Xiaoya Liu

A novel non-enzymatic glucose sensor based on Cu nanoparticle modified graphene sheets electrode.

A novel, stable and sensitive non-enzymatic glucose sensor was developed by potentiostatically electrodepositing metallic Cu nanoparticles on graphene sheets. The electrochemical performance of the Cu-graphene sheets electrode for detection of glucose was investigated by cyclic voltammetry and chronamperometry. The Cu-graphene sheets electrode displayed a synergistic effect of copper nanoparticles and graphene sheets towards the oxidation of glucose in alkaline solution, showing higher oxidation current and negative shift in peak potential. At detection potential of 500 mV, the Cu-graphene electrode sensor presented a wide linear range up to 4.5mM glucose with a detection limit of 0.5 μM (signal/noise=3). In addition, the sensor responds very quickly (<2s) with addition of glucose. Furthermore, the Cu-graphene sheets electrode exhibits high stability and selectivity to glucose, and the poisoning by chloride ion as well as interference from the oxidation of common interfering species (ascorbic, dopamine, uric acid and carbohydrate) are effectively avoided. The Cu-graphene sheets electrode allows highly selective and sensitive, stable and fast amperometric sensing of glucose, which is promising for the development of non-enzymatic glucose sensor.

Glucose sensors based on electrodeposition of molecularly imprinted polymeric micelles: A novel strategy for MIP sensors

A voltammetric glucose sensor was prepared from novel molecularly imprinted polymeric micelles (MIPMs) through direct electrodeposition. The MIPMs, which were photo-crosslinkable and nano-scaled with high specific surface area, were prepared via macromolecule self-assembly of an amphiphilic photo-crosslinkable copolymer, combined with a molecular imprinting technique using glucose as the template molecule. A MIP film was formed in situ on the electrode surface by electrodeposition of the MIPMs, while photo-crosslinking led to a robust film which showed good solvent resistant to dissolution. With these features, the resulting sensor showed good response and selectivity towards glucose. In particular, the linear response of this glucose sensor ranged from 0.2 mM to 8 mM and its comparatively higher detection limit, about 10 mM, indicated numerous effective recognition sites among the polymer matrix due to the large specific surface area of MIPM. In addition, this MIP sensor also showed good stability and reversibility. The contribution of this work lies in not only the invention of a new type of glucose MIP sensor with good performance, but also the creation of a novel strategy to develop advanced MIP sensors for a wide range of templates in viewing of the versatility of the amphiphilic copolymers and the ease of control and applicability of the electrodeposition process.

Highly flexible magnetic composite aerogels prepared by using cellulose nanofibril networks as templates.

Nanostructured cellulose nanofibrils can form ductile or tough networks that are suitable templates for the creation of materials with functional properties. In this work, a facile method has been developed for the preparation of magnetic hybrid cellulose aerogels. The preparation processes followed by two steps, firstly, preparation of cellulose hydrogel films from LiOH/urea solvent, then CoFe2O4 nanoparticles were synthesized in the porous structured cellulose scaffolds. After being freeze-dried, CoFe2O4/cellulose magnetic aerogels were obtained. The porosity of the composite aerogels ranged from 78 to 52% with pore size distribution in a few tens of nanometers. The internal specific surface areas were around 300-320 m2/g, and the densities were in the range of 0.25-0.39 g/cm3. The hybrid aerogels showed improved mechanical strength, superparamagnetic properties. Unlike solvent-swollen gels and ferrogels, the magnetic composite aerogels were lightweight, flexibility, high porosity and with large specific surface area and could be expected to be used in many fields.

Highly cross-linked fluorescent poly(cyclotriphosphazene-co-curcumin) microspheres for the selective detection of picric acid in solution phase

