Enzyme electrode system for oxalate determination utilizing oxalate decarboxylase immobilized on a carbon dioxide sensor

A highly selective enzyme electrode system for oxalate is described in which the enzyme oxalate decarboxylase is immobilized on a carbon dioxide gas-sensing electrode. The response of the system is linear with the logarithm of the oxalate concentration between 2 × 10^-4 and I × 10^-2 M with a slope of 57–60 mV/decade. The oxalate detection limit is 4 × 10^-5 M. Electrodes used with chemically immobilized enzyme are not affected by phosphate and sulfate at levels normally found in urine and are very stable showing no decrease in response after one month of operation. The enzyme electrode system functions well in urine, requiring minimal sample pretreatment. The recovery of oxalate added to five aliquots of a human control urine sample averaged 97.7% with an average relative standard deviation of 4.5%.     

A carbon dioxide sensor based on fluorescence

The optical carbon dioxide sensor is prepared by covering a pH sensor based on fluorescence with a CO₂-permeable membrane and contacting the pH-sensitive membrane with a reservoir of hydrogen carbonate. As carbon dioxide diffuses across the membrane it causes a chnage in pH which is detected by measuring the change in fluorescence from the base form of the pH-sensitive fluorescentdye. The usable range of response depends on the concentration of hydrogen carbonate in contact with the membrane. The sensor also responds to sulfide and sulfite.     

基于染料吸收的光导纤维SO2传感器

建立于气液两相平衡的气敏电极已为人们所熟知。近年来研究了气液两相平衡的光纤化学传感器。作者之一曾报道了CO_2荧光传感器。本文在文献基础上对基于染料吸收的光纤SO_2传感器进行了探讨性的研究。光纤SO_2传感器在其结构上与气敏电极相似,所不同是采用感应膜光信号变化的特征而不用指示电极进行测定。由于测定方法不同才使它具有光纤化学传感器的特殊优点。     

An amperometric sensor for hydrazine based on nano-copper oxide modified electrode

A sensitive hydrazine sensor has been fabricated using copper oxide nanoparticles modified glassy carbon electrode (GCE) to form nano-copper oxide/GCE. The nano-copper oxide was electrodeposited on the surface of GCE in CuCl₂ solution at −0.4 V and was characterized by Scanning electron microscopy and X-ray diffraction. The prepared modified electrode showed a good electrocatalytic activity toward oxidation of hydrazine. The electrochemical behavior of hydrazine on nano-copper oxide/GCE was explored. The oxidative current increased linearly with improving concentration of hydrazine on nano-copper oxide/GCE from 0.1 to 600 μM and detection limit for hydrazine was evaluated to be 0.03 μM at a signal-to-noise ratio of 3. The oxidation mechanism of hydrazine on the nano-copper oxide/GCE was also discussed. The fabricated sensor could be used to determine hydrazine in real water.     

An amperometric ethanol sensor based on foam nickel electrode

An amperometric sensor using foam nickel electrode as the working electrode for the measurement of ethanol in alkaline solution has been developed. Cyclic voltammetry and chronoamperometry are employed to analyze electrochemical behavior of the electrode. The results show that the oxidation of ethanol is more efficient on the foam nickel electrode than that on the nickel foil electrode. The sensor exhibits a good linear relationship between response current and ethanol concentration in the range of 4 to 1400 ppm with a detection limit of 0.8 ppm. The sensitivity and the response time of the sensor are 4.63 μA/ppm and 10 s respectively. Additionally, the sensor has 60 days shelf-life time at least.     

An amperometric lactate sensor based on a NAD+-analog and lactate dehydrogenase coimmobilized on reticulated vitreous carbon

A NAD⁺-analog was coimmobilized with lactate dehydrogenase (LDH) on reticulated vitreous carbon (RVC) to give an amperometric lactate biosensor. Both LDH and the NAD⁺ -analog were bound covalently with carbodiimide to the surface of the porous RVC-material. The electrode was operated in a FIA-arrangement in the presence or absence of a soluble mediator. Meldola Blue. The stability was poor when the electrode was operated at +400 mV (vs. Ag/AgCl) in the absence of mediator but improved most significantly in the presence of 5 μM mediator, so that 65% of the original activity remained after 16 days. The amperometric currents were smaller with regeneration by mediator at −100 mV than with direct electrochemical oxidation at +400 mV, indicating that the additional steps slow down the reaction rate. Linear calibration plots were obtained from the detection limit, 1 μM, to 500 μM lactate with 5 μM mediator, reoxidized at −100 mV. The sample throughput was about 60 h⁻¹.     

