A graphene-laminated electrode with high glucose oxidase loading for highly-sensitive glucose detection

Graphene oxide(GO) has received considerable attention for glucose detection because of high surface area, abundant functional groups, and good biocompatibility. Defects and functional groups of the GO are beneficial to immobilization of glucose oxidase(GOD), but sacrificing electron-transfer capability for highly-sensitive detection. In order to obtain high GOD loading and highly-sensitive detection of biosensors, we first designed and fabricated a graphene-laminated electrode by combining GO and edgefunctionalized graphene(FG) layers together onto glassy-carbon electrode. The graphene-laminated electrodes exhibited faster electron transfer rate, higher GOD loading of 3.80 × 10^-9 mol·cm^-2, and higher detection sensitivity of 46.71 μA·mM^-1·cm^-2 than other graphene-based biosensors reported in literature. Such high performance is mainly attributed to the abundant functional groups of GO, high electrical conductivity of FG, and strong interactions between components in the graphene-laminated electrodes.By virtue of their high enzyme loading and highly-sensitive detection, the graphene-laminated electrodes show great potential to be widely used as high-performance biosensors in the field of medical diagnosis.     

Amperometric glucose sensor based on enhanced catalytic reduction of oxygen using glucose oxidase adsorbed onto core-shell Fe3O4@silica@Au magnetic nanoparticles

Monodisperse Fe₃O₄ magnetic nanoparticles (NPs) were prepared under facile solvothermal conditions and successively functionalized with silica and Au to form core/shell Fe₃O₄@silica@Au NPs. Furthermore, the samples were used as matrix to construct a glucose sensor based on glucose oxidase (GOD). The immobilized GOD retained its bioactivity with high protein load of 3.92 × 10^? 9 mol·cm^? 2, and exhibited a surface-controlled quasi-reversible redox reaction, with a fast heterogeneous electron transfer rate of 7.98 ± 0.6 s^? 1. The glucose biosensor showed a broad linear range up to 3.97 mM with high sensitivity of 62.45 μA·mM^? 1 cm^? 2 and fast response (less than 5 s).     

Advanced materials for drug delivery and biosensors based on magnetic label detection

Many traditional magnetic materials are not suitable for the increasing demands of microsensors for environmental control, biomedical applications, drug delivery, and homeland security. The design of magnetic biosensors can be based on different types of magnetic effects. The detection principles are measurements of the resistance, impedance, etc. in the absence and presence of magnetic nanoparticles. Variations in the measured parameters can be associated with either many individual molecular recognition events or with a specific uptake. Magnetic materials which could be used in magnetoimpedance based biosensors have been studied both for the sensitive element and for magnetic label. The self-assembling processes were observed in perpendicular field for different concentrations of the Dynabeads® M-480. Magnetic field controlled assembly is proposed for designing new composite materials which can be also useful to study the properties of the separate particles. The morphology of the particle agglomerates and dipolar chains in the external field can be controlled by using simultaneously two different suspensions of magnetic particles. A new concept is to define synergetic combinations of two or more nanostructures for the best performance.     

An electrochemical metalloimmunoassay based on a colloidal gold label

A novel, sensitive electrochemical immunoassay has been developed using a colloidal gold label that, after oxidative gold metal dissolution in an acidic solution, was indirectly determined by anodic stripping voltammetry (ASV) at a single-use carbon-based screen-printed electrode (SPE). The use of disposable electrodes allows for simplified measurement in 35 microL of solution. The method was evaluated for a noncompetitive heterogeneous immunoassay of an immunoglobulin G (IgG) and a concentration as low as 3 x 10(-12) M was determined, which is competitive with colorimetric ELISA or with immunoassays based on fluorescent europium chelate labels. The high performance of the method is related to the sensitive ASV determination of gold(III) at a SPE (detection limit of 5 x 10(-9) M) and to the release of a large number of gold(III) ions from each gold particle anchored on the immunocomplex (e.g., 1.7 x 10(5) gold atoms are theoretically contained in a 18-nm spherical gold particle).     

