pH-sensitive drug delivery based on chitosan wrapped graphene quantum dots with enhanced fluorescent stability.

Graphene quantum dots (GQDs) were prepared by the pyrolysis of citric acid (CA), which were used for the loading of hydrophilic cytarabine (Cyt), an anti-cancer drug, and then wrapped with chitosan (CS) gels for the encapsulation of the loaded Cyt. The fluorescent stability of GQDs was significantly enhanced in the presence of CS, which might be attributed to the inhibited agglomeration of GQDs by the CS gels. In addition, the burst release of Cyt from the developed carrier was also effectively relieved by the CS coating. Since the incorporation of Cyt into GQDs was achieved by amidation reaction, the delivery of Cyt from the carrier was pH-sensitive due to the hydrolysis of the amido linkage between GQDs and Cyt in acidic medium.

A facile synthesis of two ionized fluorescent carbon dots and selective detection toward Fe2+ and Cu2.

In this study, a facile synthesis of two ionized carbon dots (CDs-2 and CDs-3) is reported, in which different ionic pairs are formed at the surface of the carbon core. In contrast to CDs-3, the accumulation of carbon core can be clearly observed in the TEM image of CDs-2. This is due to the linkage of the dibromine alkyl group. Compared with naked CDs in the absence of the ionic pair, the maximum emission wavelength undergoes a red-shift of nearly 60 nm. Moreover, protic solvents (water, ethanol and N,N'-dimethyl formamide) have an apparent effect on the emission intensities of CDs-2 and CDs-3. The time-resolved average lifetimes of CDs-2 and CDs-3 are calculated as 56.34 ns and 54.50 ns, respectively. Furthermore, they both have much better fluorescence stability in the solution with pH ranging from 2 to 11 due to the presence of the imidazolium cation. It is interesting to see that CDs-2 and CDs-3 have much different responses towards Cu2+ and Fe2+. The CDs-3 solution generates clear fluorescence quenching when treated with Fe2+. In brief, we believe that these findings can inspire more research developments in the synthesis and further application of functional CDs.

Recent progress of enantioseparation under scale production (2014-2019).

Very different from enantiorecognition at an analytical level, preparative enantioseparation at scale production has to confront many problems. In recent years, various separation techniques have been developed with much progress including high-performance liquid chromatography, liquid-liquid extraction, membrane separation, enantioselective solid-phase absorption, and enantioselective precipitation. Among them, in order to achieve high enantiomerical purity of the enantiomers after separation, two approaches are commonly carried out. One is that continuous separation is necessary when one-step separation cannot have satisfactory efficiency. Another is that most of the research groups focus on the construction of novel chiral environment with much more rigid structures of the selectors. Combined with these two aspects, we mainly introduce current topics, trends, strategies related to enantioseparation under large scale.

A facile route to prepare functional mesoporous organosilica spheres with electroactive units for chiral recognition of amino acids.

Conductive materials are valuable supports and widely applied in electrochemical analysis. In the current article, a mesoporous organosilica sphere (S,S)-CPMO-3 with the chiral group and electroactive units is presented. The organosilicon framework is composed of free ions belonging to the ionic liquid and the chiral group arising from (1S,2S)-1,2-diaminocyclohexane. Next, a bare electrode was modified by the as-synthesized composite material to construct the new electrochemical sensor (S,S)-CPMO-3-GCE. It was observed that (S,S)-CPMO-3-GCE exhibited favourable enantioselective recognition in the response of the peak current (Ip) and the peak potential (Ep) to the different configurations of amino acids. Taking tryptophan as an example, the value of IL/ID is 13.84 and the peak-to-peak potential approaches 48 mV. In addition, cysteine and tyrosine were successfully distinguished by the sensor. In summary, this study not only introduces a route for the synthesis of a conductive material, but also opens up its further potential in enantioselective recognition.

Improvement of Laser Transmission Welding of Glass with Titanium Alloy by Laser Surface Treatment.

Laser surface treatment of the titanium alloy was locally oxidized on the metal surface to improve the joint strength of laser transmission welding of high borosilicate glass with titanium alloy. The results find that the welding strength was increased 5 times. The welding mechanism was investigated by the morphology of the welded parts, the tensile-fracture failure mode, the diffusion of the interface elements, and the surface free energy. The results show that there are many adherents between the titanium alloy and high borosilicate glass after tensile fracture, the welding strength was higher when the laser voltage was 460 V, and the tensile⁻fracture failure mode is mainly ductile fracture. Element-line scanning analysis revealed that elemental diffusion occurred in the two materials, which is an important reason for the high welding strength. Surface free-energy analysis shows that laser surface treatment improves the surface free energy of titanium alloy, promotes the wettability and compatibility, and increases the welding strength of titanium alloy with glass.

A facile avenue to prepare chiral graphene sheets as electrode modification for electrochemical enantiorecognition.

