Design Of Fluorescent Probes Research Articles

A Synthetic Strategy for Multi-Functionalized Phospharhodamines via Catalytic P-Arylation

Abstract The visualization of complex biological events in living cells is highly reliant on the development of sophisticated fluorescent probes with multiple functions. Herein, we report a general synthetic strategy for the synthesis of near-infrared-emissive phospharhodamines (PORs) bearing various types of aryl groups on their bridging phosphorus atoms. This versatile approach utilizes a Ni-catalyzed P-arylation that allows for the design of POR-based multi-functionalized fluorescent probes. We found that PORs substituted with an aminophenyl group exhibited pH-responsive fluorescence intensity, where photoinduced electron transfer occurs to quench the fluorescence. The combination of our new approach with conventional modification at the 9-position of the xanthene skeleton facilitates the development of multi-functionalized fluorescent probes. As one demonstration of this method, we synthesized a fluorescence probe that can selectively visualize the lysosomes that result from endosomal maturation.

Rational design of push-pull fluorescent probe with extraordinary polarity sensitivity for VOCs chromic sensing and trace water detection

Developing fluorescent probes with excellent polarity sensitivity is still meaningful, but faces some challenges. Different from previous studies, this work focusses on modifying the π-bridge to improve the polarity-sensitivity, and found that taking quinoline with electron-deficient structure as π-bridge can significantly promote the intramolecular charge transfer from the electron-donor to electron-acceptor. Such modification on π-bridge endows fluorescent probe DQN with brilliant fluorescence which is highly sensitive to changes in environmental polarity. Based on it, the DQN-based test strips have been made for fast, visual, and reversible discrimination of four volatile organic compounds with varied polarities. Moreover, 92#, 95#, and 98# gasolines can be directly discriminated with DQN, showing completely different fluorescent colors under UV lamp. In addition, trace water in organic solvents can also be accurately detected, and their limits of detection are as low as 28 ppm (1,4-dioxane) and 16 ppm (tetrahydrofuran). In short, this work provides an inspirational perspective for the rational design of fluorescent probes with excellent polarity sensitivity for multifunctional applications.

Reconsideration of the ESIPT off mechanism for fluorescent probe MNC in aqueous solution

Fluorescent probes with excited state intramolecular proton transfer (ESIPT) properties play a significant role in the research of life science and material science. Guo et al. designed 3-hydroxy-2-(6-Methoxynaphthalen-2-yl)-4H-chromen-4-one (MNC) as a control to achieve the dual-color fluorescence imaging of lipid droplets and endoplasmic reticulum (ER). They deemed that the ESIPT process would be turned off in ER with high water content [J. Am. Chem. Soc. 2021, 143, 3169–3179]. However, contrary to the conventional ESIPT off case, the enol* state fluorescence intensity that should have been enhanced was severely quenched in water. Here, combined with ultrafast spectrum, steady-state fluorescence spectrum and potential energy surface, the mechanism of ESIPT process of MNC turned off in water is revised. Furthermore, the formation of aggregated states in water is responsible for the quenching of MNC fluorescence. This work is expected to provide broader ideas for the design of hydrophobic fluorescent probes.

Rational Design of pH-Independent and High-Fidelity Near-Infrared Tunable Fluorescent Probes for Tracking Leucine Aminopeptidase In Vivo.

Accurate detection of target analytes and generation of high-fidelity fluorescence signals are particularly critical in life sciences and clinical diagnostics. However, the majority of current NIR-I fluorescent probes are vulnerable to pH effects resulting in signal distortion. In this work, a series of fluorescence-tunable and pH-independent probes are reported by combining optically tunable groups of unsymmetric Si-rhodamines and introducing the methoxy instead of the spiro ring on the benzene ring at position 9. To validate the concept, the leucine aminopeptidase response site was introduced into Si-2,6OMe-NH2 with the best optical properties to synthesize Si-LAP for monitoring the intrahepatic LAP in vivo. Therefore, the design approach may provide a new and practical strategy for designing innovative functional fluorescent probes and generating high-stability and high-fidelity fluorescent signals.

Molecular engineering of a wash-free, clover-like G-quadruplex fluorescent probe that exploits a new mechanism of disaggregation-and-binding-induced emission

In this study, we raised a brand-new principle termed disaggregation-and-binding-induced emission (DBIE) for the design of G4 fluorescent probes, which may overcome the shortcomings of the disaggregation-induced emission (DIE) and aggregation-induced emission (AIE) principles. On this basis, a wash-free, clover-like fluorescent probe (TCN3) that could detect either in vitro or cellular DNA G4s was rationally developed. To be noted, this DBIE mechanism may be utilized to design promising fluorescent probes targeting other biotargets.

