Emission In Aqueous Solution Research Articles

Ethanol and Gd3+ activated aggregation induced delayed fluorescence in copper nanoclusters for detection of Cr(VI)

In recent years, significant emphasis has been dedicated towards investigating aggregation-induced emission (AIE) phenomena, and a notable addition to this emerging field is aggregation-induced delayed fluorescence (AIDF). Here, we proposed two different strategies to produce AIDF-based luminescent materials at room temperature from glutathione-capped CuNCs (GSH-CuNCs) by (1) simply modifying the solvent environment and (2) introducing gadolinium (Gd3+) ions. The synthesized GSH-CuNCs displayed weak fluorescence (Fl) emission in aqueous solution with a short delayed lifetime of 3.2 μs and quantum yield (QY) of only 1.42 %. However, introducing GSH-CuNCs to an ethanol medium promptly led to enhanced delayed Fl emission with a significantly delayed lifetime of 21.8 μs and a high QY of 89.2 %. Moreover, introducing Gd3+ ions to the aqueous GSH-CuNC solution also enhances delayed Fl emission with a delayed lifetime of 13.6 μs and a high QY of 79.5 %. Analysis of transmission electron microscopy and dynamic light scattering data showed that both the ethanol medium and Gd3+ addition endows controlled aggregation of GSH-CuNCs, enabling successful harvesting of triplet states and ultimately leading to the AIDF phenomenon. Moreover, the AIDF harnessed from GSH-CuNCs by Gd3+ was successfully employed to detect Cr6+ ions in an aqueous solution with excellent selectivity.

A NIR fluorescent probe with large stokes shift for sensitive detection and imaging of G4s in live cells

G4s play a very important role not only in human biological systems but are associated with tumor formation, which is considered as a novel target for the exploitation of anti-tumor drugs. Therefore, it is essential to develop near-infrared (NIR) fluorescent probes to study G4s. In this article, we designed a large stokes shift probe (AOC) which can be activated NIR fluorescent by G4s in living cells and tumor tissue. In vitro experiments shown that AOC exhibited no fluorescence emission in aqueous solution, while significantly enhanced at 768 nm in the presence of the G4s. The optimal excitation wavelength of the probe is about 640 nm, indicating that the probe AOC has a large stokes shift (128 nm). Meanwhile, AOC is dynamically responsive to the concentrations of DNA G4s (22AG, Mito-160) and exhibits high selectivity toward DNA G4s with desirable stability in the physiological pH conditions. Imaging studies of different cell lines have shown that cancer cell lines fluoresced brightly than normal cell lines, implication that the expression of G4s may be higher in tumor cell lines. We further performed fluorescence imaging of tumor tissues using AOC, which showed that tumor tissues had the brightest fluorescence intensity relative to normal organ tissues. These experimental results further suggest that the NIR fluorescent probe may have tumor diagnostic properties with great potential for application.

Room temperature, long afterglow, water-soluble materials with multicolor tunability

Developing solution-processable room-temperature long afterglow (RTLA) materials with multi-color tunable emissions based on an inorganic matrix is of considerable practical importance in diverse applications but rarely reported. Herein, a series of water-soluble multicolor afterglow materials (t@LP@Rh123, t@LP@Rh6G, t@LP@RhB, respectively) with afterglow emission colors of green, orange-yellow and red were achieved through triplet-to-singlet Förster-resonance energy transfer (T1-S1 FRET), where the cyan afterglow material t@LP obtained by solventless mechanical grinding method of 4-[2,2':6′,2″-Terpyridin]-4′-ylbenzoic acid and Laponite (LP) was used as an energy donor, and fluorescent dyes Rhodamine 123, Rhodamine 6G and Rhodamine B were used as energy acceptors. Notably, the obtained series of multicolor afterglow materials still exhibit obvious afterglow emission in aqueous solution, which make them potentially useful in the fields of anti-counterfeiting and multilevel information encryption.

Rhodium-Catalyzed Two-Fold, Regioselective and Enantioselective C-H Activation: an Efficient Strategy to Chiral Single-Benzene-Based Fluorophores.

A Rh-catalyzed two-fold, regioselective and enantioselective C-H activation via chiral transient directing group strategy has been demonstrated in moderate to good yields with commendable enantioselectivities. The newly synthesized chiral fluorophores exhibit favorable photophysical properties, including large Stokes shifts, good fluorescence quantum yields, aggregation-induced emission in aqueous solution, and intense emission and circularly polarized luminescence in the solid state, indicating great potential applications as chiral fluorescent probes or optoelectronic materials.

