Heparin-stabilized gold nanoparticles embedded in graphene for the electrochemical determination of esculetin.

A conductive nanocomposite consisting of heparin-stabilized gold nanoparticles embedded in graphene was prepared and characterized to develop an electrochemical sensor for the determination of esculetin in tea and jam samples. The gold nanoparticles were characterized by spectroscopic and microscopic techniques. The different proportions of graphene in the nanocomposite were evaluated and characterized by electrochemical practices. The heterostructure material on the glassy carbon electrode with esculetin showed π-π stacking interactions with an adsorption-controlled process. The voltammetric profile of esculetin using the proposed nanomaterial presented oxidation and reduction peaks at +0.61 and +0.58 V vs. Ag/AgCl, respectively, facilitating the electron transfer with esculetin through the transfer of two moles of protons and two moles of electrons per mole of esculetin. Using optimized conditions and square wave voltammetry, the calibration curve was obtained with two linear ranges, from 0.1 to 20.5 µmol L-1, with a detection limit of 43.0 nmol L-1. The electrochemical sensor showed satisfactory results for repeatability and stability, although interferences were observed in the presence of high concentrations of ascorbic acid or quercetin. The sensor was successfully applied in the determination of esculetin in samples of mulberry jam, white mulberry leaf tea, and white mulberry powder tea, presenting adequate recovery ranges. This directive provides valuable insights for the development of novel electrochemical sensors using heparin-based conductive nanomaterials with improved sensitivity and sensibility.

Green Synthesis of Gold Nanoparticles Using Peach Extract Incorporated in Graphene for the Electrochemical Determination of Antioxidant Butylated Hydroxyanisole in Food Matrices.

Butylated hydroxyanisole (BHA) is a synthetic phenolic antioxidant widely used in various food matrices to prevent oxidative rancidity. However, its presence has been associated with liver damage and carcinogenesis in animals. Thus, an electrochemical sensor was built using a composite of gold nanoparticles synthesized in peach extract (Prunus persica (L.) Batsch) and graphene. Peach extract served as a reducing and stabilizing agent for gold nanoparticles, as a dispersing agent for graphene, and as a film former to immobilize the composite on the surface of a glassy carbon electrode. The gold nanoparticles were characterized using spectroscopic and microscopic techniques, and the electrodes were electrochemically characterized using electrochemical impedance spectroscopy and cyclic voltammetry. The sensor provided higher current responses and lower charge transfer resistances compared to the unmodified glassy carbon electrode. Under the established optimized working conditions (0.1 mol L-1 Britton-Robinson buffer, pH 4.0, and differential pulse voltammetry), the calibration curve exhibited a linear range from 0.2 to 9.8 µmol L-1, with a detection limit of 70 nmol L-1. The proposed sensor represented a sensitive and practical analytical tool for the accurate determination of BHA in mayonnaise samples.

Nanocomposite based on green synthesis of gold nanoparticles decorated with functionalized multi-walled carbon nanotubes for the electrochemical determination of hydroxychloroquine.

In this study, a selective and sensitive electrochemical approach for determining hydroxychloroquine (HCQ) was proposed. A novel nanocomposite based on gold nanoparticles synthesized by green synthesis in an extract of white pitaya (Hylocereus undatus) (AuNP-Ext) decorated with functionalized multi-walled carbon nanotubes (f-MWCNTs) was presented. AuNP-Ext was characterized by ultraviolet-visible spectroscopy and the f-MWCNTs/AuNP-Ext nanocomposite by transmission electron microscopy. The nanocomposite was used to modify a glassy carbon electrode (GCE). Using the f-MWCNT-AuNP-Ext/GCE sensor, an irreversible oxidation peak at +0.74 V vs. Ag/AgCl was verified by HCQ. The calibration plot was studied in two linear ranges, from 0.03 to 3.5 µmol/L and from 3.5 to 17.0 µmol/L, with a limit of detection of 0.0093 µmol/L and a limit of quantification of 0.031 µmol/L, regarding the first linear range. The proposed sensor was successfully applied to the determination of HCQ in pharmaceutical and clinical samples without any special purification, separation or pre-treatment steps. The accuracy was verified by UV-Vis spectrometry, and this revealed that the proposed method was accurate and precise, as evidenced by F- and t-tests.