Precise Electron-Withdrawing Strength Modulation of ESIPT Probes for Ultrasensitive and Specific Fluorescence Sensing.

The precise regulation of the electron-withdrawing/electron-donating strength in a probe is of great significance for the design of reaction-based fluorescent probes with specific functionalities. Here, a family of excited-state intramolecular proton transfer (ESIPT)-based probes with fluorescence turn-on sensing properties toward KMnO4 was designed by precisely modulating the electron-withdrawing strength of the substituents located at the para-position of the recognition group. It is found that -F, -CHO, and -H as the electron-withdrawing groups bound at the probe can specifically recognize KMnO4, which ensures a blue emission displayed by the reaction products. Especially with -CHO as the electron-withdrawing group, the reaction product shows the most stable fluorescence. The probe 2-(benzo[d]oxazol-2-yl)-4-formylphenyl acrylate (BOPA-CHO) demonstrated a more superior sensing performance toward KMnO4, including a low limit of detection (LOD, 0.96 nM), a rapid response (<3 s), and a rather good selectivity even in the presence of 21 interferents. Moreover, the practicality of the probe was further verified by a test pen comprising a BOPA-CHO-embedded sponge, which is capable of detecting KMnO4 solid with a naked-eye LOD of 11.62 ng. The present probe design and modulation strategy would open up a new path for the design of high-performance fluorescent probes.

A dual-mode fluorescent probe based on carbon dots for detecting solution polarity.

Fluorescent probes always attract huge attention. In particular, carbon dots, due to their unique biocompatibility and variable fluorescence characteristics, can be used in multiple fields and were fulled of expectation by researchers. Since the advent of the dual-mode carbon dots probe, which greatly improved the accuracy of quantitative detection, there are higher hopes for dual-mode carbon dots probes. Herein, we have successfully developed a new dual-mode fluorescent carbon dots probe based on 1,10-phenanthroline (Ph-CDs). Ph-CDs detect the object to be measured based on both down-conversion luminescence and up-conversion luminescence at the same time, different from the reported dual-mode fluorescent probes which are based on the wavelength and intensity changes in down-conversion luminescence. As-prepared Ph-CDs have good linear relationships with the polarity of solvents in down-conversion luminescence (R2=0.9909) and up-conversion luminescence (R2=0.9374), respectively. Hence, Ph-CDs provide a new in-depth insight into the design of fluorescent probes with dual-mode detection and they can give more accurate, reliable and convenient detection results.

Highly sensitive fluorescent probes for selective detection of hypochlorite: Applications in blood serum and cell imaging.

Being one of the vital reactive oxygen species (ROS), abnormal level of hypochlorite ion (ClO-) may pose detrimental threats to living organisms. Therefore, highly selective, and rapid monitoring of ClO- in living system is of prime importance to protect living organisms from its harmful effects. In this regard, design of synthetic fluorescent probes for ClO- has garnered considerable attention. However less fluorescence emission in aggregated state and less photostability of several existing probes for ClO- inspired us to design aggregation induced emission (AIE) active fluorescent probes SH1 and SH2. Probes were rationally designed by introducing thiourea moiety that selectively reacted through desulfurization reaction and resulted in highly selective detection of ClO-. Hypochlorite induced desulfurization reaction was validated through 1H NMR titration and DFT studies. Fine tuning of probes SH1 and SH2 prompted highly sensitive nanoscale (55nM and 77nM) and rapid (15 and 35 sec) detection of ClO-. Probe SH1 displayed less cytotoxic effect to live cells before it was successfully applied for bioimaging of ClO- in live MCF-7 cells. Moreover, probes displayed excellent sensing potential for ClO- in blood serum and real water samples. Advantageously, probe coated portable fluorescent films were fabricated for the easy and fast monitoring of ClO-. Of note, this work offers excellent design strategy for highly selective detection of ClO- that may lead to clinical trials.

