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Songqi Liu - One of the best experts on this subject based on the ideXlab platform.
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reagentless glucose biosensor based on direct electron transfer of glucose oxidase immobilized on Colloidal Gold modified carbon paste electrode
Biosensors and Bioelectronics, 2003Co-Authors: Songqi LiuAbstract:The direct electrochemistry of glucose oxidase (GOD) adsorbed on a Colloidal Gold modified carbon paste electrode was investigated. The adsorbed GOD displayed a pair of redox peaks with a formal potential of −(449±1) mV in 0.1 M pH 5.0 phosphate buffer solution. The response showed a surface-controlled electrode process with an electron transfer rate constant of (38.9±5.3)/s determined in the scan rate range from 10 to 100 mV/s. GOD adsorbed on Gold colloid nanoparticles maintained its bioactivity and stability. The immobilized GOD could electrocatalyze the reduction of dissolved oxygen and resulted in a great increase of the reduction peak current. Upon the addition of glucose, the reduction peak current decreased, which could be used for glucose detection with a high sensitivity (8.4 μA/mM), a linear range from 0.04 to 0.28 mM and a detection limit of 0.01 mM at a signal-to-noise ratio of 3σ. The sensor could exclude the interference of commonly coexisted uric and ascorbic acid.
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application of Colloidal Gold in protein immobilization electron transfer and biosensing
Analytical Letters, 2003Co-Authors: Songqi Liu, Donal LeechAbstract:Direct electron transfer between redox proteins and electrodes is of practical and theoretical interest and can be improved by electrode or protein modification. The direct contact of protein with electrode surfaces can lead to a significant change of the protein structure and/or function. Immobilized Colloidal Gold on electrode surfaces provides a microenvironment similar to that of the redox protein in native systems and gives the protein molecules more freedom in orientation, thus reducing the insulating property of the protein shell for the direct electron transfer and facilitating the electron transfer through the conducting tunnels of Colloidal Gold. This brief review focuses on the current state of the Colloidal Gold used for protein immobilization, electron transfer and biosensing, with emphasis on recent advances, challenges and trends.
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renewable phenol biosensor based on a tyrosinase Colloidal Gold modified carbon paste electrode
Journal of Electroanalytical Chemistry, 2003Co-Authors: Songqi LiuAbstract:Abstract A novel renewable tyrosinase-based biosensor was developed for the detection of phenol by immobilizing tyrosinase on a Colloidal Gold modified carbon paste electrode. Anionic Colloidal Gold was beneficial to the immobilization of tyrosinase and to the retention of its bioactivity to a large extent. The biosensor showed a sensitive electrochemical response to the reduction of the oxidation product of phenol by dissolved O2 in the presence of immobilized tyrosinase. The effects of pH, operating potential and the volume of the Colloidal Gold solution for sensor preparation on the amperometric response were explored for optimum analytical performance. The best performing biosensor exhibited a fast response (less than 5 s), a high sensitivity (12.3 μA cm−2 μM−1) and good storage stability for monitoring phenol. The linear range spanned the concentration of phenol from 4 to 48 μM with a correlation coefficient of 0.9973 (n=12) and a detection limit of 6.1 nM at 3σ. The response showed Michaelis–Menten behavior at larger phenol concentrations. The KMapp value of immobilized tyrosinase on Colloidal Gold was calculated to be (53.6±3.2) μM using phenol as the substrate.
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renewable reagentless hydrogen peroxide sensor based on direct electron transfer of horseradish peroxidase immobilized on Colloidal Gold modified electrode
Analytical Biochemistry, 2002Co-Authors: Songqi LiuAbstract:A novel renewable reagentless hydrogen peroxide (H2O2) sensor based on the direct electron transfer of horseradish peroxidase (HRP) is proposed. The direct electrochemistry of HRP immobilized on a Colloidal Gold-modified carbon paste electrode (Au-CPE) was investigated using electrochemical methods. The immobilized HRP displayed a pair of redox peaks in 0.1 M phosphate buffer (PB), pH 7.0, with a formal potential of −0.346 V. The response showed a surface-controlled electrode process with an electron transfer rate constant of determined in the scan rate range from 120 to 500 mV/s. The biosensor displayed an excellent electrocatalytic response to the reduction of H2O2 without the aid of an electron mediator. The sensor surface could be renewed quickly and reproducibly by a simple polish step. The calibration range of H2O2 was 0–0.3 mM with linear relation from 0.48 to 50 μM and a detection limit of 0.21 μM at 3σ. The response showed Michaelis–Menten behavior at higher H2O2 concentrations. The KappM value of HRP at HRP-Au-CPE was determined to be 3.69±0.71 mM.
