Antibody–Ferrocene Conjugates as a Platform for Electro-Chemical Detection of Low-Density Lipoprotein

Low-density lipoprotein (LDL) is a cardiac biomarker identified in the pathology of cardiovascular disease (CVD). Typically, the level of LDL is calculated using the Friedewald relationship based on measured values of total cholesterol, high-density lipoproteins (HDL), and triglycerides. Unfortunately, this approach leads to some errors in calculation. Therefore, direct methods that can be used for fast and accurate detection of LDL are needed. The purpose of this study was to develop an electrochemical platform for the detection of LDL based on an antibody–ferrocene conjugate. An anti-apolipoprotein B-100 antibody labeled with ferrocene was covalently immobilized on the layer of 4-aminothiophenol (4-ATP) on the surface of gold electrodes. Upon interaction between LDL and the antibody–ferrocene conjugate, a decrease in the ferrocene redox signal registered by square wave voltammetry was observed, which depends linearly on the concentration from 0.01 ng/mL to 1.0 ng/mL. The obtained limit of detection was equal to 0.53 ng/mL. Moreover, the satisfied selectivity toward human serum albumin (HSA), HDL, and malondialdehyde-modified low-density lipoprotein (MDA-LDL) was observed. In addition, the acceptable recovery rates of LDL in human serum samples indicate the possible application of immunosensors presented in clinical diagnostics.     

Carbon Nanotubes-Based Label-Free Affinity Sensors for Environmental Monitoring

Nanostructures, such as nanowires, nanobelts, nanosprings, and nanotubes, are receiving growing interest as transducer elements of bio/chemical sensors as they provide high sensitivity, multiplexing, small size, and portability. Single-walled carbon nanotubes (SWNTs) are one such class of nanostructure materials that exhibit superior sensing behavior due to its large-surface carbon atoms that are highly responsive to surface adsorption events. Further, their compatibility with modern microfabrication technologies and facile functionalization with molecular recognition elements make them promising candidates for bio/chemical sensors applications. Here, we review recent results on nanosensors based on SWNTs modified with biological receptors such as aptamers, antibodies, and binding proteins, to develop highly sensitive, selective, rapid, and cost-effective label-free chemiresistor/field-effect transistor nanobiosensors for applications in environmental monitoring.     

Simultaneous Determination of High-Density Lipoprotein,Very Low-Density Lipoprotein and Low-Density Lipoprotein Subclass in Human Serum by Microchip CE

Lipoproteins, especially high-density lipoproteins (HDL), very low-density lipoproteins (VLDL) and small, dense low-density lipoprotein (sdLDL), are believed to play an important role in the development of atherosclerosis. In this work, a simple, selective and sensitive method for the simultaneous monitoring of these lipoproteins in human serum using microchip capillary electrophoresis was developed. Gold nanoparticles were used as an additive to the running buffer to obtain the absolute separation of the lipoproteins. Under optimised conditions, the linear ranges of large buoyant low-density lipoproteins, sdLDL, VLDL and HDL were 10–800, 10–800, 40–1,000 and 20–800 μg L⁻¹, and their limits of detection were 5, 5, 15 and 8 μg L⁻¹, respectively. The intraassay and interassay relative standard deviation of lipoprotein peak areas were in the range of 3.8–7.4%. For practical application, variations in the serum lipoprotein of coronary heart disease patients were monitored by microchip-based CE. The results showed that the method was applicable for routine clinical use and allowed the rapid detection of different lipoprotein classes as well as their subclasses, thus greatly improving the analysis of atherosclerotic risk factors.

     

Simultaneous Determination of High-Density Lipoprotein, Very Low-Density Lipoprotein and Low-Density Lipoprotein Subclass in Human Serum by Microchip CE

Lipoproteins, especially high-density lipoproteins (HDL), very low-density lipoproteins (VLDL) and small, dense low-density lipoprotein (sdLDL), are believed to play an important role in the development of atherosclerosis. In this work, a simple, selective and sensitive method for the simultaneous monitoring of these lipoproteins in human serum using microchip capillary electrophoresis was developed. Gold nanoparticles were used as an additive to the running buffer to obtain the absolute separation of the lipoproteins. Under optimised conditions, the linear ranges of large buoyant low-density lipoproteins, sdLDL, VLDL and HDL were 10?C800, 10?C800, 40?C1,000 and 20?C800 ??g L^?1, and their limits of detection were 5, 5, 15 and 8 ??g L^?1, respectively. The intraassay and interassay relative standard deviation of lipoprotein peak areas were in the range of 3.8?C7.4%. For practical application, variations in the serum lipoprotein of coronary heart disease patients were monitored by microchip-based CE. The results showed that the method was applicable for routine clinical use and allowed the rapid detection of different lipoprotein classes as well as their subclasses, thus greatly improving the analysis of atherosclerotic risk factors.     

