Electron Microscope: Dual-Beam FIB/SEM Publications

2008

Wang J, G Liu, H Wu, and Y Lin. 2008. "Sensitive electrochemical immunoassay for 2,4,6-trinitrotoluene based on functionalized silica nanoparticle labels." Analytica Chimica Acta 610(1):112-118. doi:10.1016/j.aca.2008.01.024 Abstract We present a poly(guanine)-functionalized silica nanoparticle (NP) label-based electrochemical immunoassay for sensitively detecting 2,4,6-trinitrotoluene (TNT). This immunoassay takes advantage of magnetic bead–based platform for competitive displacement immunoreactions and separation, and use electroactive nanoparticles as labels for signal amplification. For this assay, anti-TNT-coated magnetic beads interacted with TNT analog-conjugated poly(guanine)-silica NPs and formed analog-anti-TNT immunocomplexes on magnetic beads. The immunocomplexes coated magnetic beads were exposed to TNT samples, which resulted in displacing the analog conjugated poly(guanine) silica NPs into solution by TNT. In contrast, there are no guanine residues releasing into the solution in the absence of TNT. The reaction solution was then separated from the magnetic beads and transferred to the electrode surface for electrochemical measurements of guanine oxidation with Ru(bpy)32+ as mediator. The sensitivity of this TNT assay was greatly enhanced through dual signal amplifications: 1) a large amount of guanine residues on silica nanoparticles is introduced into the test solution by displacement immunoreactions and 2) a Ru(bpy)32+-induced guanine catalytic oxidation further enhances the electrochemical signal. Some experimental parameters for the nanoparticle label-based electrochemical immunoassay were studied and the performance of this assay was evaluated. The method is found to be very sensitive and the detection limit of this assay is ~ 0.1 ng mL-1 TNT. The electrochemical immunoassay based on the poly[guanine]-functionalized silica NP label offers a new approach for sensitive detection of explosives.

2007

Liu G, J Wang, H Wu, YY Lin, and Y Lin. 2007. "Nanovehicles based Bioassay Labels." Electroanalysis 19(7-8):777-785. doi:10.1002/elan.200603787 Abstract In this article, we review recent advances of our group in nanoparticle labels based bioassay. Apoferritin and silica nanoparticles have been used as nanovehicles to load large amount of markers for highly sensitive bioassay. Markers loaded apoferritin, apoferritin-templated metallic phosphate nanoparticles, and poly [guanine] coated silica nanoparticles have been prepared, characterized and used as labels for highly sensitive bioassay of protein and DNA. Dissociation and reconstitution characteristics at different pH as well as the special cavity structure of apoferritin nanovehicle provides a simple and convenient route to prepare versatile nanoparticle labels and avoid the complicated and tedious synthesis process of conventional nanoparticle labels. The optical and electrochemical characteristics of the prepared nanoparticle labels are easily controlled by loading different optical or electrochemical markers. Additionally, the use of apoferritin nanovehicle as template for synthesis of metallic phosphate nanoparticle labels offers fast route to prepare uniform-size metallic nanoparticle labels for electrochemical bioassay and avoids the traditional harsh dissolution conditions to dissolve metallic nanoparticle tags (that is, the strong-acid dissolution of quantum dots and gold nanoparticles) during the stripping analysis step. Silica nanoparticle has also been used as nanovehicle to carry thousands of poly [guanine] tracers, which was used to enhance the oxidation current of Ru(bpy)32+, resulting in enhanced sensitivity of electrochemical immunoassay. The new nanovehicle-based labels have been used for highly sensitive electrochemical detection of DNA and protein biomarkers, such as tumor necrosis factor-alpha (TNF-a). The high sensitivity and selectivity make these labels a useful addition to the armory of nanoparticle-based bioassay. The new nanovehicles based labels hold great promise for multiplex protein and DNA detection and for enhancing the sensitivity of other bioassays.
Lin YY, G Liu, CM Wai, and Y Lin. 2007. "Magnetic Beads-based Bioelectrochemical Immunoassay of Polycyclic Aromatic Hydrocarbons." Electrochemistry Communications 9(7):1547-1552. doi:10.1016/j.elecom.2007.02.007 Abstract A simple, rapid, and sensitive bioelectrochemical immunoassay method based on magnetic beads (MBs) has been developed to detect polycyclic aromatic hydrocarbons (PAHs). The principle of this bioassay is based on a direct competitive enzyme-linked immunosorbent assay using PAH-antibody-coated MBs and horseradish peroxidase (HRP)-labeled PAH (HRP-PAH). A magnetic process platform was used to mix and shake the samples during the immunoreactions and to separate free and unbound reagents after the liquid-phase competitive immunoreaction among PAH-antibody-coated MBs, PAH analyte, and HRP-PAH. After a complete immunoassay, the HRP tracers attached to MBs were transferred to a substrate solution containing 3, 3´, 5, 5´- tetramethylbenzidine (TMB) and hydrogen peroxide (H2O2) for electrochemical detection. The voltammetric characteristics of the substrate were investigated, and the reduction peak current of TMB was used to quantify the concentration of PAH. The different parameters, including the amount of HRP-PAH conjugates, the enzyme catalytic reaction time, and the pH of the supporting electrolyte that governs the analytical performance of the immunoassay have been studied in detail and optimized. The detection limit of 50 pg mL-1 was obtained under optimum experimental conditions. The performance of this bioelectrochemical magnetic immunoassay was successfully evaluated with tap water spiked with PAHs, indicating that this convenient and sensitive technique offers great promise for decentralized environmental applications.
Liu G, H Wu, A Dohnalkova, and Y Lin. 2007. "Apoferritin-Templated Synthesis of Encoded Metallic Phosphate Nanoparticle Tags." Analytical Chemistry 79(15):5614-5619. doi:10.1021/ac070086f Abstract Encoded metallic-phosphate nanoparticle tags, with distinct encoding patterns, have been prepared using an apoferritin template. A center-cavity structure as well as the disassociation and reconstructive characteristics of apoferritin at different pH environments provide a facile route for preparing such encoded nanoparticle tags. Encapsulation and diffusion approaches have been investigated during the preparation. The encapsulation approach, which is based on the dissociation and reconstruction of apoferritin at different pHs, exhibits an effective route to prepare such encoded metallic-phosphate nanoparticle tags. The compositionally encoded nanoparticle tag leads to a high coding capacity with a large number of distinguishable voltammetric signals, reflecting the predetermined composition of the metal mixture solution (and hence the nanoparticle composition). Releasing the metal components from the nanoparticle tags at pH 4.6 acetate buffer avoids harsh dissolution conditions, such as strong acids. Such a synthesis of encoded nanoparticle tags, including single-component and compositionally encoded nanoparticle tags, is substantially simple, fast, and convenient compared to that of encoded metal nanowires and semiconductor nanoparticle (CdS, PbS, and ZnS) incorporated polystyrene beads. The encoded metallic-phosphate nanoparticle tags thus show great promise for bioanalytical or product-tracking/identification/protection applications.