Design and application of prodrug fluorescent probes for the detection of ovarian cancer cells and release of anticancer drug

Ovarian cancer is a gynecologic malignancy with high mortality. The main reason is that it is detected at an advanced stage due to a lack of early diagnosis and treatment. Therefore, it is of great interest to develop a chemical tool that can visualize ovarian cancer cells in real-time and eliminate them. Unfortunately, probes that can simultaneously monitor both modes of action for the diagnosis and treatment of ovarian cancer have not been developed. Here, we designed a novel prodrug fluorescent probe (YW-OAc) that not only visually tracks cancer cells but also enables the on-demand delivery of chemotherapeutic agents. By β-Gal-mediated glycosidic bond hydrolysis, the fluorescent signal changed from blue to green (signal 1), enabling visual tracking of ovarian cancer cells. Subsequently, the identified cancer cells were subjected to precise light irradiation to induce anticancer drug release accompanied by a fluorescence transition from green to blue (signal 2), enabling real-time information on drug release. Thus, the prodrug fluorescent probe YW-OAc provides comprehensive two-step monitoring during cancer cell recognition and clearance. Notably, YW-OAc exhibited high affinity (Km = 3.74 μM), high selectivity, and low detection limit for β-Gal (0.0035 U/mL). We also demonstrated that YW-OAc can visually trace endogenous β-Gal in different cells and exhibit high phototoxicity in ovarian cancer cells. We hope that the prodrug fluorescent probe YW-OAc, can be used as an effective tool for biomedical diagnosis and treatment.

Implement the Materials Genome Initiative: Machine Learning Assisted Fluorescent Probe Design for Cellular Substructure Staining

AbstractThe Materials Genome Initiative (MGI) is accelerating the pace of advanced materials development by integrating high‐throughput experimentation, database construction, and intelligence computation. Live‐cell imaging agents, such as fluorescent dyes, are exemplary candidates for MGI applications for two reasons: i) they are essential in visualizing cellular structures and functional processes, and ii) the unclear relationship between the chemical structure of fluorescent dyes and their live‐cell imaging properties severely restricts the current trial‐and‐error dye development. Herein, the MGI is followed to present an intelligent combinatorial methodology for predicting the staining cell ability of dyes utilizing machine learning (ML) driven by a structurally diverse combinatorial library. This study demonstrates how to high‐throughput synthesize 1,536 dyes and evaluate their imaging properties to establish a feature dataset for ML. A set of high‐precision ML‐predictors is then successfully modeled for assisting live‐cell staining and endoplasmic reticulum judgment. This approach is believed to bridge the gap between dye structure and corresponding staining behavior, and can accelerate the discovery of novel organelle‐specific stains.

Recent Progress in the Rational Design of Biothiol-Responsive Fluorescent Probes.

Biothiols such as cysteine, homocysteine, and glutathione play significant roles in important biological activities, and their abnormal concentrations have been found to be closely associated with certain diseases, making their detection a critical task. To this end, fluorescent probes have become increasingly popular due to their numerous advantages, including easy handling, desirable spatiotemporal resolution, high sensitivity, fast response, and favorable biocompatibility. As a result, intensive research has been conducted to create fluorescent probes for the detection and imaging of biothiols. This brief review summarizes recent advances in the field of biothiol-responsive fluorescent probes, with an emphasis on rational probe design, including the reaction mechanism, discriminating detection, reversible detection, and specific detection. Furthermore, the challenges and prospects of fluorescence probes for biothiols are also outlined.

Fluorescent Probes with Variable Intramolecular Charge Transfer: Constructing Closed-Circle Plots for Distinguishing D2O from H2O.

It is difficult to distinguish between H2O and D2O due to their very similar properties. Triphenylimidazole derivatives with carboxyl groups (TPI-COOH-2R) show intramolecular charge transfer that responds to polarities and pH of solvents. Here, a series of TPI-COOH-2R with very high photoluminescence quantum yields (73-98%) were synthesized to distinguish D2O from H2O by the method of wavelength-changeable fluorescence. In a mixed THF/water solution, the increase of H2O and D2O contents will separately induce different pendulum-type fluorescence variations and form plots of closed circles with the same starting and ending points from which a THF/water ratio that displays the most different emission wavelengths (up to 53 nm with an LOD of 0.064 vol %) can be determined to further distinguish D2O from H2O. This is proved to be originated from the various Lewis acidities between H2O and D2O. The results of theoretical calculations and experiments suggest that, for different substituent groups in TPI-COOH-2R, an appropriate electron-donating effect is beneficial to distinguish between H2O and D2O, while the electron-pulling effect is adverse. Moreover, because the potential hydrogen/deuterium exchange does not affect the as-responsive fluorescence, this method is reliable. And this work provides a new strategy for the design of fluorescent probes for D2O.

