Maria Del Pilar Taboada Sotomayor

Development of an enzymeless biosensor for the determination of phenolic compounds

Abstract The construction of amperometric enzymeless biosensors for phenolic compounds determination, using carbon paste electrode modified with copper phtalocyanine (CuPc) and histidine (His), based on the chemistry of the dopamine β-monooxygenase (DβM) enzyme that catalyzes the hydroxylation of the dopamine and its analogs is shown. The modified carbon paste was evaluated on electrodes constructed in two ways: putting the paste into a cavity of a rotating disk electrode and a platinum slide electrode fixed into a glass tube. The sensor in hydrodynamic conditions presented a linear response range between 30 and 250xa0μmolxa0l−1, with a sensitivity of 4.6±0.1xa0nAxa0lxa0μmol−1xa0cm−2 for catechol, response time of 3xa0s and lifetime of about 50 days when stored at room temperature. The sensor in static conditions showed a linear response range from 40 to 250xa0μmolxa0l−1, with a sensitivity of 0.30±0.01xa0nAxa0lxa0μmol−1xa0cm−2 for catechol. The sensors presented the following relative response order for dopamine and some analog species: catechol>dopamine>guaiacol>serotonin>phenol.

Tris (2,2?-bipyridil) copper (II) chloride complex: a biomimetic tyrosinase catalyst in the amperometric sensor construction

The use of tris (2,2?-bipyridil) copper (II) chloride complex, [Cu(bipy)3]Cl2/6H2O, as a biomimetic catalyst, is reported in the construction of an amperometric sensor for dopamine. The sensor was prepared modifying a glassy carbon electrode with a Nafion † membrane doped with the complex. The optimized conditions for the sensor response were obtained in 0.25 mol dm � 3 Pipes buffer (pH 7.0) containing 150 mmol dm � 3 H2O2, with an applied potential of � /50 mV versus saturated calomel electrode (SCE). In these conditions, a linear response range between 9 and 230 mmol dm � 3 , with a sensitivity of 1.439 /0.01 nA dm 3 mmol � 1 cm � 2 and a detection limit of 4.8 mmol dm � 3 were observed for dopamine. The response time for this sensor was about 1 s, presenting the same response for at least 150 successive measurements, with a good repeatability (4.8%) expressed as relative standard deviation for n � /13. After its construction, this sensor can be used after 180 days without loss of sensitivity, kept at room temperature. The difference of the sensor response between four preparations was 4.2%. A detailed investigation about the sensor response for other eighteen phenolic compounds and five interfering species was performed. The sensor was applied for dopamine determination in pharmaceutical preparation with success. # 2002 Elsevier Science Ltd. All rights reserved.

Development of an amperometric sensor for phenol compounds using a Nafion † membrane doped with copper dipyridyl complex as a biomimetic catalyst

Abstract The use of [CuDipyCl 2 ] as a biomimetic catalyst in the construction of an amperometric enzymeless biosensor for phenol determinations is reported. The sensor was prepared modifying a glassy carbon electrode with a Nafion® membrane doped with [CuDipyCl 2 ]. The sensor presented a higher response for dopamine in 0.1 mol l −1 phosphate buffer at pH 7, with an applied potential of −50 mV versus SCE. With the optimized operational conditions a linear response range between 4.0×10 −5 and 6.0×10 −4 mol l −1 , with a sensitivity of 350±10 nA l mmol −1 cm −2 and a detection limit of 9.0×10 −6 mol l −1 were observed for the sensor. The response time presented for this sensor was approximately 1 s, presenting the same response for at least 50 measurements, with good repeatability (R.S.D. 3.8%, for n =9). The difference of the response between four preparations was 7%. Detailed investigations of the sensor response for monophenol and diphenol compounds and interfering species were carried out.

Iron(III) tetra-(N-methyl-4-pyridyl)-porphyrin as a biomimetic catalyst of horseradish peroxidase on the electrode surface: An amperometric sensor for phenolic compound determinations

The use of iron(III) tetra-(N-methyl-4-pyridyl) porphyrin (FeIIIT4MpyP) and histidine (His) in the construction of an amperometric sensor for phenolic compound determinations is reported, based on horseradish peroxidase (HRP) chemistry. The sensor was prepared by modifying a glassy carbon electrode with Nafion membrane doped with FeIIIT4MpyP and His, in a mass ratio of 1:2. The sensor presented its best performance at 50 mV vs. SCE in 0.1 mol l(-1) succinate buffer (pH = 4.0) containing 125 micromol l(-1) H2O2. Under optimized operational conditions, a linear response range from 0.6 to 6.0 micromol l(-1) was obtained with a sensitivity of 61 nA cm(-2) micromol l(-1). The detection limit for catechol determination was 0.35 micromol l(-1). The response time was less than 0.5 s. The proposed sensor presented stable responses for 100 successive determinations, while satisfactory responses were observed even after 200 measurements. The repeatability, evaluated in terms of relative standard deviation, was 4% for n = 7. The signal responses for other phenolic compounds, including those of environmental and clinical interest, were also investigated.

