Development of Quantum Dots Modified Acetylcholinesterase Biosensor for the Detection of Trichlorfon

Poly (N‐vinyl‐2‐pyrrolidone) (PVP)‐capped CdS quantum dots (QCdS‐PVP) was synthesized with CdCl₂ and Na₂S in the presence of PVP. QCdS‐PVP has been used for the immobilization and stabilization of the acetylcholinesterase (AChE). The electrocatalytic activity of QCdS‐PVP leads to a greatly improved electrochemical detection of the enzymatically generated thiocholine product, and higher sensitivity and stability. The GCE/QCdS‐PVP/AChE biosensor was used for the detection of organophosphate pesticides (OPs), such as trichlorfon. The sensor performance, including pH and inhibition time, was optimized with respect to operating conditions. Under the optimal conditions, the biosensor was used to measure as low as 12 ppb trichlorfon with a 5‐min inhibition time.     

Fabricating of Acetylcholine Biosensor by a Layer‐by‐layer Deposition Technique for Determining Trichlorfon

An acetylcholine (ACh) biosensor has been fabricated with bienzymes/poly(diallyldimethylammonium chloride) (PDDA) multilayer film‐modified platinum (Pt) electrodes by a layer‐by‐layer technique (LBL). The ACh biosensor was optimized and the properties are described. This ACh biosensor was used for the detection of organophosphate pesticide trichlorfon. The detection limits (found 0.001 μg/mL for trichlorfon) make it possible to detect the pollutants. This simple protocol of biosensor preparation, high sensitivity and stability are very promising for the determination of environmental pollutants in field conditions.     

Simultaneous Determination of Caffeine,Ibuprofen, and Paracetamol by Flow‐injection Analysis with Multiple‐pulse Amperometric Detection on Boron‐doped Diamond Electrode

This work presents a simple, fast and low‐cost method for the simultaneous determination of three drugs by flow‐injection analysis with multiple‐pulse amperometric (MPA) detection using a wall‐jet flow cell with a boron‐doped diamond electrode. The amperometric determination of caffeine (CF), ibuprofen (IB) and paracetamol (PC) was performed by the application of a four‐potential waveform using the MPA technique. PC is oxidized at E₁ (1.20 V/70 ms) and thus selectively detected; PC and CF are oxidized at E₂ (1.49 V/40 ms); PC, CF and IB are oxidized at E₃ (1.70 V/70 ms); and E₄ (1.80 V/100 ms) is applied for electrode cleaning. The subtraction of currents obtained at the different potentials did not provide accurate determinations of CF and IB, thus it was required to investigate correction factors to determine CF and IB without the interference from PC and CF using the respective amperometric signals obtained at E₂ and E₃. The proposed method was successfully applied for the determination of three drugs in pharmaceutical samples with low generation of residues and a high analytical frequency (150 h^?1) in comparison with HPLC‐DAD method.     

Flow‐Injection Amperometric Detection with Solvent Polymeric Membrane Ion Sensors

An amperometric detector for hydrophobic ions based on a plasticized poly(vinyl) chloride (PVC) membrane incorporated in a flow‐injection system was developed. A four‐electrode potentiostat with ohmic drop compensation was used, while a flow‐through cell incorporated the four electrodes and the membrane, which contained tetrabutylammonium tetraphenylborate. When the influence of the applied potential and of the flow‐injection variables on the determination of tetrabutylammonium was studied, a linear relationship was observed between current peak height and ion concentration over a range of 5×10^?6–6×10^?5 M tetrabutylammonium. Good repeatability and between‐day reproducibility and high sample frequency were obtained. The effect of other ions was studied. Two different amperometric methods, indirect and direct, were also developed for the determination of dodecylsulfate in the concentration range 3×10^?5–9×10^?4 M.     

