Linear Response In Concentration Range Research Articles

Role of the anionic dopant of poly(3,4-ethylenedioxythiophene) for the electroanalytical performance: electrooxidation of acetaminophen

Poly(3,4-ethylenedioxythiophene) (PEDOT) films are synthesized in the presence of various anions and surfactants (perchlorate, dodecylsulfate (DDS), polysterenesulfonate (PSS) and poly(2-acrylamido-2-methyl-1-propanesulfonate (PAMPS), and polyoxyethylene-10-laurylether (PLE)) on glassy carbon electrodes. The electrocatalytical activity for acetaminophen electrooxidation is studied depending on the type of dopant and the polymerization charge of the PEDOT films. It is established that all PEDOT-coated electrodes show a marked electrocatalytical effect for this reaction. After exposure to acetaminophen, a new redox pair is observed to appear in the voltammetric curves measured in supporting electrolyte for all PEDOT-coated electrodes. The dopant used in the course of the PEDOT synthesis is found to play an important role for these redox currents with PEDOT/PSS-coated electrodes showing the smallest ones. The investigation of the role of the polymerization charge (i.e. the thickness of the polymer films) reveals that electrodes coated with thin PEDOT films perform better than those coated with thicker polymer films.Electroanalytical detection of acetaminophen is found to be effective by means of thin film PEDOT/PSS-coated electrodes. The concentration range of linear response is established to be 50μMdm−3 to 1mMdm−3 in linear sweep voltammetry experiments and 5μMdm−3 to 65μMdm−3 in DPV experiments. The corresponding LODs are 10μMdm−3 and 0.3μMdm−3, respectively. PEDOT/PSS-coated electrodes are used to determine acetaminophen in four medications containing various additional components.

Dissolved Hydrogen Voltammetric Probe and Its Application for Photosynthetic Bacterial Hydrogen Production Rate Evaluation

A 3-electrode probe having a construction similar to the Clark type oxygen probe was developed, elaborated, and characterized as a dissolved hydrogen sensor. A thin plastic membrane allowing the hydrogen diffusion into the sensor prevents the interference of the determined solution composition. The sensors analytical characteristics such as LOD, sensitivity, and linear response concentration range were determined employing an electrochemical hydrogen generator producing dissolved hydrogen which concentrations were calculated by the Faraday’s law application. The sensor characterization results are presented and discussed together with the results obtained from its application for real time determination of the rate of hydrogen production in 10 mL reactors by the variety IR3 of the photosynthetic strain Rhodobacter Capsulatus.

Solid-phase synthesis of highly fluorescent nitrogen-doped carbon dots for sensitive and selective probing ferric ions in living cells.

Carbon quantum dots (C-Dots) have drawn extensive attention in recent years due to their stable physicochemical and photochemical properties. However, the development of nitrogen-doped carbon quantum dots (N-doped C-Dots) is still on its early stage. In this paper, a facile and high-output solid-phase synthesis approach was proposed for the fabrication of N-doped, highly fluorescent carbon quantum dots. The obtained N-doped C-Dots exhibited a strong blue emission with an absolute quantum yield (QY) of up to 31%, owing to fluorescence enhancement effect of introduced N atoms into carbon dots. The strong coordination of oxygen-rich groups on N-doped C-Dots to Fe(3+) caused fluorescence quenching via nonradiative electron-transfer, leading to the quantitative detection of Fe(3+). The probe exhibited a wide linear response concentration range (0.01-500 μM) to Fe(3+) with a detection limit of 2.5 nM. Significantly, the N-doped C-Dots possess negligible cytotoxicity, excellent biocompatibility, and high photostability. All these features are favorable for label-free monitoring of Fe(3+) in complex biological samples. It was then successfully applied for the fluorescence imaging of intracellular Fe(3+). As an efficient chemosensor, the N-doped C-Dots hold great promise to broaden applications in biological systems.

