Intramolecular hydrogen bond-tuned thermal-responsive carbon dots and their application to abnormal body temperature imaging.

A steric hindrance strategy was used to prepare intramolecular hydrogen bond-controlled thermosensitive fluorescent carbon dots (CDs) via the solvothermal treatment of o-phenylenediamine respectively with three dihydroxybenzene isomers. The CDs obtained from different isomers have very similar morphology, surfaces, and photophysical properties but exhibited different thermal sensitivities. Meanwhile, the orange-emitting CDs (p-CDs) obtained from o-phenylenediamine and p-hydroquinone exhibited an optimal thermal sensitivity of 1.1%/°C. Comprehensive experimental characterizations and theoretical calculations revealed that even a small difference in substituent locations in the phenyl ring of the precursors can considerably affect the formation of intramolecular hydrogen bonds and that the CDs with strong intramolecular hydrogen bonds exhibited poor thermosensitivity. The p-CDs were incorporated with reference CDs (B-CDs) that exhibited heating-quenching blue emission through electrostatic self-assembly to construct a dual-emission probe (p-CDs/B-CDs), which exhibited a thermal sensitivity of 2.0%/°C. Test strips based on the p-CDs/B-CDs were prepared to measure temperature fluctuations based on sensitive and instant fluorescence color evolution. Further, this fluorescent colorimetry was successfully applied to a test strip-integrated wearable wristband to measure the body temperature. This study establishes an inherent relationship between precursors and the resulting intramolecular hydrogen bonds for precisely tuning the thermal sensitivity of CDs. It also offers a visual quantitative strategy for the early warning of abnormal body temperatures.

A colorimetric and fluorometric dual-mode carbon dots probe derived from phenanthroline precursor for the selective detection of Fe2+ and Fe3.

Iron's metabolism is heavily involved in the regulation of redox balance for cell functions, however, the simultaneous monitoring of Fe2+/3+ concentration is still a great challenge due to their transitional nature in biological systems. A novel type of carbon dots (CDs) was synthesized by solvothermal treatment with 5-amino-1,10-phenanthroline (Aphen) and salicylic acid as precursors, and the resulting targeted CDs (T-CDs) were used to simultaneously detect Fe2+ and Fe3+. Comprehensive experimental characterizations revealed that the strong binding affinity of Aphen moiety to Fe2+ leads to the formation of rigid T-CDs aggregates, which causes a substantial enhancement of fluorescence intensity, whereas Fe3+ could cause the fluorescence quenching of T-CDs due to the oxidation-reduction induced electron transfer. These different fluorescence responses allow T-CDs to sensitively differentiate Fe2+ from Fe3+, and give the limit of detection (LOD) of 1.78 and 2.78 µM for Fe2+ and Fe3+, respectively. Furthermore, the Aphen dominated structure endows the T-CDs with a colorimetric response to Fe2+ with a LOD of 0.13 µM, which is very different from Fe3+. Thus, the dynamic changes of Fe2+ and Fe3+ in solution can be accurately monitored by T-CDs within the total iron concentration of 50 µM, which is probably the most sensitive dual-mode probe reported so far. In addition, this probe is successfully applied to detect the Fe2+/3+ concentration in cells, demonstrating a huge application potential in the sensing of the dynamic equilibrium of these important transition metals during the cell metabolism or stimulated process. The dynamic changes of Fe2+ and Fe3+ in solution can be accurately monitored by carbon dots based on the colorimetric and fluorometric dual-mode.

Template-Free Synthesis of Porous Fluorescent Carbon Nanomaterials with Gluten for Intracellular Imaging and Drug Delivery.

A series of carbon nanomaterials, including carbon dots, carbon nanorings (CNRs), and porous carbon nanoballs, were facilely prepared by a template-free hydrothermal treatment of gluten as the sole carbon source. Driven by the hydrophobicity interaction, a concentration-dependent self-assembly of gluten was observed in an aqueous solution, leading to the subsequent formation of different morphologies of carbon nanomaterials in a hydrothermal treatment. Among these carbon nanomaterials, the CNRs exhibit bright photoluminescence with a quantum yield of 47.0%. Furthermore, CNRs also have a large surface area and low toxicity, making them an excellent drug carrier for chemotherapeutics. A model drug molecule doxorubicin (DOX) was successfully loaded on the CNRs, and the CNRs-DOX complexes exhibit a pH-dependent DOX release behavior. Compared with free DOX, the CNRs-DOX complexes can induce a higher level of apoptosis and lower level of necrosis, showing promise as anticancer agents.

