NO donors are routinely used as the exogenous source in in vitro studies. However, the kinetics or the dose of NO release from the existing donors is not readily monitored. This complicates the elucidation of the involvement of NO in a biological response. We report herein a series of NO donors (NOD545a-g), whose NO release is triggered by UV light at 365 nm or a two-photon laser at 740 nm, and importantly, their NO release is accompanied by a drastic fluorescence turn-on, which has been harnessed to follow the kinetics and dose of NO release in a real-time fashion with spectroscopic methods or microscopic methods in in vitro studies. These merits have rendered NOD545a-g useful molecular tools in NO biology.

NO donors have found wide medical use long before the biorelevance of nitric oxide (NO) was unveiled. From glyceryl trinitrate, amyl nitrite and nitroprusside, to nitrosothiols, NONOates and more, a wide variety of chemicals have been employed as nitric oxide donors for treating pathological conditions and investigating the NO biology. Yet, the release kinetics of these classic NO donors are hard‐to‐define and hard‐to‐monitor in biological milieu. Novel NO donors with robustly defined NO release profiles are sought after. These endeavours have introduced a plethora of novel NO donors, including stimulus‐triggered NO donors, fluorophore‐labeled NO donors. The field also sees a recent addition, i. e. photo‐triggered and photo‐calibrated NO donors, whose NO release is photo‐controlled and further accompanied by a fluorescence turn‐on as a built‐in calibration mechanism of NO release. This review provides an overview of the NO biochemistry, as a roadmap for the chemistry of NO donors. The design rationale and the release mechanism of different classes of NO donors were discussed. Some interesting and notable applications were briefly discussed, e. g. super‐resolution localization microscopic imaging of cell structures, and photo‐acoustic probes for disease diagnosis. With joint‐force, these NO donors constitutes a group of indispensable molecular tools of chemical biology and medicine in real applications.

Development of a molecular probe for selective detection of MeHg(+) in the presence of Hg(2+) is a mission impossible to accomplish. Speciation analysis of two substrates with a single kinetic trace exploiting their differential reactivity toward a single probe, i.e., multiplexing in the time domain, is a cost-effective and powerful alternative. We have developed such a probe (Hg410) for simultaneously quantification of Hg(2+) and MeHg(+) in aqueous media. Hg410 is designed via the "covalent-assembly" approach, displays a zero background, and bears a very concise molecular construct. It has harnessed proximity-based catalysis to achieve high reactivity toward Hg(2+) and MeHg(+). An unprecedentedly low detection limit of ca. 4.6 pM and 160 pM was measured for Hg(2+) and MeHg(+), respectively.

A fluorogenic hydrogen sulfide (H2S) donor is a fundamental molecular tool used as an exogenous source in biological studies and therapies.

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