Aqueous Solution Enhanced Room Temperature Phosphorescence through Coordination-Induced Structural Rigidity.

Achieving aqueous solution enhanced room temperature phosphorescence (RTP) is critical for the applications of RTP materials in solution phase, but which faces a great challenge. Herein, for the first time, a strategy of coordination-induced structural rigidity is proposed to achieve enhanced quantum efficiency of aluminum/scandium-doped phosphorescent microcubes (Al/Sc-PMCs) in aqueous solution. The Al/Sc-PMCs in a dry state exhibit a nearly invisible blue RTP. However, they emit a strong RTP emission in aqueous solution with a RTP intensity increase of up to 22.16-times, which is opposite to common solution-quenched RTP. The RTP enhancement mechanism is attributed to the abundant metal sites (Al3+ and Sc3+ ions) on the Al/Sc-PMCs surface that can tightly combine with water molecules through the strong coordination. Subsequently, these coordinated water molecules as the bridging agent can bind with surface groups by hydrogen bonding interaction, thereby rigidifying chemical groups and inhibiting their motions, resulting in the transition from the nonradiative decay to the radiative decay, which greatly enhances the RTP efficiency of the Al/Sc-PMCs. This work not only develops a coordination rigidity strategy to enhance RTP intensity in aqueous solution, but also constructs a phosphorescent probe to achieve reliable and accurate determination of analyte in complex biological matrices.

Red Room-Temperature Phosphorescence Supramolecular Assemblies Based on Cucurbit[7]uril: Reversible Temperature Stimulation Response and Cell-Specific Silver Ion Imaging.

Solid-state materials with efficient room-temperature phosphorescence (RTP) emission have been widely used in materials science, and organic RTP-emitting systems with heavy-metal doping in aqueous solutions have attracted much attention in recent years. A novel supramolecular interaction was induced by host-guest assembly using cucurbit[7]uril (Q[7]) as the host and brominated naphthalimide phosphor as the guest. This interaction was further enhanced through synergistic chelation stimulated by analytical silver ion complexation. This approach facilitated the system's structural rigidity, intersystem crossing, and oxygen shielding. We achieved deep red phosphorescence emission in aqueous solution and ambient conditions along with quantitative determination of silver ions. The new complex exhibited good reversible thermoresponsive behavior and was successfully applied for the first time to target phosphorescence imaging of silver ions in the mitochondria of A549 cancer cells. These results are beneficial for constructing novel RTP systems with stimulus-responsive luminescence in aqueous solution, contributing to future research in bioimaging, detection, optical sensors, and thermometry materials.

A novel reversible fluorescent probe for sequential detection of Al3+ and HPO42− based on caffeic acid and its applicability in cell imaging

In this work, we focused on synthesizing a new fluorescent probe HBA based on caffeic acid for detecting Al3+/HPO42− by the mode of “off-on-off”. HBA alone exhibited a weak fluorescence emission in aqueous solution. When Al3+ was added into the HBA solution, a significant green fluorescence was found at 498 nm. However, the introduction of HPO42− to the solution of [HBA-Al3+] complex induced the disappearance of green fluorescence. The detection limit of HBA was calculated as low as 41.7 nM for Al3+ and 62.1 nM for HPO42−, respectively. Probe HBA exhibited good cell-membrane penetrability and had the potential to trace Al3+/HPO42− in biological systems.

Superior white electroluminescent devices using nitrogen-doped carbon dots/TiO2 nanorods heterostructures

Nitrogen-doped carbon dots (NCDs), exhibiting strong yellow emission in aqueous solution and solid matrices, have been utilized for fabricating heterostructure white electroluminescence devices. These devices consist of nitrogen-doped carbon dots as an emissive layer sandwiched between an organic hole transport layer (PEDOT:PSS) and an array of rutile TiO2 nanorods, acting as an electron transport layer. Under an applied forward bias of 5 V, the device exhibits broadband electroluminescence covering the wavelength range of 390–900 nm, resulting in pure white light emission characteristics at room temperature. The result demonstrates the successful fabrication of all solution-processed, low-cost, eco-friendly NCDs-based LEDs with CIE (Commission Internationale d’Éclairage) coordinate of (0.31, 0.34) and color rendering index (CRI) > 90, which are close to ideal white light emission characteristics. The device functionalities are achieved based on defect-related NIR emission from TiO2 nanorods array and visible emission from nitrogen-doped carbon dots. This result paves a new opportunity to develop low-cost, solution-processed nitrogen-doped carbon dots based on warm White light emitting diodes with high CRI for large-area display and lighting applications.

