Development of an accurate hand-held sensing platform for nitrite detection based on nitrogen-doped carbon dots.

As is well known, excessive nitrite can seriously pollute the environment and can harm human health. Although existing methods can be used to determine nitrite content, they still have some drawbacks, such as relatively complicated operation and expensive equipment. Herein, a hand-held sensing platform (HSP) for NO2- determination was developed. First, ammonia-rich nitrogen-doped carbon dots with orange-yellow emission were designed and synthesised, which were suitable as fluorescent probes because of their good optical properties and stability. Then, the HSP based on fluorescence using photoelectric conversion technology was designed and manufactured using three-dimensional printing technology. Under optimum conditions, the voltage (V/V0) of the proposed HSP showed good linearity for NO2- detection in the range of 10-500 µM, with a detection limit of 1.95 µM. This portable sensor showed good stability, accuracy and reliability in detecting actual water and meat samples, which may ensure food safety in practical applications. Moreover, the HSP is compact, portable and easily assembled and is suitable for on-site real-time detection, which shows great application potential and prospects.

Synthesis of pH-Sensitive Nitrogen-Doped Carbon Dots with Biological Imaging Function and Their Application in Cu2+ and Fe2+ Determination by Ratiometric Fluorescent Probes.

pH-sensitive nitrogen-doped carbon dots (N-CDs) were synthesized using immature seeds of elm trees as a carbon source and ethylenediamine as a coreactant through a facile one-step hydrothermal method. The N-CDs were characterized using fluorescence spectroscopy, fluorescence lifetime, ultraviolet-visible absorption, X-ray photoelectron spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy, as well as transmission electron microscopy. The N-CDs displayed excellent fluorescence properties and responded to pH changes. The N-CDs exhibited low toxicity and good biocompatibility and had the potential to be used for the biological imaging of HeLa cells and mung bean sprouts. Utilizing the mechanism of fluorescence resonance energy transfer, ratiometric fluorescent probes were prepared by simple mixing of N-CDs and fluorexon in a Britton-Robinson buffer solution. The ratiometric fluorescent probe was used to detect Cu2+ and Fe2+. The linear equations were RCu = -0.0591[Q] + 3.505 (R2 = 0.992) and RFe = -0.0874[Q] + 3.61 (R2 = 0.999). The corresponding limits of detection were 0.5 and 0.31 µM, respectively. The good results had been obtained in the actual samples detection.

Fungi-enabled pore channel regulation and defect engineering of a novel micro-reactor for treating complex effluents.

Defect engineering has become a significant research area in recent years; however, little has been reported on the biological method for modulating the intrinsic carbon defects of the biochar framework. Herein, a fungi-enabled method for the fabrication of porous carbon/Fe3O4/Ag (PC/Fe3O4/Ag) composites was developed, and the mechanism underlying the hierarchical structure is elucidated for the first time. By regulating the cultivation process of fungi on water hyacinth biomass, a well-developed interconnected structure and carbon defects acting as potential catalytic active sites were formed. This new material with antibacterial, adsorption and photodegradation properties could be an excellent choice for treating the mixed dyestuff effluents with oils and bacteria, also guiding pore channel regulation and defect engineering in materials science. Numerical simulations were carried out to demonstrate the remarkable catalytic activity.

Facile and Green Synthesis of Carbon Dots from Melia Azedarach Leaves for pH Sensing and Cell Imaging.

Carbon dots (CDs) have preeminent application prospects as a new star in the nanomaterials field. In this work, a green and facile method to synthesize the blue-emitting CDs was proposed with Melia azedarach leaves as the carbon precursors. Using nature materials without other expensive reagents and instruments, the processes were simple and environmental-friendly. The CDs had high fluorescence quantum yield (11.8%) and excellent luminescence properties. The size of them were among 1.5-2.5 nm and the emission spectrum exhibited a strong peak at 460 nm when excited at 380 nm. Additionally, the CDs were stable in most ions but sensitive to different pH values. As a result, a pH sensor was established for the detection of pH with a linear range of 3-10 pH. Moreover, it was demonstrated that the synthesized CDs had extremely low cytotoxicity. Due to their low toxicity and good biocompatibility, they entered into the A549 cells successfully for cell imaging.

