Photomicrobial sensors for selective determination of phosphate

A photomicrobial sensor consisting of immobilized Chlorella vulgaris and an oxygen electrode has been developed for selective determination of phosphate. When 40 mM phosphate was added to the sensor system, the photocurrent increased to a maximum under light irradiation with a response time of 1 min. The current increased with increasing phosphate concentration in the range 8–70 mM. Selectivity of the sensor was satisfactory. Good agreement was obtained between the phosphate concentrations in lake water determined by the photomicrobial sensor and by conventional colorimetry (correlation coefficient 0.96).     

Amperometric biosensor for determining human salivary phosphate

An amperometric biosensor was constructed for analysis of human salivary phosphate without sample pretreatment. The biosensor was constructed by immobilizing pyruvate oxidase (PyOD) on a screen-printed electrode. The presence of phosphate in the sample causes the enzymatic generation of hydrogen peroxide (H(2)O(2)), which was monitored by a potentiostat and was in proportion to the concentration of human salivary phosphate. The sensor shows response within 2s after the addition of standard solution or sample and has a short recovery time (2 min). The time required for one measurement using this phosphate biosensor was 4 min, which was faster than the time required using a commercial phosphate testing kit (10 min). The sensor has a linear range from 7.5 to 625 microM phosphate with a detection limit of 3.6 microM. A total of 50 salivary samples were collected for the determination of phosphate. A good level of agreement (R(2)=0.9646) was found between a commercial phosphate testing kit and the phosphate sensor. This sensor maintained a high working stability (>85%) after 12h operation and required only a simple operation procedure. The amperometric biosensor using PyOD is a simple and accurate tool for rapid determinations of human salivary phosphate, and it explores the application of biosensors in oral and dental research and diagnosis.     

A disposable on-chip phosphate sensor with planar cobalt microelectrodes on polymer substrate

Disposable microsensors on polymer substrates consisting of fully integrated on-chip planar cobalt (Co) microelectrodes, Ag/AgCl reference electrodes, and microfluidic channels have been designed, fabricated, and characterized for phosphate concentration measurement in aqueous solution. The planar Co microelectrode shows phosphate-selective potential response over the range from 10(-5) to 10(-2)M in acidic medium (pH 5.0) for both inorganic (KH(2)PO(4)) and organic (adenosine 5'-triphosphate (ATP) and adenosine 5'-diphosphates (ADP)) phosphate compounds. This microfabricated sensor also demonstrates significant reproducibility with a small repeated sensing deviation (i.e. relative standard deviation (R.S.D.)<1%) on a single chip and a small chip-to-chip deviation (i.e. R.S.D.<2.5%). Specifically, while keeping the high selectivity, sensitivity, and stability of a conventional bulk Co-wire electrode, the proposed phosphate sensor yields advantages such as ease of use, cost effectiveness, reduced analyte consumption, and ease of integrating into disposable polymer lab-on-a-chip devices. The capability to sense both inorganic and organic phosphate compounds makes this sensor applicable in diverse areas such as environmental monitoring, soil extract analysis, and clinical diagnostics.     

羧基化石墨烯/半胱胺修饰金电极对多巴胺的电化学行为研究

为了基于羧基化石墨烯/半胱胺修饰金电极建立更为先进的多巴胺生物传感器，以定量检测儿茶酚胺类神经递质多巴胺，利用自组装技术将半胱胺修饰于金电极上，再利用1-乙基-\[3-二甲基氨基丙基\]碳酰二亚胺盐酸化物/N-羟基琥珀酰亚胺（EDC/NHS）交联剂将羧基化石墨烯固定在修饰后的金电极上制成多巴胺电化学传感器。先对修饰电极进行表征以检验其灵敏度，再利用循环伏安法研究该电极在多巴胺溶液中的电化学行为，包括检测条件的优化和传感器性能的测定。修饰电极表征结果表明，羧基化石墨烯/半胱胺修饰金电极提高了电极传递电子的能力，具有较高的灵敏度。经单因素实验得出，最佳检测条件为利用pH 6.00的0.30 mol·L-1磷酸盐缓冲溶液（PBS）配制多巴胺溶液，扫描速率设定为200 mV·s-1。在最佳检测条件下，制备的多巴胺电化学传感器电流的大小随着多巴胺浓度的增大而增大，在1.0×10-3~3.5×10-3 mol·L-1范围内呈现良好的线性关系，线性回归方程为I=8.120 6C+7.017，相关系数R2为0.999 5。且该传感器精密度好，稳定性强，具有一定的抗干扰能力。研究结果为药物盐酸多巴胺注射液中多巴胺含量测定提供了支撑。     