Graphene and gold nanoparticle-based bionanocomposite for the voltammetric determination of bisphenol A in (micro)plastics.

The monitoring of endocrine disruptors in the environment is one of the main strategies in the investigation of potential risks associated with exposure to these chemicals. Bisphenol A is one of the most prevalent endocrine-disrupting compounds and is prone to leaching out from polycarbonate plastic in both freshwater and marine environments. Additionally, microplastics also can leach out bisphenol A during their fragmentation in the water environment. In the quest for a highly sensitive sensor to determine bisphenol A in different matrices, an innovative bionanocomposite material has been achieved. This material is composed of gold nanoparticles and graphene, and was synthesized using a green approach that utilized guava (Psidium guajava) extract for reduction, stabilization, and dispersion purposes. Transmission electron microscopy images revealed well-spread gold nanoparticles with an average diameter of 31 nm on laminated graphene sheets in the composite material. An electrochemical sensor was developed by depositing the bionanocomposite onto a glassy carbon surface, which displayed remarkable responsiveness towards bisphenol A. Experimental conditions such as the amount of graphene, extract: water ratio of bionanocomposite and pH of the supporting electrolyte were optimized to improve the electrochemical performance. The modified electrode displayed a marked improvement in current responses for the oxidation of bisphenol A as compared to the uncovered glassy carbon electrode. A calibration plot was established for bisphenol A in 0.1 mol L-1 Britton-Robinson buffer (pH 4.0), and the detection limit was determined to equal to 15.0 nmol L-1. Recovery data from 92 to 109% were obtained in (micro)plastics samples using the electrochemical sensor and were compared with UV-vis spectrometry, demonstrating its successful application with accurate responses.

Ratiometric Electrochemical Sensor for Butralin Determination Using a Quinazoline-Engineered Prussian Blue Analogue.

A ratiometric electrochemical sensor based on a carbon paste electrode modified with quinazoline-engineered ZnFe Prussian blue analogue (PBA-qnz) was developed for the determination of herbicide butralin. The PBA-qnz was synthesized by mixing an excess aqueous solution of zinc chloride with an aqueous solution of precursor sodium pentacyanido(quinazoline)ferrate. The PBA-qnz was characterized by spectroscopic and electrochemical techniques. The stable signal of PBA-qnz at +0.15 V vs. Ag/AgCl, referring to the reduction of iron ions, was used as an internal reference for the ratiometric sensor, which minimized deviations among multiple assays and improved the precision of the method. Furthermore, the PBA-qnz-based sensor provided higher current responses for butralin compared to the bare carbon paste electrode. The calibration plot for butralin was obtained by square wave voltammetry in the range of 0.5 to 30.0 µmol L-1, with a limit of detection of 0.17 µmol L-1. The ratiometric sensor showed excellent precision and accuracy and was applied to determine butralin in lettuce and potato samples.

Label-Free Immunosensor Based on Liquid Crystal and Gold Nanoparticles for Cardiac Troponin I Detection.

According to the World Health Organization (WHO), cardiovascular diseases (CVDs) are the leading cause of mortality and morbidity worldwide. The development of electrochemical biosensors for CVD markers detection, such as cardiac troponin I (cTnI), becomes an important diagnostic strategy. Thus, a glassy carbon electrode (GCE) was modified with columnar liquid crystal (LCcol) and gold nanoparticles stabilized in polyallylamine hydrochloride (AuNPs-PAH), and the surface was employed to evaluate the interaction of the cTnI antibody (anti-cTnI) and cTnI for detection in blood plasma. Morphological and electrochemical investigations were used in the characterization and optimization of the materials used in the construction of the immunosensor. The specific interaction of cTnI with the surface of the immunosensor containing anti-cTnI was monitored indirectly using a redox probe. The formation of the immunocomplex caused the suppression of the analytical signal, which was observed due to the insulating characteristics of the protein. The cTnI-immunosensor interaction showed linear responses from 0.01 to 0.3 ng mL-1 and a low limit of detection (LOD) of 0.005 ng mL-1 for linear sweep voltammetry (LSV) and 0.01 ng mL-1 for electrochemical impedance spectroscopy (EIS), showing good diagnostic capacity for point-of-care applications.