A novel and ultrasensitive fluorescent probe derived from labeled carbon dots for recognitions of copper ions and glyphosate.

Labeling materials with special functional groups are very valuable for the creation of novel probes. Hence, a novel fluorescent probe was constructed by conjugating 4-butyl-3-thiosemicarbazide (BTSC) with carbon dots (CDs). The CDs labeled by BTSC (BTSC-CDs) displayed a strong capability for recognition of Cu2+ and Cu2+ could quench the emission of BTSC-CDs significantly. The fluorescence quenching was proved to be a static quenching which was resulted from the interaction between BTSC-CDs and Cu2+ to form a ground-state BTSC-CDs/Cu2+complex, and the fluorescence intensities showed a good linear correlation with Cu2+ concentrations in the range of 0.20-30 µM. What is more important, by adding glyphosate into the sensor system of BTSC-CDs/Cu2+ the fluorescence of the probe turned on again owing to the stronger chelating between glyphosate and Cu2+ than between BTSC-CDs and Cu2+. This could realize the specific detection of glyphosate and the limit of detection was low to 0.27 µM. Detecting glyphosate using the complex BTSC-CDs/Cu2+ system in actual samples with satisfactory outcomes indicated that a novel fluorescent probe for Cu2+ and subsequent glyphosate detections has been provided.

One step synthesis of ultra-high quantum yield fluorescent carbon dots for "on-off-on" detection of Hg2+ and biothiols.

In this paper, the carbon dots (CDs) with strong blue fluorescence were synthesized through hydrothermal method, which using folic acid, ammonium citrate and ethylenediamine as precursors. The prepared CDs with a high absolute quantum yield of 81.94% and showed excellent stability in high concentration salt solution and different pH conditions. With the addition of Hg2+, the signal of CDs was selectively quenched. At the same time, the CDs-Hg2+ system could be recovered after the introduction of biothiols. Moreover, the fluorescence of CDs showed a good linear relationship with Hg2+ (1-15 µM), and the detection limit as low as 0.08 µM. In addition, the prepared CDs with low toxicity could be used to detect Hg2+ in living cells and actual water samples.

Enhanced photocatalytic activity of Cu2O for visible light-driven dye degradation by carbon quantum dots.

Cuprous oxide (Cu2O), a p-type semiconductor material, plays an important role in photocatalysis, which has narrower band gap (~2.1 eV), abundant availability, and low toxicity. However, the applications of Cu2O are mainly restricted by its high recombination rate and low charge collection. Hence, it is of great significance to find an efficient method to improve the photocatalytic activity of Cu2O. In this work, the CQDs-loaded Cu2O nanocomposites (CQDs/Cu2O) were successfully obtained via hydrothermal method. It was worth noting that the CQDs/Cu2O nanocomposite displayed improved photocatalytic activity compared to that of pure Cu2O with a lower dosage (25 mg) under visible light, which could completely degrade the methylene blue in 8 min. The recycling experiments also showed that the photocatalytic activity still remained up to 90% after 8 cycles. In addition to the photodegradation of methylene blue, the CQDs/Cu2O nanocomposite also had an excellent antibacterial activity against Escherichia coli (100%, 30 min). These results demonstrated that introducing CQDs to Cu2O was a feasible method to improve the photocatalytic performance of Cu2O.

Conformational dynamics is critical for the allosteric inhibition of cGAS upon acetyl-mimic mutations.

Detection of cytosolic dsDNA by cyclic GMP-AMP synthase (cGAS) is critical for the immune system to sense and fight against infection, but chronic activation of cGAS by self-DNA leads to autoimmune diseases without effective treatment yet. It was found that acetylation on either Lys384, Lys394, or Lys414 could inhibit the catalytic production of cGAMP by cGAS, and further suppressed self-DNA-induced autoimmunity. However, the implied mechanism remains unclear. Here, extensive molecular dynamics simulations combined with multiple analytical approaches were employed to uncover the allosteric inhibition mechanisms by using the K-to-Q mutations to mimic acetylation. Results suggested that the exterior loops contributed most to the conformational dynamics of cGAS, and two concerted intrinsic motions were observed: the inward/outward or twisting movement for the outer appendage of lobe 1 and the open/closed swing of the active-site loops. Mutations slightly affected the binding of dsDNA and cGAMP. The shift of the conformational sampling of the active-site loops or residues around cGAMP upon mutation might potentially explain the inhibition of cGAS activity. Moreover, the intra- and inter-molecular coupling was weakened upon mutations more or less but via distinct pathways. Hence, conformational dynamics play a vital role in the allosteric inhibition of cGAS upon the studied acetyl-mimic mutations. As the studied acetyl-mimic mutations are located at either the inter-lobe or inter-molecular interfaces, hence except for acetylation, our findings might help the development of new therapeutics against autoimmune diseases due to abnormal cGAS activation by designing inter-lobe or intermolecular allosteric inhibitors.

