A novel ratiometric mitochondrial cysteine (Cys)-selective two-photon fluorescence probe has been developed on the basis of a merocyanine as the fluorophore and an acrylate moiety as the biothiol ...reaction site. The biocompatible and photostable acrylate-functionalized merocyanine probe shows not only a mitochondria-targeting property but also highly selective detection and monitoring of Cys over other biothiols such as homocysteine (Hcy) and glutathione (GSH) and hydrogen sulfide (H2S) in live cells. In addition, this probe exhibits ratiometric fluorescence emission characteristics (F 518/F 452), which are linearly proportional to Cys concentrations in the range of 0.5–40 μM. More importantly, the probe and its released fluorophore, merocyanine, exhibit strong two-photon excited fluorescence (TPEF) with two-photon action cross-section (Φσmax) of 65.2 GM at 740 nm and 72.6 GM at 760 nm in aqueous medium, respectively, which is highly desirable for high contrast and brightness ratiometric two-photon fluorescence imaging of the living samples. The probe has been successfully applied to ratiometrically image and detect mitochondrial Cys in live cells and intact tissues down to a depth of 150 μm by two-photon fluorescence microscopy. Thus, this ratiometric two-photon fluorescent probe is practically useful for an investigation of Cys in living biological systems.
Nucleic acids hold promise as biomolecules for future applications in biomedicine and biotechnology. Their well-defined structures and compositions afford unique chemical properties and biological ...functions. Moreover, the specificity of hydrogen-bonded Watson-Crick interactions allows the construction of nucleic acid sequences with multiple functions. In particular, the development of nucleic acid probes as essential molecular engineering tools will make a significant contribution to advancements in biosensing, bioimaging and therapy. The molecular beacon (MB), first conceptualized by Tyagi and Kramer in 1996, is an excellent example of a double-stranded nucleic acid (dsDNA) probe. Although inactive in the absence of a target, dsDNA probes can report the presence of a specific target through hybridization or a specific recognition-triggered change in conformation. MB probes are typically fluorescently labeled oligonucleotides that range from 25 to 35 nucleotides (nt) in length, and their structure can be divided into three components: stem, loop and reporter. The intrinsic merit of MBs depends on predictable design, reproducibility of synthesis, simplicity of modification, and built-in signal transduction. Using resonance energy transfer (RET) for signal transduction, MBs are further endowed with increased sensitivity, rapid response and universality, making them ideal for chemical sensing, environmental monitoring and biological imaging, in contrast to other nucleic acid probes. Furthermore, integrating MBs with targeting ligands or molecular drugs can substantially support their in vivo applications in theranositics. In this review, we survey advances in bioanalytical and biomedical applications of rationally designed MBs, as they have evolved through the collaborative efforts of many researchers. We first discuss improvements to the three components of MBs: stem, loop and reporter. The current applications of MBs in biosensing, bioimaging and therapy will then be described. In particular, we emphasize recent progress in constructing MB-based biosensors in homogeneous solution or on solid surfaces. We expect that such rationally designed and functionalized MBs will open up new and exciting avenues for biological and medical research and applications.
Intracellular pH is an important parameter associated with cellular behaviors and pathological conditions. Quantitative sensing pH and monitoring its changes by near-infrared (NIR) fluorescence ...imaging with high resolution in living systems are essential but challenging due to the lack of effective probes. To achieve good adaptability, in this study, a class of resolution-tunable ratiometric NIR fluorescent probes, which possess a stable NIR hemicyanine skeleton bearing different substituents, are rationally designed and synthesized, enabling detection through noninvasive optical imaging of organisms. Based on the protonation/deprotonation of the hydroxy group, a marked NIR emission shift provides a ratio signal in response to pH. Meanwhile, two states exhibit good photostability, sensitivity and reversibility, conducive to longtime monitoring of persistent pH changes without disturbance of other biological active species. Among the series, NIR-Ratio-BTZ modified with an electron-withdrawing substituent of benzothiazole exhibited the largest emission shift of about 76 nm from 672 to 748 nm with the pH environment changing from acidic to basic, which could be considered as a good candidate for high resolution pH imaging in live cells, tissues and organisms. Moreover, NIR-Ratio-BTZ has an ideal pK a value (pK a ≈ 7.2) for monitoring the minor fluctuations of physiological pH near neutrality. The ratiometric fluorescence measurement is beneficial to ensure the accuracy of quantitative measuring pH changes, as well as the real-time monitoring pH-related physiological effects both in living cells and living mice. The results demonstrate that NIR-Ratio-BTZ is a highly sensitive ratiometric pH probe in vivo, giving it potential for biological applications.
