叶酸在聚苯胺修饰铂电极上的电催化氧化行为

采用电化学聚合法制备了聚苯胺修饰的铂电极(PAN/Pt),并用循环伏安法(CV)研究了该电极对叶酸(FA)的电催化氧化性能。结果显示:FA在裸铂电极上的直接电化学氧化十分迟缓,无氧化峰出现,而在PAN/Pt修饰电极上0.561V处出现氧化峰,表明此电极对FA有很良好的电催化作用。另外,氧化峰电流与叶酸浓度在1×10-12 mol/L~1×10-6 mol/L范围内呈线性关系,检测限为1×10-11 mol/L。利用该电极测定市售叶酸片中的叶酸,获得令人满意的结果。     

多孔的修饰电极对抗坏血酸的电催化氧化

通过循环伏安(CV)法制备了聚苯胺/聚砜(PAN/PSF)复合膜修饰电极,考察了电极对抗坏血酸(AA)的电催化性能。结果显示,PAN/PSF复合膜修饰电极对AA有很好的电催化氧化作用和高的稳定性。氧化峰电流与AA浓度在一定浓度范围内呈良好的线性关系,检测限为6×10-6 mol/L。该电极制备简单、灵敏度高、检测限低,对水果中AA具有很好的检测效果。     

基于离子液体/纳米材料及亚甲基蓝复合膜的电化学免疫传感研究

构建一种基于离子液体/纳米材料及亚甲基蓝复合膜的新型电化学免疫传感界面.该界面以碳纳米管/壳聚糖/离子液体复合物为基质,随后利用静电作用将亚甲基蓝与纳米金交替吸附于基质上并利用外层纳米金固定抗体分子.采用电化学阻抗及循环伏安法考察了界面的逐层修饰过程.以鼠IgG为免疫物质模型,在优化的实验条件下,亚甲基蓝的峰电流改变与鼠IgG浓度在5～50ng/mL和50～250ng/mL范围内存在良好的线性关系.     

基于[C_(10)-mim~+]Br~-固定HRP于Au/石墨烯复合材料电极表面的新型H_2O_2酶生物传感器

利用长链离子液体特殊的性质,用其固定HRP于Au/graphene电极表面(Nafion/HRP/[C10-mim+]Br-/Au/Gr/GCE)组装成H2O2传感器。用透射电镜来表征Au/氧化石墨烯的形貌,金纳米颗粒很均匀的分散在石墨烯表面,并不存在团聚现像。电化学技术检测Nafion/HRP/[C10-mim+]Br-/Au/Gr修饰电极对H2O2的响应情况,显示修饰电极对H2O2有很好的响应,在H2O2浓度2.0×10-6~1.2×10-3 mol/L的范围内,还原电流与浓度存在线性关系(R=0.997),检测限为3.0×10-7 mol/L;另外传感器具有很好的稳定性和选择性,为生物分子的检测提供新方法。     

桑色素功能化碳纳米管修饰电极对多巴胺与抗坏血酸的电化学行为研究

通过电聚合的方法构置了桑色素功能化碳纳米管修饰电极(morin/MWNTs/GCE),以多巴胺(DA)和抗坏血酸(AA)为模型化合物,考察了该修饰电极的电催化作用与机理.结果表明:DA与AA在Morin/MWNTs/GCE上的峰电流比裸电极、碳纳米管修饰电极明显增大,氧化峰电位差达210 mV,可实现多巴胺的灵敏测定.AA存在下,DA在1.0×10-7～5.0×10-4mol/L浓度范围内与峰电流有良好的线性关系,方法检出限2.0×10-8mol/L.     

氨基-β-环糊精-石墨烯-二茂铁修饰电极对多巴胺的电化学行为研究

利用制备的氨基-β-环糊精-石墨烯-二茂铁(β-CD-NH2/GNs/Fc)复合膜修饰电极,研究了多巴胺(DA)的电化学行为。结果表明,该复合膜修饰电极在pH值=7.00的磷酸盐缓冲溶液(PBS)中对DA有良好的电催化性能,DA的氧化峰电流在0.1～100μmol/L浓度范围内呈良好的线性关系,检出限为8.5×10-8mol/L。结果表明该修饰电极具有较高的检测灵敏度,可用于实际样品的检测。     

