Programmable DNA Templates for Silver Nanoclusters Synthesis To Develop On-Demand FRET Aptasensor.

DNA-templated silver nanoclusters (AgNCs-DNA) can be synthesized via a one-pot method bypassing the tedious process of biomolecular labeling. Appending an aptamer to DNA templates results in dual-functionalized DNA strands that can be utilized for synthesizing aptamer-modified AgNCs, thereby enabling the development of label-free fluorescence aptasensors. However, a major challenge lies in the necessity to redesign the dual-functionalized DNA strand for each specific target, thus increasing the complexity and hindering widespread application of these aptasensors. To overcome this challenge, we designed six DNA strands (DNA1-DNA6) that incorporate the templates for AgNCs synthesis and A4-linker for further aptamer coupling. Among all the synthesized AgNCs-DNA samples, it was found that both AgNCs-DNA1 and AgNCs-DNA2 stood out for their excellent long-term stability. After capturing the T4-linker that connected with aptamer1 specific for aflatoxin B1 (AFB1), however, we found that only AgNCs-DNA1/aptamer1 maintained excellent long-term stability. This finding highlighted the potential of AgNCs-DNA1 as a versatile label-free fluorescence probe for the development of on-demand fluorescence aptasensors. To emphasize its benefits in aptasensing applications, we utilized AgNCs-DNA1/aptamer1 as the fluorescence probe and MoS2 nanosheets as the quencher to develop a FRET aptasensor for AFB1 detection. This aptasensor demonstrated remarkable sensitivity, enabling the detection of AFB1 within a wide concentration range of 0.03-120 ng/mL, with a limit of detection as low as 3.6 pg/mL (S/N = 3). The versatility of the aptasensor has been validated through the recognition of diverse targets, employing aptamer2 specific for ochratoxin A and aptamer3 specific for zearalenone, thereby showcasing its extensive applicability for on-demand detection. The universal applicability of this aptasensor holds great promise for future applications in diverse fields including food safety, environmental monitoring, and clinical diagnosis.

On-Site Quantitative Visualization of Singlet Oxygen in Crops via an Organic Small Molecule-Based Ratiometric Fluorescent Probe and a Mobile Fluorescence Analysis Device.

Singlet oxygen (1O2) plays imperative roles in a variety of biotic or abiotic stresses in crops. The change of its concentration within a crop is closely related to the crop growth and development. Accordingly, there is an urgent need to develop an efficient analytical method for on-site quantitative detection of 1O2 in crops. Here, we judiciously constructed a novel ratiometric fluorescent probe, SX-2, for the detection of 1O2 in crops. Upon treating with 1O2, probe SX-2 displayed highly selective ratiometric fluorescence response, which is favorable for the quantitative detection of 1O2. Concurrently, the fluorescence solution color of probe SX-2 was varied, obviously from blue to yellow, indicating that the probe is beneficial for on-site detection by the naked eye. Sensing reaction mechanism studies showed that the 2,3-diphenyl imidazole group in SX-2 could function as a new selective recognition group for 1O2. Probe SX-2 was utilized for the detection of photoirradiation-induced 1O2 and endogenous 1O2 in living cells. The changes in the 1O2 level in zebrafish were also tracked by fluorescence imaging. In addition, the production of 1O2 in crop leaves under a light source of different wavelengths was studied. The results demonstrated more 1O2 were produced under a light source of 365 nm. Furthermore, to achieve on-site quantitative detection, a mobile fluorescence analysis device has been made. Probe SX-2 and mobile fluorescence analysis device were capable of on-site quantitative detecting of 1O2 in crops. The method developed herein will be convenient for the on-site quantitative measurement of 1O2 in distinct crops.

Visualizing the Interplay of Lipid Droplets and Protein Aggregates During Aging via a Dual-Functional Fluorescent Probe.