微流控芯片电泳分离血清中小而密低密度脂蛋白的研究

应用微流控芯片电泳,以40 mmol/L Tricine(pH9.8)作为电泳缓冲体系,十二烷基硫酸钠(SDS)作为添加剂(0.1 mmol/L SDS样品溶液,0.02 mmol/L SDS分离缓冲液),分离血清小而密低密度脂蛋白(sdLDL)。研究荧光染料硝基苯并噁二唑-C6-酰基鞘胺醇(NBD C6-ceramide)与脂蛋白结合的特异性、饱和性以及血清保存和检测时间对脂蛋白电泳行为的影响;探讨SDS有效降低蛋白吸附,提高血清脂蛋白分辨率的作用。冠心病(CHD)组sdLDL检出率(75%)显著高于对照组(6%,P<0.01)。该法具有简易、快速、高效等优点,可望成为CHD危险性评估的常规分析手段。     

Determination of Trace Thiocyanate by a Chitosan-Modified Glassy Carbon Electrode

IntroductionMany methods for the determination ofthiocyanate,such as spectrophotometry[1— 6] ,ion-selective electrodes[7— 10 ] ,chromatography[11,12 ] ,flow- injection analysis[13 ] ,voltammetry[14 ] ,fluorimetry[15] ,amperometry[16] ,potentiometricprecipitation titration[17] have been reported. Sincethe methods have been used for the determinationof thiocyanate in waste water,biological samples,food and chemical reagents,the determination ofthiocyanate is of great significance. But theexist…     

Inhibition of Low-Density Lipoprotein Peroxidation by BHA Use: Fluorimetric Assay

Abstract

In the presence of free radicals, low-density lipoproteins (LDL) undergo oxidation that leads to the formation of lipoperoxides, which cause various damaging effects. Starting from the classical oxygen radical absorption capacity (ORAC) method, a modified method was formulated to develop a laboratory model that is able to deliver information about the use of polyphenols as nutrient supplements. The aim of this work was to establish the possible inhibition of LDL peroxidation by two different antioxidants, Trolox and BHA, and to assess if the effect is either of prevention or repair. 2,2,-Azobis(2-methylpropionamidine) dihydrochloride (AAPH) was used as free radical generator, and fluorescein was used as fluorescent probe. It was noticed that the radical scavenging effect decreases in the order BHA to Trolox to LDL itself. Trolox shows a higher efficacy against the free radicals generated by AAPH than against lipoperoxides, whereas BHA is more efficient against lipoperoxides.     

Analysis of Fatty Acid, and Lipoprotein, Metabolism by GC and HPLC: Effect of Low-Density Lipoprotein Apheresis

 Blood samples from 5 hyperlipidemic patients on chronic treatment with low-density lipoprotein (LDL) – apheresis were analysed for lipids and fatty acids in serum, lipoprotein fractions and erythrocyte membrane by capillary gas chromatography (GC), reversed-phase high-performance liquid chromatography (LC), spectrofluorometry and spectrophotometry. LDL-apheresis has been associated with significant changes of fatty acids metabolism in relation to triglyceride-rich lipoproteins. Oleic acid may exert its hypotriglyceridemic effect via VLDL, IDL, LDL and HDL fractions. Polyunsaturated fatty acids, associated with triglyceride metabolism via IDL or VLDL, are linoleic, gamma-linolenic and docosahexaenoic fatty acids. Received November 25, 1999. Revision September 5, 2000.     

Chitosan-Modified Calcium Alginate Microspheres for Cefotaxime Immobilization

Russian Journal of Applied Chemistry - Chitosan-modified calcium alginate microspheres with the mean diameter of 2.0 ± 0.05 mm for immobilizing Cefotaxime antibiotic were prepared by...     

