Protein vicinal dithiols play fundamental roles in intracellular redox homeostasis due to their involvement in protein synthesis and function through the reversible vicinal dithiol oxidation to disulfide. To provide quantitative information about the global distribution and dynamic changes of protein vicinal dithiols in living cells, we have designed and synthesized a ratiometric fluorescent probe (VTAF) for trapping of vicinal dithiol-containing proteins (VDPs) in living cells. VTAF exhibits a ratiometric fluorescence signal upon single excitation, which enables self-calibration of the fluorescence signal and quantification of endogenous vicinal dithiols of VDPs. Its potential for in situ dynamic tracing of changes of protein vicinal dithiols under different cellular redox conditions was exemplified. VTAF facilitated the direct observation of subcellular distribution of endogenous VDPs via ratiometric fluorescence imaging and colocalization assay. And the results suggested that there are abundant VDPs in mitochondria. Moreover, some redox-sensitive VDPs are also present on cell surface which can respond to redox stimulus. This ratiometric fluorescence technique presents an important extension to previous fluorescence intensity-based probes for trapping and quantifying protein vicinal dithiols in living cells, as well as its visible dynamic tracing of VDPs.

Fluorescence polarization (FP)-based signal is a self-referencing fluorescence signal, and it is less dependent on dye concentration and environmental interferences, which makes FP measurement an attractive alternative sensing technology to fluorescence intensity-based detection. However, most of the fluorescence polarization probes were constructed by introducing fluorescein, rhodamine, and cyanine dyes, which have relatively shorter excited-state lifetimes compared with BODIPY and naphthalimide dyes. Herein, a first naphthalimide based fluorescence polarization probe (BIO) was designed and synthesized for selective and direct detection of cancer cells. The relatively longer excited-state lifetimes and high photostability of naphthalimide makes BIO more sensitive and accuracy in quantitative determination of HeLa cells in homogeneous solution without cell lysis and further separation steps. The detection limit of BIO for HeLa cells was about 85 cells mL(-1), the linear range was from 2.5 × 10(2) cells mL(-1) to 1 × 10(6) cells mL(-1) and the response time is no more than 25 min. Moreover, due to the relatively high photostability of naphthalimide, BIO was particularly suitable for live cell imaging under continuous irradiation with confocal microscopy, and the specific interaction of BIO with CD44-overexpressing cell lines was clearly visualized. Importantly, this BIO based sensing platform offers a direct and real-time tool for cancer cell diagnosis when complemented with the use of naphthalimide-based fluorescence polarization probe.

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Hypoxia, which has been well established as a key feature of the tumor microenvironment, significantly influences tumor behavior and treatment response. Therefore, imaging for tumor hypoxia in vivo is warranted. Although some imaging modalities for detecting tumor hypoxia have been developed, such as magnetic resonance imaging, positron emission tomography, and optical imaging, these technologies still have their own specific limitations. As computed tomography (CT) is one of the most useful imaging tools in terms of availability, efficiency, and convenience, the feasibility of using a hypoxia-sensitive nanoprobe (Au@BSA-NHA) for CT imaging of tumor hypoxia is investigated, with emphasis on identifying different levels of hypoxia in two xenografts. The nanoprobe is composed of Au nanoparticles and nitroimidazole moiety which can be electively reduced by nitroreductase under hypoxic condition. In vitro, Au@BSA-NHA attain the higher cellular uptake under hypoxic condition. Attractively, after in vivo administration, Au@BSA-NHA can not only monitor the tumor hypoxic environment with CT enhancement but also detect the hypoxic status by the degree of enhancement in two xenograft tumors with different hypoxic levels. The results demonstrate that Au@BSA-NHA may potentially be used as a sensitive CT imaging agent for detecting tumor hypoxia.

An easily available naphthalimide-based fluorescent probe NPA for Pb(2+) detection was successfully developed. NPA exhibited an obvious fluorescence turn-on response toward Pb(2+) in aqueous solution and in living cells. Moreover, a series of model compounds were rationally designed and synthesized in order to explore the sensing mechanism and binding mode of NPA with Pb(2+) .

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A versatile probe for serum albumin and its application in monitoring wounds in live zebrafish.

Three fluorescent probes TP1–3 for thiols were rationally designed and synthesized to distinguish cysteine (Cys) from glutathione (GSH)/homocysteine (Hcy). TP1–3 are almost non-fluorescent and colorless 4-nitro-1,8-naphthalimide derivatives. Upon the substitution of nitro by Cys, TP1–3 were transformed into weakly fluorescent green-emitting 4-amino analogs via highly fluorescent blue-emitting thioether intermediates. The three-channel signaling capability allows discrimination between Cys and GSH/Hcy. The fluorescence intensity at 498 nm was linearly proportional to GSH concentration in the range of 0-20 μM, and the detection limit was 5 × 10(-8) mol L(-1). A good linear relationship between A446/A350 and Cys concentration was found in the range of 0-70 μM, and the detection limit was 2 × 10(-7) mol L(-1). Moreover, TP3 was used for living cell imaging as well as for detecting mercapto-containing proteins.