Ammonium ion sensor based on immobilized nitrifying bacteria and a cation-exchange membrane

The ammonium ion sensor is based on nitrifying bacteria isolated from activated sludge. The sensor comprises a cation-exchange membrane, an alkaline solution layer (pH 10), a gas-permeable membrane, an immobilized microbial membrane, and an oxygen electrode. This novel combination provides accurate amperometric determinations of ammonium ions in aqueous solutions within 7 min in the range 10^-4– 4.5 × 10^-2 M. Volatile amines or other ions do not interfere. The relative error is within 4% and the sensor can be used continually for more than 10 days.     

An amperometric sensor for uric acid based on ordered mesoporous carbon-modified pyrolytic graphite electrode

A novel amperometric sensor for uric acid based on ordered mesoporous carbon modified pyrolytic graphite electrode was developed. Uric acid oxidation was easily catalyzed by this electrode in a phosphate buffer solution at pH 7.0, with an anodic potential decrease about 140 mV compared to bare pyrolytic graphite electrode. The uric acid level was determined by the amperometric method, at a constant potential of 0.31 mV, the catalytic current of uric acid vs. its concentration showed a good linearity in the range of 1.0 × 10⁻⁶−1.0 × 10⁻⁴ mol L⁻¹, with a correlation coefficient of 0.999. The detection limit was 4.0 × 10⁻⁷ mol L⁻¹. The proposed method could be effectively used for uric acid amperometric sensing in human urine.     

High-sensitive amperometric hydrazine sensor based on chemically synthesized zinc nitroprusside nanoparticle-supported carbon ceramic electrode

Zinc nitroprusside (ZnNP) nanoparticles were fabricated at the surface of zinc powder-doped carbon ceramic electrode (CCE) by a chemical derivatization process. This modified electrode was characterized by scanning electron microscopy, atomic force microscopy and cyclic voltammetry techniques. The charge transfer rate constant (k _s) and charge transfer coefficient (α) were calculated for the electron exchange reaction of the ZnNP thin film. The ZnNP nanoparticle-modified CCE (ZnNP|CCE) showed good electrocatalytic activity toward hydrazine oxidation. The limit of detection (S/N = 3) and sensitivity were found to be 0.16 µM and 0.21 µA/µM, respectively. The mechanism of hydrazine electrooxidation at the electrode surface was studied. Finally, the ZnNP|CCE was successfully used for the determination of trace amount of hydrazine in different spiked and real samples.     

A miniature chemiresistor sensor for carbon dioxide

A carpet-like nanostructure of polyaniline (PANI) nanothin film functionalized with poly(ethyleneimine), PEI, was used as a miniature chemiresistor sensor for detection of CO₂ at room temperature. Good sensing performance was observed upon exposing the PEI–PANI device to 50–5000 ppm CO₂ in presence of humidity with negligible interference from ammonia, carbon monoxide, methane and nitrogen dioxide. The sensing mechanism relied on acid–base reaction, CO₂ dissolution and amine-catalyzed hydration that yielded carbamates and carbonic acid for a subsequent pH detection. The sensing device showed reliable results in detecting an unknown concentration of CO₂ in air.     

Amperometric glucose sensor based on glucose oxidase immobilized on gelatin-multiwalled carbon nanotube modified glassy carbon electrode

We investigated the direct electrochemistry of glucose oxidase (GOx) at gelatin-multiwalled carbon nanotube (GCNT) modified glassy carbon electrode (GCE). GOx was covalently immobilized onto GCNT modified GCE through the well known glutaraldehyde (GAD) chemistry. The immobilized GOx showed a pair of well-defined reversible redox peaks with a formal potential (E⁰′) of ? 0.40 V and a peak to peak separation (ΔE_p) of 47 mV. The surface coverage concentration (Г) of GOx in GCNT/GOx/GAD composite film modified GCE was 3.88 × 10^? 9 mol cm^? 2 which indicates the high enzyme loading. The electron transfer rate constant (k_s) of GOx immobilized onto GCNT was 1.08 s^? 1 which validates a rapid electron transfer processes. The composite film shows linear response towards 6.30 to 20.09 mM glucose. We observed a good sensitivity of 2.47 μA mM^?1 cm^? 2 for glucose at the composite film. The fabricated biosensor displayed two weeks stability. Moreover, it shows no response to 0.5 mM of ascorbic acid (AA), uric acid (UA), acetaminophen (AP), pyruvate (PA) and lactate (LA) which shows its potential application in the determination of glucose from human serum samples. The composite film exhibits excellent recovery for glucose in human serum at physiological pH with good practical applicability.     