Rational design of water-soluble mitochondrial-targeting near-infrared fluorescent probes with large Stokes shift for distinguishing cancerous cells and bioimaging

In the paper, two new near-infrared fluorescent probes (TTHPs) with D-π-A structure were successfully synthesized. TTHPs exhibited polarity and viscosity sensitivity and mitochondrial targeting under physiological conditions. The emission spectra of TTHPs showed strong polarity/viscosity dependence with more than a large Stokes shift of 200 nm. Based on their unique merits, TTHPs were used to distinguish cancerous and normal cells, which could be new tools for cancer diagnosis. Moreover, TTHPs were the first to achieve biological imaging of Caenorhabditis elegans, which could be labeling probes to apply in multicellular organisms.

Perovskite quantum dots modulating upconversion nanomaterials for cancer early detections

The accurate diagnosis and treatment of cancer cell lesions need a high standard of detection technology. Fluorescent probes to perform cancer biomarker detection have become a popular research issue. However, fluorescent probes still face enormous challenges of complex design and difficult detection. In this work, we propose a novel composite material UCNP@SiO2 + QDs based on the combination of rare earth upconversion (UCNPs) and perovskite quantum dots (QDs) and design a new fluorescent probe MB-UCNP@SiO2 + QDs with molecular beacon (MB) as the carrier, that can be excited by near-infrared light, emitted in the visible wavelength, specifically identified and highly sensitive. Under the excitation of 980 nm near-infrared light, the UCNPs and QDs in the composite produced the maximum efficiency of energy transfer through fluorescence resonance, and the multi-emission light of UCNPs synergistically excited the re-emission of QDs, and the energy transfer efficiency is 70.6%. By changing the doping ratio of QDs halogen elements in UCNP@SiO2 + QDs, it is possible to modulate the precise luminescence of UCNP@SiO2 + QDs in the entire wavelength range of visible light at different positions. The novel fluorescent probe is obtained using UCNP@SiO2 + QDs and Black Hole Quencher-1 (BHQ1) quenching groups linked to the two respective sides of MB, selecting as the target of detection the myeloma cancer biomarker miRNA-155, a difficult diagnostic and complex developmental type, and have achieved specific recognition and low concentration of miRNA-155 and a detection limit of 73.5 pM. This fluorescent probe design can provide new ideas for the early diagnosis and treatment of cancer, tumors, and cardiovascular diseases.Graphical

A Systematic Design and Synthesis of PET-based Fluorescent Probes for Monitoring pH During Mitophagy.

Mitochondria are the powerhouse of the cell and function at pH ∼8.0. Dysfunctions of mitochondria, includes mitochondrial damage, leading to pH alteration. Hence, researchers aim to develop efficient pH probes for tracking mitochondrial pH dynamics. Herein, we developed a PET-based fluorescent probe for pH monitoring during mitochondrial dysfunctions. Three derivatives were synthesized with a variable spacer's length in pentacyclic pyridinium fluorophores (PM-C2, PM-C3, and PM-C6). An efficient electron transfers from the receptor (tertiary amine) was observed in the case of PM-C2 compared to the other two derivatives. This PET process was inhibited when tertiary amine was protonated in acidic pH. However, PM-C3 showed minimal fluorescence intensity at similar conditions and almost negligible change in case of PM-C6, suggesting poor PET process for both the derivatives. Furthermore, DFT/TD-DFT quantum chemical calculation well supported this optical phenomena and PET process. Biocompatible, photostable, and mitochondria-specific PM-C2 could monitor pH dynamics during mitochondrial damage which were engulfed by lysosome, also known as mitophagy. This mitophagy process were induced by rapamycin and starvation, which can be monitored by turn-on fluorescence enhancement. This process was further validated by tracking Parkin-protein translocation from cytoplasm to damaged mitochondria using our developed probe.

Rational Design of MMP-Independent Near-Infrared Fluorescent Probes for Accurately Monitoring Mitochondrial Viscosity.

