RESUMO
Owing to the rise in multidrug-resistant bacterial diseases and the dwindling supply of newer antibiotics, it is crucial to discover newer compounds or modify current compounds for more effective antimicrobial therapies. According to reports, more than 80% of bacterial infections have been linked to bacterial biofilms. In addition to having antimicrobial properties, the hydrophobic polyphenol curcumin (Cur) also inhibits quorum sensing. The application of curcumin was constrained by its weak aqueous solubility and quick degradation. Over the past years, nanotechnology-based biomaterials with multi-functional characteristics have been engineered with high interest. The present study focused on the development of nano-biomaterials with excellent testifiers for bacterial infection in vitro. In this study, water dispersibility and stability of curcumin were improved through conjugation with gold nanoparticles. The successful synthesis of curcumin-conjugated gold nanoparticles (Cur-AuNPs) was confirmed using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and UV-vis absorbance spectroscopy. Transmission electron microscopy (TEM) revealed an average particle size of about 10-13 nm. The antibacterial characteristics in terms of the minimum inhibitory concentration (MIC) of Cur-AuNP treatments were found to be lowest than those with AuNPs and Cur treatments. The quantitative analysis revealed the superior antibacterial characteristics of Cur-AuNP-treated bacterial cells compared to the untreated samples. In addition, curcumin-conjugated AuNPs, produced more reactive oxygen species and increased the membrane permeability. Besides, the biocompatibility of Cur-AuNPs was also assessed quantitatively and qualitatively. Statistical analyses revealed the augmented MG-63 cell proliferation in Cur-AuNPs compared to those with Cur and AuNPs treatments. Overall, Cur-AuNPs exhibited enhanced antibacterial, and antibiofilm characteristics and cytocompatibility.
Assuntos
Curcumina , Nanopartículas Metálicas , Ouro/química , Curcumina/farmacologia , Curcumina/química , Nanopartículas Metálicas/química , Antibacterianos/farmacologia , Antibacterianos/química , ÁguaRESUMO
The synthesis of gold nanoparticles (AuNPs) having better dispersibility and catalytic ability than the conventional AuNPs is the challenging task. The fact that aldehydes and ketones results in the formation of catalytic hybrid material with amino functionalized silanes directed the use of carbonyl functional group (aldehydes and ketones) specifically formaldehyde, acetaldehyde, acetone and t-butyl methyl ketone alongwith 3-aminopropyltrimethoxysilane (3-APTMS) to meet such requirement. Accordingly, a comparative study on the synthesis of 3-APTMS and organic reducing agent mediated synthesis of AuNPs are reported herein. The findings reveal that 3-APTMS capped gold ions are converted into AuNPs with precise control of pH- and salt- sensitivity. The major findings reveal the following: (1) 3-APTMS being amphiphilic, dispersibility of as prepared AuNPs largely depends on the organic reducing agents. (2) An increase in the hydrocarbon content of the reducing agent facilitate the dispersibility of AuNPs in organic solvent whereas decrease of the same increases the dispersibility in water, (3) AuNPs made through aldehydic reducing agents (formaldehyde and acetaldehyde) have relatively better salt and pH tolerance as compared to ketonic reducing agents (acetone, t-butyl methyl ketone), and (4) an increase in 3-APTMS concentrations imparts better salt- and pH- resistant property to AuNPs irrespective of organic reducing agents. A typical example on the role of AuNPs in homogeneous catalysis during potassium ferricyanide mediated oxidation of ascorbic acid is also reported.
Assuntos
Aldeídos/química , Ouro/química , Cetonas/química , Nanopartículas Metálicas/química , Nanotecnologia/métodos , Propilaminas/química , Sais/química , Silanos/química , Eletroquímica , Ferricianetos/química , Concentração de Íons de Hidrogênio , Substâncias Redutoras/químicaRESUMO
The effect of carboxylic acid functionality present in polymer backbone is reported on electrochemical sensing of dopamine (DA). The electropolymerized conducting polymers made from carboxylic acid substituted indole at positions -5 and -6 are found processable in aqueous medium and are compatible with suitable additives/precursors for fabricating polymer modified electrodes (PMEs). The modified electrodes are fabricated following two methods, i.e.: (1) the processable polymers are cast over glassy carbon electrode (GCE) using Nafion® followed by chemical modification using hydrophobic organic redox mediators and (2) the processable polymers are encapsulated within organically modified silicate (Ormosil) matrix along with the hydrophilic redox mediator followed by incorporation of silver and gold nanoparticles. The electrochemical performances of these modified electrodes show selective sensing of DA with major findings: (i) both polymers introduced selectivity in electrochemical sensing of DA with analogous sensitivity, (ii) sensitivity is enhanced when hydrophobic organic redox mediators are coupled with modified electrode matrix involving Nafion®, (iii) the polymers are suitable for encapsulation within ormosil matrix thus introducing nanostructured network for further improvement in sensitivity of DA analysis, (iv) the presence of gold and silver nanoparticles within ormosil matrix along with polymers caused >100 fold increase in sensitivity of DA sensing with lowest detection limit to the order of 100 nM.