Determination of paracetamol using a sensor based on green synthesis of silver nanoparticles in plant extract.

The biosynthesis of nanometals using a plant extract is simple, efficient, fast, cost-effective and eco-friendly. In this study, a pine nut extract (Araucaria angustifolia) was obtained and used as a reducing and stabilizing agent in the synthesis of silver nanoparticles. An electrochemical sensor based on the silver nanoparticles obtained and exfoliated graphite nanoplatelets applied to a glassy carbon electrode was developed for the determination of paracetamol. To optimize the synthesis of the silver nanoparticles, important factors such as temperature, extract:water ratio, silver nitrate concentration and extract stability time were studied. The factors influencing the performance of the sensor were studied in detail and the results demonstrated good repeatability and electrode-to-electrode repeatability (relative standard deviations of 1.8 and 4.0 %, respectively). Under optimized conditions, there was a linear response to paracetamol concentrations of 4.98 × 10-6 to 3.38 × 10-5 mol L-1, with a detection limit of 8.50 × 10-8 mol L-1. No reports on the biosynthesis of AgNPs using Araucaria angustifolia could be found in the literature. The sensor developed showed good stability and was used successfully for the quantification of paracetamol in pharmaceutical products.

Microcystin-LR label-free immunosensor based on exfoliated graphite nanoplatelets and silver nanoparticles.

This paper describes a simple, rapid and accurate label-free immunosensor for the determination of MC-LR in water samples. The anti-MC-LR was immobilized in a hybrid nanocomposite, comprised of exfoliated graphite nanoplatelets dispersed in a suspension of silver nanoparticles (AgNP-Nafion-xGnP), by adsorption. The nanomaterial obtained was then employed to prepare an immunosensor using a glassy carbon electrode (GCE) in one-step. Under optimized conditions, using square-wave voltammetry (SWV) and an incubation time of 10min, the immunosensor showed a linear relationship between the oxidation current and MC-LR concentration in the range of 0.5-5000ngmL-1 with a detection limit of 0.017ngmL-1. The immunosensor demonstrated good precision, with coefficients of variation of 4.5% (inter-day; n = 7) and 3.1% (intra-day; n = 5), and acceptable selectivity (low interference in the presence of potential interferents), indicating that it is suitable for analytical applications. The immunosensor was successfully applied in the determination of MC-LR in a water sample and this platform offers advantages when compared to other electrochemical sensors reported in the literature, especially with regard to the time of incubation.

A biosensor based on gold nanoparticles stabilized in poly(allylamine hydrochloride) and decorated with laccase for determination of dopamine.

Gold nanoparticles stabilized in poly(allylamine hydrochloride) (AuNP-PAH) were used as a support for the immobilization of the enzyme laccase obtained from genetically-modified microorganisms (Aspergillus oryzae) and successfully applied in the development of a new biosensor for the determination of dopamine by square-wave voltammetry. The electrochemical characterization of the biosensor was performed by cyclic voltammetry and electrochemical impedance spectroscopy and indicated that the nanomaterial used for the electrode modification facilitated the electron transfer. Under optimized conditions, the calibration curve showed a linear range for dopamine from 0.49 to 23.0 µmol L(-1), with a limit of detection of 0.26 µmol L(-1). The biosensor demonstrated suitable selectivity and stability, good intra-day and inter-day repeatability and electrode-to-electrode repeatability, with relative standard deviations of 4.95, 4.85 and 4.21%, respectively. The proposed biosensor was successfully applied to the determination of dopamine in pharmaceutical samples and the results were in agreement with those obtained using a spectrophotometric method. The recoveries of 97.6 to 105.5% obtained for the samples demonstrate that the proposed method is suitable for practical applications. The good analytical performance of the proposed method can be attributed to the efficient immobilization of laccase in the nanomaterial and the facilitation of electron transfer between the protein and the electrode surface due to the presence of the Au nanoparticles and the PAH polymer.