Naked eye detection of glucose in urine using glucose oxidase immobilized gold nanoparticles

Colloidal gold is extensively used for molecular sensing because of the flexibilities it offers in terms of modification of the gold nanoparticle surface with a variety of functional groups using thiol chemistry. We describe a simple assay that allows the visual detection of glucose in aqueous samples and demonstrates its applicability by estimating glucose in urine. To enable the glucose detection, we functionalized the thiol capped gold nanoparticles with glucose oxidase, the enzyme specific to β-D glucose, using carbodiimide chemistry. The visible color change of the GOD-functionalized gold nanoparticles from red to blue on interaction with glucose is the principle applied here for the sensing of urine glucose level. The solution turns blue when the glucose concentration exceeds 100 μg/mL. The approach depicted here seems to be important, particularly in third world countries where high tech diagnostics aids are inaccessible to the bulk of the population.     

Graphene-Au nanoparticle based electrochemical immunosensor for fish pathogen Aphanomyces invadans detection

Epizootic ulcerative syndrome (EUS) that is primarily caused by an invasive oomycete fungus Aphanomyces invadans is a devastating fish disease. Rapid diagnosis of EUS is significantly important for the control and treatment of this highly invasive disease. In our study, a label-free immunosensor constructed with G-AuNPs/SAM-Ab-BSA/GCE was proposed for the determination of Aphanomyces invadans. The electrode was prepared by the immobilization of anti-mycelium antibodies on graphene-AuNPs nanocomposite-cysteamine monolayers modified GCE. The optimized parameters were as follows: 90 min as the immersion time of SAM modified electrode in the anti-mycelium solution, 0.20 µg/mL as the concentration of anti-mycelium solution and 10 min as the interaction time of immunoreaction. The immunosensors exhibited low limit detection of 309 ng/mL and good reproducibility.     

显微视觉结合光功率检测的光纤耦合方法

分析了光功率损耗的理论模型,指出横向偏移、光纤角度和端面间隙是影响对接损耗的主要参数,由此提出了显微视觉结合光功率检测的光纤耦合方法。在显微视觉系统引导下,采用精密并联机器人消除光纤角度及端面间隙的影响,并实现横向偏移的粗调整;利用压电陶瓷驱动的五自由度微动机器人精确调整横向偏移,通过设计合理策略,实现损耗极值区域的快速精确搜索。光纤耦合实验表明,粗调整后平均损耗0.3db;微动调整并熔接后,对接损耗减小到0.02db以下。     

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.     

A localized surface plasmon resonance based immunosensor for the detection of casein in milk

In this research, a localized surface plasmon resonance (LSPR) immunosensor based on gold-capped nanoparticle substrate for detecting casein, one of the most potent allergens in milk, was developed. The fabrication of the gold-capped nanoparticle substrate involved a surface-modified silica nanoparticle layer (core) on the slide glass substrate between bottom and top gold layers (shell). The absorbance peak of the gold-capped nanoparticle substrate was observed at ∼520 nm. In addition, the atomic force microscopy (AFM) images demonstrated that the nanoparticles formed a monolayer on the slide glass. After immobilizing anti-casein antibody on the surface, our device, casein immunosensor, could be applied easily for the detection of casein in the raw milk sample without a difficult pretreatment. Under the optimum conditions, the detection limit of the casein immunosensor was determined as 10 ng/mL. Our device brings several advantages to the existing LSPR-based biosensors with its easy fabrication, simple handling, low-cost, and high sensitivity.     

基于累积光流的运动对象检测

利用解析小波和M估计求解光流约束方程,得到一种精度高的、稳健的光流计算方法,并在此基础上引入扩展累积光流,针对累积光流计算中的几个特殊问题进行了相应的处理,实现了一种稳健的运动对象检测算法.实验结果表明,该算法正确检测运动对象的精度高,能够检测出慢速物体和小目标的运动,并较好地解决了遮挡问题.     

A localized surface plasmon resonance based immunosensor for the detection of casein in milk

In this research, a localized surface plasmon resonance (LSPR) immunosensor based on gold-capped nanoparticle substrate for detecting casein, one of the most potent allergens in milk, was developed. The fabrication of the gold-capped nanoparticle substrate involved a surface-modified silica nanoparticle layer (core) on the slide glass substrate between bottom and top gold layers (shell). The absorbance peak of the gold-capped nanoparticle substrate was observed at ～520 nm. In addition, the atomic force microscopy (AFM) images demonstrated that the nanoparticles formed a monolayer on the slide glass. After immobilizing anti-casein antibody on the surface, our device, casein immunosensor, could be applied easily for the detection of casein in the raw milk sample without a difficult pretreatment. Under the optimum conditions, the detection limit of the casein immunosensor was determined as 10 ng/mL. Our device brings several advantages to the existing LSPR-based biosensors with its easy fabrication, simple handling, low-cost, and high sensitivity.     