Amperometric Glucose Biosensor Based on Rhodium Dioxide‐Modified Carbon Ink

An amperometric method for the determination of glucose using a screen printed carbon electrode is reported. The electrode material was bulk modified with rhodium dioxide and the enzyme glucose oxidase immobilized in a Nafion‐film on the electrode surface and investigated for its ability to serve as a detector of glucose in flow injection analysis. The sensor exhibited a linear increase of the amperometric signal with the concentration of glucose in the range of 1–250 mg L^?1 with a detection limit (evaluated as 3σ) of 0.2 mg L^?1 under optimized flow rate of 0.4 mL min^?1 in 0.1 M phosphate buffer (pH 7.5) carrier. At the potential applied (?0.2 V vs. Ag/AgCl), interferences from redox species present in the sample matrix were negligible. The biosensor reported here retained its activity for more than 40 injections or 4 months of storage at 6 °C. The RSD was determined as 1.8% for a glucose concentration of 25 mg L^?1 (n=5) with a typical response time of about 28 s.     

利用流动注射型乙酰胆碱酯酶传感器监测海水中马拉硫磷

将乙酰胆碱酯酶(AChE)传感器引入流动注射系统中，研究了传感器连续监测海水中马拉硫磷的可行性。系统中的载液为不含马拉硫磷的海水。传感器适宜的工作条件为：载液和样品的流速为0．39mL／min，进样时间为20min；底物(碘化硫代乙酰胆碱)溶液的浓度为41．6mmol／L，注射量为40μL。利用次氯酸钠溶液对含马拉硫磷的海水样品进行预氧化处理，可以大大提高传感器的灵敏度，对马拉硫磷的检出限达到0．05μg/L；而不进行氧化时的检出限为1．3μg/L。另外，海水样品经过预氧化处理后，传感器对其中0．1-10μg／L的马拉硫磷具有良好的线性响应关系(r=0．991)。测定含马拉硫磷的海水样品后，向传感器持续通入0．5mmol／L的2-PAM溶液15min，可以完全恢复受到100μg／L马拉硫磷抑制的固定化酶活性。结果表明：所设计的酶传感器适于海水中马拉硫磷的连续、灵敏和准确监测。     

AuNPs/Sol-gel复合膜法固定乙酰胆碱酯酶生物传感器检测有机磷农药

基于有机磷农药对乙酰胆碱酯酶(Acetylcholinesterase,AChE)的抑制作用,用金纳米粒子(Au nanoparticles,AuNPs)与壳聚糖/SiO2杂化溶胶-凝胶构成复合固酶基质,将AChE固定于玻碳电极表面,制备了电流型AChE生物传感器选用久效磷进行实验,以氯化硫代乙酰胆碱为底物,建立了电化...     

Amperometric Glucose Biosensor Based on Pt‐Pd Nanoparticles Supported by Reduced Graphene Oxide and Integrated with Glucose Oxidase

A novel glucose biosensor was developed based on the immobilization of glucose oxidase (GOx) on reduced graphene oxide incorporated with electrochemically deposited platinum and palladium nanoparticles (PtPdNPs). Reduced graphene oxide (RGO) was more hybridized by chemical and heat treatment. Bimetallic nanoparticles were deposited electrochemically on the RGO surface for potential application of the Pd? Pt alloy in biosensor preparation. The as‐prepared hybrid electrode exhibited high electrocatalytic activities toward H₂O₂, with a wide linear response range from 0.5 to 8 mM (R²=0.997) and high sensitivity of 814×10^?6 A/mMcm². Furthermore, glucose oxidase with active material was integrated by a simple casting method on the RGO/PdPtNPs surface. The as‐prepared biosensor showed good amperometric response to glucose in the linear range from 2 mM to 12 mM, with a sensitivity of 24×10^?6 A/mMcm², a low detection limit of 0.001 mM, and a short response time (5 s). Moreover, the effect of interference materials, reproducibility and the stability of the sensor were also investigated.     