Dissolved Hydrogen Voltammetric Probe and Its Application for Photosynthetic Bacterial Hydrogen Production Rate Evaluation

As known, the dissolved hydrogen undergoes electrochemical oxidation, the mechanism of which depends on the electrolyte pH. In alkaline solutions the OH- participates in the hydrogen oxidation according to the reaction: H+ OH-= H2O+2e-, while in acid solutions the electrochemical oxidation is direct: H2=2H++2e-. In both cases electrolyte acidifying occurs because of the OH- consumption or H+generation, making suitable the application of very acid electrolytes to avoid the sensor characteristics changes caused by a great pH changes over time. A 3-electrode probe similar to the Clark type oxygen probe construction was proposed, elaborated, and characterized as a dissolved hydrogen sensor. Its analytical characteristics such as LOD, sensitivity, response time, and linear response concentration range were determined as a function of the temperature, membranes materials, the electrolytes composition, and pH. Coulometric controlled electrochemical hydrogen generator was applied for standard solution preparation.The sensor characterization results are presented and discussed together with the results obtained from its application for the real time determination of the rate of hydrogen production by the varieties B10 and IR3 of the photosynthetic strain Phodobacter Capsulatus. Acknowledgement. This work was supported by CONACyT Mexico: Research grant No. 152961, CONACYT-SENER “Sustentabilidad Energética” 2010-01.

Detection of trace amounts of Hg2+ in different real samples based on immobilization of novel unsymmetrical tetradentate Schiff base within PVC membrane

A novel fluorescence optical sensor for sensitive and selective determination of Hg2+ ions in aqueous solution has been prepared. The sensing system is made of a novel unsymmetrical tetradentate Schiff base namely N-(2-hydroxyphenyl)-N′-(2-mercaptophenyl)-o-phthalylidene (HMP), as a neutral Hg2+-selective fluoroionophore immobilized in a plasticized PVC membrane containing potassium tetrakis-(4-chlorophenyl) borate (KTpClPB) as a lipophilic anionic additive. The response of the optode is based on the strong fluorescence enhancement of HMP upon exposure to Hg2+ ions. Under the optimum conditions, the proposed sensor displays a linear response in concentration range of 2.27×10−11 to 1.13×10−3mol/L, with a detection limit of 9.57×10−12mol/L. Furthermore, the proposed optode displays a good selectivity toward Hg2+ ions in comparison with common coexisting cations. The sensor was applied successfully for determination of mercury ions in different real samples.

High-Sensitivity Naphthalene-Based Two-Photon Fluorescent Probe Suitable for Direct Bioimaging of H2S in Living Cells

H2S is the third endogenously generated gaseous signaling compound and has also been known to involve a variety of physiological processes. To better understand its physiological and pathological functions, efficient methods for monitoring of H2S in living systems are desired. Although quite a few one photon fluorescence probes have been reported for H2S, two-photon (TP) probes are more favorable for intracellular imaging. In this work, by employing a donor-π-acceptor-structured naphthalene derivative as the two-photon fluorophore and an azide group as the recognition unit, we reported a new two-photon bioimaging probe 6-(benzo[d]thiazol-2'-yl)-2-azidonaphthalene (NHS1) for H2S with improved sensitivity. The probe shows very low background fluorescence in the absence of H2S. In the presence of H2S, however, a significant enhancement for both one photon and TP excited fluorescence were observed, resulting in a high sensitivity to H2S in aqueous solutions with a detection limit of 20 nM observed, much lower than the previously reported TP probe. The probe also exhibits a wide linear response concentration range (0-5 μM) to H2S with high selectivity. All these features are favorable for direct monitoring of H2S in complex biological samples. It was then applied for direct TP imaging of H2S in living cells with satisfactory sensitivity, demonstrating its value of practical application in biological systems.

Formation and electroanalytical performance of polyaniline–palladium nanocomposites obtained via Layer-by-Layer adsorption and electroless metal deposition

The Layer-by-Layer (LbL) adsorption technique is used to produce thin composite layers consisting of polyaniline (PANI) and Pd particles in two different ways: (i) multistep adsorption of PANI and pre-synthesized Pd nanoparticles (NPs) and (ii) multistep adsorption of PANI and polysterene sulfonate (PSS) followed by electroless deposition of palladium particles (Pdeless). The formation of both types of composite layers is characterized by electrochemical and microgravimetric measurements.Electrochemical measurements for hydrogen peroxide reduction are carried out at neutral pH under voltammetric and amperometric conditions. It is established that the PANI–Pd NPs composites show a sensitive voltammetric response for H2O2 reduction in the 40–300μM concentration range whereas the (PANI–PSS)Pdeless composites have high intrinsic electroactivity that masks the H2O2 reductive response. The amperometric data show high sensitivity for both types of composites: PANI–Pd NPs and (PANI–PSS)Pdeless (with Pd incorporated in several electroless deposition steps). For the PANI–Pd NPs material the concentration range of linear response is 10–700μM and the limit of detection 2.6μM. The obtained non-enzymatic electrocatalytic materials are suitable for monitoring the levels of H2O2 in drinking and waste waters.

