Yonghe Tang

Development of a Two‐Photon Fluorescent Probe for Imaging of Endogenous Formaldehyde in Living Tissues

Investigation of the physiological and pathological functions of formaldehyde (FA) are largely restricted by a lack of useful FA imaging agents, in particular, those that allow detection of FA in the context of living tissues. Herein, we present the rational design, synthesis, and photophysical property studies of the first two-photon fluorescent FA probe, Na-FA. Importantly, the highly desirable attributes of the probe Na-FA (such as a very large turn-on signal (up to 900-fold), a low detection limit, and a very fast onset imparted by the unique design aspects of the probe), make it possible to monitor endogenous FA in living tissues for the first time. Furthermore, sodium bisulfite was identified as a simple and convenient inhibitor of FA within biological environments.

Simultaneous Near-Infrared and Two-Photon In Vivo Imaging of H2O2 Using a Ratiometric Fluorescent Probe based on the Unique Oxidative Rearrangement of Oxonium

A new ratiometric fluorescent H2 O2 probe, benzopyrylium-coumarin (BC), is designed by using an oxonium moiety as the unique H2 O2 response site. The BC probe exhibits an extremely large emission shift of 221 nm in response to H2 O2 , and is successfully applied for the simultaneous near-infrared and two-photon imaging of H2 O2 in living cells, mouse-liver tissues, and zebrafish.

Coumarin-Based Turn-On Fluorescence Probe for Specific Detection of Glutathione over Cysteine and Homocysteine.

We have prepared a turn-on fluorescent probe for biothiols based on bromoketo coumarin (KC-Br). The emission intensity of the coumarin chromophore is modulated by both the heavy atom effect and internal charge transfer (ICT) process. The probe KC-Br is intrinsically nonfluorescent; however, after being reacted with thiols, the bromide moiety is substituted by the -SH group, which elicits a significant fluorescence increase. We surmised the free -NH2 group would further react with carbonyl in the Cys/Hcy-substituted intermediate product yielding to Schiff base compound KC-Cys/KC-Hcy, but not in compound KC-GSH. The ICT effect has a stronger influence in compound KC-GSH than that in compound KC-Cys/KC-Hcy, resulting in compound KC-GSH having a stronger fluorescence. Thus, the probe has a good selectivity for GSH over other various biologically relevant species and even two other similar biothiols (Cys/Hcy) and could image glutathione (GSH) in living cells. We expect the design concept presented in this work would be widely used for the design of fluorescent probes for distinguishing among biothiols.

Corrigendum: Construction of a Near-Infrared Fluorescent Turn-On Probe for Selenol and Its Bioimaging Application in Living Animals.

As selenocysteine (Sec) carries out the majority of the functions of the various Se-containing species in vivo, it is of high importance to develop reliable and rapid assays with biocompatibility to detect Sec. Herein, an NIR fluorescent turn-on probe for highly selective detection of selenol was designed and synthesized. The probe exhibits large turn-on signal upon treatment with selenocysteine (R-SeH), and it was further demonstrated that the new NIR fluorescent probe can be employed to image selenol in living animals.

A biotin-guided formaldehyde sensor selectively detecting endogenous concentrations in cancerous cells and tissues

A biotin appended formaldehyde sensor was found to specifically visualise both exogenous and endogenous levels of formaldehyde in biotin receptor positive cells over biotin negative cells by means of one- and two-photon excitation. The probe furthermore visualised endogenous levels of formaldehyde in tumour tissue slices up to 70 μm depth.

A new fluorescent probe with a large turn-on signal for imaging nitroreductase in tumor cells and tissues by two-photon microscopy

Hypoxia is the important characteristic of solid tumors, and it may cause the bioactivity of nitroreductase (NTR) to display an elevated level. Hence, the development of effective monitoring methods of NTR in living systems is of great importance for detecting the occurrence and progress of tumors. Toward this goal, a novel two-photon fluorescence turn-on NTR probe GCTPOC-HY, based on the two-photon platform GCTPOC and the NTR recognition site p-nitrobenzyl ether, is designed and synthesized. The probe GCTPOC-HY exhibits eminent properties such as high sensitivity and selectivity, highly stable photo-stability, and low cytotoxicity. Besides, the probe responds to 1.5μg/mL NTR with a 130-fold fluorescence enhancement, which is larger than the reported two-photon fluorescent NTR probes. Moreover, the probe GCTPOC-HY is suitable for fluorescence imaging of NTR in living cells by one- and two-photon modes. Importantly, the probe GCTPOC-HY is successfully applied to monitor NTR in the tumor tissues with a significant fluorescence signal and a penetration depth of 70µm by using two-photon microscopy.

