Weiying Lin

Hypochlorous acid (HOCl), a reactive oxygen species (ROS), plays a significant biological role in living systems. However, abnormal levels of HOCl are implicated in many inflammation‐associated diseases. Therefore, the detection of HOCl is of great importance. In this work, we describe the HOCl‐promoted cyclization of rhodamine‐thiosemicarbazides to rhodamine‐oxadiazoles, which is then exploited as a novel design strategy for the development of a new fluorescence turn‐on HOCl probe 2. On the basis of the fluorescence resonance energy transfer (FRET) signaling mechanism, 2 was further converted into 1 a and 1 b, which represent the first paradigm of FRET‐based ratiometric fluorescent HOCl probes. The outstanding features of 1 a and 1 b include well‐resolved emission peaks, high sensitivity, high selectivity, good functionality at physiological pH, rapid response, low cytotoxicity, and good cell‐membrane permeability. Furthermore, these excellent attributes enable us to demonstrate, for the first time, the ratiometric imaging of endogenously produced HOCl in living cells by using these novel ratiometric probes. We expect that 1 a and 1 b will be useful molecular tools for studies of HOCl biology. In addition, the HOCl‐promoted cyclization reaction of rhodamine‐thiosemicarbazides to rhodamine‐oxadiazoles should be widely applicable for the development of different types of fluorescent HOCl probes.

Dual‐excitation ratiometric fluorescent probes allow the measurement of fluorescence intensities at two excitation wavelengths, which should provide a built‐in correction for environmental effects. However, most of the small‐molecule dual‐excitation ratiometric probes that have been reported thus far have shown rather limited separation between the excitation wavelengths (20–70 nm) and/or a very small molar absorption coefficient at one of the excitation wavelengths. These shortcomings can lead to cross‐excitation and thus to errors in the measurement of fluorescence intensities and ratios. Herein, we report a FRET‐based molecular strategy for the construction of small‐molecule dual‐excitation ratiometric probes in which the donor and acceptor excitation bands exhibit large separations between the excitation wavelengths and comparable excitation intensities, which is highly desirable for determining the fluorescence intensities and signal ratios with high accuracy. Based on this strategy, we created a coumarin–rhodamine FRET platform that was then employed to develop the first class of FRET‐based dual‐excitation ratiometric pH probes that have two well‐resolved excitation bands (excitation separations>160 nm) and comparable excitation intensities. In addition, these pH probes may be considered as in a kind of “secured ratioing mode”. As a further application of these pH probes, the dual‐excitation ratiometric pH probes were transformed into the first examples of photocaged dual‐excitation ratiometric pH probes to improve the spatiotemporal resolution. It is expected that the modular nature of our FRET‐based molecular strategy should render it applicable to other small‐molecule dual‐dye energy‐transfer systems based on diverse fluorescent dyes for the development of a wide range of dual‐excitation ratiometric probes with outstanding spectral features, including large separations between the excitation wavelengths and comparable excitation intensities.

We have designed and synthesized the highly selective and reversible fluorescent chemosensor 1 for Au³⁺ by modifications on the fluorescent copper chemodosimeter 2, and we have further demonstrated that chemosensor 1 could be employed to image Au³⁺ in living cells.

The first NIR fluorescent sensor for sulfide anions was constructed based on the displacement approach. The sensing ensemble is composed of a cyanine dye, a piperazine linker, an 8-aminoquinoline ligand, and copper. The favorable attributes of the sensor include a large NIR fluorescence turn-on signal in aqueous ethanol, high sensitivity, and high selectivity. The transition-metal-based displacement strategy may open an avenue for development of NIR fluorescent sensors for a wide variety of anion targets.

We described the development of Cou-Rho-NO as the first small-molecule suitable for ratiometric fluorescent imaging of endogenously produced nitric oxide in macrophage cells.

The first ratiometric fluorescent probe for specific detection of cysteine over homocysteine and glutathione was developed based on the drastic distinction in the kinetic profiles.

We have constructed a fast-responsive fluorescent gold ion probe based on the unexpected gold ion-mediated hydrolysis of acylsemicarbazides to carboxylic acids. The probe has been applied for sensing gold ions in the living cells and detecting residual gold content in gold-catalyzed synthetic samples for the first time.

A novel strategy to systematically tune the pK_a values of rhodamines is described. This strategy was applied to rationally develop compound 1e with a pK_a of 6.5, the highest among rhodamine amide derivatives, and it could be employed to detect acidic pH variations in living cells with a turn-on signal.

Analyte‐responsive fluorescent probes are valuable chemical tools for dissecting complex living systems. However, the major shortcoming of fluorescent probes is that once they enter the cells, control over them is basically lost. It is critical to regulate fluorescent probes in a spatial and temporal manner, as functions of biomolecules are spatiotemporal. On the other hand, light can be manipulated in time and in the application site, so the photocaging technique allows researchers to control the biomolecules of interest in a temporal and spatial fashion. Herein, we propose for the first time the combination of the merits of sensing and photocaging technologies, which may afford the caging version of analyte‐responsive fluorescent probes, referred to as photocontrollable analyte‐responsive fluorescent probes (PCAFPs). These “smart” fluorescent probes apparently have the intrinsic advantage of spatiotemporal control when compared to traditional fluorescent probes, as the “sensing activity” of PCAFPs is photocontrollable. This should enable biologists to interrogate complex biological systems in a spatial and temporal manner with an innovative chemical tool. In this work, for proof of concept, we report the rational design, synthesis, photocontrollable sensing in solution and in living cells, and mechanistic studies of a molecular prototype of PCAFP for copper as the first paradigm of this new class of smart fluorescent probes. We believe that PCAFPs represent a substantial breakthrough in the sensing and photocaging fields, and that the general concept of PCAFPs should be broadly applicable for a wide variety of biologically relevant species.