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electrochemistry of cytochrome c immobilized on Colloidal Gold modified carbon paste electrodes and its electrocatalytic activity
Electroanalysis, 2002Co-Authors: Songqi Liu, Fred Lisda, Friede W SchelleAbstract:Colloidal Gold modified carbon paste electrodes were prepared by mixing 24-nm-diameter Colloidal Au particles with carbon paste. The modified electrodes displayed a low charging current and a favorable electrochemical response of hexacyanoferrate (III). The direct electrochemical behavior of a horse-heart cytochrome c (cyt.c) adsorbed on this electrode surface is described. It showed a surface-controlled electrode process with the electron transfer rate constant of (1.21±0.08) s−1 and α of 0.67. Cyclic voltammograms showed small peak-to-peak separations at low scan rates. The adsorbed cyt.c maintained its activity and could also electrocatalyze the reduction of hydrogen peroxide. Since this behavior was quite pronounced the electrode was used for H2O2 detection. The KMapp value for this sensor was found to be 2.28±0.17 mM, allowing measurements down to 0.01 mM H2O2.
Mostafa A Elsayed - One of the best experts on this subject based on the ideXlab platform.
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surface plasmon resonance scattering and absorption of anti egfr antibody conjugated Gold nanoparticles in cancer diagnostics applications in oral cancer
Nano Letters, 2005Co-Authors: Ivan H Elsayed, Xiaohua Huang, Mostafa A ElsayedAbstract:Gold nanoparticles with unique optical properties may be useful as biosensors in living whole cells. Using a simple and inexpensive technique, we recorded surface plasmon resonance (SPR) scattering images and SPR absorption spectra from both Colloidal Gold nanoparticles and from Gold nanoparticles conjugated to monoclonal anti-epidermal growth factor receptor (anti-EGFR) antibodies after incubation in cell cultures with a nonmalignant epithelial cell line (HaCaT) and two malignant oral epithelial cell lines (HOC 313 clone 8 and HSC 3). Colloidal Gold nanoparticles are found in dispersed and aggregated forms within the cell cytoplasm and provide anatomic labeling information, but their uptake is nonspecific for malignant cells. The anti-EGFR antibody conjugated nanoparticles specifically and homogeneously bind to the surface of the cancer type cells with 600% greater affinity than to the noncancerous cells. This specific and homogeneous binding is found to give a relatively sharper SPR absorption band with...
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femtosecond transient absorption dynamics of Colloidal Gold nanorods shape independence of the electron phonon relaxation time
Physical Review B, 2000Co-Authors: Clemens Urda, Mona Mohamed, Abak Nikoobakh, Mostafa A ElsayedAbstract:We studied the femtosecond dynamics of Colloidal Gold nanorods encapsulated in micelles after excitation with 400 nm pulses of 100 fs duration. It is found that the laser heating of the electron gas of Gold nanorods with an average aspect ratio of 3.8 leads to the bleaching of both the transverse and longitudinal mode of the surface plasmon oscillation at 520 and 750 nm. The bleach recovers with the same time constant for both the transverse and longitudinal oscillation, for Gold nanodots prepared by photothermal reshaping of the rods as well as for nanodots synthesized chemically by citrate reduction (and known to have twin boundaries and surface defects). Since the bleach recovery on the 3 ps time scale is assigned to electron-phonon relaxation processes, these results suggest that phonon dependent relaxation processes in Gold nanoparticles are independent of the shape, size, type of the surfaces, or the mode of the surface plasmon, oscillation excited. The fact that the mean free path of the electron in metallic Gold is in the nanometer length scale (\ensuremath{\sim}50 nm) raised the question of the importance of surface scattering to the electron-phonon relaxation process in Gold nanoparticles. Our previous studies showed little dependence of the relaxation rate of the size of Gold nanodots (from 9 to 48 nm). In the present study, the electron-phonon relaxation is measured in Gold nanorods, which have different facets from those of Gold nanodots.
Ralph M Albrech - One of the best experts on this subject based on the ideXlab platform.
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gastrointestinal persorption and tissue distribution of differently sized Colloidal Gold nanoparticles
Journal of Pharmaceutical Sciences, 2001Co-Authors: Julia F Hillye, Ralph M AlbrechAbstract:The gastrointestinal uptake of micro- and nanoparticles has been the subject of recent efforts to develop effective carriers that enhance the oral uptake of drugs and vaccines. Here, we used correlative instrumental neutron activation analysis and electron microscopy to quantitatively and qualitatively study the gastrointestinal uptake and subsequent tissue/organ distribution of 4, 10, 28, and 58 nm diameter metallic Colloidal Gold particles following oral administration to mice. In our quantitative studies we found that Colloidal Gold uptake is dependent on particle size: smaller particles cross the gastrointestinal tract more readily. Electron microscopic studies showed that particle uptake occurred in the small intestine by persorption through single, degrading enterocytes in the process of being extruded from a villus. To our knowledge this is the first report, at the ultrastructural level, of gastrointestinal uptake of particulates by persorption through holes created by extruding enterocytes.