Boosting Solid-State Luminescence of Thiazolothiazole Viologen by Incorporating Metal Halide Clusters to Hinder π-Stacking.

A new strategy is developed herein to improve the solid fluorescence of thiazolothiazole viologen by using the ZnCl42- cluster as a scaffold to hinder π-stacking. Importantly, the Cl···H bonds are formed in the solid state to sustain the framework and can be automatically dissociated when dissolved in H2O, thus having no impact on the strong emission in aqueous solution. As such, the first case of organic-inorganic viologen-zinc halide named 4PV·ZnCl4 was designed and synthesized, and a significant increase in photoluminescence quantum yield (ΦF) is realized from 4PV·2Br (ΦF = 0%) to 4PV·ZnCl4 (ΦF = 27.0%) in solid and from 97% to 98% in H2O. 4PV·ZnCl4 also displays pH stimuli-responsive naked-eye chromic behavior and photoluminescence with different coloring states and intensities. The multifunctional performance of 4PV·ZnCl4 provides a prerequisite for carrying different information, expanding their promising application in multilevel information encryption.

Detection of acid protease using the fluorescent probe 3,3′-dipentylthiacarbocyanine iodide-BSA

In this work, an ‘on-off’ fluorescent probe was developed for detection of acid protease (ACP) based on bovine serum albumin (BSA) as the substrate. 3,3′-Dipentylthiacarbocyanine iodide, DiSC5(3), exhibits very weak fluorescence emission in aqueous solution, but following the addition of BSA, due to hydrophobic interactions between them, DiSC5(3) forms an aggregate with BSA and emits strong red fluorescence. When ACP is added, the fluorescence emission of the DiSC5(3)-BSA system is quenched because BSA is hydrolysed into peptide fragments and amino acids by ACP, destroying the DiSC5(3)-BSA system. The degree of fluorescence quenching of the DiSC5(3)-BSA system is proportional to the concentration of ACP over a range of 10–40 μg/mL, with a linear equation y = −4.8270x + 509.7066, a correlation coefficient R2 = 0.9986, and a detection limit of 1.44 μg/mL. The method has advantages including simple operation, high sensitivity and good selectivity, and can be used for detection of ACP in real samples.

Investigation of the Superoxide Anion-Triggered Chemiluminescence of Coelenterazine Analogs

Reactive oxygen species (ROS), including superoxide anion, are involved in regulating various signaling pathways and are also responsible for oxidative stress. Sensing superoxide anion is of particular importance due to its biological significance. One potential approach is to use Coelenterazine as a chemiluminescent probe for the dynamic sensing of this ROS. In this study, we investigated the superoxide anion-triggered chemiluminescence of native Coelenterazine and two halogenated analogs and found that they showed a ~100-fold enhancement of light emission in aqueous solution, which was significantly reduced in methanol and nonexistent in aprotic solvents. In fact, Coelenterazine showed more intense light emission in aprotic solvents and, interestingly, although the light emission of the analogs seemed relatively unaffected by the solvents, their chemiluminescence was significantly quenched in water compared to methanol and, especially, to aprotic media. This suggests that the quenching effect observed for Coelenterazine is responsible for the differences in aqueous media, rather than an intrinsic enhanced emission by the analogs. In summary, we present Coelenterazine analogs that could serve as a basis for enhanced sensing of superoxide anion, providing information that could further our understanding of this chemiluminescent system.

Evaluation of the anticancer activity and chemiluminescence of a halogenated coelenterazine analog

Chemiluminescence is a remarkable process in which light is emitted due to a chemical reaction, without the need for photoexcitation. Among some of the most well-known chemiluminescent systems is that of marine Coelenterazine. Herein, we report the synthesis of a novel halogenated Coelenterazine analog, as well as the characterization of its potential anticancer activity and chemiluminescence. We have found that this analog is capable of significantly enhanced emission in aqueous solution when triggered by superoxide anion while being compatible with human cell lines. So, this compound presents great potential for the sensitive and dynamic sensing of a molecule of interest in biological media. Furthermore, the analysis of its cytotoxicity provided structural insight into the properties of brominated Coelenterazines, which were previously found to possess selective anticancer activity. Namely, the introduction of bromine heteroatoms is not enough to provide cytotoxicity, while the introduction of electro-withdrawing groups eliminates all previously reported anticancer activity. Finally, while this compound is not active, its use in a combination approach allowed to improve the profile of a known chemotherapeutic agent. These results should be useful to guide future optimizations of halogenated Coelenterazine analogs.