An electrochemical immunosensor based on chemical assembly of vertically aligned carbon nanotubes on carbon substrates for direct detection of the pesticide endosulfan in environmental water

A glassy carbon substrate was covalently modified with a mixed layer of 4-aminophenyl and phenyl via in situ electrografting of their aryldiazonium salts in acidic solutions. Single-walled carbon nanotubes (SWNTs) were covalently and vertically anchored on the electrode surface via the formation of amide bonds from the reaction between the amines located on the modified substrate and the carboxylic groups at the ends of the nanotubes. Ferrocenedimethylamine (FDMA) was subsequently attached to the ends of SWNTs through amide bonding followed by the attachment of an epitope, i.e., endosulfan hapten to which an antibody would bind. Association or dissociation of the antibody with the sensing interface causes a modulation of the ferrocene electrochemistry. Antibody-complexed electrodes were exposed to samples containing spiked endosulfan (unbound target analyte) in environment water and interrogated using the square wave voltammetry (SWV) technique. The modified sensing surfaces were characterized by atomic force microscopy, XPS, and electrochemistry. The fabricated electrochemical immunosensor can be successfully used for the detection of endosulfan over the range of 0.01-20 ppb by a displacement assay. The lowest detection limit of this immunosensor is 0.01 ppb endosulfan in 50 mM phosphate buffer at pH 7.0.     

An indirect perfluorosulfonated ionomer-coated electrochemical immunosensor for the detection of the protein human chorionic gonadotrophin.

The development of an amperometric immunosensor for the detection of human chorionic gonadotrophin (hCG) is described. In this immunosensor, Nafion was used to immobilize an anti-hCG monoclonal antibody onto a glassy carbon electrode. A systematic study on the effects of experimental parameters such as the quantity of ethanol present in the Nafion solution, the percentage composition of Nafion, the pH of the immobilization buffer, and the concentration of antibody used for entrapment experiments on the binding between the immobilized antibody and 125I-labeled hCG has been carried out. Two immobilization methods, coimmobilization and adsorption immobilization, have then been attempted. A binding of approximately 3% was obtained in the former method, while 5.5% binding was achieved in the latter. On the basis of these results, adsorption immobilization was employed to entrap antibody on the electrode surface. A sandwich assay was then developed for hCG in which the enzyme horseradish peroxidase was conjugated to a second anti-hCG monoclonal antibody. The activity of the enzyme was determined electrochemically by the reduction of benzoquinone to hydroquinone. Binding of hCG to immobilized antibody determines the quantity of enzyme-conjugated antibody at the electrode surface, permitting the quantification of hCG. By a standard additions calibration method of hCG performed in blank human serum samples, the immunosensor exhibits a limit of linearity at 200 mIU mL-1 and a detection limit of 11.2 mIU mL-1 (based on twice the standard deviation of the blank solution).     

Conductometric biosensor based on glucose oxidase and beta-galactosidase for specific lactose determination in milk

This paper investigates the development of a biosensor associating two distinct enzymatic activities, that of the beta-galactosidase and that of the glucose oxidase, in order to apply it for the quantitative detection of lactose in milk. To eliminate interferences with glucose, a differential mode of measurement was used. Results show a linear calibration curve for lactose concentration between 60 and 800 μM (0.03 to 0.3 g/L). Tests with real commercial milk samples were carried out to validate the conductometric biosensor.     

An optical polarization-bistable element based on the Faraday effect

An optical polarization-bistable element scheme based on an He-Ne laser (λ = 3.39 μm) with a Faraday cell in the cavity is considered for the first time. A sample of such cavity having the shape of a parallelepiped has been manufactured from an yttrium iron garnet single crystal and a theoretical analysis of this element in terms of the Jones matrices has been performed. It is established that the polarization bistability can be observed for a single-trip Faraday rotation of 45°. Experiments with the device based on a hybrid bistability scheme showed that, under certain conditions, the circular polarization is reversibly switched between σ⁺ and σ^?.     