A novel palygorskite-modified carbon paste amperometric sensor for catechol determination

A palygorskite-modified carbon paste electrode (CPE) was constructed using graphite powder mixed with palygorskite particles. Compared with the unmodified CPE, the resulting palygorskite-modified CPE remarkably increases the peak currents of catechol, and greatly lowers the peak potential separation. Therefore, the palygorskite exhibits catalytic activity to catechol and significantly improves the determining sensitivity. The electrocatalytic activity of palygorskite is attributed to its high adsorption capability and the –OH groups on its surface, which plays an important role in the electron transfer between the modified CPE and the catechol in the solution. The sensor shows a linear response range between 5 and 100 μM catechol with a correlation coefficient of 0.998. The detection limit was calculated as 0.57 μM (s/n = 3).     

An amperometric biosensor based on acetylcholinesterase immobilized onto iron oxide nanoparticles/multi-walled carbon nanotubes modified gold electrode for measurement of organophosphorus insecticides

An acetylcholinesterase (AChE) purified from maize seedlings was immobilized covalently onto iron oxide nanoparticles (Fe₃O₄NP) and carboxylated multi walled carbon nanotubes (c-MWCNT) modified Au electrode. An organophosphorus (OP) biosensor was fabricated using this AChE/Fe₃O₄/c-MWCNT/Au electrode as a working electrode, Ag/AgCl as standard and Pt wire as an auxiliary electrode connected through a potentiostat. The biosensor was based on inhibition of AChE by OP compounds/insecticides. The properties of nanoparticles modified electrodes were studied by scanning electron microscopy (SEM), Fourier transform infrared (FTIR), cyclic voltammograms (CVs) and electrochemical impedance spectroscopy (EIS). The synergistic action of Fe₃O₄NP and c-MWCNT showed excellent electrocatalytic activity at low potential (+0.4 V). The optimum working conditions for the sensor were pH 7.5, 35 °C, 600 μM substrate concentration and 10 min for inhibition by pesticide. Under optimum conditions, the inhibition rates of OP pesticides were proportional to their concentrations in the range of 0.1–40 nM, 0.1–50 nM, 1–50 nM and 10–100 nM for malathion, chlorpyrifos, monocrotophos and endosulfan respectively. The detection limits were 0.1 nM for malathion and chlorpyrifos, 1 nM for monocrotophos and 10 nM for endosulfan. The biosensor exhibited good sensitivity (0.475 mA μM⁻¹), reusability (more than 50 times) and stability (2 months). The sensor was suitable for trace detection of OP pesticide residues in milk and water.     

Serine-selective membrane probe based on immobilized anaerobic bacteria and a potentiometric ammonia gas sensor

A new class of bioselective membrane probes using anaerobic bacteria is introduced with the successful construction of a L-serine-selective probe consisting of Clostridium acidiurici cells coupled to a potentiometric ammonia gas sensor. The intact cells containing the enzyme serine dehydratase are physically immobilized at the electrode surface in conjunction with iron(II) stearate, which is shown to enhance response characteristics. The potential vs. log concentration plot is linear from 1.6 × 10^-2 to 1.8 × 10^-4M serine with an average slope of 54 mV/decade and response times of 3–5 min. Optimal behavior of the probe is retained even in non-deaerated media for at least three days, and significant interference is posed only by L-glutamine. Quantitative conversion of serine is demonstrated over the linear concentration range, suggesting possible analytical or clinical applications for these probes utilizing anaerobic bacteria     

Fiber-optic fluorescence carbon dioxide sensor for environmental monitoring

Fiber-optic sensors were developed for monitoring dissolved carbon dioxide in water samples in the 0 to 900 ppm concentration range. A pH-sensitive fluorescent dye (HPTS) was reacted with a cationic quaternary ammonium salt to form an ion pair which was electrostatically bound to the surface of particles of aminocellulose which then were dispersed into a gas-permeable silicone polymer. The green fluorescence of the base form was monitored using a fiber optic fluorometer. The use of the aminocellulose enhanced the stability and lifetime of the sensor and also increased the fluorescence of the sensor membrane because the particles act as scattering centers. The characteristics of the sensors are described with respect to dynamic range, reproducibility, long-term stability and temperature dependence.     

Titanium dioxide nanorod-based amperometric sensor for highly sensitive enzymatic detection of hydrogen peroxide

Titanium dioxide nanorods (TNR) were grown on a titanium electrode by a hydrothermal route and further employed as a supporting matrix for the immobilization of nafion-coated horseradish peroxidase (HRP). The strong electrostatic interaction between HRP and TNR favors the adsorption of HRP and facilitates direct electron transfer on the electrode. The electrocatalytic activity towards hydrogen peroxide (H₂O₂) was investigated via cyclic voltammetry and amperometry. The biosensor exhibits fast response, a high sensitivity (416.9 μA·mM⁻¹), a wide linear response range (2.5 nM to 0.46 mM), a detection limit as low as 12 nM, and a small apparent Michaelis-Menten constant (33.6 μM). The results indicate that this method is a promising technique for enzyme immobilization and for the fabrication of electrochemical biosensors.