Highly cross-linked and organic–inorganic hybrid poly(cyclotriphosphazene-co-curcumin) microspheres (PCPC-MS) were facilely prepared by a one-step precipitation copolymerization method, and served as a fluorescent chemical sensor for the detection of picric acid (PA) in solution phase. The photochemically inert cyclotriphosphazene moieties intentionally introduced into the structure of the sensor could play a role not only in connecting curcumin fluorophores to construct a highly cross-linked fluorescent architecture with excellent thermal stability and photobleaching stability, but also in effectively enriching PA from bulk solution to the surface of the sensor by the acid–base interaction between the acidic phenolic hydroxyl groups of PA molecules and the electron-rich nitrogen atoms of the cyclotriphosphazene units, which might facilitate the formation of a ground-state non-fluorescent complex of the microspheres and PA as well as the excited-state energy transfer from the microspheres to PA. Therefore, PCPC-MS exhibited a fluorescence quenching response towards PA with high sensitivity, efficiency, and selectivity over a number of other analytes such as 2,4,6-trinitrotoluene, 2,4-dinitrotoluene, 1,3-dinitrobenzene, 4-nitrotoluene, nitrobenzene, 4-benzoquinone, chlorobenzene, and nitromethane in methanol. In addition, PCPC-MS could also effectively detect PA in the presence of the other analytes, indicating their remarkable ability for resisting interferences and specific recognition of PA. This study provides new insights into the design and preparation of a polymer-based fluorescence chemical sensor for PA with low toxicity, a simple preparation process, and high selectivity.

A facile approach for imprinting protein on the surface of multi-walled carbon nanotubes.

This study describes a green, facile and low cost approach for imprinting protein on the surface of multi-walled carbon nanotubes (MWNTs) using papain as the template, dopamine as the functional monomer. By simply mixing MWNTs, dopamine, template protein in weak alkaline aqueous solution, a thin adherent polydopamine (PDA) film imprinted with protein was spontaneously obtained on the surface of MWNTs to produce the imprinted nanomaterials (MWNTs@MIPs). The obtained MWNTs@MIPs were characterized with Fourier transform infrared spectrometer (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The adsorption process of the MWNTs@MIPs towards template protein was investigated in detail. The effects of the concentration of the monomer and template, polymerization time, extraction process were optimized. The prepared MWNTs@MIPs show fast binding kinetics, high binding capacity and acceptable specific recognition behavior towards template proteins. Furthermore, the stability and regeneration were also investigated, which indicated that the MWNTs@MIPs had good reusability. The good recognizing behavior coupled to the low cost and facile one-step preparation make the MWNTs@MIPs attractive for separation and specific protein recognition.

In situ green synthesis of Au nanoparticles onto polydopamine-functionalized graphene for catalytic reduction of nitrophenol

In this paper, a simple, green and environmental-friendly method is developed for depositing gold nanoparticles (Au NPs) on the surface of polydopamine (PDA)-functionalized graphene (graphene/PDA) for highly efficient catalysis. In this approach, graphene/PDA was prepared through the self-polymerization of dopamine in the presence of graphene oxide (GO) in aqueous solution. With the addition of HAuCl4, AuCl4−1 ions were adsorbed on the surface of graphene/PDA and in situ reduced to metallic Au NPs owing to the abundant catechol groups on the PDA chain. In the whole procedure, PDA not only acts as the surface modifier of graphene, but more importantly it also serves as the reducing agent and stabilizer for Au NPs simultaneously, avoiding the usage of any toxic reducing reagent or special stabilizing agent. The graphene/PDA–Au NPs were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X-Ray Diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It was found that the size and amount of Au NPs are tunable by changing the experimental conditions. The obtained graphene/PDA–Au NPs nanocomposite, combining the advantages of graphene and Au NPs, exhibits remarkable catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol. Considering its green facile preparation procedure and high catalytic activity, the prepared graphene/PDA–Au NPs holds great promise as a highly efficient, cost-effective and environmental-friendly catalyst for industrial applications.

A facile approach for synthesizing molecularly imprinted graphene for ultrasensitive and selective electrochemical detecting 4-nitrophenol.

In this work, a novel and convenient strategy was developed to prepare molecularly imprinted polymers (MIPs) on the surface of graphene sheet. In this route, vinyl group functionalized graphene (GR/NVC) was first prepared by immobilizing 4-vinylcarbazole onto the surface of graphene via π-π interaction. The subsequent grafting copolymerization of methacrylic acid and ethylene glycol dimethacrylate in the presence of 4-nitrophenol (4-NP, template molecule) was carried out at GR/NVC surface, leading to the formation of GR/MIPs composite. The GR/MIPs composite was characterized by FTIR, fluorescence, TGA, SEM and AFM, and was used to fabricate electrochemical sensor for the detection of 4-NP. The electrochemical behavior of GR/MIPs sensor for 4-NP was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The effects of the preparation conditions, such as concentration of the NVC and template, the solution pH, and incubation time, were also optimized. Under optimized conditions, the DPV current response of GR/MIPs sensor was nearly 12 times than that of the GR/NIPs sensor. It also should be noted that as compared to traditional MIP, shorter response time and much higher current response were demonstrated. In addition, the GR/MIPs sensor could recognize 4-NP from its structural analogs, indicating the excellent selectivity of the GR/MIPs sensor. The peak current is linearly proportional to the concentration of 4-NP ranging from 0.01 μM to 100 μM and 200 μM to 1000 μM with a significantly low detection limit of 5 nM, a wider response range and lower detection limits as compared to most of the previously reported electrochemical sensors for 4-NP. Furthermore, the GR/MIPs sensor exhibits good stability with adequate reproducibility and has been successfully used to determine 4-NP in water samples.