Piezoelectric immunosensor based on gold nanoparticles capped with mixed self-assembled monolayer for detection of carcinoembryonic antigen

It is very important for a piezoelectric immunosensor to increase specific binding and decrease nonspecific adsorption. This study presents the development of such a piezoelectric immunosensor for the detection of carcinoembryonic antigen. An AT-cut quartz crystal's Au electrode surface was first modified with homogenous self-assembled monolayer of cysteamine (CE). Gold nanoparticles capped with mixed self-assembled monolayer of CE and MH (6-mercapto-1-haxanol) were then attached to the CE monolayer via glutaraldehyde (GA). Antibodies were immobilized onto a mixed self-assembled monolayer of CE and MH with GA as a reactive intermediate too. The binding of target antigens onto the immobilized antibodies decreased the sensor's resonant frequency, and the frequency shift was correlated to the antigen concentration. The stepwise assembly of the immunosensor was characterized by means of cyclic voltammetry technique. This immunoassay was shown to be specific and sensitive, thus providing a viable alternative to carcinoembryonic antigen detection method.     

An immunosensor for haemoglobin based on impedimetric properties of a new mixed self-assembled monolayer

A novel impedimetric immunosensor for the detection of haemoglobin has been developed by mixed self-assembled monolayers on Au. First, a mixed self-assembled monolayer (SAMs) consisting of 1,2 dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-(biotinyl) (biotinyl-PE) and 16-mercaptohexadecanoic acid (MHDA) on gold electrodes was studied. The conformational properties of the SAMs were characterised by cyclic voltammetry and impedance spectroscopy. After blocking non-specific binding sites in the mixed monolayer using non-specific IgG, neutravidin was used to bind to biotinyl sites present in the mixed monolayer. Finally, biotinylated anti-haemoglobin IgG was immobilised to the tethered neutravidin. The membrane resistance R_m, obtained from the assembly, decreased gradually after the addition of non-specific IgG, neutravidin and anti-haemoglobin to the monolayer. This decrease could be attributed to a rearrangement in the structure of the SAMs. The detection of antibody–antigen reaction demonstrates that the potentiometric immunosensor exhibited high sensitivity and a detection limit of 20 ng/ml (approximately 0.3 nM).     

A glucose oxidase electrode based on electropolymerized conducting polymer with polyanion-enzyme conjugated dopant

An enzyme immobilization method has been developed by electropolymerization chemistry of conducting polymer which results in a more effective and reproducible enzyme electrode. As a model system, in this study, glucose oxidase (GOD) was conjugated with a polyanion, poly(2-acrylamido-2-methylpropane sulfonic acid), via a poly(ethylene oxide) spacer to improve the efficiency of enzyme immobilization into a conducting polymer. GOD was successfully conjugated with a high conjugation yield of more than 90%, and its bioactivity was preserved. The resulting polyanion-GOD conjugate was used as a dopant for the electrochemical polymerization of pyrrole. Polypyrrole was effectively deposited on a Pt wire working electrode with the polyanion-GOD conjugate. The enzyme electrode responded to glucose concentrations of up to 20 mM with a sensitivity of 40 nA/mM at an applied potential of 0.4 V within a response time of 30 s. Although the response signal decreased at the low applied potential of 0.3 V, the enzyme electrode showed sensitive response signals of about 16 nA/mM up to 20 mM in glucose concentration. Under the deoxygenated condition, reduced but clear response current signal was obtained. The results show that the current signal response of the enzyme electrode to glucose concentration may be produced by mixed mechanisms.     

溶胶—凝胶法制备基于荧光猝灭原理的光纤氧传感器在线监测水中溶解氧

利用氧分子对金属钌化合物的荧光具有猝灭作用的特性,构造出基于荧光猝灭原理的光纤氧传感器。就用于水中溶解氧在线监测的光纤光谱仪的搭建、传感器探头的设制及传感膜的制作过程进行探索,并对传感器的响应性能进行考察。结果表明以联吡啶钌等作为荧光指示剂以溶胶-凝胶法制备的传感膜对溶解氧的响应具有良好的可逆性,稳定性,较快的响应时间和较长的使用寿命。与标准法相对照,用本仪器系统测定了不同盐度的人工海水中的溶解氧浓度,两种方法在不同浓度水平下的溶解氧测定值均无显著性差异。本法的日内和日间RSD在1.7％～5.0％之间。     

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.