Fluorescence imaging the interplay between lipid droplets (LDs) and protein aggregates (PAs) is extremely valuable for elucidating molecular mechanisms of aging. Here, we describe the first dual-functional fluorescent probe, LW-1, for simultaneously imaging LDs and PAs in distinct fluorescence channels to dissect interplaying roles between LDs and PAs during aging. Notably, based on an intriguing mechanism of hydrogen bonds regulating single bond rotation, LW-1 selectively detected LDs in a red channel. Meanwhile, based on another mechanism of the hydrogen bond regulating intramolecular charge transfer efficiency, probe LW-1 further detected PAs in an NIR channel. Practical applications showed that LW-1 was capable of concurrently detecting LDs and PAs in living cells. Moreover, simultaneously imaging LDs and PAs in intestine tissues of mice at different aging degrees was conducted. The results denoted that the PAs level in the intestine tissue increased dramatically with aging, accompanying the buildup of LDs. Significantly, the interplay between LDs and PAs during aging was observed. These evidences demonstrated that the PAs level was closely related with aging processes in intestine tissues, while LDs were formed correspondingly to interact with PAs, suggesting that excessive PAs can be loaded into LDs and then be removed by lipophagy.

Controlling the ligands of CdZnTe quantum dots to design a super simple ratiometric fluorescence nanosensor for silver ion detection.

A super simple ratiometric fluorescence nanosensor has been fabricated by controlling the ligands of CdZnTe quantum dots (QDs), allowing the sensitive and visual detection of silver ions (Ag+). The green-emitting L-cysteine-protected CdZnTe QDs (Lcys-CdZnTe QDs) had a specific response to Ag+ and were used as the reporting probe, while the red-emitting N-acetyl-L-cysteine-protected CdZnTe QDs (NAC-CdZnTe QDs) showed no obvious response to all tested metal ions and were selected as the reference probe. Simply mixing them without any encapsulated synthesis ultimately produced a time-saving, low-cost detection method, allowing the sensitive and visual detection of Ag+ in samples. The proposed nanosensor exhibited a linear range of 0.5-4.0 µM along with a detection limit of 0.17 µM, and has been successfully applied in real tap water and lake water samples. This nanosensor also showed obvious color changes in the detection process and has potential in visual semi-quantitative detection. Our approach may provide a general and feasible strategy for designing ratiometric fluorescence nanosensors, which will attract a wide range of interest in sensing-related fields.

Simultaneous Discrimination of Hypochlorite and Single Oxygen during Sepsis by a Dual-Functional Fluorescent Probe.

Hypochlorite (ClO-) and singlet oxygen (1O2) commonly coexist in living systems and exert important interplaying roles in many diseases. To dissect their complex inter-relationship, it is urgently required to construct a fluorescent probe that can discriminate ClO- and 1O2 in living organisms. Herein, by taking the 3-(aliphaticthio)-propan-1-one group as the unique recognition unit for both ClO- and 1O2, we proposed the first fluorescent probe, Hy-2, to simultaneously discriminate ClO- and 1O2 with high sensitivity and selectivity. Probe Hy-2 itself showed fluorescence in blue channel. After treatment with ClO- and 1O2, respectively, pronounced fluorescence enhancements were observed in the green channel and red channel correspondingly. Moreover, upon development of the probe with aggregation-induced emission (AIE) characteristics, the probe could work well in a solution with high water volume fraction. Probe Hy-2 was also able to accumulate into mitochondria and was utilized as an effective tool to image exogenous and endogenous ClO- and 1O2 in mitochondria. Significantly, as the first trial, probe Hy-2 was employed to simultaneously monitor the variation of ClO- and 1O2 level in cecal tissues of rat in the cecal ligation and puncture (CLP)-induced polymicrobial sepsis model. The results demonstrated that the expressed ClO- and 1O2 levels were tightly correlated with the severity of sepsis, inferring that the overproduction of ClO- and 1O2 is an important factor in the pathogenesis of sepsis. The probe illustrated herein may provide a guide for further exploring the functions of ClO- and 1O2 in various diseases.

Soft Materials Constructed Using Calix[4]pyrrole- and "Texas-Sized" Box-Based Anion Receptors.