Assuntos
Dopamina/análise , Eletroquímica/métodos , Eletrodos , Indóis/química , Eletroquímica/instrumentação , Polímeros de Fluorcarboneto/química , Limite de Detecção , Nanopartículas Metálicas/química , Nanoestruturas , Polímeros/química , Sensibilidade e Especificidade , Siloxanas/químicaRESUMO
Purple membrane (PM) has been extracted and purified from archaebacteria for thin film development. The purified purple membrane is isolated in 1 % polyvinyl alcohol solution for making thin film within gelatin and organically modified silicate matrices. For thin film within gelatin matrix, homogenized purple membrane suspension is mixed with 8 % gelatin and poured into a specially designed block with desired thickness of spacer having hydrophobicity followed by gelatinization of the same over home-made thermostatic control unit at 38 °C. The gelatinized matrix is then allowed to dry under controlled conditions of humidity and temperature. The films of varying thicknesses ranging between 40, 50, and 60 µ are used for photo-electrochemical measurements. The results on photo-electrochemistry of non-oriented purple membrane film provides valuable information on the generation of forward (light on) and backward (light off) photocurrent as a function of: (a) applied potential and (b) film thickness. An increase in applied negative potential increases the amplitude of photocurrent whereas decrease in film thickness facilitates the reversibility of photocurrent response.
Assuntos
Fracionamento Celular/métodos , Eletroquímica/métodos , Processos Fotoquímicos , Membrana Purpúrea/química , Bacteriorodopsinas/química , Cor , Halobacterium salinarum/citologia , Proteínas Imobilizadas/química , Fenômenos Ópticos , Álcool de Polivinil/química , Dióxido de Silício/química , Espectrofotometria , Suspensões , Compostos de Estanho/químicaRESUMO
The aim of this article is to provide insight on the use of a biological molecule--bacteriorhodopsin (bR) having all the basic properties necessary for the assembly of nanoscale electronic devices. Recent developments made during last decade supported by key references are reviewed in this contribution. Major emphasis on bR-based observations conducted in our laboratory has been elaborated. Important issues concerning structure, widely accepted photocycle of bR has been summarized. The possibility of nano-devices emanating from this biomolecule is briefly presented.
RESUMO
We report herein the preparation of few chemically sensitized organically modified sol-gel glass (ormosil) films and sensing of dopamine at the surface of the modified electrodes derived from these films. The chemical sensitization in ormosil-modified electrodes is introduced by incorporating: (a) potassium ferricyanide and (b) either Nafion, or dibenzo-18-crown-6 or in situ generated Prussian blue from potassium ferricyanide. Electrochemical sensing of dopamine on the surfaces of these modified electrodes have been investigated and found that: (i) the presence of dibenzo-18-crown-6 facilitate the magnitude of dopamine sensing, (ii) conversion of potassium ferricyanide into Prussian blue also enhances the magnitude of dopamine sensing as compared to that of control and Nafion sensitized modified electrodes, (iii) both dibenzo-18-crown-6 and Nafion sensitized ormosil-modified electrodes are found selective to dopamine in the presence of ascorbic acid present under physiological concentration range. These finding again directed our attention to investigate the sensing of dopamine: (a) on dibenzo-18-crown-6 incorporated within Prussian blue sensitized modified electrode and (b) in the presence of varying concentrations of dibenzo-18-crown-6 in the Prussian blue modified electrodes. The investigations made on these lines again suggested the following: (1) increase in dibenzo-18-crown-6 concentrations in the modified electrode increases the magnitude of dopamine sensing upto an optimum concentration of macrocycle; (2) the detection limit of dopamine sensing goes down to 30nM as compared to that of dibenzo-18-crown-6 incorporated with potassium ferricyanide which was found to the order of 100nM. Investigations of the interference of ascorbic acid revealed that the presence of dibenzo-18-crown-6 introduces selectivity in dopamine sensing in the presence such common interfering analyte like ascorbic acid.