Potentiometric Determination of Aluminum in Foods, Pharmaceuticals, and Alloys by AlMCM-41-Modified Carbon Paste Electrode

A new chemically modified electrode is constructed by incorporating AlMCM-41 into carbon paste matrix (AlMCM-41-MCPE) and used as a sensitive sensor for detection of aluminum in aqueous and nonaqueous solutions. The rapid exchange kinetics in the membrane results in a near-Nernstian behavior of the modified electrode and makes it a suitable potentiometric sensor for detection of aluminum. A linear response in concentration range from 1.0 × 10−6 to 1.0 × 10−1 mol/L (0.027 μg/mL–2.7 mg/mL) was obtained with a detection limit of 4.6 × 10−7 mol/L for the potentiometric detection of aluminum. Selectivity coefficients of a number of interfering cations have been estimated. The interference from many of the investigated ions is negligible. The AlMCM-41-MCPE is suitable for use in aqueous solution of pH 2–6 and in partially nonaqueous medium. The modified electrode exhibited a fast response time (~8 s), good stability, and an extended lifetime. The developed sensor was used successfully for the determination of Al3+ in some alloys, drugs, and food products.

Chemiluminescence resonance energy transfer-based detection for microchip electrophoresis.

Since the channels in micro- and nanofluidic devices are extremely small, a sensitive detection is required following microchip electrophoresis (MCE). This work describes a highly sensitive and yet universal detection scheme based on chemiluminescence resonance energy transfer (CRET) for MCE. It was found that an efficient CRET occurred between a luminol donor and a CdTe quantum dot (QD) acceptor in the luminol-NaBrO-QD system and that it was sensitively suppressed by the presence of certain organic compounds of biological interest including biogenic amines and thiols, amino acids, organic acids, and steroids. These findings allowed developing sensitive MCE-CL assays for the tested compounds. The proposed MCE-CL methods showed desired analytical figures of merit such as a wide concentration range of linear response. Detection limits obtained were approximately 10(-9) M for biogenic amines including dopamine and epinephrine and approximately 10(-8) M for biogenic thiols (e.g., glutathione and acetylcysteine), organic acids (i.e., ascorbic acid and uric acid), estrogens, and native amino acids. These were 10-1000 times more sensitive than those of previously reported MCE-based methods with chemiluminescence, electrochemical, or laser-induced fluorescence detection for quantifying corresponding compounds. To evaluate the applicability of the present MCE-CL method for analyzing real biological samples, it was used to determine amino acids in individual human red blood cells. Nine amino acids, including Lys, Ser, Ala, Glu, Trp, etc., were detected. The contents ranged from 3 to 31 amol/cell. The assay proved to be simple, quick, reproducible, and very sensitive.

New luminol chemiluminescence reaction using diperiodatoargentate as oxidate for the determination of amikacin sulfate

A new chemiluminescence (CL) reaction between luminol and diperiodatoargentate [K(2) [Ag (H(2)IO(6)) (OH)(2)]] was observed in alkaline medium. The CL intensity could be greatly enhanced by amikacin sulfate. Therefore a new CL method for the determination of amikacin sulfate was built by combining with flow injection technology. A possible mechanism of the CL reaction was proposed via the investigation of the CL kinetic characteristics, the CL spectrum and the UV absorption spectra of some related substance. The concentration range of linear response was 5.1 x 10(-8) to 5.1 x 10(-6)mol L(-1) with a detection limit of 1.9 x 10(-8) mol L(-1) (3sigma). The proposed method had good reproducibility with a relative standard deviation of 2.8% (n = 7) for 5.1 x 10(-7) mol L(-1) of amikacin sulfate. It was successfully applied to determine amikacin sulfate in serum.

A Butyl Methacrylate Monolithic Column Prepared In-Situ on a Microfluidic Chip and its Applications

A butyl methacrylate (BMA) monolithic column was polymerized in-situ with UV irradiation in an ultraviolet transparent PDMS micro-channel on a homemade micro-fluidic chip. Under the optimized conditions and using a typical polymerization mixture consisting of 75% porogenic solvents and 25% monomers, the BMA monolithic column was obtained as expected. The BET surface area ratio of the BMA monolithic column was 366 m2·g-1. The corresponding SEM images showed that the monolithic column material polymerized in a glass channel was composed of uniform pores and spherical particles with diameters ranging from 3 to 5 μm. The promethazine–luminal–potassium ferricyanide chemiluminescence system was selected for testing the capability of the column. A flow injection analytical technique–chemiluminescence (FIA–CL) system on the microfluidic chip with a BMA monolithic column pretreatment unit was established to determine promethazine. Trace promethazine was enriched by the BMA monolithic column, with more than a 10-fold average enrichment ratio. The proposed method has a linear response concentration range of 1.0×10-8 - 1.0×10-6g·mL-1 and the detection limit was 1.6×10-9g·mL-1.