Biosensor Based on Self‐Assembling Glucose Oxidase and Dendrimer‐Encapsulated Pt Nanoparticles on Carbon Nanotubes for Glucose Detection

A novel amperometric glucose biosensor based on layer‐by‐layer (LbL) electrostatic adsorption of glucose oxidase (GOx) and dendrimer‐encapsulated Pt nanoparticles (Pt‐DENs) on multiwalled carbon nanotubes (CNTs) was described. Anionic GOx was immobilized on the negatively charged CNTs surface by alternatively assembling a cationic Pt‐DENs layer and an anionic GOx layer. Transmission electron microscopy images and ζ‐potentials proved the formation of layer‐by‐layer nanostructures on carboxyl‐functionalized CNTs. LbL technique provided a favorable microenvironment to keep the bioactivity of GOx and prevent enzyme molecule leakage. The excellent electrocatalytic activity of CNTs and Pt‐DENs toward H₂O₂ and special three‐dimensional structure of the enzyme electrode resulted in good characteristics such as a low detection limit of 2.5 μM, a wide linear range of 5 μM–0.65 mM, a short response time (within 5 s), and high sensitivity (30.64 μA mM^?1 cm^?2) and stability (80% remains after 30 days).     

Acetylcholinesterase Immobilization on 3‐Mercaptopropionic Acid Self Assembled Monolayer for Determination of Pesticides

Studies on the immobilization of acetylcholinesterase onto a SAM gold electrode and the use of the fabricated biosensor for the determination of carbaryl and parathion are presented. The influence of pH, ionic strength, enzyme loading and concentration of glutaraldehyde on the response of the biosensor was investigated . The amperometric biosensor developed in this study provided linearity to parathion and carbaryl in the 2.0 a 30.0×10^?6 mol L^?1 concentration range. The detection limits under the optimum working conditions were found to be 9.3 μg L^?1 for parathion and 9.0 μg L^?1 for carbaryl. The enzyme electrode was found to be stable for 7 days.     

Amperometric Flow‐Injection Determination of Phenolic Compounds Using a Biosensor with Immobilized Laccase,Peroxidase and Tyrosinase

A screen‐printed four‐electrode sensor based on immobilization of laccase (Coriolus hirsutus), peroxidase (horseradish) and tyrosinase (mushroom) in the same array was developed for monitoring of phenols. The enzymes were immobilized onto a self‐assembled monolayer (4‐mercapto‐1‐butanol) modified gold surface via covalent attachment by epichlorohydrin coupling. The experimental conditions for simultaneous operation of the three enzymes were optimized based on catechol determination. The sensors were further applied for the amperometric detection of several substituted phenolic compounds, carried out using a single line flow‐injection system. Hydrogen peroxide served as co‐substrate for peroxidase. The limits of detection for phenols in aqueous solutions were in the micromolar range, one assay was completed in less than 5 min. The preliminary studies showed that the compatibility of the above mentioned enzyme array enabled the multielectrode biosensor to be applied to real samples including industrial wastewaters and surface waters.     

Flow‐Through Assay of Quinine Using Solid Contact Potentiometric Sensors Based on Molecularly Imprinted Polymers

Miniaturized potentiometric membrane sensors for quinine incorporated with molecular imprinted polymer (MIP) were synthesized and implemented. Planar PVC based polymeric membrane sensors containing quinine‐methacrylic and/or acrylic acid‐ethylene glycol methacrylate were dispensed into anisotropically etched wells on polyimide wafers. The determination of quinine was carried out in acidic solution at pH 6, where positively charged species predominated prevalently. The suggested miniaturized planner sensors exhibited marked selectivity, sensitivity, long‐term stability and reproducibility. At their optimum conditions, the sensors displayed wide concentration ranges of 4.0×10^?6–1.0×10^?2mol L^?1 and 1.0×10^?5–1.0×10^?2 mol L^?1 with slopes of about 61.3–55.7 mV decade^?1; respectively. Sensors exhibit detection limits of 1.2×10^?6 and 8.2×10^?6 mol L^?1 upon the use of methacrylic and acrylic acid monomers in the imprinted polymer, respectively. Validation of the assay method according to the quality assurance standards (range, within‐day repeatability, between‐day variability, standard deviation, accuracy, and good performance characteristics) which could assure good reliable novel sensors for quinine estimation was justified. Application of the proposed flow‐through assay method for routine determination of quinine in soft drinks was assayed and the results compared favorably with data obtained by the standard fluorimetric method.     