Cadmium induced aggregation of orange-red emissive carbon dots with enhanced fluorescence for intracellular imaging.

Cadmium is a notorious toxic heavy metal, that poses serious threat to human health. Sensitive and selective detection of cadmium in cells is of great significance in poison screening and disease diagnosis. Orange-red emissive carbon dots (OR-CDs), prepared from the calcination of selected carbon sources 5-amino-1, 10-phenanthroline (Aphen) and salicylic acid (SA), were found to act as a "turn on" type fluorescence probe for Cd2+ detection. The structure and optical properties of OR-CDs were comprehensively investigated by both experimental characterizations and density functional theory (DFT) calculations. The OR-CDs consist of a basic unit of nine aromatic rings, and the N/O binding sites on the OR-CDs can specifically bind with Cd2+, leading to aggregation induced enhanced emission (AIEE). A detection limit of 0.30 µM was achieved for Cd2+ with a linear range of 0.80-100 µM. OR-CDs can not only be used for intracellular Cd2+ imaging but also have the potential to alleviate cadmium poison in living organisms.

Fabrication of nitrogen-doped graphene nanosheets anchored with carbon nanotubes for the degradation of tetracycline in saline water.

The treatment of wastewater with high salinity is still a challenge because of the quenching effect of various anions on radical processes. The nonradical process may be a more promising pathway. Herein, a 3D structured nitrogen-doped graphene nanosheet anchored with carbon nanotubes (N-GS-CNTs) was prepared by direct pyrolysis of K3Fe(CN)6. The as-prepared catalyst can effectively activate peroxymonosulfate (PMS) for mineralization of tetracycline (TC) over a wide pH range (from 3 to 11) and even in high saline water (500 mM Cl-, HCO3-, etc.). The degradation mechanism was elucidated by both experimental characterizations and DFT calculations. The high catalytic efficiency was attributed to accelerated electron transfer from donor (TC) to acceptor (PMS) in the presence of the catalyst, which acts as electron shuttle mediators to promote a nonradical process. At the same time, the catalyst also enhances the production of singlet oxygen (1O2), hence further increasing the degradation rate. This study not only provides a simple method for synthesizing N-GS-CNT catalysts but also provides new insights into the electron transfer pathway for the removal of organic pollutants under high salinity conditions.

Protein-stabilized Ir nanoparticles with usual charge-selective peroxidase properties.

Selective removal of an organic compound in the coexistence of other constituents is a great challenge in separation and purification processes. In this work, bovine serum albumin (BSA)-stabilized iridium nanoparticles (IrNPs) were prepared via a facile one-step precipitation method. The resulting BSA-IrNPs were comprehensively characterized by TEM, XRD, XPS, UV-vis, FT-IR, and fluorescence spectroscopy as well as circular dichroism spectrometry. It was found that the nanoparticles with an average diameter of 3.6 nm were embedded in the aggregated protein matrix and the structure of the coating agent was maintained well on the surface of nanoparticles. The as-prepared nanozymes (BSA-IrNPs) exhibit strong peroxidase-like activity and can selectively catalyse the degradation of cationic compounds by H2O2 in the coexistence of other inorganic or organic substances at room temperature. Interestingly, the degradation of amino acids could be precisely controlled by adjusting the pH above or below their isoelectric points. The catalytic selectivity of BSA-IrNPs should be ascribed to the anchoring effect between the amidogen-containing molecules and BSA through electrostatic adsorption. The nanozyme also exhibits excellent reusability as it can be readily recycled from solution by static settlement or centrifugation. Therefore, BSA-IrNPs have great potential for the selective removal of cationic compounds and amino acids in a complex matrix.

Electrochemical Detection of Phosphate Ion in Body Fluids with a Magnesium Phosphate Modified Electrode.

An electrochemical sensor for phosphate detection in body fluids was developed based on the hydration transition of magnesium hydrogen phosphate (newberyite, MgHPO4·3H2O). The sensor was fabricated through incubation of a multi-walled carbon nanotube/Nafion (MWCNT/Nafion) modified glassy carbon electrode (GCE) in magnesium phosphate solution, where MgHPO4·3H2O was self-assembled on the electrode surface (denoted as MgP/MWCNT/Nafion). An electrooxidation peak at 1.0 V vs. Ag/AgCl was observed when the as-prepared electrode was subjected to a differential pulse voltammetry (DPV) scan in the presence of phosphate in acetate solution. When the DPV scan was performed in 0.4 - 1.3 V vs. Ag/AgCl, a linear relationship was observed between the peak height and the phosphate concentration in the range from 0.01 to 25 µM in the presence of 0.1 mM Mg2+ in the acetate solution with a limit of detection of 32 nM. And the sensor was successfully applied for phosphate detection in human urine and saliva samples with recoveries of 94.7 - 104.4 and 96 - 103.3%, respectively.

