Juan Qiao

Folic acid-functionalized fluorescent gold nanoclusters with polymers as linkers for cancer cell imaging

A novel nano-conjugate containing ultrasmall water-soluble AuNCs protected by ovalbumin as the fluorescent part, folic acid as the targeting ligand and a homopolymer N-acryloxysuccinimide as the linker has been investigated. Moreover, specific staining of HeLa cells by the nano-conjugate has been demonstrated.

Facile one-pot synthesis of l-proline-stabilized fluorescent gold nanoclusters and its application as sensing probes for serum iron

Gold nanoclusters (Au NCs) possess outstanding physical and chemical attributes that make them excellent scaffolds for the construction of novel chemical and biological sensors. In this study, a simple one-pot synthesis method, employing l-proline as the stabilizer, was presented for preparation of fluorescent Au NCs. This strategy allowed the generation of water-soluble Au NCs within a short time of 15 min. The as-prepared Au NCs exhibited a bluish fluorescence emission at 440 nm and a quantum yield of 2.94%. Based on the aggregation-induced fluorescence quenching mechanism, the Au NCs provided favorable biocompatibility, high sensitivity and good selectivity for the measurement of ferric ion (Fe(3+)). Furthermore, serum samples were analyzed for the serum iron contents by using this proposed biocompatible fluorescent sensor, indicating the potential value of this Au NCs-based fluorescent sensor for application in biological and clinical analysis.

Immobilization of trypsin via reactive polymer grafting from magnetic nanoparticles for microwave-assisted digestion

The effort to stabilize enzymes and improve their activity has generated great interest because of their wide application in proteomics research, bioenergy conversion, bioassays and so on. In this work, biocompatible reactive polymer, poly (glycidyl methacrylate), grafted from magnetic nanoparticles by atom transfer radical polymerization method, has been firstly proposed to immobilize enzymes for microwave-assisted digestion. Meanwhile, trypsin was chosen as a model enzyme. Resulting from the increased functionality, the immobilization amount of the enzyme on the magnetic nanoparticle surface has been greatly improved. Furthermore, the enzyme immobilized magnetic nanoparticles have exhibited excellent repeatability and stability. The influence of the polymer chain length on digestion efficiency has been investigated both at 37 °C and under microwave. It has been found that the digestion efficiency increases with the lengthened polymer brushes due to the increased immobilization amount. Utilizing cytochrome C as a model protein for digestion, the performance of this immobilized biocatalyst has been demonstrated and this digestion assisted with microwave could be completed within 15 s. This study offers insight into the design of polymer brushes on the surface of magnetic nanoparticles for high digestion efficiency in the future.

Ratiometric fluorescent probe based on gold nanoclusters and alizarin red-boronic acid for monitoring glucose in brain microdialysate

Glucose monitoring with high sensitivity and accuracy in the cerebrospinal fluid is a challenge for evaluating the role of glucose in the physiological and pathological processes. In this work, a ratiometric fluorescent probe for sensing glucose was developed. In the probe, the gold nanoclusters protected by ovalbumin played the role as the reference of fluorophore and the Alizarin Red S-3-aminophenyl boronic acid immobilized on the poly(N-acryloxysuccinimide) acted as both the response signal and specific recognition unit for sensing glucose. Once the ratiometric fluorescent probe reacted with glucose in the biological system, its fluorescence intensity at 567 nm was quenched, while the fluorescence intensity at 610 nm was essentially unchanged. In addition, the prepared ratiometric fluorescent probe showed higher stability against environmental effects. As a result, the present ratiometric fluorescent probe was successfully used for monitoring of glucose in the rat brain following the cerebral calm/ischemia.

Ionic liquids with amino acids as cations: novel chiral ligands in chiral ligand-exchange capillary electrophoresis

Ionic liquids (ILs) with L-proline (L-Pro) as cations have been developed for the novel chiral ligands coordinated with Cu(II) in chiral ligand exchange capillary electrophoresis (CLE-CE). Four kinds of amino acid ionic liquids (AAILs), including [L-Pro][CF(3)COO], [L-Pro][NO(3)], [L-Pro][BF(4)] and [L-Pro(2)][SO(4)], were successfully synthesized. Among them, [L-Pro][CF(3)COO] was selected as the model ligand to optimize the separation conditions. The influences of AAIL concentration, pH, and methanol concentration on efficiency of chiral separation were investigated. Then it has been testified that the optimal buffer solution consisted of 25.0mM Cu(Ac)(2), 50.0 mM AAIL and 20% (v/v) methanol at pH 4.0. The interesting thing is well enantioresolution could be observed with [L-Pro][CF(3)COO] as the new chiral ligand and nine pairs of labeled D,L-AAs were successfully separated with the resolution ranging from 0.93 to 6.72. Meanwhile, the baseline separation of labeled D,L-AAs could be achieved with the other three kinds of AAILs as ligands. The results have demonstrated the good applicability of AAILs with AAs as cations for chiral separation in CLE-CE system. In addition, comparative study was also conducted for exploring the mechanism of the AAILs as new ligands in CLE-CE.

