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Biomedical subjects

Guodong Liu

Publications and source records attributed to Guodong Liu.

At least 19 recordsLinked to original sources
PubMed2006

Versatile apoferritin nanoparticle labels for assay of protein.

A versatile bioassay label based on marker-loaded apoferritin nanoparticles (MLANs) has been developed for sensitive protein detection. Dissociation and reconstitution characteristics at different pH as well as the special cavity structure of apoferritin provides a facile route to prepare 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. A fluorescence marker (fluorescein anion) and a redox marker [hexacyanoferrate(III)] were used as model markers to load into the cavity of apoferritin nanoparticles for microscopic fluorescence immunoassay and electrochemical immunoassay, respectively. Detection limits of 0.06 (0.39 pM) and 0.08 ng mL(-1) (0.52 pM) IgG were obtained with fluorescein MLAN and hexacyanoferrate MLANs, respectively. The new nanoparticle labels hold great promise for multiplex protein detection (in connection with nanoparticles loaded with different markers) and for enhancing the sensitivity of other bioassays.

Apoferritins↗
PubMed2006

Development of a non-invasive biomonitoring approach to determine exposure to the organophosphorus insecticide chlorpyrifos in rat saliva.

Non-invasive biomonitoring approaches are being developed using reliable portable analytical systems to quantify dosimetry utilizing readily obtainable body fluids, such as saliva. In the current study, rats were given single oral gavage doses (1, 10, or 50 mg/kg) of the insecticide chlorpyrifos (CPF). Saliva and blood were then collected from groups of animals (4/time-point) at 3, 6, and 12 h post-dosing, and were analyzed for the CPF metabolite trichloropyridinol (TCP). Trichloropyridinol was detected in both blood and saliva at all doses and the TCP concentration in blood exceeded saliva, although the kinetics in blood and saliva were comparable. A physiologically based pharmacokinetic and pharmacodynamic (PBPK/PD) model for CPF incorporated a compartment model to describe the time-course of TCP in blood and saliva. The model adequately simulated the experimental results over the dose ranges evaluated. A rapid and sensitive sequential injection (SI) electrochemical immunoassay was developed to monitor TCP, and the reported detection limit for TCP was 6 ng/L (in water). Computer model simulation in the range of the Allowable Daily Intake (ADI) or Reference Dose (RfD) for CPF (0.01-0.003 mg/kg/day) suggests that the electrochemical immunoassay has adequate sensitivity to detect and quantify TCP in saliva at these low exposure levels. However, to validate this approach, further studies are needed to more fully understand the pharmacokinetics of CPF and TCP excretion in saliva. These initial findings suggest that the utilization of saliva as a biomonitoring matrix, coupled to real-time quantitation and PBPK/PD modeling represents a novel approach with broad application for evaluating both occupational and environmental exposures to CPF.

Animals↗
PubMed2006

Sensitive immunoassay of a biomarker tumor necrosis factor-alpha based on poly(guanine)-functionalized silica nanoparticle label.

A novel electrochemical immunosensor for the detection of tumor necrosis factor-alpha (TNF-alpha) based on poly(guanine)-functionalized silica nanoparticles (NPs) label is presented. The detection of mouse TNF-alpha via immunological reaction is based on a dual signal amplification: (1) a large amount of guanine residues introduced on the electrode surface through sandwich immunoreaction and poly(guanine)-functionalized silica NP label; (2) Ru(bpy)3(2+)-induced catalytic oxidation of guanine, which results in great enhancement of anodic current. The synthesized silica NP conjugates were characterized with atomic force microscopy, X-ray photoelectron spectroscopy, and electrochemistry. These experiments confirmed that poly(guanine) and avidin were immobilized on the surface of silica NPs. The performance of the electrochemical immunosensor was evaluated and some experiment parameters (e.g., concentration of Ru(bpy)3(2+), incubation time of TNF-alpha, etc.) were optimized. The detection limit for TNF-alpha is found to be 5.0 x 10(-11) g mL(-1) (2.0 pM), which corresponds to 60 amol of TNF-alpha in 30 microL of sample. This immunosensor based on the poly(guanine)-functionalized silica NP label offers great promise for rapid, simple, cost-effective analysis of biological samples.

Animals↗
PubMed2006

Electrochemical proteolytic beacon for detection of matrix metalloproteinase activities.