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gastrointestinal persorption and tissue distribution of differently sized Colloidal Gold nanoparticles
Journal of Pharmaceutical Sciences, 2001Co-Authors: Julia F Hillye, Ralph M AlbrechAbstract:Abstract The gastrointestinal uptake of micro‐ and nanoparticles has been the subject of recent efforts to develop effective carriers that enhance the oral uptake of drugs and vaccines. Here, we used correlative instrumental neutron activation analysis and electron microscopy to quantitatively and qualitatively study the gastrointestinal uptake and subsequent tissue/organ distribution of 4, 10, 28, and 58 nm diameter metallic Colloidal Gold particles following oral administration to mice. In our quantitative studies we found that Colloidal Gold uptake is dependent on particle size: smaller particles cross the gastrointestinal tract more readily. Electron microscopic studies showed that particle uptake occurred in the small intestine by persorption through single, degrading enterocytes in the process of being extruded from a villus. To our knowledge this is the first report, at the ultrastructural level, of gastrointestinal uptake of particulates by persorption through holes created by extruding enterocytes. © 2001 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:1927–1936, 2001
Giulio F Paciotti - One of the best experts on this subject based on the ideXlab platform.
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phase i and pharmacokinetic studies of cyt 6091 a novel pegylated Colloidal Gold rhtnf nanomedicine
Clinical Cancer Research, 2010Co-Authors: Steve K Libutti, Giulio F Paciotti, Adriana A Yrnes, Richard H Alexande, William E Ganno, Melissa Walke, Geoffrey Seidel, Nargiza YuldashevaAbstract:Purpose: A novel nanomedicine, CYT-6091, constructed by simultaneously binding recombinant human tumor necrosis factor alpha (rhTNF) and thiolyated polyethylene glycol to the surface of 27-nm Colloidal Gold particles, was tested in a phase I dose escalation clinical trial in advanced stage cancer patients. Experimental Design: CYT-6091, whose dosing was based on the amount of rhTNF in the nanomedicine, was injected intravenously, and 1 cycle of treatment consisted of 2 treatments administered 14 days apart. Results: Doses from 50 mg/m 2 to 600 mg/m 2 were well tolerated, and no maximum tolerated dose (MTD) was reached, as the highest dose exceeded the target dosage of 1-mg rhTNF per treatment, exceeding the previous MTD for native rhTNF by 3-fold. The first 2 patients on the study, each receiving 50 mg/m 2 , did not receive any prophylactic antipyretics or H2 blockade. A predicted, yet controllable fever occurred in these patients, so all subsequently treated patients received prophylactic antipyretics and H2 blockers. However, even at the highest dose rhTNF’s dose-limiting toxic effect of hypotension was not seen. Using electron microscopy to visualize nanoparticles of Gold in patient biopsies of tumor and healthy tissue showed that patient biopsies taken 24 hours after treatment had nanoparticles of Gold in tumor tissue. Conclusions:These data indicate that rhTNF formulated as CYT-6091 may be administered systemically at doses of rhTNF that were previously shown to be toxic and that CYT-6091 may target to tumors. Future clinical studies will focus on combining CYT-6091 with approved chemotherapies for the systemic treatment of nonresectable cancers. Clin Cancer Res; 16(24); 6139–49. � 2010 AACR.
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Colloidal Gold nanoparticles a novel nanoparticle platform for developing multifunctional tumor targeted drug delivery vectors
Drug Development Research, 2006Co-Authors: Giulio F Paciotti, David G I Kingston, Lawrence TamarkinAbstract:Nanotechnology applied to biological problems represents an emerging field with the potential to offer extremely sensitive diagnostics and targeted cancer therapies. However, to achieve these goals, nanoparticle delivery systems must outwit the many barriers that are intrinsic to the body's defenses, as well as those that develop during the growth and progression of tumors. The science is advancing and, for example, true nanoscale tumor-targeted drug delivery vectors are now able to reduce the likelihood of opsonization in the bloodstream and uptake by the reticuloendothelial system. Other advances hold promise for delivering multiple therapeutic agents to non-homogeneous populations of cancer cells in solid tumors. We briefly summarize herein our attempts to build such multifunctional nanotherapeutics using Colloidal Gold nanoparticles. Specifically we discuss the development of Colloidal Gold-based drugs that are designed to target the delivery of TNF and paclitaxel to solid tumors. Drug Dev. Res. 67:47–54, 2006. © 2006 Wiley-Liss, Inc.