Acid–base disorders disrupt proper cellular functions, which are associated with diverse diseases. Development of highly sensitive pH probes being capable of detecting and monitoring the minor ...changes of pH environment in living systems is of considerable interest to diagnose disease as well as investigate biochemical processes in vivo. We report herein two novel high-resolution ratiometric two-photon (TP) fluorescent probes, namely, PSIOH and PSIBOH derived from carbazole–oxazolidine π-conjugated system for effective sensing and monitoring acid pH in a biological system. Remarkably, PSIOH exhibited the largest emission shift of ∼169 nm from 435 to 604 nm upon pH changing from basic to acidic with an ideal pK a value of 6.6 within a linear pH variation range of 6.2–7.0, which is highly desirable for high-resolution tracking and imaging the minor fluctuation of pH in live cells and tissues. PSIOH also exhibits high pH sensitivity, excellent photostability, and reversibility as well as low cytotoxicity. More importantly, this probe was successfully applied to (i) sense and visualize the pH alteration in HeLa cells caused by various types of exogenous stimulation and (ii) detect and differentiate cancer and tumors in liver tissues and a mouse model, realizing its practical in vitro and in vivo applications.
The development of nanoprobes suitable for two-photon microscopy techniques is highly desirable for mapping biological species in living systems. However, at the current stage, the nanoprobes are ...restricted to single-color fluorescence changes, making it unsuitable for quantitative detection. To circumvent this problem, we report here a rational design of a dual-emission and two-photon (TP) graphene quantum dot (GQD420) probe for imaging of hydrogen peroxide (H2O2). For specific recognition of H2O2 and lighting the fluorescence of TPGQD420, a boronate ester-functionalized merocyanine (BMC) fluorophore was used as both target-activated trigger and the dual-emission fluorescence modulator. Upon two-photon excitation at 740 nm, TPGQD420–BMC displays a green-to-blue resolved emission band in response to H2O2 with an emission shift of 110 nm, and the H2O2 can be determined from 0.2 to 40 μM with a detection limit of 0.05 μM. Moreover, the fluorescence response of the TPGQD420–BMC toward H2O2 is rapid and extremely specific. The feasibility of the proposed method is demonstrated by two-photon ratiometrically mapping the production of endogenous H2O2 in living cells as well as in deep tissues of murine mode at 0–600 μm. To the best of our knowledge, this is the first paradigm to rationally design a dual-emission and two-photon nanoprobe via fluorescence modulation of GQDs with switchable molecules, which will extend new possibility to design powerful molecular tools for in vivo bioimaging applications.
Multifunctional nanoparticles integrated with an imaging module and therapeutic drugs are promising candidates for future cancer diagnosis and therapy. Mesoporous silica coated gold nanorods ...(AuNR@MS) have emerged as a novel multifunctional cancer theranostic platform combining the large specific surface area of mesoporous silica, which guarantees a high drug payload, and the photothermal modality of AuNRs. However, premature release and side effects of exogenous stimulus still hinder the further application of AuNR@MS. To address these issues, herein, we proposed a glutathione (GSH)-responsive multifunctional AuNR@MS nanocarrier with in situ formed silver nanoparticles (AgNPs) as the capping agent. The inner AuNR core functions as a hyperthermia agent, while the outer mesoporous silica shell exhibits the potential to allow a high drug payload, thus posing itself as an effective drug carrier. With the incorporation of targeting aptamers, the constructed nanocarriers show drug release in accordance with an intracellular GSH level with maximum drug release into tumors and minimum systemic release in the blood. Meanwhile, the photothermal effect of the AuNRs upon application to near-infrared (NIR) light led to a rapid rise in the local temperature, resulting in an enhanced cell cytotoxicity. Such a versatile theranostic system as AuNR@MS@AgNPs is expected to have a wide biomedical application and may be particularly useful for cancer therapy.