电化学法制备铁氰化铜/Nafion及其对卡托普利的检测

为对药片中卡托普利的含量进行精确测定,采用电聚合的方法,在玻碳电极表面沉积均匀分布的铁氰化铜/Nafion复合物。用扫描电镜(SEM)和X射线能量色散光谱(EDX)分别对样品的形貌和成分进行表征。利用循环伏安法(CV)研究药物分子卡托普利在该修饰电极上的电化学行为。研究结果显示,该修饰电极对卡托普利具有非常好的电催化性能。一定条件下,卡托普利在6.62×10-5~3.80×10-3mol/L范围内,其氧化峰电流与物质量浓度呈现很好的线性关系,其相关系数是0.996,检出限为5.0×10-6mol/L。该修饰电极具有快速、灵敏和高效的特点,并且可用于卡托普利实际样品的检测。     

聚吡咯/聚砜复合膜修饰电极的制备及其对对苯二酚的电化学催化性能

采用循环伏安法电化学聚合制备了聚吡咯(PPY)/聚砜(PSF)复合膜修饰电极.结果发现:复合膜的正面(与工作电极接触的一面)是黑色的;而反面(与溶液接触的一面)是白色的.复合膜的表面形态和化学组分分别用SEM和FTIR表征,用电化学循环伏安法对PPY/PSF复合膜修饰电极的电化学催化性能进行了研究.实验结果表明:所得复合膜修饰电极电化学可逆性好并且对对苯二酚有显著的催化效果,其氧化峰电流在5～30mM的范围内与对苯二酚的浓度呈线性关系,表明该复合膜修饰电极在对苯二酚H2Q的监测方面将有潜在的用途.     

电化学法直接制备石墨烯/纳米金复合膜修饰电极及用于水中Cr(Ⅵ)检测

采用电还原氧化石墨烯(ERGO)和电沉积纳米金(AuNPs)粒子的方法修饰玻碳电极(GCE),直接制得ERGO/AuNPs/GCE复合膜修饰电极。探究了Cr(Ⅵ)在此修饰电极上的电化学行为。用扫描电子显微镜(SEM)、循环伏安法(CV)、电化学交流阻抗法(EIS)对修饰电极进行了表征。结果表明:ERGO/AuNPs/GCE复合膜修饰电极具有较大的电活性表面积和良好的电子传递能力。在最优条件下,即金的沉积电位及沉积时间分别为-0.4V和120s,1mg/mL的氧化石墨烯的滴涂量为3μL,制得的ERGO/AuNPs/GCE复合膜修饰电极,能实现对水体中Cr(Ⅵ)的高效、快速检测,检测限为0.3μmol/L,线性范围为1~100μmol/L。     

壳聚糖-多壁碳纳米管/二茂铁修饰玻碳电极的电催化研究

利用多壁碳纳米管(MWCNTs)分散在壳聚糖/二茂铁形成的混合溶液,采用滴涂法对玻碳电极进行修饰,对多巴胺(DA)进行测定。结果表明,修饰后的玻碳电极能够有效促进DA在电极表面的电子传递速率,并且修饰电极对DA具有很好的催化氧化作用。DA氧化峰电流与其浓度在0.5～25μmol/L范围内呈良好的线性关系,检出限为3.89×10-7mol/L,并且常见物质对DA检测无干扰,DA注射液样品检测回收率为98.1%～100.9%。     

Immunosensor based on the ZnO nanorod networks for the detection of H1N1 swine influenza virus

This paper presents an immunosensor fabricated on patterned zinc oxide nanorod networks (ZNNs) for detecting the H1N1 swine influenza virus (H1N1 SIV). Nanostructured ZnO with a high isoelectric point (IEP, approximately 9.5) possesses good absorbability for proteins with low IEPs. Hydrothermally grown ZNNs were fabricated on a patterned Au electrode (0.02 cm2) through a lift-off process. To detect the H1N1 SIV, the sandwich enzyme-linked immunosorbent assay (ELISA) method was employed in the immunosensor. The immunosensor was evaluated in an acetate buffer solution containing 3,3',5,5'-tetramethylbenzidine (TMB) via cyclic voltammetry at various H1N1 SIV concentrations (1 pg/mL-5 ng/mL). The measurement results of the fabricated immunosensor showed that the reduction currents of TMB at 0.25 V logarithmically increased from 259.37 to 577.98 nA as the H1N1 SIV concentration changed from 1 pg/mL to 5 ng/mL. An H1N1 SIV immunosensor, based on the patterned ZNNs, was successfully realized for detecting 1 pg/mL-5 ng/mL H1N1 SIV concentrations, with a detection limit of 1 pg/mL for H1N1 SIV.     