2006

Chen G, Y Lin, and J Wang. 2006. "Microchip Capillary Electrophoresis with Electrochemical Detection for Monitoring Environmental Pollutants." Current Analytical Chemistry 2(1):43-50. Abstract This invited paper reviews recent advances and the key strategies in microchip capillary electrophoresis (CE) with electrochemical detection (ECD) for separating and detecting a variety of environmental pollutants. The subjects covered include the fabrication of microfluidic chips, sample pretreatments, ECD, typical applications of microchip CE with ECD in environmental analysis, and future prospects. It is expected that microchip CE-ECD will become a powerful tool in the environmental field and will lead to the creation of truly portable devices.
Lin Y, and X Cui. 2006. "Electrosynthesis, Characterization, and Application of Novel Hybrid Materials Based on Carbon Nanotube-Polyaniline-Nickel Hexacyanoferrate Nanocomposites." Journal of Materials Chemistry 16(6):585-592. Abstract Incorporating nanoclusters of nickel hexacyanoferrates (NiHCF) onto a porous polyaniline (PANI)–carbon nanotube (CNT) matrix provides a novel class of hybrid materials with a good ion exchange capacity, high stability, and a selectivity for caesium ions. The CNT-PANI-NiHCF nanocomposite films have been synthesized by electrodeposition step-by-step on glassy carbon electrodes and characterized with cyclic voltammetry (CV), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) techniques. CV and XPS investigations confirmed the formation of PANI and NiHCF on the surface of CNTs. The microscopy of NiHCF hybrid materials was characterized by SEM and TEM; the size of NiHCF particles is approximately 20 to 50 nm. The porous high surface area CNT matrix provides the high loading capacity for the deposition of NiHCF nanoparticles, while the PANI thin-film further stabilizes the nanoparticles. The selectivity for caesium ion adsorption of the hybrid materials was investigated. The high selectivity for caesium provides the base to develop a novel electrochemical ion exchange process for the treatment of nuclear wastes and radioactive-caesium contaminated waters.
Chen G, Y Lin, and J Wang. 2006. "Monitoring environmental pollutants by microchip capillary electrophoresis with electrochemical detection ." Talanta 68(3):497-503. Abstract This is a review article. During the past decade, significant progress in the development of miniaturized rnicrofluidic systems has Occurred due to the numerous advantages of microchip analysis. This review focuses on recent advances and the key strategies in microchip capillary electrophoresis (CE) with electrochemical detection (ECD) for separating and detecting a variety of environmental pollutants. The subjects covered include the fabrication of ruicrofluidic chips, ECD, typical applications of microchip CE with ECD in environmental analysis, and future prospects. It is expected that microchip CE-ECD will become a powerful tool in the environmental field and will lead to the creation of truly portable devices.
Liu G, J Wang, H Wu, and Y Lin. 2006. "Versatile Apoferritin Nanoparticle Labels for Assay of Protein ." Analytical Chemistry 78(21):7417-7423. doi:10.1021/ac060653j Abstract A versatile bioassay label based on marker-loaded-apoferritin nanoparticles (MLAN) have been developed for sensitive protein detection. Dissociation and reconstitution characteristics at different pH as well as the special cavity structure of apoferritin provide a facile route to prepare nanoparticle labels, and avoid complicated and tedious synthesis process of conventional nanoparticle labels. The optical and electrochemical characteristics of the prepared nanoparticle labels are easily controlled by loading different optical or electrochemical markers. A fluorescence marker (fluorescein anion) and a redox marker [hexacyanoferrate (III)] were used as model markers to load into the cavity of apoferritin nanoparticle and developed for microscopic fluorescence immunoassay and electrochemical immunoassay, respectively. Detection limits of 0.06 ng mL-1 (0.39 pM) and 0.08 ng mL-1 (0.51 pM) of IgG were obtained with fluorescein MLAP and hexacyanoferrate MLAN, respectively. The new nanoparticle labels hold great promise for multiplex protein detection (in connection to nanoparticles loaded with different markers) and for enhancing the sensitivity of other bioassay.

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