Oxidation of Linoleic Acid in Low-Density Lipoprotein: An Important Event in Atherogenesis

Contrary to earlier views the main oxidation products of low-density lipoprotein (LDL) are derived from linoleic acid and not arachidonic acid, as determined by GC/MS investigations of the in vitro oxidation of LDL samples. A similar product spectrum, in which epoxyhydroxyoctadecenoic acids such as 1 and 2 have been identified for the first time, is obtained from minimally oxidized (that is, aged) LDL. Since this is still recognized by the LDL receptor, it is concluded that toxic oxidation products are introduced in endothelial cells in vivo and cause damage there.     

Identification of Toxic 2,4-Decadienal in Oxidized, Low-Density Lipoprotein by Solid-Phase Microextraction

The oxidation of low-density lipoprotein (LDL) in vitro was studied by a combination of solid-phase microextraction and GC/MS. 2-trans,4-cis-2,4-Decadienal, which is strongly toxic in vitro, was detected as the early oxidation product. This compound is degraded further to hexanal and (by cyclization of 4-hydroxy-2-nonenal) to 2-pentylfuran.     

Fabrication of Single Wall Carbon Nanotubes-Based Poly(vinyl butyral) Nanocomposites with Enhanced Mechanical and Thermal Properties

In this research, poly(vinyl butyral) (PVB)/single wall carbon nanotubes (SWCNT) composites were prepared via solution blending method. Dispersion degree of SWCNT in the composites was characterized by Scanning Electron Microscopy (SEM) and mechanical properties were measured with tensile testing. Thermal degradation of composites was investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). SEM analysis confirmed good dispersion of the nanotubes in the PVB. The tensile tests showed significant increases in mechanical properties such as exceptional improvement in tensile strength, Young's modulus and flexibility for the composites compared to PVB at low SWCNT content.The TGA curves indicated that adding SWCNT improved the thermal stability of the PVB significantly and the degradation of the polymer matrix shifted to the higher temperatures. For the sample containing 0.6 wt%, an increase of 171% in modulus and a 258.4% enhancement of tensile strength were achieved. Also, elongation at break increased 28.7% at this loading. In fact, intrinsic properties of nanotubes caused enhancement of strength and flexibility simultaneously. Also, for this composite, T_onset and T_max enhanced remarkably and weight loss reduced greatly and residue at 600°C increased to high values. These results are promising for application of the PVB in industry.     

Monodispersed Gold Nanoparticles Decorated Carbon Nanotubes as an Enhanced Sensing Platform for Nanomolar Detection of Tramadol

A promising composite‐modified glassy carbon electrode is fabricated by electrodeposition of mono‐dispersed gold nanoparticles onto carbon nanotubes (AuNPs/CNTs/GCE). The electroanalysis of Tramadol (TRA) was achieved by different electrochemical techniques. The effect of different parameters including pH, concentration and potential scan on the oxidation current signal of TRA was investigated. Large excess of ascorbic acid (AA) and uric acid (UA) with a maximum molar ratio of 1/1000 and 1/100, respectively, did not interfere with the response of TRA. The detection limit with high sensitivity is 68 nM. TRA was successfully determined in pharmaceutical dosage forms, without any pretreatment of the samples.     

磺化碳纳米管/活性炭复合微球的制备及其对低密度脂蛋白的吸附性能

采用悬浮聚合、炭化、活化制得碳纳米管/活性炭复合微球; 而后利用重氮盐偶合法将对氨基苯磺酸接枝到此复合微球上, 得到磺化碳纳米管/活性炭复合微球; 将其用于吸附血清中的低密度脂蛋白(LDL). 结果表明: 所制备的磺化碳纳米管/活性炭复合微球球形度好, 表面光洁, 中孔发达, 并且接枝有对氨基苯磺酸. 此复合微球对LDL的吸附量随着碳纳米管加入量的增加而逐渐增大; 当碳纳米管加入量为45% (w)时, LDL吸附量达6.564 mg·g^-1, 是未添加碳纳米管的3.3倍. 此复合微球在作为血液灌流LDL吸附剂方面有较好的应用前景.     

Electrically Conductive Low-Density Sealing Composites Based on Hollow Carbon Microspheres and Epoxy-Diane Resin

The dependence of the current-conducting and physicomechanical properties of epoxyamine composites on the content of hollow carbon microspheres serving as a filler for these composites was investigated. It is shown that the percolation point, which is a point of transition from an insulator to a current-conducting material, is observed at the content of carbon microspheres of 29 vol %, and the maximum absorption of electromagnetic radiation by the sealing material in the centimeter superhigh-radio-frequency band is observed with an approximation to the range of transition of the composite to an electrically conductive state.     