This communication describes a novel method for detecting matrix metalloproteinase-7 activity using a peptide substrate labeled with a ferrocene reporter. The substrate serves as a selective "electrochemical proteolytic beacon" (EPB) for this metalloproteinase. The EPB is immobilized on a gold electrode surface to enable "on-off" electrochemical signaling capability for uncleaved and cleaved events. The EPB is efficiently and selectively cleaved by MMP-7 as measured by the rate of decrease in redox current of ferrocene. Direct transduction of a signal corresponding to peptide cleavage events into an electronic signal thus provides a simple, sensitive route for detecting the MMP activity. The new method allows for identification of the activity of MMP-7 in concentrations as low as 3.4 pM. The concept can be extended to design a multiple peptide substrate labeled with different electroactive reporters for assaying multiple MMPs activities.

Electrochemistry↗
PubMed2006

Antisense oligonucleotide targeting c-fos mRNA limits retinal pigment epithelial cell proliferation: a key step in the progression of proliferative vitreoretinopathy.

The purpose of this work was to investigate the effect of c-fos antisense oligonucleotide (c-fos-AS-ON) on proliferative vitreoretinopathy (PVR). Cultures of human retinal pigment epithelial (hRPE) cells were established from adult human corneal donors. These cells were positively stained for cytokeratins. C-fos-AS-ON effect on serum-stimulated cell proliferation was estimated by evaluating the incorporation of 5-bromo-2'-deoxy-uridine (BrdU) into cellular DNA. Reverse transcriptase polymerase chain reaction (RT-PCR) and Western blotting were respectively performed to quantify the serum-stimulated c-fos gene mRNA and protein expression in hRPE cells. Eight rabbits (16 eyes) were divided into c-fos-AS-ON treatment group and control group. 2.5 x 10(5) cultured hRPE cells were injected into the vitreous cavity of eyes to establish a PVR model. Prevalence of PVR and retinal detachment were determined by indirect ophthalmoscopy on days 1, 3, 7, 14, 21 and 28 post-injection and by pathological study on days 28 post-injection. The results showed that blocking the expression of c-fos by the addition of c-fos-AS-ON to the culture medium significantly inhibited the hRPE cells proliferation. This effect of c-fos-AS-ON was found to be sequence specific (the use of a sense or a mismatch sense oligonucleotide had no such an effect) and dose-dependent (0.375 microM was the lowest effective dose tested). Growth inhibition by c-fos-AS-ON remained for at least 72 h. By using RT-PCR and Western blotting, we found that the c-fos-AS-ON could specifically inhibit c-fos mRNA and protein synthesis in cultured hRPE cells. Though the eyes injected with c-fos-AS-ON also developed features of PVR, the severities of days 14, 21 and 28 post-injection were significantly lower than those in the control eyes (P<0.05). We conclude that c-fos-AS-ON can inhibit cultured hRPE cell proliferation, which mechanism may relate to blocking the expression of c-fos and can reduce the prevalence of experimental PVR. These findings establish a rationale for investigating the potential use of a c-fos-AS-ON as a novel therapeutical tool in the treatment of PVR.

Animals↗
PubMed2006

Templated one-step synthesis of compositionally encoded nanowire tags.

Multimetal nanowire tags, with distinct encoding patterns, have been prepared using a one-step templated electrodeposition from solutions containing different concentrations of various metal ions. Such synthesis of compositionally encoded nanowire tags is substantially faster and simpler than the preparation of striped nanowires based on sequential plating steps from different metal solutions and leads to high identification accuracy. The alloy nanowire preparation route leads to a high coding capacity with a large number of distinguishable voltammetric signatures, reflecting the predetermined composition of the metal mixture plating solution (and hence the nanowire composition). Factors influencing the identification accuracy are evaluated using three-metal (In, Pb, Bi) alloy nanowires, and the relative advantages and disadvantages of the new route are discussed.

Alloys↗
PubMed2006

Amperometric choline biosensor fabricated through electrostatic assembly of bienzyme/polyelectrolyte hybrid layers on carbon nanotubes.