Amperometric ascorbic acid sensor based on doped ferrites nanoparticles modified glassy carbon paste electrode

In this study, a novel electrochemical sensor for quantification of ascorbic acid with amperometric detection in physiological conditions was constructed. For this purpose, cobalt and nickel ferrites were synthesized using microwave and ultrasound assistance, characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray powder diffraction (XRPD), and used for modification of glassy carbon paste electrode (GCPE). It was shown that introducing these nanoparticles to the structure of GCPE led to increasing analytical performance. Co ferrite modified GCPE (CoFeGCPE) showed better characteristics toward ascorbic acid sensing. The limit of detection (LOD) obtained by sensor was calculated to be 0.0270 mg/L, with linear range from 0.1758 to 2.6010 mg/L. This sensor was successfully applied for practical analysis, and the obtained results demonstrated that the proposed procedure could be a promising replacement for the conventional electrode materials and time-consuming and expensive separation methods.     

Fabrication of a sensing module using micromachined biosensors

Micromachining is a powerful tool in constructing micro biosensors and micro systems which incorporate them. A sensing module for blood components was fabricated using the technology. The analytes include glucose, urea, uric acid, creatine, and creatinine. Transducers used to construct the corresponding sensors were a Severinghaus-type carbon dioxide electrode for the urea sensor and a Clark-type oxygen electrode for the other analytes. In these electrodes, detecting electrode patterns were formed on a glass substrate by photolithography and the micro container for the internal electrolyte solution was formed on a silicon substrate by anisotropic etching. A through-hole was formed in the sensitive area, where a silicone gas-permeable membrane was formed and an enzyme was immobilized. The sensors were characterized in terms of pH and temperature dependence and calibration curves along with detection limits. Furthermore, the sensors were incorporated in an acrylate flow cell. Simultaneous operation of these sensors was successfully conducted and distinct and stable responses were observed for respective sensors.     

双酶电极法测定L-苯丙氨酸的研究

本文以Ｃｌａｒｋ氧电极为基础,把水杨酸羟化酶和苯丙氨酸脱氨酶同时固定在氧电极的表面,制成了双酶生物传感器。在磷酸缓冲液中,水杨酸浓度为０．５ｍｍｏｌ／Ｌ,烟酰胺腺嘌呤二核甘酸（ＮＡＤ＾＋）的浓度为１．０ｍｍｏｌ／Ｌ,其响应电流的变化对应反池中Ｌ－苯丙氨酸的浓度在０－０．１５ｍｍｏｌ／Ｌ之内有良好的线性范围。     

Modified carbon paste electrodes for flow injection amperometric determination of isocitrate dehydrogenase activity in serum

A carbon paste electrode modified with the adsorbed products of the electrochemical oxidation of adenosine triphosphate is described. The electrode was applied to the amperometric electrocatalytic detection of the reduced form of both nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate. The catalytic oxidation current shows a linear dependence on the concentration of the reduced form of nicotinamide adenine dinucleotide up to 1x10(-4)M, with a detection limit of 5x10(-9)M. Modified carbon paste electrodes were coated with an electrogenerated film of nonconducting poly(o-phenylenediamine) to obtain a stable amperometric response for at least 150h. In addition to static measurements, determination of both reduced cofactors was carried out in a flow injection analysis system with a thin-layer amperometric detection cell. The electrocatalytic monitoring of reduced nicotinamide adenine dinucleotide phosphate was applied to flow injection measurement of isocitrate dehydrogenase activity in serum. The results were in good agreement with those for the standard spectrophotometric test kit. The proposed method consumed less time and reagents and provided better precision than the standard method.     

