Showing papers by "Chuanlai Xu published in 2010"

Side-by-side and end-to-end gold nanorod assemblies for environmental toxin sensing.

Abstract: Controllable assembly of nanoscale building blocks (monomers) is a necessary part of practical realization of the unique optical, electrical, magnetic, and chemical properties of nanoscale matter in macroscale materials. Such assemblies also contain much fundamental information about collective behavior of nanocolloids, which we are just beginning to understand. The key decisive factors for the successful assembly of nanocolloids is the anisotropy of nanoscale interactions, which stems from both the shape of nanocolloids and unequal distribution of organic molecules on their surface. Gold nanorods (Au NRs) have both geometrical and chemical anisotropy components and demonstrate strong optical extinction in the range of visible and near-infrared (NIR) wavelengths convenient for both research and practical purposes. Au NRs can be assembled by interactions with organic molecules, polymers, an antibody–antigen reaction, biotin–strepavidin connectors, and DNA, leading to superstructures with different degree of organization and complexity of collective behavior. Besides the utilization of NR monomers in non-linear optics, cellular imaging, and cancer therapy, optical effects corresponding to monomer!superstructure transitions allowed preparation of excellent biosensors because of large changes in oscillation frequencies of plasmons when NR pairs are formed. These studies mostly targeted biomedical applications. Simultaneously, their unique sensing capabilities have been virtually unexplored for the needs of environmental detection and monitoring. These challenges and impact can equal or exceed those encountered in detection of cancer. A better understanding of methods for the realization of speed/selectivity/sensitivity detection of common environmental pollutants is thus of great importance. Therefore, we decided to explore the potential of NR assemblies taking a pervasive environmental toxin, namely microcystin-LR (MC-LR), as the model while also addressing the general questions about the choice of different assembly motif for different sensing tasks. MC-LR is common in both developed and developing countries, with recorded cases of mass poisoning. MC-LR originates from common bluegreen algae and causes rapid liver failure; prolonged exposure to small concentrations of MC-LR in drinking water causes liver cancer. Herein, we describe the successful use of Au NRs for detection of MC-LR, which is significantly more sensitive than the traditional techniques, such as ELISA, yielding detection limit of 5 pgmL . It is also much simpler and faster than any other methods. These two factors are critical for environmental monitoring and have been a long-standing challenge. The pattern of the assembly strongly affects the sensitivity parameters for MC-LR detection. To realize different modes of assembly, such as side-byside and end-to-end motifs, with a degree of control sufficient for conclusive evaluation of sensing implications, two kinds of protein-carrying Au NRs were synthesized (Figure 1). One type of NR carried MC-LR antibodies (ABs) preferentially on the sides, while the other type carried antibodies located almost exclusively in the ends. These motifs were formed by using either electrostatic binding or covalent attachment of the antibodies mediated by a bifinctional linker, thioctic acid (TA).When electrostatic forces govern the placement of ABs, they attach primarily to the sides of NRs due to the larger area of contact and thus stronger electrostatic interactions. When a TA anchor covalently binds by a S Au bond, the conjugation of the ABs occurs predominantly in the ends of the rods due to better accessibility of the gold surface to the reactive thiol end. Variation of pH also allows varying repulsion or attraction of NRs and MC-LR, modality of attachment, and geometrical characteristics of assemblies (see the Supporting Information). The number of AB molecules on the surface of one Au NR was estimated to be 31 and 10 for the side-by-side [*] L. Wang, Y. Zhu, L. Xu, Dr. W. Chen, H. Kuang, L. Liu, Prof. C. Xu School of Food Science and Technology, State Key Laboratory of Food Science and Technology Jiangnan University, Wuxi, 214122 (China) E-mail: xcl@jiangnan.edu.cn Dr. W. Chen, A. Agarwal, Prof. N. A. Kotov Department of Chemical Engineering, Department of Biomedical Engineering Department of Materials Science and Engineering University of Michigan, Ann Arbor, MI 48109 (USA) E-mail: kotov@umich.edu [] These authors contributed equally to this paper.