Polyetherimide functionalized carbon dots with enhanced red emission in aqueous solution for bioimaging

Red emissive carbon dots (CDs) are highly desired for biological applications. However, serious luminescence quenching of red emissive CDs in aqueous solution greatly hinders their application in high performance biological imaging. Herein, we reported a facile strategy to realize enhanced red emission of CDs in aqueous solution by surface modification with polyetherimide (PEI) via microwave heating method. High photoluminescence quantum yield (PLQY) of 25% was realized from the PEI functionalized CDs (CDs@PEI) in aqueous solution. The proposed PEI functionalization strategy not only protects the red emission against water molecules quenching, but also reverses the surface charges from negativity to positivity to promote cellular uptake of CDs, leading to clear cell imaging in red fluorescence region. More important, CDs@PEI exhibits much better photostability than commercial red emissive dye (MitoTracker red) in cell fluorescent imaging. Potential application of CDs@PEI on fast staining of cells for clonogenic assay has also been demonstrated.

Water-soluble naphthalimide derivatives probe with near-infrared fluorescence “turn-on” characteristics for the detection of bovine serum albumin

A novel near-infrared fluorescence dye NAPTAM as a water-soluble biological probe was developed. The results showed that the probe has a highly sensitive "turn-on" response to BSA in deionized water, and the emission range of near-infrared spectroscopy is 500–800 nm. A limit of detection of NAPTAM sensing BSA was 0.027 μM. The free NAPTAM has almost no emission in aqueous solution, but the sharp increase of near-infrared emission is observed due to the aggregation state and self-assembly formed by the electrostatic interaction between the positive charged ammonium group of NAPTAM and the negative charged BSA. The zeta potential values displayed that -2.69 mV of BSA was up to -5 mV of NAPTAM/BSA assembly. The relatively experiments of other chemical species to the probe testified that NAPTAM has good selectivity for BSA.

A Novel Fluorescent Probe for ATP Detection Based on Synergetic Effect of Aggregation-induced Emission and Counterion Displacement

In this work, a fluorescent probe(TPEBe-I) was developed for adenosine triphosphate(ATP) detection based on the synergetic effect of aggregation-induced emission and counterion displacement. TPEBe-I gave weak emission in aqueous solution due to the heavy-atom effect of counter iodide ion. However, upon the addition of ATP, the new aggregate complex(TPEBe-ATP) was formed between the cationic unit of TPEBe-I and ATP through electrostatic interactions, which not only restricted the intramolecular motion of luminogen but also eliminated the quenching effect of iodide ion. As a result, the fluorescent light-up detection for ATP was successfully achieved. Moreover, TPEBe-I exhibited high selectivity towards ATP and showed a wide linear detection region towards the logarithm of ATP concentration(5—600 µmol/L) with a detection limit of 1.0 µmol/L, enabling TPEBe-I as a promising probe for ATP quantitative analysis.

Turn-on fluorescent probe for lipid droplet specific imaging of fatty liver and atherosclerosis.

Fluorescence imaging plays an important role in researching the biological function of lipid droplets (LDs). However, the short-wave emission, tedious synthesis process and insufficient specificity have significantly limited the applications of commercially available probes. Herein, we have prepared a novel one-step synthesized near-infrared (NIR) fluorescent probe, TNBD, with a very low emission in aqueous solution and the solid state, but a significantly enhanced fluorescence emission is exhibited in oleic acid. Moreover, TNBD exhibited an impressive lipid droplet (LD) specific fluorescence turn-on ability in cells, fatty liver and atherosclerosis (AS) samples with a good biocompatibility and high signal-to-noise ratio. Our study not only establishes a novel LD turn-on fluorescence probe, but also provides a novel way to prepare a NIR LD targeted fluorescence probe.

Multi-responsive fluorescent probe based on AIE for the determination of Fe3+, total inorganic iron, and CN- in aqueous medium and its application in logic gates

A novel and simple probe (denoted LN-1) with AIE property based on malononitrile and 4-diethylaminobenzaldehyde was designed and synthesized. The use of two different mechanisms for the independent detection of Fe3+ and CN− is more convenient and efficient than the continuous detection of anions and cations. The detection mechanism was verified by mass spectrometry (MS), nuclear magnetic resonance (NMR) spectrum, and particle size distribution. Under optimized experimental conditions, excellent calibration curves were obtained for the LN-1-Fe3+ and the LN-1-CN− with detection limits of 0.17 and 0.39 μM, respectively. This method was successfully applied to detect the content of Fe3+ and total inorganic iron in actual samples. Owing to its low cytotoxicity, good biocompatibility, and enhanced orange emission in aqueous solution, the LN-1 was successfully applied for CN− imaging in live cells. In addition, Fe3+ and EDTA incorporation into the LN-1 changed the fluorescent intensity, which is beneficial in constructing ultrasensitive INHIBIT logic gate.

