorite. BPI-MAL showed a selective turn-on fluorescence for ClO- through hypochlorite-promoted de-diaminomaleonitrile reaction. It also could detect ClO- in the presence of various competitive anions including reactive oxygen species. Interestingly, sensor BPI-MAL was successfully applied as a fluorescent test kit for ClO- determination. The sensing property and mechanism of BPI-MAL toward ClO- were studied by fluorescence and UV-vis spectroscopy, NMR titration and DFT calculations.

A novel coumarin-indole based chemodosimeter with a simple structure was designed and prepared via a condensation reaction in high yield. The probe exhibited very high selectivity towards cyanide on both fluorescence and UV-vis spectra, which allowed it to quantitatively detect and imaging cyanide ions in organic-aqueous solution by either fluorescence enhancement or colorimetric changes. Confirmed by (1)H NMR and HRMS spectra, the detection mechanism was proved to be related with the Michael addition reaction induced by cyanide ions, which blocked the intramolecular charge transfer (ICT) of the probe. Moreover, the probe was able to be utilized efficiently in a wide pH range (7.5-10) with negligible interference from other anions and a low detection limit of 0.51μM. Application in 5 kinds of natural water source and accurate detection of cyanide in tap water solvent system also indicated the high practical significance of the probe.