Radical detection has attracted significant attention recently. Here we have developed a scaffold through covalent assembly principle (OR570), which could facile applications in detection of oxidative radicals. The primary advantage of the assembly type probe lies at the turn-on fluorescence signal from a zero background and hence high fluorescence turn-on ratio for sensitive detection of weak signal.Download high-res image (58KB)Download full-size imageRadicals have profound biorelevance and their robust detections are warranted. We have devised a novel “covalent-assembly” type scaffold for sensitive detection of oxidative radicals.

The development of biocompatible two-photon fluorophores with a large absorption cross-section is challenging, despite the presence of theoretical guidelines. By rendering asymmetric PRODAN dye centrosymmetric, we designed and synthesized a novel class of two-photon fluorophores (TPZ). Their photophysical properties were investigated and their imaging potentials in cells, tissues and zebrafish were showcased.

In situ generation of diazoalkanes under mild conditions is desired. A mechanism based on a Smiles rearrangement has been devised that releases a fluorophore-labeled unstabilized diazoalkane in the presence of various chemical triggers. Notably, the release of this diazoalkane is accompanied by an intense fluorescence turn-on, which calibrates the release of the diazoalkane. Carboxylic acids can trap this short-lived diazoalkane intermediate and yield the corresponding esters. This transformation has potential for broad applications.

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.

Peroxynitrite is a prominent biological reactive nitrogen species from radical combination of nitric oxide and superoxide and fundamentally involved in broad spectrum physiological and pathological processes. Though redox-inert itself, peroxynitrite anion (OONO–) attacks various biological electrophiles to generate an array of potent 2-e– or 1-e– oxidants, which result in cell injuries. Development of fluorescent probes for peroxynitrite, free from interference from hypochlorite, has been an active endeavor of the chemical community. We previously reported a peroxynitrite probe (PN600), which could differentiate hypochlorite from peroxynitrite through a multichannel signaling mechanism. Herein, this intriguing selectivity was accounted for through a structure–reactivity relationship study. Also, this work, together with rich literature contributions, has allowed a qualitative guideline in the use of electron-rich aromatic moieties to design probes against peroxynitrite and/or hypochlorite. The viability of this guideline was further testified by development of another list of peroxynitrite selective probes.

Nitrite is a heavily assayed substrate in the fields of food safety, water quality control, disease diagnosis, and forensic investigation and more recently in basic biological studies on nitric oxide physiology and pathology. The colorimetric Griess assay and the fluorimetric 2,3-diaminonaphthalene (DAN) assay are the current gold standards for nitrite quantification. They are not without limitations, yet have amazingly survived 156 and 44 years, respectively, due to the lack of a practical alternative. Both assays exhibit slow detection kinetics due to inactivation of nucleophiles under strongly acidic media, require an extensive incubation time for reaction to go completion, and hence offer a limited detection throughput. By converting an intermolecular reaction of the Griess assay intramolecularly, we designed a novel probe (NT555) for nitrite detection, which displays superior detection kinetics and sensitivity. NT555 was constructed following our “covalent-assembly” probe design principle. Upon detection, it affords a gigantic bathochromic shift of the absorption spectrum and a sensitive turn-on fluorescence signal from a zero background, both of which are typical of an “assembly” type probe. Overall, NT555 has addressed various difficulties associated with the Griess and the DAN assays and represents an attractive alternative for practical applications.

Substitution of the xanthene scaffold with bulky groups at C-3′ and C-7′ is expected to protect the electrophilic central methine carbon against nucleophilic attack and inhibit stacking. However, such structures are not readily prepared via traditional xanthene syntheses. We have devised an alternative and convenient synthesis to enable facile preparation of this subset of xanthene dyes under mild conditions and in good yields.

Classic fluorescent dyes, such as coumarin, naphthalimide, fluorescein, BODIPY, rhodamine, and cyanines, are cornerstones of various spectroscopic and microscopic methods, which hold a prominent position in biological studies. We recently found that 9-amino-benzo[c]cinnoliniums make up a novel group of fluorophores that can be used in biological studies. They are featured with a succinct conjugative push–pull backbone, a broad absorption band, and a large Stokes shift. They are potentially useful as a small-molecule alternative to R-phycoerythrin to pair with fluorescein in multiplexing applications.

A turn-on signal from zero background allows sensitive detection of a weak signal and is highly desired. The “covalent-assembly” probe design principle is powerful in this regard. Herein, we report an embodiment of this principle (NA570) for detection of Sarin related threats, based on a phenylogous Vilsmeier–Haack reaction. NA570 bears a concise molecular construct, exhibits a colorimetric and a fluorimetric signal, and has potential for real applications.

Development of a molecular probe for selective detection of MeHg+ in the presence of Hg2+ 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 Hg2+ 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 Hg2+ and MeHg+. An unprecedentedly low detection limit of ca. 4.6 pM and 160 pM was measured for Hg2+ and MeHg+, respectively.

We herein report a novel fluorescent probe for Hg2+ based on the deprotection of 1,3-dithiolane, via the covalent assembly principle. Presence of Hg2+ triggers a cascade, which ultimately furnishes the push–pull backbone of a fluorescent dye, rendering a turn-on signal from a zero background and hence high detection sensitivity.

A convenient and scalable synthesis of 1-amino-5-cyanonaphthalene was described.A convenient synthesis of 1-amino-5-cyanonaphthalene was reported.

A novel fluorescent probe for peroxynitrite, PN600, was rationally designed on the basis of a unique fluorophore assembly approach. PN600 is a green-emitting coumarin derivative. Upon oxidation by peroxynitrite, PN600 is transformed into a highly fluorescent red-emitting resorufin derivative via an orange-emitting intermediate. This three-channel signaling capability enables PN600 to differentiate peroxynitrite from other reactive oxygen and nitrogen species, including hypochlorite and hydroxyl radical. Moreover, PN600 is membrane-permeable and compatible with common TRITC filter sets and displays low cytotoxicity. Therefore, PN600 is a promising candidate for in vitro peroxynitrite imaging.

We herein report a novel fluorescent probe for Hg2+ based on the deprotection of 1,3-dithiolane, via the covalent assembly principle. Presence of Hg2+ triggers a cascade, which ultimately furnishes the push–pull backbone of a fluorescent dye, rendering a turn-on signal from a zero background and hence high detection sensitivity.