3D confined self-assembling of QD within super-engineering block copolymers as biocompatible superparticles enabling stimulus responsive solid state fluorescence

Eliminating colloidal toxicity and enabling its intrinsic fluorescence in aggressive environmental conditions are the key challenges for commercializing hydrophobic cadmium based quantum dots (QD). Polyarylene ether nitriles (PEN) are an example of super-engineering thermoplastics that possess a unique combination of thermal stability, intrinsic fluorescence, biocompatibility and distinct emulsion self-assembly feature. Herein, the co-self-assembly of amphiphilic PEN with hydrophobic CdSe@ZnS QD, confined in the three dimensional (3D) oil-in-water emulsion droplets, has been explored to fabricate fluorescent microparticles (FMP). It was found that these FMP demonstrated good biocompatibility (cell viability above 90%), while exhibiting a fluorescence emission in aqueous solution that was retained (intensity retention ratio above 80%) within the whole pH range of 1–14, as well as, after being subjected to autoclaving at 120 °C for 1 h. Interestingly, it was discovered that introduction of calcium ions in the emulsion self-assembly contributed to in-situ generation of phase changing nanoplates inside the FMP, which led to the photo-thermal modulated solid state fluorescence from drop-casted FMP film. Thanks to their versatile fluorescence, these FMP colloids were exploited as fluorescent probes for macrophages imaging, while micro-patterns with reversible changing of emission color were induced via thermal treatment and direct laser lithography.

Fluorescent Properties of Morin in Aqueous Solution: A Conversion from Aggregation Causing Quenching (ACQ) to Aggregation Induced Emission Enhancement (AIEE) by Polyethyleneimine Assembly.

Unlike normal conversion from aggregation caused quenching (ACQ) to aggregation induced emission enhancement (AIEE) by introducing aromatic rotors tuning aggregation modes, in this study, it is achieved through a supramolecular assembly with polymer. Thus, it provides an easy approach for the inhibition of unwanted H-aggregation between luminogens. As a kind of flavonoid, morin has shown great potential in therapeutics. However, its poor solubility and weak emission in aqueous solution greatly limit its bioapplications. When morin is dissolved in aqueous solution, the presence of 30× 10-6 m polyethyleneimine (PEI) induces significant emission enhancement and bathochromic shift. Consequently, the quantum yield (QY) of 24.5% is either achieved by assembling with PEI, versus 0.76% of its ACQ state composed of H-aggregation in aqueous solution. Particularly, the in-depth mechanism studies reveal that it is the assembly with PEI that disassociates the H-aggregation in aqueous solution and further restricts the stretching and/or rotation of morin, which eventually reduce the nonradiative decays and enhance the emission. Therefore, the present study reports a unique phenomenon of AIEE effects on morin. Particularly the in-depth investigation on intrinsic mechanisms will highlight and greatly expand the development of more luminogens from traditional Chinese herbals.

Triazole-based osmium(ii) complexes displaying red/near-IR luminescence: antimicrobial activity and super-resolution imaging.

Cellular uptake, luminescence imaging and antimicrobial activity against clinically relevant methicillin-resistant S. aureus (MRSA) bacteria are reported. The osmium(ii) complexes [Os(N^N)3]2+ (N^N = 1-benzyl-4-(pyrid-2-yl)-1,2,3-triazole (12+); 1-benzyl-4-(pyrimidin-2-yl)-1,2,3-triazole (22+); 1-benzyl-4-(pyrazin-2-yl)-1,2,3-triazole (32+)) were prepared and isolated as the chloride salts of their meridional and facial isomers. The complexes display prominent spin-forbidden ground state to triplet metal-to-ligand charge transfer (3MLCT) state absorption bands enabling excitation as low as 600 nm for fac/mer-32+ and observation of emission in aqueous solution in the deep-red/near-IR regions of the spectrum. Cellular uptake studies within MRSA cells show antimicrobial activity for 12+ and 22+ with greater toxicity for the meridional isomers in each case and mer-12+ showing the greatest potency (32 μg mL−1 in defined minimal media). Super-resolution imaging experiments demonstrate binding of mer- and fac-12+ to bacterial DNA with high Pearson's colocalisation coefficients (up to 0.95 using DAPI). Phototoxicity studies showed the complexes exhibited a higher antimicrobial activity upon irradiation with light.