Minbo Lan

Highly Sensitive and Selective Nonenzymatic Detection of Glucose Using Three-Dimensional Porous Nickel Nanostructures

Highly sensitive and selective nonenzymatic detection of glucose has been achieved using a novel disposable electrochemical sensor based on three-dimensional (3D) porous nickel nanostructures. The enzyme-free sensor was fabricated through in situ growing porous nickel networks on a homemade screen-printed carbon electrode substrate via electrochemically reducing the Ni(2+) precursor, along with continuously liberating hydrogen bubbles. The resulting nickel-modified electrode was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDX), powder X-ray diffractometry (XRD), and electrochemical techniques. Cyclic voltammetric, alternating-current impedance, and amperometric methods were used to investigate the catalytic properties of the assembled sensor for glucose electro-oxidation in alkaline media. Under optimized conditions, the enzymeless sensor exhibited excellent performance for glucose analysis selectively, offering a much wider linear range (from 0.5 μM to 4 mM), an extremely low detection limit (0.07 μM, signal-to-noise ratio (S/N) of 3), and an ultrahigh sensitivity of 2.9 mA/(cm(2) mM). Importantly, favorable reproducibility and long-term performance stability were obtained thanks to the robust frameworks. Application of the proposed sensor in monitoring blood glucose was also demonstrated.

A novel lactoferrin-modified β-cyclodextrin nanocarrier for brain-targeting drug delivery.

The blood-brain barrier (BBB) restricts the transfer and delivery of most drug substances to brain. In this study, a novel nano-drug delivery system for brain-targeting was developed and investigated in vitro and in vivo. Lactoferrin (Lf) was selected as a brain-targeting ligand and conjugated to β-cyclodextrin (β-CD) via the heterobifunctional polyethyleneglycol (PEG) linker NHS-PEG-MAL, yielding Lf conjugated β-cyclodextrin (Lf-CD). UV-vis, FTIR, NMR and transmission electron microscopy (TEM) techniques clearly demonstrated the successful synthesis of Lf-CD nanoparticles with the average diameter of 92.9 ± 16.5 nm. Using near-infrared fluorescent dye IR-775 chloride (IR) as a model compound of poorly water-soluble drugs, IR-loaded Lf-CD nanoparticles (Lf-CD/IR) were successfully prepared with a high entrapment efficiency of 98.1 ± 4.8%. Biodistribution and pharmacokinetics of Lf-CD/IR were evaluated in KM mice after intravenous administration. The results of tissue distribution studies revealed that Lf-CD/IR treatment showed greatly improved BBB transport efficiency. In addition, AUC0-2h of IR in brain after Lf-CD/IR treatment was seven fold higher compared with that of IR treatment without Lf-CD nano-carriers, demonstrating that the introduction of Lf-CD drug-delivery system positively resulted in a higher AUC located in brain tissue. These results provide evidence that Lf-CD nanoparticles could be exploited as a potential brain-targeting drug delivery system for hydrophobic drugs and diagnostic reagents which normally fail to pass through the BBB.

Direct electron transfer of Horseradish peroxidase on porous structure of screen-printed electrode

Disposable hydrogen peroxide biosensor was developed based on the direct electron transfer of horseradish peroxidase (HRP) on porous screen-printed carbon electrodes. Conventional screen-printing process was manually performed to fabricate the planar carbon electrodes, which were endowed with porous surfaces especially after anodizing pretreatment. The cyclic voltammetry experiment indicated a pair of stable and well-defined redox peaks with a formal potential of -0.33 V. And the formal potential was pH-dependent, having a slope of -55.2 mV/pH which indicated one electron transfer. The heterogeneous electron transfer rate constant k(s) was estimated to be 13.28+/-4.80s(-1). Additionally, the sensitivity was 143.3 mAM(-1)cm(-2) and the linear range was from 5.98 to 35.36 microM. In conclusion, the present work achieved the direct electron transfer of HRP on screen-printed electrodes without any promoters. The porous structure of screen-printed carbon electrodes facilitated the direct electron transfer between the active sites of HRP and the electrodes due to large amounts of conductive sites available on the surface for contacting with enzyme molecules. Moreover, the proposed biosensor could be mass-produced at low price, promising for commercial application.

Electrochemical sensing interfaces with tunable porosity for nonenzymatic glucose detection: a Cu foam case.