Voltammetric detection of inorganic phosphate using ion-channel sensing with self-assembled monolayers of a hydrogen bond-forming receptor

A voltammetric ion-channel sensing for phosphate based on gold electrodes modified with the self-assembled monolayers of a bis-thiourea receptor was developed to detect phosphate. The working principle of this voltammetric sensor conceptually mimics that of ligand gated ion-channel proteins, as to chemically stimulated changes in membrane permeability. The response to analytes is based on the change in electron transfer rate constant of the redox reaction of [Fe(CN)(6)](4-/3-) marker, before and after binding of phosphate to the receptor on the electrode surface; where the electrostatic repulsion between a phosphate-receptor complex and the marker induced the decrease in the rate constant. In a solution of pH 7.0, a high selectivity was observed for phosphate and the sensor was virtually insensitive at all to many of other anions, such as SO(4)(2-), AcO(-), NO(3)(-), and Cl(-). The sensor response was obtained with phosphate concentrations above 5.0 x 10(-4) M using cyclic voltammetry and differential pulse voltammetry.     

固定化尿酸酶丝素膜的性质及其尿酸传感器

应用电化学分析法对固定化酶丝素膜的性质进行了分析,结果表明这种酶经丝素膜固定后,活性得率高、性能稳定、能长期存放.用这种酶膜和氧电极等组成的流动注射分析式尿酸传感器对生物样品进行的百次重复分析结果表明,这种传感器的重现性良好,每小时能分析60个人血清样品.     

ELECTROCHEMICAL CYSTEINE DETERMINATION IN SERUM SAMPLES BY Hg THIN FILM SENSOR

Cysteine is a nonessential aminoacid, meaning that cysteine can be made in the human body. It is one of the few amino acids that contain sulfur. This allows cysteine to bond in a special way and maintain the structures of proteins in the body. Cysteine strengthens the protective lining of the stomach and intestines, which may help prevent damage caused by aspirin and similar drugs. In addition, cysteine may play an important role in the communication between immune system cells.

In this study, glassy carbon electrodes modified with mercury (Hg) were used as working electrode. Mercury thin film on glassy carbon electrode was deposited by holding the electrode potential at ?0.7 V; the measurement period for the coating process was 2 minutes. pH and temperature effects on the electrode response were carried out by working at different pHs and temperatures. The calibration graph for cysteine was drawn in the range of 5–120 μM cysteine. Repeatability and interferences studies were investigated. GSH had an interference effect of about 13% of cysteine response. Finally, the sensor was applied to real samples for cysteine determination and the method was validated by Ellman's reagent.     

A multilayer membrane amperometric glucose sensor fabricated using planar techniques for large-scale production

This paper reports on a multilayer membrane amperometric glucose sensor fabricated using planar techniques. It is characterized by good reproducibility and suitable for large-scale production. The glucose sensor has 82 electrode sets formed on a single glass substrate, each with a platinum working electrode (WE), a platinum counter electrode (CE) and an Ag/AgCl reference electrode (RE). The electrode sets are coated with a membrane consisting of five layers: gamma-aminopropyltriethoxysilane (gamma-APTES), Nafion, glucose oxidase (GOX), gamma-APTES and perfluorocarbon polymer (PFCP), in that order. Tests have shown that the sensor has acceptably low dispersion (relative standard deviation, R.S.D.=42.9%, n=82), a wide measurement range (1.11-111 mM) and measurement stability over a 27-day period. Measurements of the glucose concentration in a control human urine sample demonstrated that the sensor has very low dispersion (R.S.D.=2.49%, n=10).     

Silver electrode as a sensor for determination of zinc in cell cultivation medium.