Short communication: Rapid detection of milk fat adulteration with vegetable oil by fluorescence spectroscopy

This study assessed the potential application of fluorescence spectroscopy in detecting adulteration of milk fat with vegetable oil and characterizing the samples according to the source of the fat. Pure butterfat was adulterated with different vegetable oils at various concentrations (0, 5, 10, 15, 20, 30, and 40%). Nonfat and reduced-fat milk were also adulterated with vegetable oils to simulate full-fat milk (3.2%). The 2- and 3-dimensional front-face fluorescence spectroscopy and gas chromatography were used to obtain the fluorescence spectra and fatty acid profile, respectively. Principal component analysis and 3-way partial least squares regression analysis were applied to analyze the data. The pure and adulterated samples were discriminated based on the total concentration of saturated fatty acids and unsaturated fatty acids, and also on the 3 major fluorophores: tryptophan, tocopherols, and riboflavin. Fluorescence spectroscopy was able to detect up to 5% of adulteration of vegetable oil into the butterfat. The saturated fatty acids showed higher predictability than the unsaturated fatty acids (R(2) = 0.73-0.92 vs. 0.20-0.65, respectively). The study demonstrated the high potential of fluorescence spectroscopy to rapidly detect adulteration of milk fat with vegetable oil, and discriminate commercial butter and milk according to the source of the fat.

Cross-linked micelles of graftlike block copolymer bearing biodegradable ε-caprolactone branches: a novel delivery carrier for paclitaxel

The poor stability of micellar drug delivery system in vivo due to large volume dilution often leads to premature drug release with low therapeutic efficacy. In this study, shell cross-linked micelles of graftlike block copolymer bearing biodegradable e-caprolactone branches (PMAA-b-PFM) were prepared to be used as a novel carrier for paclitaxel (PTX). PTX was successfully encapsulated into the hydrophobic cores of the cross-linked micelles using the dialysis method. The resultant PTX-loaded cross-linked micelles were about 99 nm in diameter with spherical shape and high encapsulation efficiency. The PTX-loaded cross-linked micelles had smaller sizes and better stability as compared to the non-cross-linked controls. Fluorescence microscopy and flow cytometry studies showed that PTX-loaded cross-linked micelles had excellent cellular uptake ability by bone marrow derived macrophages and human glioma U87 cells. Cellular uptake of cross-linked micelles was found to be higher than non-cross-linked controls due to smaller size. In vitro cytotoxicity studies also revealed that the PTX-loaded cross-linked micelles exhibit high anti-cancer activity to U87 cells. These results suggested that cross-linked PMAA-b-PFM micelles could be a potential vehicle for delivering hydrophobic chemotherapeutic drugs to tumors.

Tannic acid functionalized graphene hydrogel for entrapping gold nanoparticles with high catalytic performance toward dye reduction.

In this work, a simple, cost-effective, and environmental-friendly strategy was developed to synthesize gold nanoparticles (Au NPs) decorated graphene hydrogel with the use of tannic acid. This facile route involved the reduction of graphene oxide (GO) in the presence of tannic acid to form tannic acid functionalized graphene hydrogel, followed by loading and in situ reduction of AuCl4(-) ions in the graphene hydrogel network benefiting from the abundant phenol groups of tannic acid. Tannic acid (TA), a typical plant polyphenol widely present in woods, not only reduced GO and induced the self-assembly of reduced graphene oxide into graphene hydrogel, but also served as the reducing agent and stabilizer for the synthesis and immobilization of Au NPs, avoiding extra chemical reagent and any stabilizer. The obtained Au NPs decorated graphene hydrogel (Au@TA-GH) was fully characterized and exhibited much higher catalytic activities than the unsupported and other polymer-supported Au NPs toward the reduction of methylene blue (MB). In addition, the high catalytic activity of Au@TA-GH could withhold in different pH solution conditions. Another distinct advantage of Au@TA-GH as catalysts is that it can be easily recovered and reused for five cycles.