Aggregation-Induced Room-Temperature Phosphorescence Obtained from Water-Dispersible Carbon Dot-Based Composite Materials.

Room-temperature phosphorescence (RTP) materials are desirable in chemical sensing because of their long emission lifetime and they are free from background autofluorescence. Nevertheless, the achievement of RTP in aqueous solution is still a highly challenging task. Herein, a molten salt method to prepare carbon dot (CD)-based RTP materials is presented by direct calcination of carbon sources in the presence of inorganic salts. The resultant CD composites (CDs@MP) exhibit bright RTP with a quantum yield of 26.4% and a lifetime of 1.28 s, which lasts for about 6 s to the naked eye. Importantly, their aqueous dispersion also has good RTP characteristics. This is the first time that the long-lived CDs@MP with RTP are achieved in aqueous solution owing to the synergistic effect of crystalline confinement and aggregation-induced phosphorescence. Further investigations reveal that three key processes may be responsible for the observed RTP of the composite materials: (1) The rigid crystalline salt shell can preserve the triplet states of CDs@MP in water and suppress the nonradiative deactivation; (2) The addition of high-charge-density metal ions Mg(II) and phosphorus element in the composite facilitates the singlet-to-triplet intersystem crossing process and enhances the RTP emission; (3) The aggregation of CDs@MP nanocomposites enables the matrix shell to self-assemble into a network, which further improves the rigidity of the shell and prevents the intermolecular motions, hence prolonging the RTP lifetime. The unique RTP feature and good water dispersibility allow the CD-based composite materials to be applicable in detection of temperature and pH in the aqueous phase. Our approach for producing long-lived RTP CDs@MP is effective, simple, and low-cost, which opens a new route to develop RTP materials that are applicable in aqueous solution.

Direct Electrochemical Sensing of Phosphate in Aqueous Solutions Based on Phase Transition of Calcium Phosphate.

Electrochemical determination of phosphate in aqueous solutions attracts considerable interests in both biological and environmental fields. Because of the electrochemically inactive nature of phosphate, direct electrochemical detection of phosphate is still a highly challenging task. Herein, we reported a direct electrochemical approach for the determination of phosphate based on the oxidation of coordinated OH during the phase transition of calcium phosphates (CaPs). The mixture of amorphous CaPs and octacalcium phosphate (Ca8(HPO4)2(PO4)4·5H2O), which acts as the starting material for hydroxyapatite (Ca10(PO4)6(OH)2), was self-assembled on a Nafion-modified glassy carbon electrode. The as-prepared electrode (CaPs/Nafion) showed a distinct oxidation peak at 1.0 V versus Ag/AgCl in phosphate solution. The peak heights were directly proportional to the concentration of phosphate from 0.1 to 10 µM in the presence of 1 mM Ca2+. After comprehensive characterization of the CaPs/Nafion electrode, it was understood that phosphate ions as a proton acceptor could stimulate the generation of coordinated OH from coordinated water (H2O) in CaP. The addition of Ca2+ could magnify the coordinated H2O source because of its hydration to H2O. The CaPs/Nafion electrode also displayed good selectivity as the electrochemical oxidization response was not affected by up to 10 µM of potentially competitive species like CO32-, NO3-, CH3COO-, SO42-, and Cl-. The results obtained in this work not only provided a new method for direct detection of phosphate in aqueous solution but also suggested that Ca2+ could be a promoter for electrochemical oxygen generation.

Potassium Ferrate(VI) as a Highly Efficient and Environmentally Friendly Chemiluminescence Reagent in Acidic Solution.