A TiO₂ nanorod film was directly grown on Ti substrate by a hydrothermal route, and was further employed for a supporting matrix to immobilize horseradish peroxidase as a biosensor electrode. The as-prepared hydrogen peroxide biosensor based on Nafion/HRP/TNR/Ti electrode exhibited fast response and excellent electrocatalytic activity toward H₂O₂, i.e., a high sensitivity (416.9 μA mM⁻¹), a wide linear range (2.5 × 10⁻⁸ to 4.6 × 10⁻⁴ M) with a low detection limit (0.012 μM) and a small apparent Michaelis-Menten constant (33.6 μM).

     

Titanium dioxide nanorod-based amperometric sensor for highly sensitive enzymatic detection of hydrogen peroxide

Titanium dioxide nanorods (TNR) were grown on a titanium electrode by a hydrothermal route and further employed as a supporting matrix for the immobilization of nafion-coated horseradish peroxidase (HRP). The strong electrostatic interaction between HRP and TNR favors the adsorption of HRP and facilitates direct electron transfer on the electrode. The electrocatalytic activity towards hydrogen peroxide (H₂O₂) was investigated via cyclic voltammetry and amperometry. The biosensor exhibits fast response, a high sensitivity (416.9 μA·mM^?1), a wide linear response range (2.5 nM to 0.46 mM), a detection limit as low as 12 nM, and a small apparent Michaelis-Menten constant (33.6 μM). The results indicate that this method is a promising technique for enzyme immobilization and for the fabrication of electrochemical biosensors.

A sensitive amperometric sensor for hydrazine and hydrogen peroxide based on palladium nanoparticles/onion-like mesoporous carbon vesicle

Onion-like mesoporous carbon vesicle (MCV) with multilayer lamellar structure was synthesized by a simply aqueous emulsion co-assembly approach. Palladium (Pd) nanoparticles were deposited on the MCV matrix (Pd/MCV) by chemical reduction of H₂PdCl₄ with NaBH₄ in aqueous media. Pd(X)/MCV (X wt.% indicates the Pd loading amount) nanocomposites with different Pd loading amount were obtained by adjusting the ratio of precursors. The particular structure of the MCV results in efficient mass transport and the onion-like layers of MCV allows for the obtainment of highly dispersed Pd nanoparticles. The introduction of Pd nanoparticles on the MCV matrix facilitates hydrazine oxidation at more negative potential and delivers higher oxidation current in comparison with MCV. A linear range from 2.0 × 10⁻⁸ to 7.1 × 10⁻⁵ M and a low detection limit of 14.9 nM for hydrazine are obtained at Pd(25)/MCV nanocomposite modified glassy carbon (GC) electrode. A nonenzymatic amperometric sensor for hydrogen peroxide based on the Pd(25)/MCV nanocomposite modified GC electrode is also developed. Compared with MCV modified GC electrode, the Pd(25)/MCV nanocomposite modified GC electrode displays enhanced amperometric responses towards hydrogen peroxide and gives a linear range from 1.0 × 10⁻⁷ to 6.1 × 10⁻³ M. The Pd(25)/MCV nanocomposite modified GC electrode achieves 95% of the steady-current for hydrogen peroxide within 1 s. The combination of the unique properties of Pd nanoparticles and the porous mesostructure of MCV matrix guarantees the improved analytical performance for hydrazine and hydrogen peroxide.     

An improved polymer electrolyte-based amperometric hydrogen sensor

An improved polymer electrolyte membrane (PEM) fuel cell-based amperometric hydrogen sensor that operates at room temperature has been developed. The electrolyte used in the sensor is a PVA/H₃PO₄ blend, which is a proton-conducting solid polymer electrolyte. A thin film of palladium is used as the anode and platinum supported on carbon as the cathode. The sensor functions as a fuel cell, H₂/Pd//PVA-H₃PO₄//Pt/O₂, and the short-circuit current is found to be linearly related to the hydrogen concentration. The basic principle, details of assembly, response behaviour of the sensor and its application are discussed.     

毒莠定印迹邻氨基苯硫酚/金纳米粒子复合膜安培传感器

在模板分子存在下,在金电极上自组装邻氨基苯硫酚（oATP）,通过电聚合制得毒莠定印迹的oATP/金纳米粒子聚合薄膜及其安培传感器.采用循环伏安法和交流阻抗技术对传感器制备过程进行表征,用紫外光谱法研究了单体与模板间的相互作用.以K3Fe（CN）6为探针,示差脉冲伏安曲线的峰电流与毒莠定浓度在2.0×10^-7-2.4×10 4mol/L范围内呈现良好的线性关系（r=0.9963）,毒莠定的检出限为6.5×10 8mol/L（S/N=3）.将该印迹膜传感器用于环境水样加标回收检测,结果令人满意.