Use of the silver electrode as a sensor for the monitoring of zinc in cell growth medium is described. Zinc at silver electrodes provides specific voltammetric signal, which is affected by solution components. Signals of zinc ions in phosphate buffer solutions with and without cell growth medium were compared. Common DMEM cell culture medium was used for the cultivation of a cell line of v-myb-transformed chicken monoblasts and its variants expressing v-jun and c-jun in a zinc-dependent manner. Electrochemical results showed zinc concentrations in the medium coincide very well with the jun expression. With respect to the low toxicity of silver for eukaryotic cells, silver electrodes represent promising tools for the determination of zinc concentrations in vivo without the potential risk of a cell culture damage.     

AL Amyloid Imaging and Therapy with a Monoclonal Antibody to a Cryptic Epitope on Amyloid Fibrils

The monoclonal antibody 2A4 binds an epitope derived from a cleavage site of serum amyloid protein A (sAA) containing a -Glu-Asp- amino acid pairing. In addition to its reactivity with sAA amyloid deposits, the antibody was also found to bind amyloid fibrils composed of immunoglobulin light chains. The antibody binds to synthetic fibrils and human light chain (AL) amyloid extracts with high affinity even in the presence of soluble light chain proteins. Immunohistochemistry with biotinylated 2A4 demonstrated positive reaction with ALκ and ALλ human amyloid deposits in various organs. Surface plasmon resonance analyses using synthetic AL fibrils as a substrate revealed that 2A4 bound with a K_D of ∼10 nM. Binding was inhibited in the presence of the –Glu-Asp- containing immunogen peptide. Radiolabeled 2A4 specifically localized with human AL amyloid extracts implanted in mice (amyloidomas) as evidenced by single photon emission (SPECT) imaging. Furthermore, co-localization of the radiolabeled mAb with amyloid was shown in biodistribution and micro-autoradiography studies. Treatment with 2A4 expedited regression of ALκ amyloidomas in mice, likely mediated by the action of macrophages and neutrophils, relative to animals that received a control antibody. These data indicate that the 2A4 mAb might be of interest for potential imaging and immunotherapy in patients with AL amyloidosis.     

Determination of catalase-like activity in plants based on the amperometric monitoring of hydrogen peroxide consumption using a carbon paste electrode modified with ruthenium(IV) Oxide

A carbon paste electrode containing ruthenium(IV) oxide as a modifier was tested as an effective hydrogen peroxide amperometric sensor in bulk measurements (hydrodynamic amperometry). Factors that influence its overall analytical perform ance, such as pH and the applied potential, were examined. The RuO2-modified electrode displayed high sensitivity towards hydrogen peroxide, with detection limits as low as 0.02 mm at pH 7.4 and 0.007 mM at pH 9.0. The method was applied for monitoring the decomposition of hydrogen peroxide (by catalase) in phosphate buffer of pH 7.4. The relative response of the electrode towards ascorbic acid was assessed and it was found that the selectivity of the RuO2-modified electrode towards hydrogen peroxide over ascorbic acid could be significantly improved by electro-polymerizing m-phenylenediamine on its surface prior to measurements. The RuO2-modified electrode was used for the kinetic (fixed time) determination of catalase activity in the range of 4-40 U/mL (detection limit 1.2 U/mL). The method was applied to the determination of catalase-like activity in various plant materials (recov-ery ranged from 93 to 101%, detection limit 480 U/100 g).     

酶电极流动注射分析法测定葡萄糖

 一种酶电极流动注射分析系统(EFIA)用于血糖和发酵葡萄糖的快速测定。研究了酶电极及其工作系统的性能和各种影响参数,,奠定了实用化基础。     

Amperometric sulfide detection using Coprinus cinereus peroxidase immobilized on screen printed electrode in an enzyme inhibition based biosensor