Carbon Nanohorn Sensitized Electrochemical Immunosensor for Rapid Detection of Microcystin-LR

Abstract: A sensitive electrochemical immunosensor was proposed by functionalizing single-walled carbon nanohorns (SWNHs) with analyte for microcystin-LR (MC-LR) detection. The functionalization of SWNHs was performed by covalently binding MC-LR to the abundant carboxylic groups on the cone-shaped tips of SWNHs in the presence of linkage reagents and characterized with Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and a transmission electron micrograph. Compared with single-walled carbon nanotubes, SWNHs as immobilization matrixes showed a better sensitizing effect. Using home-prepared horseradish peroxidase-labeled MC-LR antibody for the competitive immunoassay, under optimal conditions, the immunosensor exhibited a wide linear response to MC-LR ranging from 0.05 to 20 μg/L with a detection limit of 0.03 μg/L at a signal-to-noise of 3. This method showed good accuracy, acceptable precision, and reproducibility. The assay results of MC-LR in polluted water were in a good agreem...

Analytical methods and recent developments in the detection of melamine

Abstract: Melamine (MEL) is an emerging contaminant in milk, infant formula and pet food, and is the subject of much recent research. This review focuses on analytical methods for detecting MEL residue. We present and discuss the advantages, the disadvantages and the applicability of methods, including common techniques [e.g., capillary electrophoresis, high-performance liquid chromatography (HPLC), LC with mass spectrometry (LC-MS), LC with tandem (LC-MS2), gas chromatography with MS (GC-MS), matrix-assisted laser desorption/ionization MS (MALDI-MS), nuclear magnetic resonance spectroscopy, vibrational spectroscopy, chemiluminescence analysis and immunoassay] and several novel detection methods. We propose that the new generation of analytical methods for detecting MEL requires development of powerful analytical devices, combination of multiple techniques, and application of new materials.

Nanoparticle-based environmental sensors

Abstract: Environmental monitoring requires rapid and reliable analytical tools that can perform sample analysis with minimal sample handling. Nanoparticle (NP)-based environmental sensors have the potential to detect toxins, heavy metals, and organic pollutants in air, water, and soil, and are expected to play an increasingly important role in environmental monitoring. They can both improve detection and sensing of pollutants, and be used to develop new remediation technologies. Compared to traditional detection methods, NP sensors may have higher selectivity, sensitivity and stability and lower cost. This review reports on the development of sensing principles based on NP, including synthesis of specific NP components, optical sensors, electrochemical biosensors and magnetic-relaxation sensors. Advantages over other environmental monitoring methods are discussed.

Multifunctional magnetoplasmonic nanoparticle assemblies for cancer therapy and diagnostics (theranostics).

Abstract: In this work, we describe the preparation and biomedical functionalities of complex nanoparticle assemblies with magnetoplasmonic properties suitable for simultaneous cancer therapy and diagnostics (theranostics). Most commonly magnetoplasmonic nanostructures are made by careful adaptation of metal reduction protocols which is both tedious and restrictive. Here we apply the strategy of nanoscale assemblies to prepare such systems from individual building blocks. The prepared superstructures are based on magnetic Fe(3) O(4) nanoparticles encapsulated in silica shell representing the magnetic module. The cores are surrounded in a corona-like fashion by gold nanoparticles representing the plasmonic module. As additional functionality they were also coated by poly(ethyleneglycol) chains as a cloaking agent to extend the blood circulation time. The preparation is exceptionally simple and allows one to vary the contribution of each function. Both modules can carry drugs and, in this study, they were loaded with the potential anticancer drug curcumin. A comprehensive set of microscopy, spectroscopy and biochemical methods were applied to characterize both imaging and therapeutic function of the nanoparticle assemblies against leukemia HL-60 cells. High contrast magnetic resonance images and high apoptosis rates demonstrate the success of assembly approach for the preparation of magnetoplasmonic nanoparticles. This technology allows one to easily "dial in" the functionalities in the clinical setting for personalized theranostic regiments.

Immunoaffinity removal and immunoassay for rhodamine B in chilli powder

Abstract: Summary A rapid and simple immunoassay and a sol–gel-based immunoaffinity chromatography (IAC) purification method for Rhodamine B (RB) were developed using spiked chilli powder. A polyclonal antibody against RB was generated by immunisation of rabbits with an immunogen hapten. An enzyme-linked immunosorbent assay (ELISA) was developed that achieved a 50% inhibition (IC50) value of 0.94 ± 0.05 ng mL−1. The limit of detection of the ELISA method was 1 ng g−1 in chilli powder. For the IAC, recovery was 68.1–86.2% at 1 ng g−1 and 72.6–89.3% at 5 ng g−1 in spiked chilli powder. Fortified samples were analysed by high performance liquid chromatography–mass spectrometry (HPLC–MS) after IAC purification, and the results showed a good agreement between the two methods. The ELISA could be a convenient tool for screening RB residue in foods, and the IAC cleanup procedure coupled with HPLC–MS could be an effective alternative method for the determination of RB in various substances.