Mitochondrial viscosity affects metabolite diffusion and mitochondrial metabolism and is associated with many diseases. However, the accuracy of mitochondria-targeting fluorescent probes in measuring viscosity is unsatisfactory because these probes can diffuse from mitochondria during mitophagy with a decreased mitochondrial membrane potential (MMP). To avoid this problem, by incorporating different alkyl side chains into dihydroxanthene fluorophores (denoted as DHX), we developed six near-infrared (NIR) probes for the accurate detection of mitochondrial viscosity, and the sensitivity to viscosity and the mitochondrial targeting and anchoring capability of these probes increased by increasing the alkyl chain length. Among them, DHX-V-C12 had a highly selective response to viscosity variations with minimum interference from polarity, pH, and other biologically relevant species. Furthermore, DHX-V-C12 was used to monitor the mitochondrial viscosity changes of HeLa cells treated by ionophores (nystatin, monensin) or under starvation conditions. We hope that this mitochondrial targeting and anchoring strategy based on increasing the alkyl chain length will be a general strategy for the accurate detection of mitochondrial analytes, enabling the accurate study of mitochondrial functions.

Design and Preparation of Ethylene Fluorescence Probes Based on Arylolefins and Grubbs Catalysts.

To detect the plant hormone ethylene, three arylolefins were employed to react with ethylene based on olefin metathesis. In this study, three fluorescence probes were successfully prepared using a first-generation Grubbs catalyst (G-1) and arylolefin with terminal vinyl groups. The probes were characterized using various techniques, including UV-vis, fluorescence, FT-IR, 1H NMR, 13C NMR, and 31P NMR spectroscopies and HRMS. The probes exhibited an emission maximum at 394 nm and showed excellent ethylene response. The detection limits for the probes were calculated to be 0.128, 0.074, and 0.188 μL/mL (3σ), respectively, based on fluorescence stimulation by ethylene gas. Additionally, the YGTZ-2 probe was used to detect ethylene gas during the storage process of tomatoes. This work expands the application of arylolefin in ethylene detection and provides a foundation for the development of economic, rapid, and convenient photosensitive sensors for ethylene in the future.

A new highly selective fluorescent probe design for visualizing hydrogen sulfide in food sample

We report herein a new highly selective fluorescent probe QVPB-DNP for selective evaluation of H2S in the solid states and food samples. In this probe, a quinoline-phenol vinylic conjugated skeleton as well as the expanded benzothiazole moiety (QVPB-OH) is selected as the fluorophore and a 2,4‑dinitrophenyl (DNP) ether is chosen as binding site of H2S. The probe shows significant variations in UV/visible absorption (Stokes Shift = 160 nm) and fluorescence emission enhancement at 605 nm for selective detection of H2S in DMSO/PBS system (v/v, 7:3, PBS buffer; pH 7.4). Moreover, probe QVPB-DNP-loaded test strips are successfully applied for the visual and real-time detection of gaseous H2S in practical food samples.

A portable paper-based testing device for fast and on-site determination of nitroxynil in food

Nitroxynil (NTX) is a common anthelmintic veterinary drug for the management of fascioliasis in food-producing sheep and cattle. Since excessive NTX residue in food can lead to several adverse side effects, such as allergic skin reaction and respiratory irritation, it is of great importance to develop an efficient analytical method for NTX determination. Herein, we report a simple fluorescent detection method based on a novel supramolecular probe capable of detecting NTX with a fast response (5 s), high sensitivity (107 nM), high selectivity, and acceptable anti-interference property. Moreover, the portable paper-based test strips were facilely prepared and successfully realized on-site determination of NTX in real edible animal products simply with the aid of a smartphone. To the best of our knowledge, this is the very first report on the portable detection of NTX. This study also provides a promising strategy for the fast and portable detection of analyte based on the host-guest system, which will lead to improved fluorescent probe design for food analysis.

Synthesis of novel coordination polymer Cd-MOF and fluorescence recognition of tryptophan

The coordination polymer Cd-MOF with three-dimensional network structure was successfully synthesized by conventional solvothermal method, which possesses excellent chemical and structural stability. Among the 20 amino acids, only tryptophan (Trp) showed a significant fluorescence enhancement effect on Cd-MOF, which was attributed to the large overlap between the UV absorption peak of tryptophan and the fluorescence excitation spectrum of Cd-MOF, indicating that the UV absorption of them is competitive, which enhanced the UV absorption of Cd-MOF and thus enhanced the luminescence intensity simultaneously. The Cd-MOF was further found to have a low detection limit of 1.7µM, a relatively wide linear range (0-100µM) and a stable response time for the recognition of tryptophan, as well as a good resistance to the interference of other amino acids. The method has been successfully applied to the spiked recovery determination of tryptophan in milk with the recoveries of 99.6%-101% and RSD≤1.50%. Therefore, this work demonstrated that Cd-MOF can be used as a fluorescent probe for the selective detection of tryptophan, and also may provide new opportunities for the rational design of future tryptophan fluorescent probes.