Electrogenerated chemiluminescence. 72. Determination of immobilized DNA and C-reactive protein on Au(111) electrodes using tris(2,2'-bipyridyl)ruthenium(II) labels

Anodic electrogenerated chemiluminescence (ECL) with tri-n-propylamine (TPrA) as a coreactant was used to determine DNA and C-reactive protein (CRP) by immobilizations on Au(111) electrodes using tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)(3)(2+)) labels. A 23-mer synthetic single-stranded (ss) DNA derived from the Bacillus anthracis with an amino-modified group at the 5' end position was covalently attached to the Au(111) substrate precoated with a self-assembled thiol monolayer of 3-mercaptopropanoic acid (3-MPA) in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDAC) and then hybridized with a target ssDNA tagged with Ru(bpy)(3)(2+) ECL labels. Similarly, biotinylated anti-CRP species were immobilized effectively onto the Au(111) substrate precovered with a layer of avidin linked covalently via the reaction between avidin and a mixed thiol monolayer of 3-MPA and 16-mercaptohexadecanoic acid on Au(111) in the presence of EDAC and N-hydroxysuccinimide. CRP and anti-CRP tagged with Ru(bpy)(3)(2+) labels were then conjugated to the surface layer. ECL responses were generated from the modified electrodes described above by immersing them in a TPrA-containing electrolyte solution. A series of electrode treatments, including blocking free -COOH groups with ethanol amine, pinhole blocking with bovine serum albumin, washing with EDTA/NaCl/Tris buffer, and spraying with inert gases, were used to reduce the nonspecific adsorption of the labeled species. The ECL peak intensity was linearly proportional to the analyte CRP concentration over the range 1-24 microg/mL. CRP concentrations of two unknown human plasma/serum specimens were measured by the standard addition method based on this technique.     

Electrochemically reduced graphene modified carbon ionic liquid electrode for the sensitive sensing of rutin

In this paper a graphene (GR) modified carbon ionic liquid electrode that was obtained by one-step potentiostatic electroreduction of a graphene oxide solution was described. The resulting electrode displayed excellent electrochemical performance due to the formation of highly conductive GR film on the electrode surface. Electrochemistry of rutin was carefully studied with a pair of well-defined redox peaks appeared in pH 2.5 buffer solution. Rutin exhibited a diffusion-controlled two-electron and two-proton transfer reaction on the modified electrode with the electrochemical parameters calculated. The reduction peak currents are linearly related to rutin concentration in the concentration range from 0.070 to 100.0 μmol/L with a detection limit as low as 24.0 nmol/L (3σ). The modified electrode displayed excellent selectivity with good stability, and was applied to the determination of rutin content in tablet, human serum and urine samples with satisfactory results.     

Electrochemical biosensor based on multi-walled carbon nanotubes and Au nanoparticles synthesized in chitosan

A new biosensor is prepared by cross-linking glucose oxidase (GOD) with glutaradehyde at the electrode combining Au nanoparticles (AuNP) with multi-walled carbon nanotubes (MWCNTs). Au nanoparticles-doped chitosan (CS) solution (AuNP-CS) is prepared by treating the CS solution followed by chemical reduction of Au (III) with NaBH4. MWCNTs are then dispersed in AuNP-CS solution. TEM, FT-IR, and UV-Vis show that the AuNP-CS solution is highly dispersed and stable. The synergistic effect between AuNP and CNTs of the AuNP-CNTs-CS material has been investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and amperometric methods. The modified glassy carbon electrode (GCE) allows low-potential detection of H2O2 with high sensitivity and fast response time. With the immobilization of GOD, a biosensor has been constructed. In phosphate buffer solutions (PBS, pH 7.0), nearly free interference determination of glucose has been realized at 0.4 V(vs. Ag/AgCl/3.0 M KCI) with a wide linear range from 2.0 x 10(-5) to 1.5 x 10(-2) M and a fast response time within 5s. The biosensor has been used to determine glucose in human serum samples and the results are satisfactory.     