Development of determination of di-n-octyl phthalate (DOP) residue by an indirect enzyme-linked immunosorbent assay

Abstract: In this research, the hapten di-n-octyl 4-aminophthalate (DOAP) was designed and synthesised successfully. It was used to couple with carrier proteins, bovine serum albumin (BSA) and ovalbumin (OVA) by diazotization reaction for immunogen (DOP–BSA) and coating antigen (DOP–OVA), respectively. Rabbits were immunised with DOP–BSA; polyclonal antiserum was raised and determined by competitive indirect enzyme-linked immunosorbent assay (ciELISA). After optimisation, a ciELISA was established. The quantitative working range for DOP was 5–75 ng/mL with the detection limit of 1.9±0.1 ng/mL and the IC50 of 19.2±1.1 ng/mL. The optimised ELISA had cross-reactivity of 22.6%, 17.6% and 21.2% with di-iso-octyl phthalate (DIOP), di-n-butyl phthalate (DBP) and di-hexyl phthalate (DHP), respectively. The result of the detection of polyvinyl chloride (PVC) samples showed that the immunoassay we developed had high-accuracy contrast with high-performance liquid chromatography electrospray ionisation tandem mass spe...

Facile preparation of fluorescence-encoded microspheres based on microfluidic system.

Abstract: The fluorescence-encoded microspheres were prepared by the simple and controllable microfluidic device for the first time. The polycaprolactone (PCL) microspheres were encoded with different quantum dots (QDs) at various ratios, and the fluorescence was decoded successfully. The designed fluorescence encoding method was easily manipulated, and generated the uniform microspheres with different size. This research demonstrated a very facile and promising technique for fluorescence encoding over traditional methods.

An empirical analysis of the impact of EU’s new food safety standards on china’s tea export

Abstract: Summary Stricter pesticide residue standards have severe negative impacts on the trade in developing countries, leading to a considerable decrease in the export of food and agricultural products from developing countries. For example, officials of the EU Health and Consumer Protection Bureau published the new EU Act 2000/42/EC on 30 June 30, 2000. This act amended the maximum residue levels (MRLs) for some pesticides. From 1 July 1, 2001 onwards, the EU implemented new 134 MRLs for pesticides in tea products. This measure above will limit market entry opportunities and will lead to a decrease in exports from these developing countries. This study aimed to utilise the Gravity Model in international trade, to empirically analyse the impact of the new EU Food Safety Act on the major tea exporters of the world. It is shown that the new EU Food Safety Act has had a significant impact on the major tea exporters of the world as shown in the decline in export volume. Quantitative analysis indicates that tea export has reduced by 61.6% following the MRL reduction to 5% significance level. In recent years the Chinese tea traded to EU supported the accuracy of this conclusion. Practically, China’s tea exported to the EU did not drop fast as the theoretical result shows.

Enantioselective determination of cypermethrin in pig muscle tissue by immunoaffinity extraction and high performance liquid chromatography

Abstract: Summary A high performance liquid chromatography method was developed to detect enantiomers of cypermethrin in pork muscle. Eight isomers of racemic cypermethrin were separated using a normal mobile phase of hexane–isopropyl alcohol (99.3–0.7, v/v) on a chiral CD-ph column in 25 min. The elution order of isomers was ascertained using enantiomer/diastereomer enriched cypermethrin standards. The extracts from pork samples were cleaned up by immunoaffinity column before detection. The recoveries from samples fortified levels of 0.1 and 1 mg kg−1 ranged from 67.3% to 113.5% with a relative standard deviation 6.7–16.8%; sufficient to effectively measure cypermethrin enantiomer concentrations in pig muscle tissue samples in the future.

Multifunctional vectors system for cancer therapy using single-walled carbon nanotubes and antisense oligonucleotide-modified gold nanoparticles composite materials

Abstract: A novel transfection vector was designed to deliver the antisense oligodeoxynucleotide into the cancer cells (HL-60). Antisense oligodeoxynucleotides (ASODNs) were conjugated to the gold nanoparticles (GNPs) through a chemical reaction. The conjugates were then bound to the single-walled carbon nanotubes (SWNTs). This vector system can effectively for induced apoptosis of the cancer cells. The gold nanoparticles helped to improve both transfection and Raman signal. This vector system can effectively for induced apoptosis of the cancer cells, and thus has the potential to be used as a cancer therapy.