Soft materials have received considerable attention from supramolecular chemists and material scientists alike. This interest reflects the advantages provided by their soft, flexible nature and the convenience of the molecular self-assembly that underlies their preparation. Common soft supramolecular materials include polymeric gels, supramolecular polymers, nanoaggregates, and membranes. Polymeric gels are solidlike networks of cross-linked polymer chains. Supramolecular polymers contain repeat units connected through reversible non-covalent bonds. Nanoaggregates are formed as a result of hydrophobic interactions involving amphiphilic building blocks. Because of the presence of non-covalent interactions, supramolecular soft materials typically display stimuli-responsive or adaptive features. Various macrocyclic hosts, such as cyclodextrins, crown ethers, calixarenes, cucurbiturils, and pillararenes, and many classic non-covalent interactions have been harnessed to construct supramolecular soft materials. Only recently has anion binding been used as the underlying recognition motif. Anions are ubiquitous in the natural world. Their importance has inspired efforts to achieve good anion binding and to exploit anion recognition in a number of fields, including extraction, transport, sensing, and catalysis. Most of this effort has involved the use of stand-alone anion receptors. On the other hand, soft materials with anion recognition features could lead to new macromolecular systems of interest in the context of many application areas. In this Account, we summarize the latest efforts from our laboratory to prepare supramolecular soft materials, including polymeric gels, supramolecular polymers, and nanoaggregates, with bona fide anion recognition features. Two anion receptor systems, namely, calix[4]pyrroles (C4Ps) and a tetraimidazolium macrocycle known as the "Texas-sized" molecular box (TxSB), have been used for this purpose. To date, TxSB-based hydrogels have been utilized to capture anions from water and for coded information applications; C4P-based organic polymeric gels have been used to extract dianions from aqueous source phases and for the on-site detection of chloride anions. Polymers containing C4P and TxSB anion recognition subunits typically display responsive features and can be modified through application of appropriately chosen external stimuli. For instance, nanoaggregates may be formed as a result of the hydrophobic interactions of C4P- and TxSB-based amphiphiles. The resulting aggregates were found to mimic the structural evolution of organelles and could be used as effective anion and ion pair extractants. This Account summarizes progress to date while underscoring potential opportunities associated with combining anion recognition and soft materials chemistry. The hope is to stimulate further advances in broad areas, including polymer science, supramolecular chemistry, biology, materials research, and information storage.

A novel fluorescent probe with extremely low background fluorescence for sensing hypochlorite in zebrafish.

Development of an efficient fluorescent probe for sensing hypochlorite in water samples and biological samples is highly demanded. However, the currently reported fluorescent probes for hypochlorite frequently suffered from the problem of high background fluorescence. Herein, based on the combined effect of two different fluorescence quenching groups, we rationally developed a novel fluorescent probe for hypochlorite with extremely low background fluorescence. Notably, due to the doubly quenching groups, the probe could even keep low background fluorescence in a solution with high viscosity. Furthermore, the probe displayed highly sensitive and selective response to hypochlorite, with the detection limits calculated to be 10.5 nM. Practical application demonstrated that the probe was able to quantitatively detect hypochlorite in various water samples with good recovery. Significantly, the probe showed extremely low background fluorescence in living cells and was capable of detecting minor variation of endogenous hypochlorite in RAW 264.7 cells. Moreover, the fluorescence imaging different concentration of hypochlorite in zebrafish has been successfully conducted. The probe developed herein will be widely used as a reliable tool to accurately monitor the variation of hypochlorite in living organism.

Adhesive supramolecular polymeric materials constructed from macrocycle-based host-guest interactions.

Nature uses the power of non-covalent interactions as the basis for many kinds of adhesion phenomena. Inspired by nature, scientists have prepared various synthetic adhesive materials that rely on a number of non-covalent interactions at the interfaces. Commonly used non-covalent interactions include hydrogen bonding, π-π stacking, charge transfer interactions, electrostatic interactions, hydrophobic interactions, macrocycle-based host-guest interactions, among others. Within this context, macrocycle-based host-guest interactions are of particular interest. Often they give rise to distinct properties, such as multiple combined noncovalent interactions and a diversity of stimuli-based responsiveness. In this tutorial review, we will summarise recent advances in adhesive supramolecular polymeric materials that rely primarily on macrocycle-based host-guest interactions. An overview of future challenges and a perspective of this sub-field are also provided.