Poly(2-Vinyl-4,4-dimethylazlactone)-Functionalized Magnetic Nanoparticles as Carriers for Enzyme Immobilization and Its Application

Fabrication of various efficient enzyme reactors has triggered increasing interests for its extensive applications in biological and clinical research. In this study, magnetic nanoparticles were functionalized by a biocompatible reactive polymer, poly(2-vinyl-4,4-dimethylazlactone), which was synthesized by reversible addition-fragmentation chain transfer polymerization. Then, the prepared polymer-modified magnetic nanoparticles were employed as favorable carriers for enzyme immobilization. l-Asparaginase was selected as the model enzyme to fabricate the enzyme reactor, and the prepared enzyme reactor exhibited high loading capacity of 318.0 μg mg(-1) magnetic nanoparticle. Interestingly, it has been observed that the enzymolysis efficiency increased slightly with the lengthened polymer chain, resulting from the increased immobilization amount of enzyme. Meanwhile, the immobilized enzyme could retain more than 95.7% activity after 10 repeated uses and maintain more than 72.6% activity after 10 weeks storage. Moreover, an extracorporeal shunt system was simulated to estimate the potential application capability of the prepared l-asparaginase reactor in acute lymphoblastic leukemia treatment.

Novel Oligo(ethylene glycol)-Based Molecularly Imprinted Magnetic Nanoparticles for Thermally Modulated Capture and Release of Lysozyme

In this study, oligo(ethylene glycol) (OEG)-based thermoresponsive molecularly imprinted polymers (MIPs) for lysozyme on the surface of magnetic nanoparticles were synthesized. Thermoresponsive monomer 2-(2-methoxyethoxy)ethyl methacrylate, chelate monomer N-(4-vinyl)-benzyl iminodiacetic acid, and acidic monomer methacrylic acid were selected as the ingredients for preparing the MIP layer. The thermoresponsive behavior of the novel imprinted magnetic nanoparticles was evaluated by dynamic light scattering and swelling ratios measurements. Interestingly, in analysis of lysozyme, the capture/release process could be modulated by changing the temperature, avoiding tedious washing steps. Meanwhile, high adsorption capacity (204.1 mg/g) and good selectivity for capturing lysozyme were achieved. Additionally, surface imprinting with magnetic nanoparticles as substrate allowed for short adsorption time (2 h) and rapid magnetic separation. Furthermore, the proposed imprinted magnetic nanoparticles were used to selectively extract lysozyme in human urine with recoveries ranging from 89.2% to 97.3%. The results indicated that the OEG-based monomers are promising for responsive MIP preparation, and the proposed imprinted material is efficient for thermally modulated capture and release of target protein.

Chiral ligand-exchange CE assays for separation of amino acid enantiomers and determination of enzyme kinetic constant

This paper deals with studies on the use of Zn(II)‐L‐ornithine complex as a chiral selecting system for the enantioseparation and UV detection of amino acids (AAs) by using the principle of ligand‐exchange CE. Successful enantioseparation of three pairs of label‐free aromatic AAs and four pairs of labeled AA enantiomers have been achieved with a buffer of 100.0 mM boric acid, 5.0 mM ammonium acetate, 3.0 mM ZnSO4 and 6.0 mM L‐Orn at pH 8.2. This new method was shown to be applicable to the quantitative analysis of D‐ and L‐aromatic AAs, with a linear range between 12.5 and 800.0 μg/mL, and a correlation coefficient above 0.99. Thus this assay, which is facile and relatively rapid, allows us to measure the enzyme catalytic activity in the incubation of D,L‐AAs with D‐AA oxidase. Using this new method, we can determine the enzyme kinetic constant, lending insight into potential enzyme mechanism.

Thermal responsive fluorescent block copolymer for intracellular temperature sensing

In this study, a novel fluorescent and temperature responsive block copolymer has been designed and synthesized by a reversible addition–fragmentation chain transfer (RAFT) polymerization method in terms of the strategy that N-isopropylacrylamide (NIPAm), maleic anhydride (MAn) and 7-amino-4-methylcoumarin (AMC) act as the temperature responsive unit, the hydrophilic unit and the fluorescent unit, respectively. The successfully synthesized block copolymer was characterized by gel permeation chromatography (GPC) and nuclear magnetic resonance (1H NMR) spectroscopy. Meanwhile, the self-aggregation behaviour in aqueous solution and the thermo-responsive property of the block copolymer were demonstrated by particle size measurement, transmission electron microscopy (TEM) observations and lower critical solution temperature (LCST) determination, respectively. Then the variation of fluorescence intensity with temperature was confirmed. With increasing temperature, shrinking of PNIPAm chains caused the block copolymer to become more hydrophobic above the LCST, assembling larger aggregates with lower interfacial curvature. Thus a part of the fluorescent groups would be embedded inside the enlarged block copolymer micelles, resulting in lower fluorescence intensity. Furthermore, the superior hydrophilicity and biocompatibility of the block copolymer as a thermometer have been demonstrated by application in intracellular temperature sensing of MDCK cells ranging from 24 °C to 38 °C.

A chiral ligand exchange CE essay with zinc(II)–l-valine complex for determining enzyme kinetic constant of l-amino acid oxidase

A new strategy for the enantioseparation of D,L-amino acids employing the principle of ligand exchange capillary electrophoresis with Zn(II)-L-valine complex as a chiral selecting system in the presence of beta-cyclodextrin has been designed. Successful enantioseparation of label free and labeled amino acids have been achieved with a buffer of 100.0mM boric acid, 5.0mM ammonium acetate, 4.0mM beta-cyclodextrin, 4.0mM ZnSO(4) and 8.0mM L-valine at pH 8.1. This new method was shown to be applicable to the quantitative analysis of label free D- and L-aromatic amino acids. Furthermore, the expanding enzymatic use of L-amino acid oxidase to incubate with different L-amino acids has allowed understanding of the substrates specificity. An on-column incubation assay has been developed to study the L-amino acid oxidases catalytic efficiency. It was demonstrated that the enzyme kinetic constant could be determined by using this new method.