Synthesis of Carbon Dots and their Application as Turn Off-On Fluorescent Sensor for Mercury (II) and Glutathione.

In this paper, we present a new method for the detection of mercury (II) and glutathione using carbon dots as fluorescent sensor. The synthesized carbon dots have the advantages of simple manipulation, low cost and the high fluorescence quantum yield of them which was22.79%. The combination of mercury (II) and carbon dots caused the turn off of carbon dots fluorescence. With the reaction between mercury (II) and glutathione, the carbon dots were released and the fluorescence was turned on when the glutathione added. According to this, the carbon dots could be developed to detect mercury (II) and glutathione specifically, and the detection limit of mercury (II) is as low as 0.41 µM.

Utilizing the interfacial reaction of naphthalenyl thiosemicarbazide-modified carbon dots for the ultrasensitive determination of Fe (III) ions.

Since thiosemicarbazide contains numerous nitrogen and sulfur atoms in its structural formula that enhance its strong coordinating abilities with metal ions, it is always selected as the mother molecule for the design of metal-ion sensors. In this report, a thiosemicarbazide derivative (4-naphthalenyl-3-thiosemicarbazide (NTSC)) was synthesized via a single step process and covalently conjugated onto the surfaces of carbon dots (CDs). The modified CDs demonstrated excellent monodispersity, good photostability, and tunable luminescence properties. More importantly, the CDs retained a highly specific Fe3+ recognition capacity in contrast to other competing metal ions. Fe3+ can efficiently quench the fluorescence of CDs even at fairly low concentration (30µM) with a detection limit as low as 1.68nM. The fluorescence quenching kinetics are likely to involve static quenching, which is caused by specific interactions between NTSC-CDs and Fe3+ toward the formation of a ground state complex. Due to their excellent optical performance, low toxicity, and good biocompatibility the NTSC-CDs may be applied to the imaging and monitoring of Fe3+ in bacillus subtilis. In effect we successfully fabricated an effective fluorescent nanosensor for both the quantitative detection of Fe3+ in aqueous solutions, and its real-time imaging in vivo.

Study on the stereoselective binding of cytosine nucleoside enantiomers to human serum albumin.

Nucleoside drugs are known for their remarkable anticancer and antiviral properties. The development of nucleoside drugs has attracted much attention and generated a great deal of research interest. ß-L-cytidine and ß-D-cytidine are a pair of cytosine nucleoside enantiomers. In this work, the interactions between cytosine nucleoside enantiomers and human serum albumin were studied by ultraviolet-visible spectra, fluorescence spectrum and circular dichroism spectrum under simulated human physiological environment. The data of fluorescence spectra were corrected for the inner-filter effect to improve accuracy. Stern-Volmer quenching constants and binding constants in addition to thermodynamic parameters have been analyzed, which established that complexes formation have taken place via static quenching mechanism, and that hydrophobic force involved in these interactions. CD spectrum revealed that on addition of cytosine nucleoside enantiomers, the α-helix% of HSA increased slightly. What's more, molecular modeling method indicated that cytosine nucleoside enantiomers prefer binding at the IIIA site of HSA.

Modeling techniques and fluorescence imaging investigation of the interactions of an anthraquinone derivative with HSA and ctDNA.