Azobenzene-Bridged Expanded "Texas-sized" Box: A Dual-Responsive Receptor for Aryl Dianion Encapsulation.

We report an expanded "Texas-sized" molecular box (AzoTxSB) that incorporates photoresponsive azobenzene bridging subunits and anion recognition motifs. The shape of this box can be switched through light induced E ↔ Z photoisomerization of the constituent azobenzenes. This allows various anionic substrates to be bound and released by using different forms of the box. Control can also be achieved using other environmental stimuli, such as pH and anion competition.

A Mitochondria-Specific Fluorescent Probe for Visualizing Endogenous Hydrogen Cyanide Fluctuations in Neurons.

An ability to visualize HCN in mitochondria in real time may permit additional insights into the critical toxicological and physiological roles this classic toxin plays in living organisms. Herein, we report a mitochondria-specific coumarin pyrrolidinium-derived fluorescence probe (MRP1) that permits the real-time ratiometric imaging of HCN in living cells. The response is specific, sensitive (detection limit is ca. 65.6 nM), rapid (within 1 s), and reversible. Probe MRP1 contains a benzyl chloride subunit designed to enhance retention within the mitochondria under conditions where the mitochondria membrane potential is eliminated. It has proved effective in visualizing different concentrations of exogenous HCN in the mitochondria of HepG2 cells, as well as the imaging of endogenous HCN in the mitochondria of PC12 cells and within neurons. Fluctuations in HCN levels arising from the intracellular generation of HCN could be readily detected.

Physical Removal of Anions from Aqueous Media by Means of a Macrocycle-Containing Polymeric Network.

Reported here is a hydrogel-forming polymer network that contains a water-soluble tetracationic macrocycle. Upon immersion of this polymer network in aqueous solutions containing various inorganic and organic salts, changes in the physical properties are observed that are consistent with absorption of the constituent anions into the polymer network. This absorption is ascribed to host-guest interactions involving the tetracationic macrocyclic receptor. Removal of the anions may then be achieved by lifting the resulting hydrogels out of the aqueous phase. Treating the anion-containing hydrogels with dilute HCl leads to the protonation-induced release of the bound anions. This allows the hydrogels to be recycled for reuse. The present polymer network thus provides a potentially attractive approach to removing undesired anions from aqueous environments.

Removal of Anions from Aqueous Media by Means of a Thermoresponsive Calix[4]pyrrole Amphiphilic Polymer.

To address the challenge of removing unwanted anions from aqueous media under extraction-free conditions we have prepared a thermoresponsive amphiphilic polymer with pendent calix[4]pyrrole (C4P) receptors. Because of its amphipathicity, this polymer self-assembles into micelles in water. These micelles contain the C4P receptors buried in a hydrophobic core. This allows uptake of various cesium anions into the micelles. Due to the thermal responsiveness of the hydrophilic block chain, the anion-bearing micelles precipitate in water upon heating. Simple filtration allows their removal from the aqueous environment, thus allowing for effective water purification. Treating the anion-trapped micelles with acidic aqueous solution leads to the competition-induced release of the bound anion and thus recycling the polymeric material.

A coumarin-based fluorescent probe for monitoring labile ferrous iron in living systems.

Labile Fe2+ has been considered to be a metabolically active and regulatory form of cellular iron. Monitoring the dynamic level of labile Fe2+ in biological systems is vital for evaluating the iron related biological processes and diseases as well as dissecting the exact physiological and pathophysiological functions of the labile Fe2+. Herein, we rationally constructed a coumarin-based fluorescent probe for sensing labile Fe2+ in living systems based on a novel Fe2+ meditated cyclization reaction strategy. The probe showed a highly selective and sensitive response to Fe2+, and the detection limit was determined to be 45 nM. Significantly, the probe displayed fast response to Fe2+, with the sensing reaction completed in 2 min, which is beneficial for real time sensing. The application of the probe for sensing different concentrations of labile Fe2+ in living cells has been conducted. In addition, the basal and endogenous levels of labile Fe2+ in living systems were also successfully monitored.