We report a flow injection amperometric choline biosensor based on the electrostatic assembly of the choline oxidase (ChO) enzyme and a bienzyme of ChO and horseradish peroxidase (HRP) onto multi-wall carbon nanotubes (MWCNT) modified glassy carbon (GC) electrodes. These choline biosensors were fabricated by immobilization of enzymes on the negatively charged MWCNT surface through alternately assembling a cationic poly(diallydimethylammonium chloride) (PDDA) layer and an enzyme layer. Using this layer-by-layer assembling approach, a bioactive nanocomposite film of PDDA/ChO/PDDA/HRP/PDDA/CNT (ChO/HRP/CNT) and PDDA/ChO/PDDA/CNT (ChO/CNT) was fabricated on the GC surface. Owing to the electrocatalytic effect of carbon nanotubes, the measurement of faradic responses resulting from enzymatic reactions has been realized at low potential with acceptable sensitivity. The ChO/HRP/CNT biosensor is more sensitive than the ChO/CNT one. Experimental parameters affecting the sensitivity of biosensors, e.g., applied potential, flow rate, etc., were optimized and potential interference was examined. The response time for this choline biosensor is fast (few seconds). The linear range of detection for the choline biosensor is from 5.0 x 10(-5) to 5.0 x 10(-3) M and the detection limit is about 1.0 x 10(-5) M.

Biosensing Techniques↗
PubMed2006

Biosensor based on self-assembling acetylcholinesterase on carbon nanotubes for flow injection/amperometric detection of organophosphate pesticides and nerve agents.

A highly sensitive flow injection amperometric biosensor for organophosphate pesticides and nerve agents based on self-assembled acetylcholinesterase (AChE) on a carbon nanotube (CNT)-modified glassy carbon (GC) electrode is described. AChE is immobilized on the negatively charged CNT surface by alternatively assembling a cationic poly(diallyldimethylammonium chloride) (PDDA) layer and an AChE layer. Transmission electron microscopy images confirm the formation of layer-by-layer nanostructures on carboxyl-functionalized CNTs. Fourier transform infrared reflectance spectrum indicates the AChE was immobilized successfully on the CNT/PDDA surface. The unique sandwich-like structure (PDDA/AChE/PDDA) on the CNT surface formed by self-assembling provides a favorable microenvironment to keep the bioactivity of AChE. The electrocatalytic activity of CNT leads to a greatly improved electrochemical detection of the enzymatically generated thiocholine product, including a low oxidation overvoltage (+150 mV), higher sensitivity, and stability. The developed PDDA/AChE/PDDA/CNT/GC biosensor integrated into a flow injection system was used to monitor organophosphate pesticides and nerve agents, such as paraoxon. The sensor performance, including inhibition time and regeneration conditions, was optimized with respect to operating conditions. Under the optimal conditions, the biosensor was used to measure as low as 0.4 pM paraoxon with a 6-min inhibition time. The biosensor had excellent operational lifetime stability with no decrease in the activity of enzymes for more than 20 repeated measurements over a 1-week period. The developed biosensor system is an ideal tool for online monitoring of organophosphate pesticides and nerve agents.

Acetylcholinesterase↗
PubMed2006

Carbon nanotube-templated assembly of protein.

This paper describes a novel general strategy for fabricating protein-polyion multilayers by electrostatic layer-by-layer (LBL) self-assembly on carbon nanotube templates. Such a noncovalent functionalization method is important for preserving the activity of biomolecular, the mechanical, and electrical properties of carbon nanotubes. Glucose oxidase and poly(diallyldimethylammonium) chloride polymer (PDDA) were used as models to investigate the LBL process on CNT templates. High-resolution TEM and electrochemical characterization confirm the formation of LBL nanostructures on carboxyl functionalized carbon nanotubes. We have also demonstrated the applications of these nanoshell bioreactors to direct electrochemistry of protein and biosensing. This strategy can be applied to assemble other biological molecules such as antibody, antigen, and DNA for wide bioassay applications.

Coated Materials, Biocompatible↗
PubMed2005

Electrochemical sensor for organophosphate pesticides and nerve agents using zirconia nanoparticles as selective sorbents.

An electrochemical sensor for detection of organophosphate (OP) pesticides and nerve agents using zirconia (ZrO2) nanoparticles as selective sorbents is presented. Zirconia nanoparticles were electrodynamically deposited onto the polycrystalline gold electrode by cyclic voltammetry. Because of the strong affinity of zirconia for the phosphoric group, nitroaromatic OPs strongly bind to the ZrO2 nanoparticle surface. The electrochemical characterization and anodic stripping voltammetric performance of bound OPs were evaluated using cyclic voltammetric and square-wave voltammetric (SWV) analysis. SWV was used to monitor the amount of bound OPs and provide simple, fast, and facile quantitative methods for nitroaromatic OP compounds. The sensor surface can be regenerated by successively running SWV scanning. Operational parameters, including the amount of nanoparticles, adsorption time, and pH of the reaction medium have been optimized. The stripping voltammetric response is highly linear over the 5-100 ng/mL (ppb) methyl parathion range examined (2-min adsorption), with a detection limit of 3 ng/mL and good precision (RSD = 5.3%, n = 10). The detection limit was improved to 1 ng/mL by using 10-min adsorption time. The promising stripping voltammetric performances open new opportunities for fast, simple, and sensitive analysis of OPs in environmental and biological samples. These findings can lead to a widespread use of electrochemical sensors to detect OP contaminates.