A new anthraquinone derivative (AORha) was synthesized. Its interactions with human serum albumin (HSA) and calf thymus DNA (ctDNA) were investigated by fluorescence spectroscopy, UV-visible absorption spectroscopy and molecular modeling. Cell viability assay and cell imaging experiment were performed using cervical cancer cells (HepG2 cells). The fluorescence results revealed that the quenching mechanism was static quenching. At different temperatures (290, 300, 310 K), the binding constants (K) and the number of binding sites (n) were determined, respectively. The positive ΔH and ΔS values showed that the binding of AORha with HSA was hydrophobic force, which was identical with the molecular docking result. Studying the fluorescence spectra, UV spectra and molecular modeling also verified that the binding mode of AORha and ctDNA might be intercalative. When HepG2 cells were treated with AORha, the fluorescence became brighter and turned green, which could be used for bioimaging.

Three-dimensional excitation-emission matrix fluorescence spectroscopy and fractions of dissolved organic matter change in landfill leachate by biological treatment.

The water quality improvement of landfill leachate after sequencing batch reactor (SBR) activated sludge process were evaluated by chemical oxygen demand (COD), dissolved organic matter (DOM) fractions, and three-dimensional excitation-emission matrix (EEM), from which the new understanding was obtained. The results indicated that less than 14% COD was removed by SBR. The EEM of leachate and SBR effluent showed that HPO-A and TPI-A were appeared in the peak C, while the HPI, HPO-N, and TPI-N could not be found due to dilution. Although humic acid appeared in peak C, not all the organic materials in peak C are humic acid. And because landfill leachate is a kind of complicated wastewater, therefore, only EEM cannot efficiently reflect the water quality.

Interaction of Anthracycline 3'-azido-epirubicin with Calf Thymus DNA via Spectral and Molecular Modeling Techniques.

Anthracycline antibiotics are extensively applied to clinical antitumor therapy. The binding mode and mechanism of a new anthracycline 3'-azido-epirubicin (AEPI) with calf thymus deoxyribonucleic acid (ctDNA) were investigated employing multiple spectroscopy techniques in Tris-HCl buffer solution (pH 7.4). Effect of pH on the interaction was provided to determine the proper environment for whole research. Iodide quenching studies and fluorescence polarization measurement indicated that ctDNA quenched the fluorescence of AEPI significantly via intercalation binding mode. The binding constants and binding sites for the interaction were calculated. From binding constant dependence on the temperature, static quenching mechanism of AEPI by ctDNA was confirmed based on the Stern-Volmer equation. Additionally, the thermodynamic parameters for the reaction revealed that the van der Waals force and hydrogen bonding were the main acting forces in the binding process. Molecular modeling result indicated that the hydrogen bonding played a major role in the binding of AEPI to ctDNA.

Probing the interaction of anthraquinone with DNA by spectroscopy, molecular modeling and cancer cell imaging technique.

A new anthraquinone derivative, (E)-2-(1-(4,5-dihydroxy-6-(hydroxymethyl)-tetrahydro-2H-pyran-2-yloxyimino)ethyl)-1,4-dihydroxyanthracene-9,10-dione (AODGlc), was synthesized and its binding properties towards DNA were explored under physiological conditions by fluorescence spectroscopy, DNA melting as well as docking techniques. The experimental results revealed that AODGlc could bind to calf thymus DNA (ctDNA) through intercalation between DNA base pairs. The values of thermodynamic parameters at different temperatures including ΔG, ΔH, and ΔS and the molecular modeling study implied that hydrophobic interactions and hydrogen bonds were the main interactions in the AODGlc-ctDNA system. Cervical cancer cells (HepG2 cells) were used in cell viability assay and cell imaging experiment. AODGlc could interact with HepG2 cells and kill HepG2 cells under high concentration with nice curative effect, indicating its potential bioapplication in the future.

Interaction of one anthraquinone derivative with ctDNA analyzed by spectroscopic and modeling methods.

The interaction of one anthraquinone derivative (AOMan) with calf thymus deoxyribonucleic acid (ctDNA) was systematically investigated at physiological pH 7.4 by fluorescence spectroscopy and molecular modeling. Binding constants of ctDNA with AOMan were calculated at different temperatures. Thermodynamic parameters, enthalpy and entropy changes were calculated according to Van't Hoff equation, which indicated that the reaction was spontaneous and predominantly enthalpically driven. The increasing viscosity of ctDNA indicated that AOMan could intercalate into the base pairs of ctDNA. This conclusion was also demonstrated by the results obtained from KI quenching, denatured DNA studies and fluorescence polarization experiment. Furthermore, the molecular modeling results showed that anthraquinone ring tended to slide into the G-C rich region of ctDNA through the hydrogen bond, which are consistent with the results from experimental methods. Studying the binding interaction of target anthraquinones with DNA is one of the key steps in their DNA-changing action and the design of new drugs.