Exploring Multiwalled Carbon Nanotubes for Naproxen Detection

The electrochemical oxidation of naproxen was investigated at a multiwalled carbon nanotube (MWCNT)‐modified electrode. A decrease (200 mV) in the overpotential of the naproxen oxidation reaction and considerable (4‐fold) current increase (compared to the bare glassy‐carbon electrode) was observed. Two one‐electron transfers were verified at both bare and MWCNT‐modified electrodes and thus a new mechanism for the electrochemical oxidation of naproxen is proposed. Indicative of a mass transport regime that includes a thin‐layer diffusional process (entrapment of naproxen species within the MWCNT film) is presented as a possible explanation for the lowered oxidation potential and substantial current increase. The anti‐fouling properties of MWCNTs on the amperometric detection of naproxen using a batch‐injection analysis (BIA) system is demonstrated.     

Implantable Nanotube Sensor Platform for Rapid Analyte Detection

The use of nanoparticles within living systems is a growing field, but the long‐term effects of introducing nanoparticles to a biological system are unknown. If nanoparticles remain localized after in vivo implantation unanticipated side effects due to unknown biodistribution can be avoided. Unfortunately, stabilization and retention of nanoparticles frequently alters their function.[1] In this work multiple hydrogel platforms are developed to look at long‐term localization of nanoparticle sensors with the goal of developing a sensor platform that will stabilize and localize the nanoparticles without altering their function. Two different hydrogel platforms are presented, one with a liquid core of sensors and another with sensors decorating the hydrogel's exterior, that are capable of localizing the nanoparticles without inhibiting their function. With the use of these new hydrogel platforms nanoparticle sensors can be easily implanted in vivo and utilized without concerns of nanoparticle impact on the animal.     

Nanostructured Iron Oxide Platform for Impedimetric Cholesterol Detection

A nanostructured iron oxide (NanoFe₃O₄, particle size ca. 25 nm and roughness ca. 21 nm) film deposited onto a hydrolyzed indium‐tin‐oxide (ITO) coated glass plate has been used to immobilize cholesterol oxidase (ChOx) to fabricate an impedimetric cholesterol sensor. Electrochemical studies reveal that surface charged Fe₃O₄ nanoparticles provide better conformation for ChOx loading resulting in enhanced electron transfer between ChOx and the electrode. Impedimetric response studies of the ChOx/NanoFe₃O₄/ITO bioelectrode exhibit improved linearity (2.5–400 mg/dL), low detection limit (0.25 mg/dL), fast response time (25 s), high sensitivity (86 Ω/mg dL^?1/cm^?2) and a low value of the Michaelis‐Menten constant (K_m, 0.8 mg/dL) with a regression coefficient of 0.997.     

Electrochemical Biosensing Platform Using Carbon Nanotube Activated Glassy Carbon Electrode

Carbon nanotube enhanced electrochemically activated glassy carbon electrode (GCE) has been prepared and applied for sensitive electrochemical determination of DNA and DNA bases. The results indicate that the relative activation could efficiently enhance electron transfer at the pretreated GCE so that this carbon nanotube activated glassy carbon electrode could provide relatively low detection limit with good reproducibility for the respective biomolecular determination. Besides, greatly enhanced sensitivity could be obtained for the relevant electrochemical detection of the bio‐recognition process including DNA biosensing by using the carbon nanotube activated GCE. This approach provided a detection limit of 7.5 nM for guanine and 150 ng/mL for acid denatured DNA. These observations suggest that the carbon nanotube activated glassy carbon electrode could be utilized as a very sensitive and stable biosensor for some specific biological process.     

Carbon Fiber-gold/mercury Dual-electrode Detection for Capillary Electrophoresis

Capillary electrophoresis (CE) has become a useful and powerful separation technique and has many applications. Electrochemical detection (ED) has been shown to be one of the most sensitive detection techniques available for use in CE. Dual-electrode detection can expand the applicability of CE-ED1-5, the materials such as gold/mercury1,3, carbon fiber2, Pt4 and Au3,5 have been used for the two electrodes in dual-electrodes. As is well known, the electrochemical response of different c…