Immobilization of tyrosinase in chitosan film for an optical detection of phenol

An optical biosensor based on the immobilized tyrosinase enzyme in a chitosan film is described for the detection of phenol. The film was prepared by depositing a chitosan solution containing tyrosinase onto a microscope glass slide via spin coating technique. The quinone produced from the enzymatic oxidation of phenol was reacted with 3-methyl-2-benzothiazolinone hydrazone (MBTH) to produce a maroon color adduct. The color intensity of the adduct was found to increase proportionally with the increase of the substrate concentrations after 15 min exposure to the substrate. The optimum enzyme loading and chitosan concentrations were found to be 0.9 mg and 2% (w/v), respectively. The biosensor also demonstrated optimum activity at pH 6–7, optimum temperature of 45 °C and a linear response in the phenol concentration range of 2.5–70.0 μM. The response characteristics of the biosensor towards different phenolic compounds were determined. It was found that the biosensor gave a linear response in the concentration range of 2.5–50.0 μM for 4-chlorophenol, 2.5–100.0 μM for m-cresol and 12.5–400.0 μM for p-cresol. The limit of detection and the apparent Michaels–Menten constant ( K m) of the biosensor were 0.9, 1.0, 1.0, 3.0 μM and 0.038, 0.037, 0.056, 0.201 mM for 4-chlorophenol, phenol, m-cresol and p-cresol, respectively. It showed good stability for at least 2 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 ∼2 μM to 0.01 M was obtained with a detection limit of 1 μM 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.

Microdevice with integrated dialysis probe and biosensor array for continuous multi-analyte monitoring

The simultaneous on-line determination of glucose and lactate using a microdevice that consisted of a dialysis sampling system incorporated to the flow-through cell of a microfabricated biosensor array is presented. The fluidic connections between the different device's components were realized by subsequent processing of stacked dry resist layers on a plastic support that provided also the means for electric connections. The performance of the device was evaluated in vitro. The cross-talk effect on the downstream sensor was investigated and found to be negligible. Recoveries of over 95% for both analytes were achieved when flow rates of the perfusion fluid ≤0.5 μl/min were used. At this flow rate, the response time of the device was 2.4 min, which is acceptable for on-line analysis. The linear response concentration range extended up to 30 mM for glucose and 15 mM for lactate. Interference from electroactive species such as ascorbic acid, 2-acetamidophenol and uric acid, was minimal (less than 5% increase in biosensors signal for all substances tested). In addition, the device presented long-term run stability both in buffer and serum samples.

Aluminum electrode modified with manganese hexacyanoferrate as a chemical sensor for hydrogen peroxide

A chemically modified electrode was fabricated based on manganese hexacyanoferrate (MnHCF) film. The MnHCF was used as a modifier immobilized onto an aluminum electrode. Stability of the electroactive film formed on the Al electrode surface indicated that MnHCF is a suitable material for the preparation of modified electrodes. The analytical applicability of the modified electrode for the determination of hydrogen peroxide was examined. A linear response in concentration range of 6.0×10 −7–7.4×10 −3 M ( r=0.9997) was obtained with detection limit of 2.0×10 −7 M for the determination of hydrogen peroxide. The modified electrode exhibited a good selectivity for H 2O 2 in real samples. The mentioned electrode has advantages of being highly stable, sensitive, inexpensive, ease of construction and use.

Iron(II) Phthalocyanine-Modified Carbon-Paste Electrode for Potentiometric Detection of Ascorbic Acid

A chemically modified electrode constructed by incorporating iron(II) phthalocyanine [Fe(II)Pc] into carbon-paste matrix was used as a sensitive potentiometric sensor for detection of ascorbic acid. The resulting electrode exhibits catalytic properties for the electrooxidation of ascorbic acid, 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 sensor for detection of ascorbic acid. A linear response in concentration range from 10−6 to 10−2 M (0.18–1800 μg ml−1) was obtained with a detection limit of 5 × 10−7 M for the potentiometric detection of ascorbic acid. The modified electrode was used for the determination of ascorbic acid in vitamin preparations. The recovery was 97.2–102.4% for the vitamin added to the preparations with a relative standard deviation of less than 5%. The modified electrode exhibited a fast response time (<10 s),had good stability, and had an extended lifetime.