RESUMO
We report herein the effect of palladium on the redox electrochemistry of ferrocene monocarboxylic acid encapsulated within an organically modified sol-gel glass network (ORMOSIL). It has been found that amount of palladium and its geometrical distribution significantly alter the redox electrochemistry of FcMCA. The geometrical distribution of palladium has been controlled by two methods: (i) palladium is allowed to link within nanostructured network of the ORMOSIL which was subsequently availed from the reactivity of palladium chloride and trimethoxysilane; (ii) palladium powder is encapsulated together FcMCA thus allowing the presence of palladium within the nanoporous domain. The content of palladium is varied by controlling the reaction dynamics of palladium chloride and trimethoxysilane interaction. For this we initially allowed to trigger hydrolysis, condensation and poly-condensation of trimethoxysilane and dimethyldiethoxysilane in acidic medium and subsequently partially dried ORMOSIL film was allowed to interact with palladium chloride. Even with partially dried ORMOSIL derived from trimethoxysilane and dimethyldiethoxysilane undergoes rapid interaction with palladium chloride and the transparent color of ORMOSIL changed to a black colour due to the formation of palladium silicon linkage. The palladium-silicon linkage has been identified by NMR, UV-VIS and transmission electron spectroscopy. The electrochemistry of FcMCA encapsulated within such an ORMOSIL matrix has been studied. Excellent redox electrochemistry of ferrocene monocarboxylic acid having peak potential separation tending to 0 for a multilayered electrode was investigated. The palladium content has been found to affect the redox electrochemistry of ferrocene as well as electrocatalytic efficiency of new ORMOSIL material. The electroanalysis of NADH is reported. The modified electrode is very sensitive to NADH with lowest detection limit of < 1 microM.
Assuntos
Eletroquímica/métodos , Compostos Ferrosos/química , Paládio/química , Siloxanas/química , Ácidos Carboxílicos , Eletrodos , Metalocenos , NAD , OxirreduçãoRESUMO
The electrochemical performance of a new glucose biosensor is reported. The glucose biosensor is developed using glucose oxidase (GOD) and ferrocene encapsulated palladium (Pd)-linked organically modified sol-gel glass (ORMOSIL) material incorporated within graphite paste electrode. The ORMOSIL material incorporated within graphite paste electrode behaves as an excellent electrocatalyst for the oxidation of enzymatically reduced GOD. The electrochemical behavior of new glucose biosensor has been examined by cyclic volammetry and amperometric measurements. The bioelectrocatalysis of ORMOSIL embedded within graphite paste as a function of storage time and varying concentration of ORMOSIL is reported. The initial amperometric response on glucose sensing is recorded to be 145 microA at 15% (w/w) concentration of the ORMOSIL which is decreased to 20 microA at 5% of the same keeping GOD concentration constant. The variation of electrochemical behavior of the ORMOSIL embedded within graphite paste as a function of time has also been studied based on cyclic voltammetry. The voltammograms showing the reversible electrochemistry of ORMOSIL encapsulated ferrocene is changed into a plateau shape as a function of time, however, the electrocatalytic behavior is still retained. The practical usability of new glucose sensor has been compared with earlier developed glucose sensor. The sensitivity, response time and linearity of the new glucose biosensor are found to be excellent over earlier reported glucose biosensor. The amperometric response, calibration curve and practical applications of new glucose sensor are reported.
Assuntos
Compostos Ferrosos , Glucose Oxidase/metabolismo , Glucose/análise , Grafite , Técnicas Biossensoriais , Eletrodos , Vidro , Metalocenos , PaládioRESUMO
We report a novel method for screening and quantifying tubulin-binding antimitotic agents that promote microtubule formation. The method is based on the shift in the peak of the fluorescence emission difference spectrum of tubulin complexed to metal free tetrakis(4-carboxyphenyl)porphyrin (TCPP) in the presence of antimitotic agents. Taxol (paclitaxel), an anti-tumor drug approved for the treatment of a variety of cancers, caused the appearance of a new fluorescence peak at 645 nm at concentrations as low as 125 nM, the intensity of which was a function of the paclitaxel concentration. Cephalomannine caused the induction of a new fluorescence peak at 651 nm only above 1 muM. Baccatin did not induce the appearance of any new peak within detectable operating measurement conditions. These observations are in accordance with the biological activities/cytotoxicities of these compounds. Accordingly, it is proposed that the new method can be used for high throughput screening of antimitotic compounds.