7-Di-ethyl-amino-3-{(E)-4-[(E)-2-(pyridin-4-yl)ethen-yl]styr-yl}-2H-chromen-2-one.

In the title coumarin derivative, C28H26N2O2, the coumarin unit is approximately planar, with a maximum deviation of 0.048 (3) Å. The central benzene ring is oriented at dihedral angles of 30.15 (14) and 10.51 (11)°, respectively, to the pyridine ring and coumarin ring system. In the crystal, weak C-H⋯O and C-H⋯N hydrogen bonds and weak C-H⋯π inter-actions link the mol-ecules into a three-dimensional supra-molecular architecture.

Construction of a Colorimetric and Near-Infrared Ratiometric Fluorescent Sensor and Portable Sensing System for On-Site Quantitative Measurement of Sulfite in Food.

Sulfites play imperative roles in food crops and food products, serving as sulfur nutrients for food crops and as food additives in various foods. It is necessary to develop an effective method for the on-site quantification of sulfites in food samples. Here, 7-(diethylamino) quinoline is used as a fluorescent group and electron donor, alongside the pyridinium salt group as an electron acceptor and the C=C bond as the sulfite-specific recognition group. We present a novel fluorescent sensor based on a mechanism that modulates the efficiency of intramolecular charge transfer (ICT), CY, for on-site quantitative measurement of sulfite in food. The fluorescent sensor itself exhibited fluorescence in the near-infrared light (NIR) region, effectively minimizing the interference of background fluorescence in food samples. Upon exposure to sulfite, the sensor CY displayed a ratiometric fluorescence response (I447/I692) with a high sensitivity (LOD = 0.061 µM), enabling accurate quantitative measurements in complex food environments. Moreover, sensor CY also displayed a colorimetric response to sulfite, making sensor CY measure sulfite in both fluorescence and colorimetric dual-signal modes. Sensor CY has been utilized for quantitatively measuring sulfite in red wine and sugar with recoveries between 99.65% and 101.90%, and the RSD was below 4.0%. The sulfite concentrations in live cells and zebrafish were also monitored via fluorescence imaging. Moreover, the sulfite assimilated by lettuce leaves was monitored, and the results demonstrated that excessive sulfite in leaf tissue could lead to leaf tissue damage. In addition, the sulfate-transformed sulfite in lettuce stem tissue was tracked, providing valuable insights for evaluating sulfur nutrients in food crops. More importantly, to accomplish the on-site quantitative measurement of sulfite in food samples, a portable sensing system was prepared. Sensor CY and the portable sensing system were successfully used for the on-site quantitative measurement of sulfite in food.

A potential-controlled electrochromic visual biosensor based on distance readout for zearalenone detection.

In this work, a potential-controlled electrochromic visual biosensor was developed for detecting zearalenone (ZEN) using a distance readout strategy. The sensor chip includes a square detection area and a folded signal output area created with laser etching technology. The detection area is modified with graphene oxide and ZEN aptamer, while Prussian blue (PB) is electrodeposited onto the signal output channel. When an appropriate voltage is applied, PB in the signal output area is reduced to colorless Prussian white (PW). The target ZEN molecules have the capability to release aptamers from graphene oxide (GO) surface in the detection area, resulting in a subsequent change in the potential of the visual signal output channel. This change determines the length of the channel that changes from blue to colorless, with the color change distance being proportional to the ZEN concentration. Using this distance readout strategy, ZEN detection within the range of 1 ng/mL to 300 ng/mL was achieved, with a detection limit of 0.29 ng/mL.

Facile synthesis and enhanced nonlinear optical properties of porphyrin-functionalized multi-walled carbon nanotubes.