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Colloidal Gold a novel nanoparticle vector for tumor directed drug delivery
Drug Delivery, 2004Co-Authors: Giulio F Paciotti, Lonnie Mye, David Weinreich, Da V Goia, Nicolae Pavel, Richard E Mclaughli, Lawrence TamarkiAbstract:Colloidal Gold, a sol comprised of nanoparticles of Au0, has been used as a therapeutic for the treatment of cancer as well as an indicator for immunodiagnostics. However, the use of these Gold nanoparticles for in vivo drug delivery has never been described. This communication outlines the development of a Colloidal Gold (cAu) nanoparticle vector that targets the delivery of tumor necrosis factor (TNF) to a solid tumor growing in mice.The optimal vector, designated PT-cAu-TNF, consists of molecules of thiol-derivatized PEG (PT) and recombinant human TNF that are directly bound onto the surface of the Gold nanoparticles. Following intravenous administration, PT-cAu-TNF rapidly accumulates in MC-38 colon carcinoma tumors and shows little to no accumulation in the livers, spleens (i.e., the RES) or other healthy organs of the animals. The tumor accumulation was evidenced by a marked change in the color of the tumor as it acquired the bright red/purple color of the Colloidal Gold sol and was coincident with ...
Weiwei Yang - One of the best experts on this subject based on the ideXlab platform.
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glucose oxidase Colloidal Gold nanoparticles immobilized in nafion film on glassy carbon electrode direct electron transfer and electrocatalysis
Bioelectrochemistry, 2006Co-Authors: Shuang Zhao, Kai Zhang, Weiwei YangAbstract:Abstract The direct electron transfer of glucose oxidase (GOD) was achieved based on the immobilization of GOD/Colloidal Gold nanoparticles on a glassy carbon electrode by a Nafion film. The immobilized GOD displayed a pair of well-defined and nearly reversible redox peaks with a formal potential (E°′) of − 0.434 V in 0.1 M pH 7.0 phosphate buffer solution and the response showed a surface-controlled electrode process. The dependence of E°′ on solution pH indicated that the direct electron transfer reaction of GOD was a two-electron-transfer coupled with a two-proton-transfer reaction process. The experimental results also demonstrated that the immobilized GOD retained its electrocatalytic activity for the oxidation of glucose. So the resulting modified electrode can be used as a biosensor for detecting glucose.
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hydrogen peroxide biosensor based on myoglobin Colloidal Gold nanoparticles immobilized on glassy carbon electrode by a nafion film
Sensors and Actuators B-chemical, 2006Co-Authors: Weiwei YangAbstract:Abstract A novel amperometric sensor of hydrogen peroxide was developed based on the immobilization of myoglobin (Mb) and Colloidal Gold nanoparticles (CGNs) on a glassy carbon electrode (GCE) by a Nafion film. The immobilized Mb displayed a pair of well-defined and nearly reversible cyclic voltammetric peaks with a formal potential (E°′) of −0.373 V in a 0.1 M phosphate buffer solution (PBS) of pH 6.9. The formal potential of the Mb heme Fe(III)/Fe(II) couple shifted linearly with pH with a slope of −49.6 mV/pH, indicating that the electron transfer is accompanied by single-proton transportation. The immobilized Mb exhibited excellent electrocatalytic response to the reduction of hydrogen peroxide, based on which an unmediated biosensor for hydrogen peroxide was achieved. The linear range for determination of hydrogen peroxide was from 1.5 × 10−6 to 9.0 × 10−5 M with a detection limit of 5.0 × 10−7 M at a signal-to-noise ratio of 3. The stability, repeatability and selectivity of the biosensor were also evaluated.
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amperometric nitrite sensor based on hemoglobin Colloidal Gold nanoparticles immobilized on a glassy carbon electrode by a titania sol gel film
Analytical and Bioanalytical Chemistry, 2005Co-Authors: Weiwei YangAbstract:A novel amperometric nitrite sensor was developed based on the immobilization of hemoglobin/Colloidal Gold nanoparticles on a glassy carbon electrode by a titania sol-gel film. The sensor shows a pair of well-defined and nearly reversible cyclic voltammogram peaks for Hb Fe(III)/Fe(II) with a formal potential (E°′) of −0.370 V, and the peak-to-peak separation at 100 mV s−1 was 66 mV vs. Ag/AgCl (3.0 M KCl) in a pH 6.9 phosphate buffer solution. The formal potential of the Hb Fe(III)/Fe(II) couple shifted linearly with pH with a slope of −50.0 mV/pH, indicating that electron transfer accompanies single-proton transportation. The sensor exhibited an excellent electrocatalytic response to the reduction of nitrite. The reduction overpotential was 0.45 V below that obtained at a Colloidal Gold nanoparticles/TiO2 sol-gel film-modified GCE. The linear range for nitrite determination for the sensor was 4.0×10−6 to 3.5×10−4 M, with a detection limit of 1.2×10−6 M. The stability, repeatability and selectivity of the sensor were also evaluated.