Electrochemical enantiorecognition has attracted much interest due to its advantages of low cost and simple equipment. In this work, a new chiral ionic liquid is prepared and applied as an electrolyte for the one-step synthesis of functional graphene sheets (GO-(S,S)-CIL). More importantly, an electrode is modified by the material for the construction of an electrochemical sensor (GO-(S,S)-CIL-GCE). Enantiomers including L/D-tryptophan, (R)-/(S)-mandelic acid, (R)-/(S)-malic acid, and L/D-tyrosine are successfully distinguished by GO-(S,S)-CIL-GCE in the response of peak currents to different forms. In addition, the peak potential of the L form is located negatively compared to the D form for tryptophan, and the value of the peak-to-peak potential separation approaches 72 mV. The recognition mechanism is assessed by the density functional theory calculation in detail. In brief, the present method offers great promise for the preparation of functional graphene sheets and their further application in chiral recognition.

Experimental Study on the Laser Transmission Joining of Polystyrene and Titanium.

To address the difficulty of joining polystyrene (PS) and titanium by laser transmission joining, two methods-laser treatment of the titanium surface and oxygen plasma treatment of the PS surface-are used to compare the laser transmission joint strengths of the different treatment methods. The results of the experiments find that joining with titanium can be achieved only when PS is treated with oxygen plasma. When the laser-treated surface of titanium is jointed to the oxygen plasma-treated PS, the joint strength is the highest, reaching 6.5 MPa. The joining mechanism of oxygen plasma-treated PS and laser oxidation-treated titanium was investigated by joint tensile failure mode, joint micromorphology observation, contact angle and surface free energy experiments, and X-ray photoelectron spectroscopy (XPS). The results show that the failure mode of the joint is an interfacial failure; the size and amount of bubbles play an important role in the joining strength, and the joints with fine and uniform bubbles have the highest joint strength. The two surface treatment methods can improve the surface energy of the joints, improve the compatibility between the two joining surfaces, and enhance the joint strength. Ti⁻C and Ti⁻O chemical bonds are formed at the joints, which are the main reason for the increase in joint strength.

Preparation of nitrogen-doped carbon using graphene Quantum dots-chitosan as the precursor and its supercapacitive behaviors.

Nitrogen-doped carbon (N-C) is pyrolytically prepared by using the nanocomposites of graphene Quantum dots (GQDs) and chitosan (CS) as the precursor. Due to the existence of GQDs nanofiller, the three-dimensional (3D) interconnected frameworks of CS are well preserved after the pyrolysis treatment; meanwhile, CS in the nanocomposites functions as nitrogen source for the N-C. The obtained N-C exhibits a considerable specific capacitance (545Fg-1 at 1Ag-1), high rate capability and excellent cyclic stability (88.9% capacitance retention after 5000cycles at 10Ag-1) when it is used as the electrode materials in supercapacitors. The well-preserved 3D frameworks and N-doping are believed to be responsible for the excellent supercapacitive behaviors of the N-C.

Enhancement of the Laser Transmission Weldability between Polyethylene and Polyoxymethylene by Plasma Surface Treatment.

Due to their large compatibility difference, polyethylene (PE) and polyoxymethylene (POM) cannot be welded together by laser transmission welding. In this study, PE and POM are pretreated using plasma that significantly enhances their laser transmission welding strength. To understand the mechanism underlying the laser welding strength enhancement, surface modification is analyzed using contact angle measurements, atomic force microscopy (AFM), optical microscopy, and X-ray photoelectron spectroscopy (XPS). Characterization results show that the plasma surface treatment improves the surface free energy, significantly enhancing the wettability of the materials. The increase in surface roughness and the generation of homogeneous bubbles contribute to the formation of mechanical micro-interlocking. The oxygen-containing groups introduced by the oxygen plasma treatment improve the compatibility of PE and POM, and facilitate the diffusion and entanglement of molecular chains and the formation of van der Waals force.

Nonenzymatic glucose sensing by CuO nanoparticles decorated nitrogen-doped graphene aerogel.

CuO nanoparticles decorated N-doped graphene aerogel (NGA-CuO) was facilely synthesized via a mild hydrothermal method followed by freeze-drying and calcination, which was characterized by TEM, FT-IR, XPS, XRD and electrochemical impedance spectroscopy (EIS). The obtained NGA-CuO was used for the construction of a nonenzymatic sensing platform for glucose, exhibiting wide linear range, low detection limit, high sensitivity, reproducibility, selectivity and stability. The excellent analytical performances of the NGA-CuO based glucose sensor might be attributed to the synergistic effect of CuO nanoparticles and N-doped graphene aerogel (NGA). The practical applications of the proposed sensor was verified by determining glucose concentrations in five human serum samples, and the obtained results were quite comparable to those measured on the standard clinical instrument.