Assuntos
Antineoplásicos Fitogênicos/análise , Bioensaio/métodos , Paclitaxel/análise , Taxoides/análise , Tubulina (Proteína)/metabolismo , Antineoplásicos Fitogênicos/química , Antineoplásicos Fitogênicos/metabolismo , Fluorescência , Estrutura Molecular , Paclitaxel/química , Paclitaxel/metabolismo , Porfirinas/química , Porfirinas/metabolismo , Taxoides/química , Taxoides/metabolismoRESUMO
A novel electrocatalytic ethanol biosensor using ferrocene-encapsulated palladium (Pd)-linked organically modified sol-gel glass (ormosil) is reported. The alkoxy precursors used to prepare the new ormosil-based electrocatalytic biosensor are Pd-linked glycidoxypropyltrimethoxysilane and trimethoxysilane. Pd-glycidoxypropyltrimethoxysilane (black solution) is made by mixing aqueous solutions of palladium chloride and glycidoxypropyltrimethoxysilane. The new ormosil is made using a Pd-linked silane precursor, trimethoxysilane, an aqueous solution of ferrocene monocarboxylic acid, and HCl. Alcohol dehydrogenase (ADH) is assembled over the ferrocene-ormosil layer using polyvinyl alcohol and then protecting the immobilized enzyme layer using Millipore filter membranes (pore size 1 microm). The electrocatalytic response of immobilized ADH, soluble nicotinamide adenine dinucleotide, and Pd-linked ormosil-encapsulated ferrocene is then observed. The electrocatalytic oxidation of NADH and the subsequent ADH-catalyzed formation of NADH are monitored electrochemically. Typical results recorded after the addition of varying concentrations of ethanol are reported; however, the sensor is sensitive to other alcohol and known ADH-sensitive substrates. The stability and reproducibility of the new ethanol biosensor are reported.
Assuntos
Técnicas Biossensoriais , Etanol/análise , Silanos/metabolismo , Álcool Desidrogenase/metabolismo , Calibragem , Composição de Medicamentos , Eletroquímica , Enzimas Imobilizadas/metabolismo , Etanol/metabolismo , Compostos Ferrosos/metabolismo , Metalocenos , Estrutura Molecular , NAD/metabolismo , Paládio , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Silanos/químicaRESUMO
A novel pH sensor suitable for use in both aqueous and non-aqueous mediums is reported. The sensor is derived from polymer modified electrode obtained from electrochemical polymerisation of aniline in dry acetonitrile containing 0.5 M tetraphenyl borate at 2.0 V versus Ag/AgCl. The light yellow colour polymer modified electrode obtained under the present experimental condition has been characterised by scanning electron microscopy (SEM). The pH sensing of polymer modified electrode in both aqueous and non-aqueous mediums is examined and reported. As the typical examples, we used weak acid (acetic acid) and weak base (ammonium hydroxide) as analytes. The acetic acid is analysed in both aqueous and dry acetonitrile whereas ammonium hydroxide is analysed only in aqueous medium. The analysis in aqueous medium is conducted in 1 mM Tris-HCl buffer pH 7.0 and also in 0.1 M KCl. The slope of pH sensing is calculated from the data recorded in typical buffers and found to be approximately 86 mV per pH. The application of polymer modified electrode for the construction of urea biosensor is described based on immobilised urease within poly vinyl alcohol (PVA) matrix and also within organically modified sol-gel glass on the surface of polymer-modified electrode. The new urea sensor has shown maximum response of 160 mV at 25 degrees C with a lowest detection limit of 20 muM. The performance of new pH sensor and urea sensor has been studied and reported in this communication.
RESUMO
Some ruthenium (II) polypyridyl complexes with a bis-chalcone (obtained by the condensation of 3-methyl-thiophene-2-carboxaldehyde and 4-acetyl pyridine) have been synthesized and characterized spectroscopically (IR, NMR, UV/Vis), conductimetric, elemental analysis and FAB mass data. Their luminescent, redox and Li(+) binding properties have been studied. The anti-HIV and antitumour activities have also been reported.