Fiber-optic pH sensor based on Poly(o-methoxyaniline)

Abstract This work describes the development of optical sensors for the measurement of pH. They work by measuring the diffuse reflectance of a conductive polymer, in the visible range of the spectrum. The pH sensitive material was poly(o-methoxyaniline) doped by p-toluene sulfonic acid (PoAnis/TSA), which was immobilized either on or within a polymeric structure. Two optodes were constructed. The first was assembled using a bifurcated bundle of borosilicate optical fibers. The sensing phase was a polymeric composite made of PoAnis/TSA and cellulose acetate, and was fixed at the common end of the bifurcate bundle. This optode allowed measurements in the pH range from 4.9 to 10.5 with a precision of ±0.01 pH. The response time for 90% change was 5.0 min for a full pH variation from acid to basic, and 22 min for the reversal change. The sensor response depends on the ionic strength of the solution and on the supporting electrolyte used to adjust the ionic strength. The second optode was built using two cables of optical fibers, each one having a single plastic fiber with 1.0 mm diameter. The two cables were fixed in a Perspex block, together with the pH sensitive layer. The sensing phase of this optode consisted of a film of PoAnis/TSA adsorbed on polyethylene. This optode yielded measurements in a working range from pH 2.0–10.0 and with relatively faster response time for 90% change for a variation from basic to acid (5.0 min). It was verified that pH sensors based on poly(o-methoxyaniline) offer a wide dynamic range but suffer from long response times and interferences from both cations and anions.

ENZYMELESS BIOSENSORS: UMA NOVA ÁREA PARA O DESENVOLVIMENTO DE SENSORES AMPEROMÉTRICOS

The aim of this work is to describe the recent area that it has been developed for the construction of amperometric sensors, with the purpose to make possible a more effective electron transfer between enzyme and electrode. The advances reported in the literature will be described, such as enzymatic configurations that can be mimic using the chemistry of the artificial enzymes.

Polímeros biomiméticos em química analítica. Parte 2: aplicações de MIP ("Molecularly Imprinted Polymers") no desenvolvimento de sensores químicos

The aim of this paper is the description of the strategies and advances in the use of MIP in the development of chemical sensors. MIP has been considered an emerging technology, which allows the synthesis of materials that can mimic some highly specific natural receptors such as antibodies and enzymes. In recent years a great number of publications have demonstrated a growth in their use as sensing phases in the construction of sensors . Thus, the MIP technology became very attractive as a promising analytical tool for the development of sensors.

Bi-enzymatic optode detection system for oxalate determination based on a natural source of enzyme

This work describes a simple and low cost methodology for oxalate determination in food samples, which employs a bromothymol blue-based pH optode for the determination of CO2 generated in the enzymatic reaction between oxalic acid and oxalate oxidase. The enzyme was immobilised on barley seeds, together with catalase enzyme, and placed in a stirring bar type enzymatic reactor. The system showed a linear response range from 0.0080 up to 0.100 mol l −1 , when the measurements were carried out in 0.050 mol l −1 succinate buffer at pH 4.0 and 25 ◦ C. In these conditions, the lifetime of the system was about 120 h, with a relative standard deviation <2% (four measurements of a 0.020 mol l −1 oxalate solution). A value of 0.075 mol l −1 was obtained for the apparent Michaelis–Menten constant, with a maximum velocity of 1908mol min −1 for oxalic acid oxidation. No significant differences were found at a confidence level of 95%, when the results were compared with those obtained with the AOAC official standard method (974.24) for oxalate determination in spinach.

Polímeros biomiméticos em química analítica. Parte 2: aplicações de MIP (Molecularly Imprinted Polymers) no desenvolvimento de sensores químicos

The aim of this paper is the description of the strategies and advances in the use of MIP in the development of chemical sensors. MIP has been considered an emerging technology, which allows the synthesis of materials that can mimic some highly specific natural receptors such as antibodies and enzymes. In recent years a great number of publications have demonstrated a growth in their use as sensing phases in the construction of sensors . Thus, the MIP technology became very attractive as a promising analytical tool for the development of sensors.

Development and Application of a Highly Selective Biomimetic Sensor for Detection of Captopril, an Important Ally in Hypertension Control

A biomimetic sensor is proposed as a promising new analytical method for determination of captopril in different classes of samples. The sensor was prepared by modifying a carbon paste electrode with iron (II) phthalocyanine bis(pyridine) [FePc(dipy)] complex. Amperometric measurements in a batch analytical mode were first carried out in order to optimize the sensor response. An applied potential lower than 0.2 V vs Ag|AgCl in 0.1 mol L-1 of TRIS buffer at pH 8.0 provided the best response, with a linear range of 2.5 x 10-5 to 1.7 x 10-4 mol L-1. A detailed investigation of the selectivity of the sensor, employing seventeen other drugs, was also performed. Recovery studies were carried out using biological and environment samples in order to evaluate the sensors potential for use with these sample classes. Finally, the performance of the biomimetic sensor was optimized in a flow injection (FIA) system using a wall jet electrochemical cell. Under optimized flow conditions, a broad linear response range, from 5.0 x 10-4 to 2.5 x 10-2 mol L-1, was obtained for captopril, with a sensitivity of 210 ± 1 μA L mol-1.