Electrochemistry↗
PubMed2005

Multiple enzyme layers on carbon nanotubes for electrochemical detection down to 80 DNA copies.

Signal amplification using enzyme multilayers on carbon nanotube (CNT) templates is shown to yield a remarkably sensitive electrochemical detection of proteins and nucleic acids. The electrostatic layer-by-layer (LBL) self-assembly onto CNT carriers maximizes the ratio of enzyme tags per binding event to offer the greatest amplification factor reported to date. Absorption spectroscopy, TEM, and electrochemical characterization confirm the formation of LBL enzyme nanostructures on individual CNT carriers. The enzymatic activity is found to increase with the number of enzyme layers. The new protocol is illustrated for monitoring sandwich hybridization and antibody-antigen interactions in connection with alkaline phosphatase tracers. Factors affecting the enzyme loading and the analytical performance have been optimized. Such amplified bioelectronic assays allow detection of DNA and proteins down to 80 copies (5.4 aM) and 2000 protein molecules (67 aM), respectively. Given the enormous amplification afforded by the new CNT-LBL biolabel, such route offers great promise for ultrasensitive detection of infectious agents and disease markers.

DNA↗
PubMed2005

Enzyme nanoparticles-based electronic biosensor.

A simple and effective method to prepare an enzyme electronic biosensor by immobilizing enzyme nanoparticles directly onto the gold electrode surface is described; prepared horseradish peroxidase nanoparticles have been successfully used to develop reagentless electronic biosensors for H2O2 detection without promoters and mediators and offer great potential to develop enzyme-based electronic biosensors.

Biosensing Techniques↗
PubMed2005

Ultrasensitive voltammetric detection of trace heavy metal ions using carbon nanotube nanoelectrode array.

We describe an ultrasensitive voltammetric detection of trace heavy metal ions using nanoelectrode arrays (NEAs) that are based on low-site density carbon nanotubes (CNTs). The NEAs were prepared by sealing the side-walls of CNTs with an epoxy passive layer that reduces the current leakage and eliminates the electrode capacitance, leading to a low background current. This provides a high signal-to-noise ratio. The CNTs-NEAs coated with a bismuth film were used successfully for voltammetric detection of trace cadmium(II) and lead(II) at the sub-ppb level. The detection limit of 0.04 microg L(-1) was obtained under optimum experimental conditions. The attractive behavior of the new carbon NEA sensing platform holds great promise for onsite environmental monitoring and biomonitoring of toxic metals.

Electrochemistry↗
PubMed2005

Alpha-trialkylsilyl amino acid stability.

Alpha-trialkylsilyl amino acids have been evaluated for their stability toward methanolysis as a model for physiological conditions. The juxtaposition of amine and carbonyl groups significantly destabilizes the silicon-carbon bond, but changing a single methyl on silicon to an ethyl led to a dramatic stability enhancement. Converting the ester to an amide gave an additional jump in stability, suggesting broad potential for these novel amino acids in bioactive peptides and pharmaceuticals. [structure: see text]

Alkylation↗
PubMed2005

Nanocrystal-based bioelectronic coding of single nucleotide polymorphisms.

A bioelectronic method for coding unknown single nucleotide polymorphisms (SNPs) based on the use of different encoding nanocrystals is described. Four such nanocrystals, ZnS, CdS, PbS, and CuS, linked to the adenosine, cytidine, guanosine and thymidine mononucleotides, respectively, are sequentially introduced to the DNA hybrid-coated magnetic-bead solution. Each mutation captures via base pairing different nanocrystal-mononucleotide conjugates, and yields a characteristic multipotential voltammogram, whose peak potentials reflect the identity of the mismatch. The mismatch recognition events are being amplified by the metal accumulation feature of the stripping voltammetric transduction mode. Each of the eight possible one-base mismatches can thus be identified in a single voltammetric run. The use of nanocrystal tracers for detecting two known mutations in a single DNA target is also illustrated in connection to nanocrystals linked to two nucleotides along with a single voltammetric run. The protocol presented should facilitate the rapid, simple, low-cost, and high throughput screening for SNPs.

Base Pair Mismatch↗