Direct Electrochemistry of Hemoglobin Immobilized on Carbon‐Coated Iron Nanoparticles for Amperometric Detection of Hydrogen Peroxide

A novel method for preparation of hydrogen peroxide biosensor was presented based on immobilization of hemoglobin (Hb) on carbon‐coated iron nanoparticles (CIN). CIN was firstly dispersed in a chitosan solution and cast onto a glassy carbon electrode to form a CIN/chitosan composite film modified electrode. Hb was then immobilized onto the composite film with the cross‐linking of glutaraldehyde. The immobilized Hb displayed a pair of stable and quasireversible redox peaks and excellent electrocatalytic reduction of hydrogen peroxide (H₂O₂), which leading to an unmediated biosensor for H₂O₂. The electrocatalytic response exhibited a linear dependence on H₂O₂ concentration in a wide range from 3.1 μM to 4.0 mM with a detection limit of 1.2 μM (S/N=3). The designed biosensor exhibited acceptable stability, long‐term life and good reproducibility.     

Flow‐Injection Pulsed‐Amperometric Determination of Free Glycerol in Biodiesel at a Gold Electrode

This work reports the highly‐sensitive amperometric determination of free glycerol in biodiesel at a gold electrode adapted in a flow‐injection analysis (FIA) cell. The amperometric method involved the continuous application of three sequential pulses to the working electrode (+250 mV, +700 mV, and ?200 mV, for 100 ms each). This sequence of potential pulses eliminated electrode passivation and dramatically increased the analytical signal. The proposed FIA‐amperometric method presented low relative standard deviation between injections (1.5 %, n=15), high analytical frequency (85 h^?1), satisfactory recovery values (93–118 %) for spiked samples, wide linear range (from 1 to 300 µmol L^?1), and low detection limit (0.5 µmol L^?1).     

Low‐Potential Detection of Glucose with a Biosensor Based on the Immobilization of Glucose Oxidase on Polymer/Manganese Oxide Layered Nanocomposite

A nanocomposite with poly(diallyldimethylammonium), PDDA, intercalated between manganese oxide layers is constructed on a graphite electrode surface through one‐step electrodeposition and used to adsorb glucose oxidase (GOD). The immobilized GOD displays a pair of stable and quasireversible redox peaks with a formal potential of ?468 mV in pH 7.0 buffer solutions and exhibits excellent electrocatalysis to the reduction of oxygen. In the presence of dissolved oxygen, the reduction peak current decreased gradually with the addition of glucose, indicating that the immobilized GOD kept its bioactivity. Thus a reagentless biosensor for glucose at a low detection potential was established. The linear concentration range is from 0.02 to 2.78 mM with a detection limit of 9.8 μM. The proposed glucose biosensor was insensitive to common interferences such as ascorbic and uric acids etc.     

Direct Determination of Phosphite in Fertilizers by Flow‐Injection Amperometry

A sensor based on graphite electrode modified with palladium‐platinum‐palladium film is proposed for phosphite determination by flow‐injection amperometry. The modified electrode was prepared by a sequential cathodic deposition of Pd, Pt and Pd on a graphite electrode from 0.5% m/v PdCl₂+28% m/v NH₄OH and 2% m/v H₂PtCl₆+10% v/v H₂SO₄ solutions. After suitable conditioning, the electrode showed catalytic activity for phosphite oxidation when 0.15 V was applied. The proposed system handles approximately 50 samples per hour (0.01–0.05 mol L^?1 Na₂HPO₃; R²=0.9997), consuming ca. 70 μL of sample per determination. The limit of detection and amperometric sensibility were 5×10^?4 mol L^?1 and 1.5 mA L mol^?1, respectively. The proposed method was applied to analysis of fertilizer samples without pre‐treatment. Results are in agreement with those obtained by spectrophotometry and titrimetry at 95% confidence level and good recoveries (96–109%) of spiked samples were found. Relative standard deviation (n= 12) of a 0.01 mol L^?1 Na₂HPO₃ sample was 2%. The useful lifetime of modified electrode was around 220 determinations. For routine purposes it means that this electrode can be continuously used for 5 hours.     