In the present work, an amperometric inhibition biosensor for the determination of sulfide has been fabricated by immobilizing Coprinus cinereus peroxidase (CIP) on the surface of screen printed electrode (SPE). Chitosan/acrylamide was applied for immobilization of peroxidase on the working electrode. The amperometric measurement was performed at an applied potential of -150 mV versus Ag/AgCl with a scan rate of 100 mV in the presence of hydroquinone as electron mediator and 0.1M phosphate buffer solution of pH 6.5. The variables influencing the performance of sensor including the amount of substrate, mediator concentration and electrolyte pH were optimized. The determination of sulfide can be achieved in a linear range of 1.09-16.3 μM with a detection limit of 0.3 μM. Developed sensor showed quicker response to sulfide compared to the previous developed sulfide biosensors. Common anions and cations in environmental water did not interfere with sulfide detection by the developed biosensor. Cyanide interference on the enzyme inhibition caused 43.25% error in the calibration assay which is less than the amounts reported by previous studies. Because of high sensitivity and the low-cost of SPE, this inhibition biosensor can be successfully used for analysis of environmental water samples.     

Eggplant tissue homogenate-based bioselective membrane electrode for determination of catechol.

A novel eggplant tissue homogenate-based membrane electrode with high selective response to catechol (5 x 10(-6)-2.5 x 10(-5) M concentration) has been constructed by immobilizing tissue of eggplant (Solanum melangena L.) at dissolved oxygen probe. In order to optimize the stability of the electrode, general immobilization techniques are used to secure the eggplant tissue section physically in a gelatin-glutaraldehyde cross-linking matrix. The electrode response was maximum when 50 mM phosphate buffer was used at pH 7.0 and 35 degrees C. The sensor is stable for more than 3 months.     

Cobalt(II) salophen-modified carbon-paste electrode for potentiometric and voltammetric determination of cysteine

A chemically modified electrode constructed by incorporating N,N(')-bis(salicylidene)-1,2-phenylenediaminocobalt(II) into carbon-paste matrix was used as a sensitive electrochemical sensor for detection of cysteine. The resulting electrode exhibits catalytic properties for the electrooxidation of cysteine and lowers the overpotential for the oxidation of this compound. The faster rate of electron transfer results in a near-Nernstian behavior of the modified electrode and makes it a suitable potentiometric and voltammetric sensor for the fast and easy determination of cysteine. A linear response in concentration range from approximately 2 microM to 0.01 M was obtained with a detection limit of 1 microM for the potentiometric detection of cysteine. The modified electrode was also used for the amperometric and differential pulse voltammetric determination of cysteine and the results were compared with those of the potentiometric method.     

Monitoring microalgal growth of Chlorella minutissima with a new all solid-state contact nitrate selective sensor

As third generation feedstock, microalgae are microorganisms that can grow only in the optimum conditions. There are parameters including the concentration of macro and microelements in nutrient solution, pH, temperature and light intensity that have significant impact on microalgal growth. In recent years, various sensing devices have been developed for sensitive measurement of these parameters during microalgal growth. In this study, a new potentiometric nitrate selective sensor was developed to indicate the nitrate uptake of microalgae and the effect of nitrate nutrient on microalgal growth, specifically, and this sensor was successfully applied to determine nitrate concentration in medium during microalgal growth. Moreover, the effects of nitrate, carbonate and phosphate concentration in the growth medium on biomass production of Chlorella minutissima were investigated by using Box–Behnken design method, and optimum conditions were determined for the highest biomass production of microalgae. As a result of the experiments, it was seen that the highest C. minutissima production was achieved using the medium consist of 2.63 g/L NaNO₃, 0.35 g/L Na₂CO₃ and 0.4 g/L KH₂PO_4. Statistically, it was observed that there was a proportional relationship between the microalgae production and investigated parameters such as carbon, nitrogen and phosphate amounts of culture mediums. The electrode showed a wide linear range between 1.0 × 10⁻¹ and 5.0 × 10⁻⁵ M with a detection limit of the 5 × 10⁻⁶ M and the response time was found as 10 s. The results showed that developed nitrate selective sensor could be successfully applied for continuous measurement of nitrate in microalgal productions at reduced cost.