Spectroscopic, viscositic and molecular modeling studies on the interaction of 3'-azido-daunorubicin thiosemicarbazone with DNA.

A new daunorubicin has been synthesized and structurally characterized. The interaction of native calf thymus DNA (ctDNA) with 3'-azido-daunorubicin thiosemicarbazone (ADNRT) was investigated under simulated physiological conditions by multi-spectroscopic techniques, viscometric measurements and molecular modeling study. It concluded that ADNRT could intercalate into the base pairs of ctDNA, and the fluorescence quenching by ctDNA was static quenching type. Thermodynamic parameters calculated suggested that the binding of ADNRT to ctDNA was mainly driven by hydrophobic interactions. The relative viscosity of ctDNA increased with the addition of ADNRT, which confirmed the intercalation mode. Furthermore, molecular modeling studies corroborate the above experimental results.

Spectroscopic study one thiosemicarbazone derivative with ctDNA using ethidium bromide as a fluorescence probe.

In this study, a thiosemicarbazone derivative (E)-2-((1,4-dihydroxy-9,10-anthraquinone-2-yl)methylene)-N-(4-fluorophenyl)hydrazinecarbothioamide (DAFPT) was synthesized, and the interaction of DAFPT with calf thymus DNA (ctDNA) was explored using ethidium bromide (EB) as a fluorescence probe. The binding mode between DAFPT and ctDNA was investigated by UV absorption spectroscopy, fluorescence spectroscopy and molecular docking. The fluorescence quenching mechanism of EB-ctDNA by DAFPT might be a combined quenching type. Thermodynamic parameters showed that the reaction was spontaneous. According to ionic strength, fluorescence polarization and melting temperature (T(m)) curve results, DAFPT-ctDNA interaction was groove binding. The molecular modeling results indicated that DAFPT could slide into the A-T rich region of ctDNA.

Investigations on the interactions of diclofenac sodium with HSA and ctDNA using molecular modeling and multispectroscopic methods.

A tentative study on interaction of diclofenac sodium (DF-Na) with human serum albumin (HSA) and calf thymus DNA (ctDNA) was conducted by using multi-spectroscopic and molecular modeling techniques under simulative physiological conditions. The results of spectroscopic measurements suggested that the quenching mechanisms were static quenching. Three-dimensional fluorescence spectroscopy clearly demonstrated the occurrence of conformational changes of HSA with addition of DF-Na. In addition, competitive studies with ethidium bromide (EB) have shown that DF-Na can bind to ctDNA relatively strong via groove binding. Based on the values of thermodynamic parameters and the results of molecular modeling, it was confirmed that hydrophobic forces and hydrogen bond were the mainly binding forces in DF-Na-HSA and DF-Na-DNA systems. The binding distance between DF-Na and HSA was also determined using the theory of the Förster energy transference.

Molecular interaction of ctDNA and HSA with sulfadiazine sodium by multispectroscopic methods and molecular modeling.

Interactions of sulfadiazine sodium (SD-Na) with calf thymus DNA (ctDNA) and human serum albumin (HSA) were studied using fluorescence spectroscopy, UV absorption spectroscopy and molecular modeling. The fluorescence experiments showed that the processes were static quenching. The results of UV spectra and molecular modeling of the interaction between SD-Na and ctDNA indicated that the binding mode might be groove binding. In addition, the interaction of SD-Na with HSA under simulative physiological conditions was also investigated. The binding constants (K) and the number of binding sites (n) at different temperatures (292, 302, 312 K) were 5.23 × 10(3) L/mol, 2.18; 4.50 × 10(3) L/mol, 2.35; and 4.08 × 10(3) L/mol, 2.47, respectively. Thermodynamic parameters including enthalpy change (ΔH) and entropy change (ΔS) were calculated, the results suggesting that hydrophobic force played a very important role in SD-Na binding to HSA, which was in good agreement with the molecular modeling study. Moreover, the effect of SD-Na on the conformation of HSA was analyzed using three-dimensional fluorescence spectra.