Development of green to near-infrared turn-on fluorescent probes for the multicolour imaging of nitroxyl in living systems

Nitroxyl (HNO) is one of the important reactive nitrogen species (RNS) and show significant biological activities with significant therapeutic potential. Herein, three novel turn-on probes (NP-1-3) based on structurally related dyes with different emission colors as fluorescent scaffolds have been developed for detecting HNO in biological systems. The probes exhibit high sensitivity, excellent selectivity, desirable performance at physiological pH and low cytotoxicity. By incubating living cells with these probes simultaneously, we demonstrate the multicolor imaging of HNO with emission colors in the range of green to near-infrared (NIR) in living systems for the first time. Furthermore, probe NP-3 responds to HNO with a significant turn-on NIR fluorescence signal upon excitation in the NIR region, and it is successfully applied for sensing HNO in living mice.

Two-Photon and Deep-Red Emission Ratiometric Fluorescent Probe with a Large Emission Shift and Signal Ratios for Sulfur Dioxide: Ultrafast Response and Applications in Living Cells, Brain Tissues, and Zebrafishes

Sulfur dioxide (SO2) is a dangerous environmental pollutant. Excessive intake of it may cause some respiratory diseases and even lung cancer. The development of effective methods for detection of SO2 is of great importance for the environment and physiology. Herein, we have designed and synthesized a novel two-photon (TP) and deep-red emission ratiometric fluorescent probe (CP) for detection of SO2. Notably, the novel probe CP exhibited ultrafast response to SO2 in less than 5 s and displayed a great emission shift (195 nm) and a large emission signal ratio variation (enhancement from 0.1347 to 100.14). In addition, the unique probe was successfully employed for imaging SO2 not only in the mitochondria of living cells but also in brain tissues and zebrafishes.

Hydrogen Sulfide Triggered Charge-Reversal Micelles for Cancer-Targeted Drug Delivery and Imaging

Currently, the development of polymeric micelles combining diagnosis and targeted therapy is theoretically and practically significant in cancer treatment. In addition, it has been reported that cancer cells can produce large amounts of hydrogen sulfide (H2S) and their survival depends on the content of H2S. In this study, a series of N-(2-hydroxyethyl)-4-azide-1,8-naphthalimide ended amphiphilic diblock copolymer poly(2-hydroxyethyl methacrylate)-block-poly(methyl methacrylate) (N3-Nap-PHEMA-b-PMMA-N3) micelles were prepared. Around cancer tissues, the N3-Nap-PHEMA45-b-PMMA42-N3 micelles exhibited dual characteristics of monitoring H2S and H2S triggered charge reversal with the reduction of the azido group. The surface charge of N3-Nap-PHEMA45-b-PMMA42-N3 micelles reversed from negative to positive after monitoring H2S. With H2S triggered charge reversal, the cellular uptake of DOX-loaded N3-Nap-PHEMA45-b-PMMA42-N3 micelles was effectively enhanced through electrostatic attraction mediated targeting, and a fast doxorubicin (DOX) release rate was observed. The MTT assay demonstrated that N3-Nap-PHEMA45-b-PMMA42-N3 micelles were biocompatible to HeLa cells, and DOX-loaded N3-Nap-PHEMA45-b-PMMA42-N3 micelles showed enhanced cytotoxicity in HeLa cells in the presence of H2S. Furthermore, in vivo fluorescence imaging and biodistribution experiments revealed that DOX-loaded N3-Nap-PHEMA45-b-PMMA42-N3 micelles could provide good tumor imaging and accumulate in tumor tissue. Therefore, N3-Nap-PHEMA45-b-PMMA42-N3 micelles can be used as a promising platform for tumor diagnosis and therapy.

Development of a two-photon fluorescent turn-on probe with far-red emission for thiophenols and its bioimaging application in living tissues

Thiophenol is a highly toxic compound which is essential in the field of organic synthesis and drug design. However, the accumulation of thiophenols in the environment may cause serious health problems for human bodies ultimately. Therefore, it is critical to develop efficient methods for visualization of thiophenol species in biological samples. In this work, an innovative two-photon fluorescent turn-on probe FR-TP with far-red emission for thiophenols based on FR-NH2 fluorophore and 2,4-dinitrophenylsulfonyl recognition site was reported. The new probe can be used for thiophenol detection with large far-red fluorescence enhancement (about 155-fold), rapid response (completed within 100s), excellent sensitivity (DL 0.363μM), high selectivity, and lower cellular auto-fluorescence interference. Importantly, the probe FR-TP can be successfully employed to visualize thiophenols not only in the living HeLa cells but also in living liver tissues. In addition, through two-photon tissue imaging, the probe was used to monitor and investigate biological thiophenol poisoning in the animal model of thiophenol inhalation for the first time.