Troponin T immunosensor based on liquid crystal and silsesquioxane-supported gold nanoparticles.

A nanostructured immunosensor based on the liquid crystal (E)-1-decyl-4-[(4-decyloxyphenyl)diazenyl]pyridinium bromide (Br-Py) and gold nanoparticles supported by the water-soluble hybrid material 3-n-propyl-4-picolinium silsesquioxane chloride (AuNP-Si4Pic(+)Cl(-)) was built for the detection of troponin T (cTnT), a cardiac marker for acute myocardial infarction (AMI). The functionalized nanostructured surface was used to bind anti-cTnT monoclonal antibodies through electrostatic interaction. The immunosensor (ab-cTnT/AuNP-Si4Pic(+)Cl(-)/Br-Py/GCE) surface was characterized by microscopy techniques. The electrochemical behavior of the immunosensor was studied by cyclic voltammetry and electrochemical impedance spectroscopy. A calibration curve was obtained by square-wave voltammetry. The immnunosensor provided a limit of detection of 0.076 ng mL(-1) and a linear range between 0.1 and 0.9 ng mL(-1) (appropriate for AMI diagnosis).

Halloysite clay nanotubes and platinum nanoparticles dispersed in ionic liquid applied in the development of a catecholamine biosensor.

Halloysite clay nanotubes were used as a support for the immobilization of the enzyme peroxidase from clover sprouts (Trifolium), and employed together with platinum nanoparticles in 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid (Pt-BMI·PF(6)) in the development of a new biosensor for the determination of catecholamines by square-wave voltammetry. Under optimized conditions, the analytical curves showed detection limits of 0.05, 0.06, 0.07, 0.12 µM for dopamine, isoproterenol, dobutamine and epinephrine, respectively. The biosensor demonstrated high sensitivity, good repeatability and reproducibility, and long-term stability (18% decrease in response over 150 days). A recovery study of dopamine in pharmaceutical samples gave values from 97.5 to 101.4%. The proposed biosensor was successfully applied to the determination of dopamine in pharmaceutical samples, with a maximum relative error of ±1.0% in relation to the standard (spectrophotometric) method. The good analytical performance of the proposed method can be attributed to the efficient immobilization of the peroxidase in the nanoclay, and the facilitation of electron transfer between the protein and the electrode surface due to the presence of the Pt nanoparticles and ionic liquid.

Gold nanoparticles in an ionic liquid phase supported in a biopolymeric matrix applied in the development of a rosmarinic acid biosensor.

Gold nanoparticles dispersed in 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid (Au-BMI·PF(6)) were supported in chitin (CTN) chemically crosslinked with glyoxal and epichlorohydrin to obtain a new supported ionic liquid phase (SILP) catalyst with high catalytic activity, and providing an excellent environment for enzyme immobilization. This modified biopolymer matrix (Au-BMI·PF(6)-CTN) was used as a support for the immobilization of the enzyme peroxidase (PER) from pea (Pisum sativum), and employed to develop a new biosensor for rosmarinic acid (RA) determination in pharmaceutical samples by square-wave voltammetry. In the presence of hydrogen peroxide, the PER catalyzes the oxidation of RA to the corresponding o-quinone, which is electrochemically reduced at a potential of +0.14 V vs. Ag/AgCl. Under optimized conditions, the resulting peak current increased linearly for the RA concentration range of 0.50 to 23.70 µM with a detection limit of 70.09 nM. The biosensor demonstrated high sensitivity, good repeatability and reproducibility, and long-term stability (15% decrease in response over 120 days). The method was successfully applied to the determination of RA content in pharmaceutical samples, with recovery values being in the range of 98.3 to 106.2%. The efficient analytical performance of the proposed biosensor can be attributed to the effective immobilization of the PER enzyme in the modified CTN matrix, the significant contribution of the high conductivity of the ionic liquid, the facilitation of electron transfer promoted by gold nanoparticles, and the inherent catalytic ability of these materials.