Cesium-ion selective electrodes based on calix[4]arene dibenzocrown ethers

Four calix[4]arene dibenzocrown ether compounds have been prepared and evaluated as Cs+-selective ligands in solvent polymeric membrane electrodes. The ionophores include 25,27-bis(1-propyloxy)calix[4]arene dibenzocrown-6 1, 25,27-bis(1-alkyloxy)calix[4]arene dibenzocrown-7s 2 and 3, and 25,27-bis(1-propyloxy)calix[4]arene dibenzocrown-8 4. For an ion-selective electrode (ISE) based on 1, the linear response concentration range is 1×10−1 to 1×10−6 M of Cs+. Potentiometric selectivities of ISEs based on 1-4 for Cs+ over other alkali metal cations, alkaline earth metal cations, and NH4+ have been assessed. For 1-ISE, a remarkably high Cs+/Na+ selectivity was observed, the selectivity coefficient (KCs,NaPot) being ca. 10−5. As the size of crown ether ring is enlarged from crown-6 (1) to crown-7 (2 and 3) to crown-8 (4), the Cs+ selectivity over other alkali metal cations, such as Na+ and K+, is reduced successively. Effects of membrane composition and pH in the aqueous solution upon the electrode properties are also discussed.

Amperometric glucose enzyme electrode by immobilizing glucose oxidase in multilayers on self-assembled monolayers surface

A novel and robust amperometric enzyme electrode for the determination of glucose was constructed by immobilizing glucose oxidase (GOD) and Os(bpy) 2Cl–poly(4-vinyl)pyridine (Os–PVP) complex multilayers on thiol self-assembled monolayers surface. The apparent Michaelis-Menton constant K m′ increased with increasing the number of Os–PVP/GOD multilayers. The concentration range of linear response and detection limit were 0.1–10 and 0.05 mM, the interference of ascorbic acid and uric acid were eliminated by the presence of SAMs and the enzyme electrodes were stable over 3 weeks. The preparation technique may be useful for controlling the performance of multilayer enzyme electrodes by changing the enzyme content.

Potentiometric Flow Injection Detection of Copper(II) with a Graphite Carbon Electrode

A graphite carbon electrode has been evaluated in a potentiometric flow injection system for the detection of Cu2+. The electrode response characteristics were investigated by both cyclic voltammetry and potentiometry, and it is suggested that the electrode potential change results in the adsorption of Cu2+ at the electrode surface. The carbon electrode was used for the flow injection potentiometric detection of Cu2+ in 0.05 mol/L NaAc-0.2 mol/L NaCl at pH of 6.0 carrier solution. A linear response in concentration range of 1x10−5-1x10−2 mol/L was obtained with a detection limit of 5x10−5 mol/L. The electrode described in this paper is simple and low cost.

Investigation of mercury-free potentiometric stripping analysis and the influence of mercury in the analysis of trace elements lead and zinc

The application of Potentiometric Stripping Analysis (PSA), without any mercury, to the determination of trace elements lead and zinc, results in linear responses between stripping-peak areas and concentrations within 0 to 2000 ng/g. The best response, as determined by the size of stripping areas, was obtained with an electrode prepared with mercury but without mercury ions in the electrolyte. Lead is analysed by a freshly polished glassy-carbon electrode in 0.09–0.1 mol/L HCl while the analysis of zinc requires an electrode activation procedure. The electrode activation is performed by stripping zinc in an electrolyte containing 0.1 mol/L HCl and 2 μg/g Zn2+ and electrolysis at −1400 mV (SCE). The concentration range of linear response occurs where the electrode is not fully covered by metal clusters during the electrolysis step. The influence of mercury is investigated and a model is proposed which explains the co-deposition of mercury and test metals in the electrolysis step in terms of a charge-distribution parameter. The model explains that the decrease of stripping peak area, as a function of concentration, is entirely due to mercury ions being simultaneously reduced together with the ions of the test metal in the electrolysis step. The influence of hydrogen evolution and oxygen reduction together with possible improvements of the method are discussed.