It is widely thought in electro-biochemical analysis that the sensing interfaces play a key role in the enzymeless detection of biomolecules like glucose, ascorbic acid, dopamine and uric acid. On the way to maximize the anti-poisoning sensitivity of nonenzymatic electrochemical glucose sensors as well as achieve favorable selectivity, we propose here a porous interface fabricated by a facile but effective approach for glucose monitoring in alkaline media containing dissolved oxygen. The sensing interface based on porous Cu foams is directly formed on a homemade disposable screen-printed carbon electrode (SPCE) substrate by electrodeposition assisted with hydrogen evolution simultaneously, and its porosity can be easily tailored through adjusting deposition conditions for the optimal electrocatalytic oxidation of glucose molecules. SEM and BET studies show that the generated Cu foam possesses robust hierarchical porous architectures with greatly enhanced surface area and pore volume, beneficial for the unimpeded mobility of glucose and reaction products. Cyclic voltammetric tests indicate that a diffusion-controlled glucose electro-oxidation reaction occurs at the Cu foam electrode at around +0.35 V vs. Ag/AgCl in 0.1 M NaOH. Chronoamperometric results obtained under optimized conditions reveal that the proposed sensor exhibits desired poison resistance ability in the presence of chloride ions and significant selectivity to glucose, providing fascinating sensitivities of 2.57 and 1.81 mA cm(-2) mM(-1) for glucose in the linear concentration ranges of 2-80 μM and 0.1-5 mM, respectively. The limit of detection is calculated to be as low as 0.98 μM according to the signal-to-noise ratio of three. In addition, the fabricated sensing interface shows attractive reproducibility (RSD of 5.1% and 7.0% for 15 repeated measurements on a sensor and for measurements on 15 prepared sensors, respectively) and outstanding long-term stability (less than 5% loss in sensitivity over 1 month) for glucose detection. The application of the Cu foam based sensor for monitoring glucose in practical samples is also successfully demonstrated.

Chitosan-graft-β-cyclodextrin nanoparticles as a carrier for controlled drug release

Chitosan (CS) grafted with β-cyclodextrin (CD-g-CS) nanoparticles as a new carrier for poorly water-soluble drugs has been developed. The CD-g-CS polymer is readily synthesized from chitosan and mono-6-deoxy-6-(p-toluenesulfonyl)-β-cyclodextrin. Three different degrees of substitution (DS) of β-cyclodextrin (β-CD) on CD-g-CS (9.6, 14.0 and 20.0%) are designed and evaluated by controlling the mole ratio of β-CD to chitosan. Then CD-g-CS nanoparticles are prepared by an ionic gelation method, with the controlled size of 202.0-589.0 nm. Stable colloidal dispersion of the nanoparticles has been formed with the zeta potential of +23.0 to +43.0 mV. In vitro stability test indicates that CD-g-CS nanoparticles are more stable in phosphate-buffered saline compared with CS nanoparticles. Finally, the poorly water-soluble drug, ketoprofen (KTP), is used as a model drug to evaluate the efficiency of the new drug delivery carrier. It is found that the encapsulation efficiency of KTP in the nanoparticles with 20% DS of CD is as high as 1.36-fold than that of CS nanoparticles. Moreover, notably KTP is released from the nanoparticles in a controlled-release manner and is pH-responsive on DS of CD. In summary, these results suggest that the CD-g-CS nanoparticles, as a general promising drug delivery system, can be used as a potential biodegradable nano-drug delivery system for controlled release of poorly water-soluble drugs with pH-responsive capability.

Novel snowflake-like Pt-Pd bimetallic clusters on screen-printed gold nanofilm electrode for H2O2 and glucose sensing.

Novel snowflake-like Pt-Pd bimetallic nanoclusters (Pt-PdBNC) were synthesized on a screen-printed gold nanofilm electrode (SPGFE) substrate by electrochemically reducing precursors with a new constant potential/multi-potential step deposition strategy. The electrocatalytic behavior of the modified electrode (SPGFE/Pt-PdBNC) towards H(2)O(2) was investigated. The results indicate that the as-prepared Pt-PdBNC significantly enhances the electrochemical reduction of H(2)O(2) in neutral media, exhibiting preferable electrocatalytic performance compared to Pt and Pd monometallic nanoclusters. Under optimum conditions, SPGFE/Pt-PdBNC offers linear responses for H(2)O(2) in the concentration range from 0.005 to 6 mM with an ultrahigh sensitivity of 804 mA M(-1) cm(-2) and excellent selectivity. Furthermore, glucose oxidase was immobilized on the Pt-PdBNC structure, and the fabricated biosensor presents favorable properties for glucose sensing.