Flow Injection Analysis of Iodate Reduction on PEDOT Modified Electrode

Poly‐(3,4‐ethylenedioxythiophene) (PEDOT) films were electrodeposited by cyclic voltammetry on glassy carbon electrode at different anodic potentials in the range of 1.0–1.5 V (Ag/AgCl) and its electrocatalytic properties towards reduction of iodate were reported. The effect of the pH of the solution on the response of PEDOT electrode towards iodate also studied. The modified electrode was employed successfully as an amperometric sensor for iodate in a flow injection apparatus. The repeatability of the method for 14 injections of a μM iodate solution was 7%. Interference from other oxidant anions such as nitrate was not noticeable, whereas bromate, chlorate and nitrite interfere at slight levels.     

A Nanocomposite Chitosan Based on Ferrocene‐Modified Silica Nanoparticles and Carbon Nanotubes for Biosensor Application

A novel amperometric biosensor for glucose was developed by entrapping glucose oxidase (GOD) in a chitosan composite doped with ferrocene monocarboxylic acid‐aminated silica nanoparticles conjugate (FMC‐ASNPs) and multiwall carbon nanotubes (MWNTs). The entrapped FMC‐ASNPs conjugate performed excellent redox electrochemistry and the presence of MWNTs improved the conductivity of the composite film. This matrix showed a biocompatible microenvironment for retaining the native activity of the entrapped GOD and was in favor of the accessibility of substrate to the active site of GOD, thus the affinity to substrates is improved greatly. Under optimal conditions this biosensor was able to detect glucose with a detection limit of 10 μM (S/N=3) in the linear range of 0.04 to 6.5 mM. The proximity of these three components FMC‐ASNPs, MWNTs and GOD enhanced the electron transfer between the film and electrode. This composite film can be extended to immobilize other enzymes and biomolecules, which will greatly facilitate the development of biosensors and other bioelectrochemical devices.     

Reagentless Biosensor for Hydrogen Peroxide Based on the Immobilization of Hemoglobin in Platinum Nanoparticles Enhanced Poly(chloromethyl thiirane) Cross‐linked Chitosan Hybrid Film

An unmediated hydrogen peroxide (H₂O₂) biosensor was prepared by co‐immobilizing hemoglobin (Hb) with platinum nanoparticles enhanced poly(chloromethyl thiirane) cross‐linked chitosan (CCCS‐PNs) hybrid film. CCCS could provide a biocompatible microenvironment for Hb and PNs could accelerate the electron transfer between Hb and the electrode. Spectroscopic analysis indicated that the immobilized Hb could maintain its native structure in the CCCS‐PNs hybrid film. Entrapped Hb exhibited direct electrochemistry for its heme Fe(III)/Fe(II) redox couples at ?0.396 V in the CCCS‐PNs hybrid film, as well as peroxidase‐like activity to the reduction of hydrogen peroxide without the aid of an electron mediator.     

A New Enzyme Immobilization Technique Based on Thionine‐Bovine Serum Albumin Conjugate and Gold Colloidal Nanoparticles for Reagentless Amperometric Biosensor Applications

A novel enzyme immobilization technique based on thionine‐bovine serum albumin conjugate (Th‐BSA) and gold colloidal nanoparticles (nano‐Au) was developed. Thionine was covalently bound onto the BSA film with glutaraldehyde(GA) as cross‐linker to achieve Th‐BSA conjugate. The free amino groups of thionine were then used to attach nano‐Au for the immobilization of horseradish peroxidase (HRP). Such nano‐Au/Th‐BSA matrix shows a favorable microenvironment for retaining the native activity of the immobilized HRP and thionine immobilized in this way can effectively shuttle electrons between the electrode and the enzyme. The proposed biosensor displays excellent catalytic activity and rapid response for H₂O₂. The linear range for the determination of H₂O₂ is from 4.9×10^?7 to 1.6×10^?3 M with a detection limit of 2.1×10^?7 M at 3σ and a Michaelies‐Menten constant K value of 0.023 mM.