Herein we report that the reactions of potassium ferrate (VI) with a number of reductants can produce strong chemiluminescence (CL) in acidic aqueous solution. The CL Spectra were registered and compared with the classical KMnO4 and NaClO-H2O2 CL systems. The characteristic emission peaks at 1268 and 1050 nm were observed, which are consistent to the spectrum obtained from the NaClO-H2O2 system. Additional emission bands at 680 nm further confirmed the formation of singlet oxygen dimers. The high CL intensity and the chemically green nature of K2FeO4, prompt us to further develop it as a novel CL reagent. Sensitive response and wide calibration ranges were obtained for dopamine, ascorbic acid, and ethanol. The linear range for the determination of three analytes were 50 nM to 50 µM for dopamine (LOD: 20 nM), 5.0 µM to 1.0 mM for ascorbic acid (LOD: 2.21 µM), and 0.5 µM to 1.0 mM for ethanol (LOD: 0.30 µM). Thus, K2FeO4 has a great potential for the postcolumn detection of those UV featureless compounds.

Color tunable room temperature phosphorescent carbon dot based nanocomposites obtainable from multiple carbon sources via a molten salt method.

A molten salt (MS) method is designed for the preparation of carbon dot-based room temperature phosphorescent (RTP) materials. Carbon dots (CDs) are in situ formed and confined in inorganic salts during the recrystallization process. The composite materials CDs@MS and their RTP were characterized by scanning electron microscopy (SEM), powder X-ray diffraction (PXRD) and low temperature (77 K) fluorescence and phosphorescence spectroscopy. The as-prepared CDs@MS exhibits long lifetime RTP (up to 886 ms) and excitation dependent phosphorescence, i.e., the emission can be facilely tuned from 510 nm to 573 nm (green to yellow color) by changing the excitation wavelength. The RTP phenomenon is ascribed to the fact that the crystallization of molten salts forms a rigid structure, which preserves the triplet state of CDs and suppresses the nonradiative transition. It was found that the high charge density of metal ions plays a critical role in reducing the energy gap for realizing effective intersystem crossing. CD-based RTP materials with yellow phosphorescent emission are achieved from a variety of carbon sources and a gram-scale synthetic method. The excitation dependent RTP feature of CDs@MS nanocomposites could provide a novel dual security protection strategy in high-level information anticounterfeiting.

Rapid and selective luminescent sensing of allergenic gluten by highly phosphorescent switch-on probe.

First time the luminescent switch-on probe using novel water-soluble cyclometallated iridium complex (Ir-dc) has been developed for sensitive and selective detection of gluten in the presence of several interfering elements. Linear concentration range of gluten is obtained from 5 to 200 µg/mL with a limit of detection 2.6 µg/mL. The Ir-dc complex responded to the broad pH range which is advantageous for the detection of gluten in various food samples. Additionally, It has been successfully employed for the detection of gluten in commercial food samples of wheat flour and oats with highest recovery values, indicating applicability of Ir-dc for practical usage.

Rational Design of Magnetic Micronanoelectrodes for Recognition and Ultrasensitive Quantification of Cysteine Enantiomers.

Driven by the urgent need for recognition and quantification of trace amino acids enantiomers in various biologic samples, we demonstrate for the first time an ultrasensitive electrochemical chiral biosensor for cysteine (Cys) based on magnetic nanoparticles (Fe3O4@PDA/Cu xO) as electrode units. d-Cys-Cu2+-d-Cys formed in the presence of cysteine exhibits strong stability and a shielding effect on the redox current of indicator Cu2+, which can be used to quantify and recognize d-Cys by square wave voltammetry. Simultaneous detection of d-Cys and homocysteine (Hcy) is achieved in the presence of other amino acids, demonstrating an excellent selectivity of the sensor. Moreover, aided by the enrichment treatment effect of magnetic micronanoelectrodes, an ultrahigh sensitivity up to 102 µA µM-1 cm-2 was achieved, the detection limit is reduced to picomolar level (83 pM) for d-Cys and can be used for the recognition of cysteine enantiomers. The proposed method has been verified by real sample analysis with satisfactory results. The results highlight the feasibility of our proposed strategy for magnetic micronanoelectrode sensor, electrochemical recognition, and quantification of d-Cys, which can be more broadly applicable than that with traditional electrode structures and further advance the field of electrochemical sensors.

Novel tungsten phosphide embedded nitrogen-doped carbon nanotubes: A portable and renewable monitoring platform for anticancer drug in whole blood.