Amplified electrochemical detection of a cancer biomarker by enhanced precipitation using horseradish peroxidase attached on carbon nanotubes

An electrochemical nanoimmunosensor based on multiwall carbon nanotubes (MWCNTs)/gold nanoparticles (AuNPs) was developed for the amplified detection of prostate specific antigen (PSA). The amplified detection was achieved by the enhanced precipitation of 4-chloro-1-naphthol (CN) using a higher number of horseradish peroxidase (HRP) molecules attached on MWCNTs. The PSA nanoimmunosensor was fabricated by immobilizing a monoclonal anti-PSA antibody (anti-PSA) on the AuNP-attached thiolated MWCNT on a gold electrode. The sensor surface was characterized using scanning electron microscope, transmission electron microscope, quartz crystal microbalance, and electrochemical techniques. Cyclic and square wave voltammetric techniques were used to monitor the enhanced precipitation of CN that accumulated on the electrode surface and subsequent decrement in the electrode surface area by monitoring the reduction process of the Fe(CN)(6)(3-)/Fe(CN)(6)(4-) redox couple. Under the optimized experimental condition, the linear range and the detection limit of PSA immunosensor were determined to be 1.0 pg/mL to 10.0 ng/mL and 0.40 ± 0.03 pg/mL, respectively. The validity of the proposed method was compared with an enzyme-linked immunosorbent assay method in various PSA spiked human serum samples.     

Electrochemiluminescence immunosensor based on CdSe nanocomposites

A novel strategy for the enhancement of electrochemiluminescence (ECL) was developed by combining CdSe nanocrystals (NCs), carbon nanotube-chitosan (CNT-CHIT), and 3-aminopropyl-triethoxysilane (APS). A label-free ECL immunosensor for the sensitive detection of human IgG (HIgG) was fabricated. The colloidal solution containing CdSe NCs/CNT-CHIT composite was first covered on the Au electrode surface to form a robust film, which showed high ECL intensity and good biocompatibility. After APS as a cross-linker was covalently conjugated to the CdSe NCs/CNT-CHIT film, the ECL intensity was greatly enhanced. And, an intensity about 20-fold higher than that of the CdSe NCs/CNT-CHIT film was observed. After antibody was bound to the functionalized film via glutaric dialdehyde (GLD), the modified electrode could be used as an ECL immunosensor for the detection of HIgG. The specific immunoreaction between HIgG and antibody resulted in the decrease in ECL intensity. The ECL intensity decreased linearly with HIgG concentration in the range of 0.02-200 ng mL(-1), and the detection limit was 0.001 ng mL(-1). The immunosensor has the advantages of high sensitivity, speed, specificity, and stability and could become a promising technique for protein detection.     

Reverse-phase versus sandwich antibody microarray, technical comparison from a clinical perspective

Protein microarrays are powerful tools to quantify and characterize proteins in multiplex assays. They have great potential within clinical diagnostics and prognostics, as they minimize consumption of both analyte and biological sample. Assays that do not require labeling of the biological specimen, henceforth called label-free, are vital for ease of clinical sample processing. Here, we evaluate two label-free techniques, reverse-phase and sandwich antibody assays, using microarrays on high-performance porous silicon surfaces and fluorescence detection. In view of increasing interest in reverse microarrays, this paper focuses on analytical sensitivity of the reverse assays compared to the more complex but highly sensitive sandwich assay. Sensitivity, linear range, and reproducibility of the two assays were compared using prostate-specific antigen (PSA) in buffer. The sandwich assay displayed 5 orders of magnitude lower detection limit (0.7 ng/mL) compared to the reverse assay (70 microg/mL). PSA at 50 nM (1.5 microg/mL) in cell lysates was detected by the sandwich assay but not by the reverse assay, demonstrating again a far lower detection limit for sandwich microarrays. In independent assay runs of PSA spiked in female serum, the sandwich assay had good linearity (R2 > 0.99) and reproducibility (coefficient of variation < or =15%), and the detection limit could be improved to 0.14 ng/mL. Without further signal amplification, the sandwich assay would be our choice for PSA analysis of clinical samples using a microarray technology platform.     