Two multi-walled carbon nanotube (MWCNT)-based nanohybrids, MWCNT-ZnTPP and MWCNT-TPP (TPP=5-[4-{2-(4-formylphenoxy)- ethyloxy}phenyl]-10,15,20-triphenylporphyrin, ZnTPP=5-[4-{(4-formylphenyl)ethynyl}phenyl]-10,15,20-triphenylporphinatozinc(II)), were prepared directly from pristine MWCNTs through 1,3-dipolar cycloaddition reactions. Covalent attachment of the porphyrins to the surfaces of the MWCNTs was confirmed by Fourier transform infrared spectroscopy, ultraviolet/visible absorption, fluorescence, Raman, and X-ray photoelectron spectroscopy, elemental analysis, transmission electron microscopy, and thermogravimetric analysis. Attachment of the porphyrin moieties to the surface of the MWCNTs significantly improves the solubility and ease of processing of these MWCNT-porphyrin composite materials. Z-scan studies reveal that these MWCNT-porphyrin nanohybrids exhibit enhanced nonlinear optical properties under both nanosecond and picosecond laser pulses at λ=532 nm in comparison with free MWCNTs and the free porphyrin chromophores, whereas superior optical limiting performance was displayed by MWCNT-porphyrin composite materials rather than MWCNTs/ZnTPP and MWCNTs/TPP blends, which is consistent with a remarkable accumulation effect as a result of the covalent linkage between the porphyrin and the MWCNTs.

A coumarin-based fluorescent probe for biological thiols and its application for living cell imaging.

In this work, compound 1 has been rationally designed and synthesized as a new fluorescent probe for biological thiols. Notably, probe 1 has almost no background fluorescence (Φf < 0.0001) in aqueous solutions; however, it exhibited fluorescence turn-on response to thiols with high sensitivity (a 246-fold fluorescence enhancement and a low detection limit of 0.22 µM for Cys). Moreover, probe 1 showed excellent thiol specificity over other biologically relevant species. The kinetic studies indicated that the probe responded to thiols rapidly, and the pseudo-first-order rate constants of probe 1 reaction with Cys, Hcy, and GSH were determined to be 1.85842, 0.67656, and 0.51519 min(-1), respectively. A possible detection mechanism was proposed to involve the Michael addition of the thiol to the α,ß-unsaturated ketone, followed by a cleavage of the hemiketal group, thereby leading to the formation of a fluorescent 7-hydroxyl coumarin derivative. Furthermore, the optical responses of probe 1 to thiols were studied by TD-DFT calculations. Finally, probe 1 has been successfully applied to the detection of biological thiols in human blood serum. And the intracellular imaging applications established that probe 1 can be used to detect different concentrations of intracellular thiols in living cells.

Cooperative enhancement of optical nonlinearities in a porphyrin derivative bearing a pyrimidine chromophore at the periphery.

A novel porphyrin derivative bearing one D-π-A-π-D pyrimidine chromophore at the periphery was designed, prepared, and studied using the Z-scan technique, the results showing that this compound exhibits enhanced nonlinear optical (NLO) absorption, refraction and optical limiting responses. The significant NLO properties can be ascribed to an effective combination of distinct nonlinear mechanisms.

Sensitive and stable detection of deoxynivalenol based on electrochemiluminescence aptasensor enhanced by 0D/2D homojunction effect in food analysis.

Sensitive detection for deoxynivalenol (DON) should be developed due to DON as a kind of harmful mycotoxins which can poses health risk to human health even at low concentrations. In this work, an electrochemiluminescence (ECL) DON aptasensor was proposed based on Ti3C2 dots/Ti3C2 nanosheet (TDTN). Compared with Ti3C2 dots and Ti3C2 nanosheet, the ECL intensity of TDTN was 4 times of Ti3C2 dots and 2 times of Ti3C2 nanosheet as emitters. This was attributed to homojunction effect which could provide continuity of band bonding and effectively accelerate charge transfer at the interface. Based on ECL signal changes generated by aptamer and DON fixed on the electrode surface, the ECL aptasensor showed "on-off-on" performances and detected DON specifically in milk, with detection range of 0.001-20 ng/mL and detection limit of 0.3 pg/mL (S/N = 3). Therefore, the constructed ECL aptasensor is a promising detection method for food safety analysis.