Biosensors based on converting the concentration of analytes in complex samples into single electrochemical signals are attractive candidates as low cost, high-throughput, portable and renewable sensor platforms. Here, we describe a simple but practical analytical device for sensing an anticancer drug in whole blood, using the detection of methotrexate (MTX) as a model system. In this biosensor, a novel carbon-based composite, tungsten phosphide embedded nitrogen-doped carbon nanotubes (WP/N-CNT), was fixed to the electrode surface that supported redox cycling. The electronic transmission channel in nitrogen doped carbon nanotubes (N-CNT) and the synergistic effect of uniform distribution tungsten phosphide (WP) ensured that the electrode materials have outstanding electrical conductivity and catalytic performance. Meanwhile, the surface electronic structure also endows its surprisingly reproducible performance. To demonstrate portable operation for MTX sensing, screen printing electrodes (SPE) was modified with WP/N-CNT. The sensor exhibited low detection limits (45 nM), wide detection range (0.01-540 µM), good selectivity and long-term stability for the determination of MTX. In addition, the technique was successfully applied for the determination of MTX in whole blood.

Synthesis and application of a water-soluble phosphorescent iridium complex as turn-on sensing material for human serum albumin.

A novel water-soluble cyclometallated iridium complex [Ir(pq-COOH)2FDS]- (pq-COOH = 2-phenylquinoline-4-carboxylic acid, FDS = 3-(2-pyridyl)-5,6-bis(4-sulfophenyl)-1,2,4-triazine dianions) (abbreviated as Ir) was synthesized and its phosphorescent property was comprehensively studied. It was found that the complex exhibited strong phosphorescence, which peaked at 634 nm in neutral conditions (maximized at pH 8.0). Its phosphorescence decreased with an increase in acidity of the aqueous solution. At pH 2.0, the quenched phosphorescence could be resumed upon the addition of human serum albumin (HSA) because of the hydrophobic and electrostatic interactions between HSA and Ir. Based on this phenomenon, a "turn on" type phosphorescence probe was developed for the detection of HSA. Under optimal conditions, a wide calibration range of 1-280 nM was obtained with a limit of detection of 0.8 nM for HSA. The phosphorescence probe was successfully used for the determination of HSA in blood serum and urine samples.

The adsorption behavior of cationic surfactant onto human hair fibers.

Quaternary ammonium surfactants are important ingredients that are frequently formulated into hair care products to modify the properties of hair surface. The adsorption kinetics, isotherms and association structures of cationic surfactants on hair surface, however, are not fully understood due to the heterogeneous nature of human hair fibers. In this work, a quaternary ammonium of surfactant, dimethylpabamidopropyl laurdimonium tosylate (DDABDT) was chosen as a probe to investigate the adsorption behavior of cationic surfactant on cuticles of scalp hair. The results reveal that the adsorption kinetics fit to a pseudo-second-order kinetic model and the adsorption isotherms fit to the Freundlich adsorption model. With the increase of DDABDT adsorption, the wettability of hair fibers changes from hydrophobic to hydrophilic. The association structure could be monolayer or bilayer depending on the initial concentration of the surfactant. In the monolayer structure, the 'anchor' surfactant molecules are believed to adsorb vertically on the surface of hair fibers through electrostatic interaction. In the bilayer structure, the second layer molecules may then pile up on top of the first layer with charged groups orienting outward. The thickness of DDABDT film on hair fibers treated with 5 x 10(-4) mol/l DDABDT solution is measured to be 5.42 nm on average with a force-distance method. This figure is very close to the two times of the theoretical molecular size of the DDABDT molecule.

Dynamic effects of leflunomide on IL-1, IL-6, and TNF-alpha activity produced from peritoneal macrophages in adjuvant arthritis rats.

AIM: To investigate the effects of leflunomide (LEF) on modulating interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor- alpha (TNF-alpha) production induced by lipopolysaccharide (LPS) in peritoneal macrophages (PMphi) in adjuvant arthritis rats and elucidate the possible mechanisms of antiinflammatory and antirheumatoid effects of LEF. METHODS: Freund's complete adjuvant was injected in the hind footpad of rats to induce adjuvant arthritis (AA) rat model. The PMphi samples were taken at different time after medication. IL-1, IL-6, and TNF-alpha activities released from PMphi were measured by ELISA method or bioassay method. RESULTS: Production of IL-1, IL-6, and TNF-alpha was increased in the culture supernatant of PMphi in AA model rat. LEF could inhibit LPS-induced release of IL-1 and TNF-alpha from PMphi of the AA rats and the inhibitory effects were extremely rapid. LEF (10, 25 mg/kg) administrated for 21d could inhibit IL-6 release from PMphi in AA rats. CONCLUSION: The antiinflammatory mechanisms of LEF in AA rats might be related to inhibitory level of IL-1, IL-6, and TNF-alpha from PMphi in vivo.