Constructing Dual-State Emissive Fluorophores via Boc Protection and Discovering a High-Fidelity Imaging Probe for Lipid Droplets.

Dual-state emissive (DSE) materials exhibit fluorescence in both solid and solution states and have become an emerging material in the fields of materials science and sensing in recent years. However, due to the lack of effective and universal preparation methods, DSE materials, especially those with long emission wavelengths, are still scarce. Developing an effective method for constructing such DSE molecules is urgently needed. In this study, we constructed three DSE molecules (NRP-Boc, DCIP-Boc, and DCMP-Boc) with far-red to near-infrared fluorescence by simply modifying three traditional aggregation-caused quenching (ACQ) fluorophores with tert-butyloxycarbonyl (Boc) groups. Density functional theory (DFT) calculations and crystal data revealed the reasons for the bright fluorescence of these three molecules in solution and solid, demonstrating that this Boc protection method is a simple and effective strategy for constructing DSE molecules. We also found that these three DSE molecules have the potential to target and visualize lipid droplets (LDs). Among them, DCIP-Boc shows advantages of a large Stokes shift, long emission wavelength, low fluorescence background, and good photostability in cells, providing a powerful new molecular tool with DSE property for high-fidelity imaging of LDs.

Cell membrane targetable NIR fluorescent polarity probe for selective visualization of cancer cells and early tumor.

The development of a sensitive method for early cancer diagnosis is very important because the early diagnosis of cancer is crucial in preventing the spread of cancer cells and improving patient survival rates. Recent studies showed that cancer cell membranes have lower polarity than normal cell membranes, which provides a new approach for cancer diagnosis at the cell membrane level. We developed herein a highly sensitive cell membrane polarity probe (Cal-M) for early diagnosis of cancer. This probe has low cytotoxicity, good photostability, near-infrared (NIR) fluorescence emission (>700 nm), large Stokes shift, high sensitivity for polarity, excellent cell membrane localization performance, and the ability to selectively light up cancer cells. Using this probe staining, the fluorescence of cancer cells is ∼63 times higher than that of normal cells, demonstrating excellent sensitivity and selectivity of Cal-M. This probe was also successfully used to detect polarity changes on cancer cell membranes and selectively visualize tumors in mice. Notably, the tumor could be visualized sensitively with a size as small as 1.37 mm3, indicating that Cal-M is promising for early diagnosis of tumors.

Kidney-Targeted Near-Infrared Fluorescence Probe Reveals That SO2 Is a Biomarker for Cisplatin-Induced Acute Kidney Injury.

With the widespread use of drugs, drug-induced acute kidney injury (AKI) has become an increasingly serious health concern worldwide. Currently, early diagnosis of drug-induced AKI remains challenging because of the lack of effective biomarkers and noninvasive imaging tools. SO2 plays important physiological roles in living systems and is an important antioxidant for maintaining redox homeostasis. However, the relationship between SO2 (in water as SO32-/HSO3-) and drug-induced AKI remains largely unknown. Herein, we report the highly sensitive near-infrared fluorescence probe DSMN, which for the first time reveals the relationship between SO2 and drug-induced AKI. The probe responds to SO32-/HSO3- selectively and rapidly (within seconds) and shows a significant turn-on fluorescence at 710 nm with a large Stokes shift (125 nm). With these properties, the probe was successfully applied to detect SO2 in living cells and mice. Importantly, the probe can selectively target the kidneys, allowing for the detection of changes in the SO2 concentration in the kidneys. Based on this, DSMN was successfully used to detect cisplatin-induced AKI and revealed an increase in the SO2 levels. The results indicate that SO2 is a new biomarker for AKI and that DSMN is a powerful tool for studying and diagnosing drug-induced AKI.

Selective Visualization of Tumor Cell Membranes and Tumors with a Viscosity-Sensitive Plasma Membrane Probe.

Cancer is a worldwide health problem. Revealing the changes in the microenvironment after cell carcinogenesis is helpful to understand cancer and develop sensitive methods for cancer diagnosis. We developed herein a viscosity-responsive plasma membrane probe (TPA-S) that was successfully used to probe the viscosity difference between normal and tumor cell plasma membranes for the first time. The probe shows AIE properties with good water solubility, significant near-infrared (NIR) fluorescence responses to viscosity with high sensitivity, and excellent cell membrane location performance. With these features, our experiments showed that TPA-S could selectively visualize cancer cell plasma membranes, revealing that the plasma membrane of tumor cells is more viscous than that of normal cells. In addition, TPA-S was successfully applied to specifically light up tumors. Altogether, this work explored the changes of cell membrane viscosity after canceration, provided a new method for selective visualization of tumor cells, and opened up a new approach for cancer diagnosis.

Dual-Channel Fluorescent Probe for Detecting Viscosity and ONOO- without Signal Crosstalk in Nonalcoholic Fatty Liver.