With the increasing promotion of new energy vehicles and the rapid popularization of digital electronic products, there is a growing demand for lithium-ion and lithium-sulfur batteries. These ...batteries have gained widespread attention due to their excellent electrochemical performance. However, with the continued demand for high-power applications in new energy vehicles and digital electronics, the safety and stability of the batteries have become critical. TiO
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is commonly utilized in battery separators owing to its capacity to enhance the thermal stability, mechanical properties, and electrochemical stability. It can inhibit the “shuttle effect” of polysulphides in lithium-sulfur batteries through physical and chemical methods to improve the cycling performance of lithium-sulfur batteries. This review will outline three methods for modifying TiO
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separators: blending (utilizing electrostatic spinning and phase conversion), coating (involving the coating method, immersion fabrication method, and vacuum filtration method), and grafting. Finally, the prospective evolution of battery separators and the concomitant challenges they confront will be contemplated.
Fluorescence anisotropy (FA) is a reliable, sensitive, and robust assay approach for determination of many biological targets. However, it is generally not applicable for the assay of small molecules ...because their molecular masses are relatively too small to produce observable FA value changes. To address this issue, we report herein the development of a FA signal amplification strategy by employing graphene oxide (GO) as the signal amplifier. Because of the extraordinarily larger volume of GO, the fluorophore exhibits very high polarization when bound to GO. Conversely, low polarization is observed when the fluorophore is dissociated from the GO. As proof-of-principle, the approach was applied to FA detection of adenosine triphosphate (ATP) with a fluorescent aptamer. The aptamer exhibits very high polarization when bound to GO, while the FA is greatly reduced when the aptamer complexes with ATP, which exhibits a maximum signal change of 0.316 and a low detection limit of 100 nM ATP in buffer solution. Successful application of this strategy has been demonstrated that it can be constructed either in a “signal-off” or in a “signal-on” detection scheme. Moreover, because FA is less affected by environmental interferences, FA measurements could be conveniently used to directly detect as low as 1.0 μM adenosine triphosphate (ATP) in human serum. The universality of the approach could be achieved to detect an array of biological analytes when complemented with the use of functional DNA structures.
Biochar adsorbents used to treat different heavy metals in water are efficient and low-cost. Appropriate raw materials, excellent selectivity and detailed adsorption mechanism are of important for ...research on biochar adsorbents. In this work, konjac starch was dispersed in polyvinylpyrrolidone (PVP) solution to prepare different sizes hydrophilic carbon spheres (HCSs) by hydrothermal synthesis method. Adsorption kinetics of the HCSs towards Pb2+ is described perfectly by the pseudo-second-order equation. With the temperature increasing, adsorption thermodynamics are more consistent with the Freundlich model. The calculated ΔG, ΔH and ΔS shows the adsorption of the HCSs towards Pb2+ is a spontaneous, endothermic and entropy increase process. In addition, HCSs have excellent selectivity for the adsorption of Pb2+ and Cu2+. HCSs prepared from konjac starch make full use of natural biomass resources, they can be used as a potential adsorbent material in treatment on heavy metal ion from water field.
Based on their enhanced cellular uptake, stability, biocompatibility, and versatile surface functionalization, spherical nucleic acids (SNAs) have become a potentially useful platform in biological ...applications. It still remains important to expand the SNAs’ “toolbox”, especially given the current interest in multimodal or theranostic nanomaterials, that is, composites capable of multiple simultaneous applications such as imaging, sensing, and drug delivery. In this paper, we have engineered a nanoparticle-conjugated initiator that triggers a cascade of hybridization reactions resulting in the formation of a long DNA polymer as the nanoparticle shell. By employing different DNA fragments, self-assembled multifunctional SNAs can be constructed. Therefore, using one capped ligand, these SNAs can combine imaging fluorescent tags, target recognition element, and targeted delivery molecules together. Since these SNAs possess high drug loading capacity and high specificity by the incorporation of an aptamer, our approach might find potential applications in new drug development, existing drug improvement, and drug delivery for cancer therapy.
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