Sensor for fisetin based on gold nanoparticles in ionic liquid and binuclear nickel complex immobilized in silica.

Gold nanoparticles dispersed in an ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (Au-BMI.PF(6)) and a binuclear nickel(II) complex ([Ni(2)(HBPPAMFF)mu-(OAc)(2)(H(2)O)]BPh(4)) immobilized on functionalized silica were successfully applied in the construction of a novel sensor for the determination of fisetin by square-wave voltammetry. Under optimized conditions, the analytical curve showed two linear ranges for fisetin concentrations from 0.28 to 1.39 microM and 2.77 to 19.50 microM with a detection limit of 0.05 microM. This sensor demonstrated suitable stability (ca. 150 days; at least 500 determinations) and good repeatability and reproducibility, with relative standard deviations of 2.91 and 5.11%, respectively. The recovery study of fisetin in apple juice samples gave values from 96.4 to 106.4%. The efficient analytical performance of the proposed sensor can be attributed to the effective immobilization of the Ni(ii)Ni(ii) complex on silica and the Au-BMI.PF(6) contribution to the electrode response.

Biosensor for luteolin based on silver or gold nanoparticles in ionic liquid and laccase immobilized in chitosan modified with cyanuric chloride.

Novel and effective biosensors based on Ag or Au nanoparticles dispersed in ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate (BMI.PF(6)) and laccase (Lac) from Aspergillus oryzae immobilized in chitosan (Chi) chemically cross-linked with cyanuric chloride (CC) were constructed. This enzyme catalyzes the oxidation of luteolin to the corresponding o-quinone, which is electrochemically reduced back to luteolin at 0.35 V vs. Ag/AgCl. Square-wave voltammetry was used for the electrochemical determination of luteolin at the Lac-nanoparticles-BMI.PF(6) biosensors. The best performance was obtained with 50:20:15:15% (w/w/w/w) as the graphite powder:Chi-CC:Nujol:Ag-BMI.PF(6) or Au-BMI.PF(6) composition (Lac 0.29 units mL(-1)) in 0.1 M acetate buffer solution (pH 4.0) with frequency, pulse amplitude and scan increment at 50 Hz, 100 mV, and 5.0 mV, respectively. Under optimized conditions, the cathodic currents increased linearly for the luteolin concentration range of 0.099-5.825 microM with detection limits of 0.054 +/- 0.004 microM (Ag-BMI.PF(6)) and 0.028 +/- 0.002 microM (Au-BMI.PF(6)). These biosensors demonstrated high sensitivity, good repeatability and reproducibility, and long-term stability (13% decrease in response over 70 days). The recovery study for luteolin in chamomile tea samples gave values of 91.8-104.8%. The influence of Lac immobilized in Chi-CC and nanoparticles-BMI.PF(6) contributes to the excellent performance of the biosensors.

Development of biosensors containing laccase and imidazolium bis(trifluoromethylsulfonyl)imide ionic liquid for the determination of rutin.