Nonalcoholic fatty liver disease (NAFLD) is a global health issue. Peroxynitrite and liver viscosity have recently been found to be potential biomarkers of NAFLD. Therefore, it is of great significance to develop dual-response fluorescent probes for simultaneous detecting peroxynitrite and viscosity. We report herein a new probe (CQ) that can simultaneously detect peroxynitrite and viscosity at two independent fluorescent channels without signal crosstalk. CQ shows high selectivity, rapid response, good water solubility, low cytotoxicity, and mitochondrial localization properties. In particular, CQ responds sensitively to viscosity and peroxynitrite with off-on fluorescence changes at 710 and 505 nm, respectively. The wavelength gap between these two channels is more than 200 nm, ensuring that there is no signal crosstalk during detection. With this property, the probe was applied to simultaneously detect mitochondrial viscosity and peroxynitrite and image the changes of liver viscosity and peroxynitrite concentration during the pathogenesis of NAFLD. All results show that the CQ probe is a powerful tool for simultaneous detection of viscosity and peroxynitrite and provides a potential new diagnostic method for NAFLD.

Polarity-Sensitive Cell Membrane Probe Reveals Lower Polarity of Tumor Cell Membrane and Its Application for Tumor Diagnosis.

Cancer is a health threat worldwide, and it is urgent to develop more sensitive cancer detection methods. Herein, a polarity-sensitive cell membrane probe (named COP) was developed for detecting cancer cells and tumors sensitively and selectively at the cell membrane level. The probe shows a strong polarity-dependent fluorescence and excellent cell membrane targeting ability to visualize cell membrane with red fluorescence with a non-washing process. Notably, COP can selectively light up the tumor cell membranes, which reveals that cancer cell membranes have lower polarity than normal cell membranes. The giant unilamellar vesicle model and cell imaging studies proved this. Moreover, COP can effectively and selectively light up tumors. Overall, this work demonstrates that the polarity of the tumor cell membrane is quite different to normal cell membranes, and based on this, sensitive membrane probes can be developed to selectively visualize cancer cells and tumors, which opens up a new way for tumor diagnosis at the cellular level.

A Pd2+-Free Near-Infrared Fluorescent Probe Based on Allyl Ether Isomerization for Tracking CORM-3 with High Contrast Imaging in Living Systems.

As a CO donor, CORM-3 is widely used nowadays to study the role of CO as a gasotransmitter and potential drug in biological systems. Developing methods to detect CORM-3 in live systems will contribute to these studies. Herein, we developed a novel Pd2+-free near-infrared fluorescent probe CORM3-AE for detecting CORM-3 both in live cells and in vivo. We found that the allyl ether group in CORM3-AE could be cleaved by CORM-3 directly via an isomerization process to release the NIR fluorophore QCy7 and cause distinct NIR fluorescence changes. Importantly, CORM3-AE responds quickly and shows high sensitivity and selectivity for CORM-3 with NIR fluorescence turn-on changes at 743 nm (λex = 662 nm), and when the excitation wavelength is 450 nm, CORM3-AE can respond to CORM-3 with ratiometric fluorescence signals at 743/605 nm. Moreover, CORM3-AE can track CORM-3 in live cells and animals with excellent imaging performance. Thus, this work not only provides a powerful new tool for CORM-3 detection in live systems but also provides a new method to construct CORM-3 probes by allyl ether isomerization.

Near-Infrared Mitochondria-Targetable Fluorescent Probe for High-Contrast Bioimaging of H2S.

To elucidate the complex role of biological H2S and study the mitochondrial damage and some related diseases, effective methods for visualization of H2S in mitochondria and in vivo are urgently needed. In this contribution, a novel near-infrared mitochondria-targetable fluorescence probe MI-H2S for H2S detection was developed. MI-H2S shows rapid detection ability for H2S in pure aqueous solution and outputs a highly selective and sensitive fluorescence-on signal at 663 nm with a large Stokes shift of 141 nm. Bioimaging experiments revealed that the probe has good mitochondrial-targeting ability and high-contrast imaging ability for detecting H2S in living systems. The probe also showed great potential in the detection of H2S during inflammation. All of the results demonstrate that MI-H2S can be applied as an effective probe for the visualization and study of H2S in mitochondria and in vivo.

In Vivo Imaging and Tracking Carbon Monoxide-Releasing Molecule-3 with an NIR Fluorescent Probe.

As a water-soluble carbon monoxide-releasing molecule, CORM-3 is widely used as a CO donor to study CO in the life system. CORM-3 can also replace gaseous CO as a therapeutic drug molecule to reveal the physiological and pathological effects of CO in life. Therefore, it is of great importance to visualize and track CORM-3 in the life system. We develop herein a near-infrared (NIR) fluorescent probe CORM3-NIR that can detect CORM-3 both in living cells and in vivo effectively. The probe is based on the unique fluorescent QCy7 and uses a 4-nitrobenzyl group to trap CORM-3, and importantly, it shows good water solubility and responds rapidly, selectively, and sensitively to CORM-3, releasing QCy-7 and producing distinct colorimetric and significant NIR fluorescence change signals at 743 nm. The Stokes shift is up to 81 nm. The probe is also able to detect CORM-3 ratiometrically with fluorescence at 743 and 600 nm. Besides, with low cytotoxicity, the probe also shows good NIR fluorescence bioimaging ability for CORM-3 in live cells and mice, which indicates that CORM3-NIR is an effective probe for tracking and studying CORM-3 in the life system.