Nonenzymatic electrochemical glucose sensor based on novel Pt–Pd nanoflakes

The sluggish kinetic-controlled glucose oxidation reaction on Pt electrodes is well recognized as the most critical issue that blocks the development and commercialization of enzyme-free glucose sensors, and increasing attention is being focused on improving the analytical performances of these nonenzymatic sensors through exploring new Pt-based catalysts. In the present research, we synthesized novel Pt-Pd nanoflakes (Pt-Pd NFs) with three-dimensional architectures on a homemade screen-printed gold film electrode (SPGFE) substrate using a facile electrochemical deposition without any template, and further investigated the properties of the as-fabricated Pt-Pd NFs/SPGFE for enzymeless glucose detection. The results reveal that the proposed Pt-Pd nanostructure can provide preeminent electrocatalytic activity and excellent selectivity for enzyme-free glucose sensing under simulative physiological conditions, mainly attributing to its attractive structure, large active surface and appropriate applied potential. The resulting Pt-Pd NFs/SPGFE offers linear current responses for glucose with the concentration upper limit to 16 mM. The obtained sensitivity is calculated to be as high as 48.0 μA cm(-2) mM(-1) in the presence of 0.15 M chlorides ions, and practical applications for blood sample analysis are also demonstrated. The proposed Pt-Pd structure is considered as a great potential building block for the fabrication of nonenzymatic electrochemical glucose sensors.

Antitumor and immunomodulatory activities of a polysaccharide from Artemisia argyi.

A water-soluble polysaccharide (FAAP-02), composed of N-acetyl-D-glucosamine, glucose, mannose, galactose, rhamnose, arabinose, xylose and ribose, with an average molecular weight of 5169 Da, was isolated from Artemisia argyi. The antitumor and immunomodulatory activities of FAAP-02 were evaluated in Sarcoma 180 (S180) tumor-bearing mice by intraperitoneal administration. As a result, FAAP-02 significantly inhibited the growth of the S180 transplanted tumors and prolonged the survival time of the tumor-bearing mice. Moreover, FAAP-02 could obviously increase the thymus and spleen indices, the levels of serum Interleukin 2 (IL-2), Interleukin 6 (IL-6), Interleukin 12 (IL-12) and tumor necrosis factor-α (TNF-α), and the expression of CD4+ and CD8+ splenic T lymphocytes which were suppressed by the transplanted tumor or/and 5-fluorouracil (5-FU) in the mice. These results indicated that the antitumor activity of FAAP-02 might be associated with its immunostimulatory effects.

Antioxidant Properties of Polysaccharide from the Brown Seaweed Sargassum graminifolium (Turn.), and Its Effects on Calcium Oxalate Crystallization

We investigated the effects of polysaccharides from the brown seaweed Sargassum graminifolium (Turn.) (SGP) on calcium oxalate crystallization, and determined its antioxidant activities. To examine the effects of SGP on calcium oxalate crystallization, we monitored nucleation and aggregation of calcium oxalate monohydrate crystals, using trisodium citrate as a positive control. We assessed antioxidant activities of SGP by determining its reducing power, its ability to scavenge superoxide radicals, and its activity in the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. The nucleation inhibition ratio of trisodium citrate and SGP was 58.5 and 69.2%, respectively, and crystal aggregation was inhibited by 71.4 and 76.8%, respectively. Increasing concentrations of SGP resulted in increased scavenging of superoxide anions and DPPH radicals (IC50 = 1.9 and 0.6 mg/mL, respectively). These results suggest that SGP could be a candidate for treating urinary stones because of its ability to inhibit calcium oxalate crystallization and its antioxidant properties.

Immobilization of superoxide dismutase on Pt–Pd/MWCNTs hybrid modified electrode surface for superoxide anion detection

Monitoring of reactive oxygen species like superoxide anion (O2(∙-)) turns to be of increasing significance considering their potential damages to organism. In the present work, we fabricated a novel O2(∙-) electrochemical sensor through immobilizing superoxide dismutase (SOD) onto a Pt-Pd/MWCNTs hybrid modified electrode surface. The Pt-Pd/MWCNTs hybrid was synthesized via a facile one-step alcohol-reduction process, and well characterized by transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. The immobilization of SOD was accomplished using a simple drop-casting method, and the performance of the assembled enzyme-based sensor for O2(∙-) detection was systematically investigated by several electrochemcial techniques. Thanks to the specific biocatalysis of SOD towards O2(∙-) and the Pt-Pd/MWCNTs - promoted fast electron transfer at the fabricated interface, the developed biosensor exhibits a fast, selective and linear amperometric response upon O2(∙-) in the concentration scope of 40-1550 μM (R(2)=0.9941), with a sensitivity of 0.601 mA cm(-2) mM(-1) and a detection limit of 0.71 μM (S/N=3). In addition, the favorable biocompatibility of this electrode interface endows the prepared biosensor with excellent long-term stability (a sensitivity loss of only 3% over a period of 30 days). It is promising that the proposed sensor will be utilized as an effective tool to quantitatively monitor the dynamic changes of O2(∙-) in biological systems.