Biosensors based on hydrophobic ionic liquids (ILs) derived from the bis(trifluoromethylsulfonyl)imide [(CF(3)SO(2))(2)N(-) = Tf(2)N(-)] anion associated with three different imidazolium cations: 1-butyl-3-methylimidazolium (BMI x Tf(2)N), 1-decyl-3-methylimidazolium (DMI x Tf(2)N) and 1-tetradecyl-3-methylimidazolium (TDMI x Tf(2)N), along with laccase from Aspergillus oryzae, were constructed and optimized for determination of rutin. The laccase catalyzes the oxidation of rutin to the corresponding o-quinone, which is electrochemically reduced back to rutin. The best performance was obtained with 50:20:15:15% (w/w/w/w) as the graphite powder:laccase:Nujol:ILs composition in 0.1 mol L(-1) acetate buffer solution (pH 5.0). The parameters for the square-wave voltammetry experiments and scanning electron microscopy images of the biosensors were studied. Under the selected conditions, the cathodic peak current increased linearly in the rutin concentration ranges of 4.77x10(-6) to 4.62x10(-5) mol L(-1), 5.84x10(-6) to 5.36x10(-5) mol L(-1) and 5.84x10(-6) to 5.36x10(-5) mol L(-1) using the (I) BMI x Tf(2)N-laccase, (II) DMI x Tf(2)N-laccase and (III) TDMI x Tf(2)N-laccase, respectively. The rutin contents of commercial samples of pharmaceuticals were successfully determined by the biosensors and the results compared well with those obtained using the official method. The studies on rutin recovery from these samples gave values of 96.9-104.6%.

Self-assembled monolayer of nickel(II) complex and thiol on gold electrode for the determination of catechin.

Self-assembled monolayers of a nickel(II) complex and 3-mercaptopropionic acid on a gold electrode were obtained for determination of catechin by square wave voltammetry. The complex [Ni(II)L] with L=[N-(methyl)-N'-(2-pyridylmethyl)-N,N'-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-1,3-propanediamine[nickel(II)] was synthesized and characterized by (1)H NMR, IR, and electronic spectroscopies and electrochemical methods. The optimized conditions obtained for the electrodes were 0.1 mol L(-1) phosphate buffer solution (pH 7.0), frequency of 80.0 Hz, pulse amplitude of 60.0 mV and scan increment of 10.0 mV. Under these optimum conditions, the resultant peak current on square wave voltammograms increases linearly with the concentration of catechin in the range of 3.31 x 10(-6) to 2.53 x 10(-5)mol L(-1) with detection limits of 8.26 x 10(-7)mol L(-1). The relative standard deviation for a solution containing 1.61 x 10(-5)mol L(-1) catechin solution was 2.45% for eight successive assays. The lifetime of the Ni(II) complex-SAM-Au electrode was investigated through testing every day over 4 weeks. The results showed apparent loss of activity after 20 days. The results obtained for catechin in green tea samples using the proposed sensor and those obtained by electrophoresis are in agreement at the 95% confidence level.

Biomimetic sensor based on MnIIIMnII complex as manganese peroxidase mimetic for determination of rutin.

A novel biomimetic sensor for rutin determination based on a dinuclear complex [Mn(III)Mn(II)(Ldtb)(mu-OAc)(2)]BPh(4) containing an unsymmetrical dinucleating ligand, 2-[N,N-bis(2-pyridylmethyl)-aminomethyl]-6-[N-(3,5-di-tert-butyl-2-oxidoben-zyl)-N-(2-pyridylamino)aminomethyl]-4-methylphenol (H(2)Ldtb), as a manganese peroxidase mimetic was developed. Several parameters were investigated to evaluate the performance of the biomimetic sensor obtained after the incorporation of the dinuclear complex in a carbon paste. The best performance was obtained in 75:15:10% (w/w/w) of the graphite powder:Nujol:Mn(III)Mn(II) complex, 0.1 mol L(-1) phosphate buffer solution (pH 6.0) and 4.0x10(-5) mol L(-1) hydrogen peroxide. The response of the sensor towards rutin concentration was linear using square wave voltammetry in the range of 9.99x10(-7) to 6.54x10(-5) mol L(-1) (r=0.9998) with a detection limit of 1.75x10(-7) mol L(-1). The recovery study performed with pharmaceuticals ranged from 96.6% to 103.2% and the relative standard deviation was 1.85% for a solution containing 1.0x10(-3) mol L(-1) rutin (n=6). The lifetime of this biomimetic sensor was 200 days (at least 750 determinations). The results obtained for rutin in pharmaceuticals using the biomimetic sensor and those obtained with the official method are in agreement at the 95% confidence level.

Biosensor based on laccase and an ionic liquid for determination of rosmarinic acid in plant extracts.