Cancer biomarker detection in serum samples using surface plasmon resonance and quartz crystal microbalance sensors with nanoparticle signal amplification

Early detection of cancer is vital for the successful treatment of the disease. Hence, a rapid and sensitive diagnosis is essential before the cancer is spread out to the other body organs. Here we describe the development of a point-of-care immunosensor for the detection of the cancer biomarker (total prostate-specific antigen, tPSA) using surface plasmon resonance (SPR) and quartz crystal microbalance (QCM) sensor platforms in human serum samples. K(D) of the antibody used toward PSA was calculated as 9.46 × 10(-10) M, indicating high affinity of the antibody used in developing the assay. By performing a sandwich assay using antibody-modified nanoparticles concentrations of 2.3 ng mL(-1) (Au, 20 nm) and 0.29 ng mL(-1) (8.5 pM) (Au, 40 nm) tPSA in 75% human serum were detected using the developed assay on an SPR sensor chip. The SPR sensor results were found to be comparable to that achieved using a QCM sensor platform, indicating that both systems can be applied for disease biomarkers screening. The clinical applicability of the developed immunoassay can therefore be successfully applied to patient's serum samples. This demonstrates the high potential of the developed sensor devices as platforms for clinical prostate cancer diagnosis and prognosis.     

Positive potential operation of a cathodic electrogenerated chemiluminescence immunosensor based on luminol and graphene for cancer biomarker detection

In this work, we report a cathodic electrogenerated chemiluminescence (ECL) of luminol at a positive potential (ca. 0.05 V vs Ag/AgCl) with a strong light emission on the graphene-modified glass carbon electrode. The resulted graphene-modified electrode offers an excellent platform for high-performance biosensing applications. On the basis of the cathodic ECL signal of luminol on the graphene-modified electrode, an ECL sandwich immunosensor for sensitive detection of cancer biomarkers at low potential was developed with a multiple signal amplification strategy from functionalized graphene and gold nanorods multilabeled with glucose oxidase (GOx) and secondary antibody (Ab(2)). The functionalized graphene improved the electron transfer on the electrode interface and was employed to attach the primary antibody (Ab(1)) due to it large surface area. The gold nanorods were not only used as carriers of secondary antibody (Ab(2)) and GOx but also catalyzed the ECL reaction of luminol, which further amplified the ECL signal of luminol in the presence of glucose and oxygen. The as-proposed low-potential ECL immunosensor exhibited high sensitivity and specificity on the detection of prostate protein antigen (PSA), a biomarker of prostate cancer that was used as a model. A linear relationship between ECL signals and the concentrations of PSA was obtained in the range from 10 pg mL(-1) to 8 ng mL(-1). The detection limit of PSA was 8 pg mL(-1) (signal-to-noise ratio of 3). Moreover, the as-proposed low-potential ECL immunosensor exhibited excellent stability and reproducibility. The graphene-based ECL immunosensor accurately detected PSA concentration in 10 human serum samples from patients demonstrated by excellent correlations with standard chemiluminescence immunoassay. The results suggest that the as-proposed graphene ECL immunosensor will be promising in the point-of-care diagnostics application of clinical screening of cancer biomarkers.     

Polyeugenol-modified platinum electrode for selective detection of dopamine in the presence of ascorbic Acid

A platinum electrode was modified with electropolymerized films of 4-allyl-2-methoxyphenol (eugenol) by its oxidative polymerization from an alkaline solution by cyclic voltammetry. The modified electrode was than used to determine dopamine (DA) in an excess of ascorbic acid (AA) by differential pulse voltammetry. The peak positions as well as relative sensitivity DA/AA were affected by the potential window applied for the polymerization. For polymerization between 0 and 2.2 V, the peak potentials recorded in a phosphate buffer solution (pH 7.4) were -61 and +152 mV vs Ag/AgCl for AA and DA, respectively. After a 5-min equilibration, relative sensitivity DA/AA was 164 and the current sensitivity for DA was 7.9 nA μM(-)(1). The detection limit for S/N = 3 is 0.1 μM. The high selectivity and sensitivity for DA was found to be due to charge discrimination/analyte accumulation and an effect of catalytic mediation of redox sites. Chronocoulometric data reveal that DA is accumulated on the electrode as a monolayer. The electrode is stable, reversible, and free of fouling problems.