A novel reaction-based fluorescence probe for rapid imaging of HClO in live cells, animals, and injured liver tissues.

Hypochlorous acid (HClO) is an important bioactive molecule, playing vital roles in a large number of physiological and pathological processes. Abnormal concentration of HClO in vivo has close contact with many diseases including inflammatory diseases and cancer. For bioimaging HClO, a new colorimetric and turn-on near-infrared (NIR) fluorescence probe (DDAO-ClO) was designed and synthesized in this work through a specific reaction of HClO with dimethylthiocarbamate. DDAO-ClO proved to show distinct and highly selective colorimetric and NIR fluorescence responses for HClO with fast response time (<3 s) and high sensitivity (LOD = 7.3 nM) in vitro. After confirming the excellent in vitro sensing ability, imaging HClO with DDAO-ClO in living HeLa cells, MCF-7 cells, zebrafish, and mice was all successfully demonstrated. And with this probe, it was further discovered that more endogenous HClO was produced in injured mice liver tissues, which demonstrates that DDAO-ClO not only is effective for in vivo detection of HClO but also has a broad application prospect.

Aggregation-induced emission and solid fluorescence of fluorescein derivatives.

We report herein for the first time that the aggregation-induced emission and strong solid fluorescence of fluorescein derivatives can be realized by slightly modifying their structure, which provides a new option for AIEgens and solid fluorescent materials.

Development of a new ratiometric probe with near-infrared fluorescence and a large Stokes shift for detection of gasotransmitter CO in living cells.

A near-infrared (NIR) ratiometric fluorescent probe, NIR-Ratio-CO, was developed for rapid detection of carbon monoxide (CO) in both solution and living cells through the strategy of Pd0-mediated Tsuji-Trost reaction. This probe shows a rapid, highly specific and sensitive detection process for CO, accompanied by colorimetric and distinct ratiometric fluorescence changes at 655 and 592 nm with a large Stokes shift up to 195 nm. The detection limit for CO was measured to be about 61 nM by the fluorescence method. In addition, this probe was successfully applied for ratiometric imaging of both exogenous and endogenous CO in living cells, indicating that it can be used as a novel tool for ratiometric fluorescent detection of CO in living systems.

Nitrobenzoxadiazole Ether-Based Near-Infrared Fluorescent Probe with Unexpected High Selectivity for H2S Imaging in Living Cells and Mice.

H2S is an important endogenous gasotransmitter, and its detection in living systems is of great significance. Especially, selective and sensitive near-infrared (NIR) fluorescent H2S probes with rapid response and large Stokes shift are highly desirable because of their superiority for in vivo detection. Probes with nitrobenzoxadiazole (NBD) ether as reaction sites have been well-explored recently to detect biothiols or H2S/biothiols simultaneously, rather than to detect H2S selectively. In this work, a new NBD ether-based NIR fluorescent probe was developed, which was unexpectedly found to show high selectivity for H2S over various other analytes including biothiols, making it practical for specific detection of H2S both in vitro and in vivo. Upon response to H2S, this probe showed rapid and significant turn-on NIR emission changes centered at 744 nm within 3 min, together with a remarkable large Stokes shift (166 nm) and high sensitivity (LOD: 26 nM). Moreover, imaging exogenous and endogenous H2S in living cells and rapid imaging of H2S in living mice with this probe was successfully applied with excellent performance.

A near-infrared fluorescent probe for imaging endogenous carbon monoxide in living systems with a large Stokes shift.

Near-infrared (NIR) fluorescent probes with a large Stokes shift are very practical tools for bioimaging applications. Carbon monoxide (CO) is a key gaseous signal molecule and its imaging in living systems has attracted great attention in recent years. In this work, a very easy-to-get NIR fluorescent probe with a remarkable large pseudo-Stokes shift (238 nm) for detection of CO was reported. This probe was found to show a rapid NIR fluorescent turn-on response for CO with high selectivity, high sensitivity and a low detection limit (38 nM). Moreover, imaging CO in living cells and animals with this probe was successfully applied with a high signal-to-noise ratio. The results indicate that this probe can be used as a new practical tool for imaging of endogenous CO in living systems.

Readily prepared iminocoumarin for rapid, colorimetric and ratiometric fluorescent detection of phosgene.

In this paper, a new colorimetric and ratiometric fluorescent probe for the rapid detection of phosgene is reported. This probe is based on a readily prepared and highly fluorescent iminocoumarin, which reacts rapidly with phosgene to form a cyclic carbamate product to produce, distinctive colorimetric and ratiometric fluorescent signal changes. The detection of phosgene with this probe is fast (complete within 2 min), highly selective and sensitive with a detection limit of 27 nM in solution. Moreover, this probe can be used to prepare easy-to-use paper test strips for convenient visual and fluorescent detection of phosgene gas even at a concentration of 0.1 mg/L. Overall, this work provides a very promising dual colorimetric and ratiometric fluorescent probe for rapid and sensitive detection of phosgene both in solution and in the gas phase.