Novel biosensors based on laccase from Aspergillus oryzae and the ionic liquids (ILs) 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMIPF(6)) and 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIBF(4)) were constructed for determination of rosmarinic acid by square-wave voltammetry. The laccase catalyzes the oxidation of rosmarinic acid to the corresponding o-quinone, which is electrochemically reduced back to rosmarinic acid at +0.2V vs. Ag/AgCl. The biosensor based on BMIPF(6) showed a better performance than that based on BMIBF(4). The best performance was obtained with 50:20:15:15% (w/w/w/w) of the graphite powder:laccase:Nujol:BMIPF(6) composition in 0.1mol L(-1) acetate buffer solution (pH 5.0). The rosmarinic acid concentration was linear in the range of 9.99 x 10(-7) to 6.54 x 10(-5)mol L(-1) (r=0.9996) with a detection limit of 1.88 x 10(-7)mol L(-1). The recovery study for rosmarinic acid in plant extract samples gave values from 96.1 to 105.0% and the concentrations determined were in agreement with those obtained using capillary electrophoresis at the 95% confidence level. The BMIPF(6)-biosensor demonstrated long-term stability (300 days; 920 determinations) and reproducibility, with a relative standard deviation of 0.56%.

Determination of chlorogenic acid in coffee using a biomimetic sensor based on a new tetranuclear copper(II) complex.

A new tetranuclear copper(II) complex which mimics the active site of catechol oxidase was synthesized and characterized by IR, CHN, electronic spectroscopic and (1)H NMR methods. The title complex [Cu(2)(mu-OH)(bpbpmp-NO(2))](2)[ClO(4)](2) was employed in the construction of a novel biomimetic sensor and used in the determination of chlorogenic acid by square wave voltammetry. The performance and optimization of the resulting biomimetic sensor were studied in detail. The best response of this sensor was obtained for 75:15:10% (w/w/w) ratio of the graphite powder:nujol:Cu(II) complex, 0.1 mol L(-1) phosphate buffer solution (pH 7.0), with frequency, pulse amplitude, and scan increment at 30 Hz, 100 mV, and 3.0 mV, respectively. The chlorogenic acid concentration was linear in the range of 5.0x10(-6) to 1.45x10(-4)mol L(-1) (r=0.9985) with a detection limit of 8.0x10(-7)mol L(-1). This biomimetic sensor demonstrated long-term stability (250 days; 640 determinations) and reproducibility, with a relative standard deviation of 10.0%. The recovery study of chlorogenic acid in coffee samples gave values from 93.2% to 106.1% and the concentrations determined showed good agreement when compared with those obtained using capillary electrophoresis at the 95% confidence level.

Rutin determination in pharmaceutical formulations using a carbon paste electrode modified with poly(vinylpyrrolidone).

A carbon paste electrode modified with poly(vinylpyrrolidone) (PVP) was developed for the determination of rutin. PVP enhances the adsorption of rutin on the electrode surface due to the presence of hydrogen bonding between the imide group in PVP and the hydroxyl group in rutin. The current responses in cyclic and linear sweep voltammetric experiments were investigated and an oxidation peak was observed at +0.87 V vs. Ag/AgCl. Several parameters were investigated to evaluate the performance of the modified electrode. The best analytical response was obtained employing (75:15:10%, w/w/w) graphite powder:Nujol:PVP, with an accumulation time of 10 min, scan rate of 100 mV s(-1) and 0.1M phosphate buffer solution (pH 6.0) as supporting electrolyte. The analytical curve was linear for rutin concentrations of 3.9 x 10(-7) to 1.3 x 10(-5)M (r=0.9991) and the detection limit was 1.5 x 10(-7)M. The recovery of rutin from pharmaceutical samples ranged from 98.3 to 101.7% and the relative standard deviation was 3.3% for a solution containing 7.7 x 10(-6)M rutin (n=5). This electrode was successfully applied to the determination of rutin in pharmaceutical formulations. The results obtained using the proposed modified carbon paste electrode and those obtained by the standard method are in agreement at the 95% confidence level.