RESUMO
Comparative studies of the electrochemical oxidation of reduced nicotinamide coenzyme (NADH) at the surfaces of chemically modified graphite paste electrodes (CMEs) are reported. Three different electroactive materials, tetracyanoquinodimethane (TCNQ), tetrathiafulvalene (TTF), and dimethyl ferrocene (dmFc), were used to construct three different chemically modified paste electrodes. The oxidation of NADH was examined on the basis of cyclic voltammetric measurements. The results show that all three mediators (TCNQ, TTF, and dmFc) behave as efficient mediators of the oxidation of NADH. The typical response curves of NADH at the CMEs surfaces are reported. Incorporating alcohol dehydrogenase and electroactive materials (TCNQ, TTF, and dmFc) within the graphite paste electrodes has led to the development of ethanol biosensors. Typical response curves for the ethanol analysis are reported. Comparative studies on the mediated electrochemical responses of the biosensors to ethanol are discussed.
Assuntos
Técnicas Biossensoriais , Etanol/análise , NAD , Eletroquímica/instrumentação , Eletroquímica/métodos , Eletrodos , Desenho de Equipamento , Compostos Ferrosos , Compostos Heterocíclicos , Indicadores e Reagentes , Nitrilas , OxirreduçãoRESUMO
This article describes the research investigations on the development of the amperometric biosensors based on mediated bioelectrochemistry. The mediated bioelectrochemistry involving horseradish peroxidase and glucose oxidase within the graphite paste is reported. The enzyme horseradish peroxidase together with electrochemical mediator was incorporated within the graphite paste electrode. The amperometric response is based on the mediated electrochemical regeneration of peroxidase within the paste. The mediated electrochemical regeneration of peroxidase and glucose oxidase was studied and compared using three different electron transfer mediators-tetracyanoquinodimethane (TCNQ), tetrathiafulvalene (TTF), and dimethyl ferrocene (dmFc). The mediated electrochemistry involving these three mediators was studied based on the cyclic voltammetry. The electrochemical measurements show that TTF is better mediator for the development of peroxide biosensor compared to TCNQ and dmFc. On the other hand, TCNQ is better mediator for the development of glucose sensor. The response curves for peroxide have been reported using these three mediators. A comparative study on the amperometric response based on the mediated electrochemical oxidation of peroxidase and glucose oxidase has also been made using these three mediators. The various parameters, i.e., background current, stability of the mediator within the graphite paste during the electrochemical measurements, and reproducibility of the amperometric response, are discussed.
Assuntos
Técnicas Biossensoriais , Eletroquímica/métodos , Enzimas/química , Enzimas/metabolismo , Compostos Ferrosos/química , Glucose Oxidase/química , Glucose Oxidase/metabolismo , Compostos Heterocíclicos/química , Nitrilas/química , Peroxidase/química , Peroxidase/metabolismoRESUMO
A flow-injection analysis (FIA) system coupled with an evanescent wave (EW) biosensor employing total internal reflection of fluorescence radiation (TIRF) for the detection of polyaromatic hydrocarbon that intercalates into DNA is reported. A highly fluorescent intercalator, "ethidium bromide," has been used as the reference compound for detection. The EW biosensor was developed according to the procedure described earlier (1,2). Data on the analysis of Naphthalene, 3-methylcholanthrene, 7,12-dimethylbenz(a)anthracene, 1,2-benzanthracene, and some standard reference materials supplied by the National Institute of Standards and Technology are reported. The relative ability of the polyaromatic hydrocarbon to displace ethidium bromide, based on the relative binding ratio, is found to be on the order of 7,12-dimethylbenz[a]anthracene > 3-methylcholanthrene > 1,2-benzanthracene > napthalene.
Assuntos
9,10-Dimetil-1,2-benzantraceno/análise , Benzo(a)Antracenos/análise , DNA/metabolismo , Análise de Injeção de Fluxo , Metilcolantreno/análise , Naftalenos/análise , 9,10-Dimetil-1,2-benzantraceno/análogos & derivados , 9,10-Dimetil-1,2-benzantraceno/metabolismo , Animais , Técnicas Biossensoriais , Adutos de DNA/metabolismo , Fluorescência , Padrões de ReferênciaRESUMO
An amperometric tetracyanoquinodimethane (TCNQ) mediated biosensor for glucose is described, based on a self-assembling alkanethiol/phospholipid bilayer laid down onto a gold surface. Gold was sputter deposited onto chromium coated silicon wafers to a thickness of 200 nm. A monolayer of alkanethiol was allowed to self-assemble from an ethanolic solution of dodecanethiol onto a freshly cleaned gold electrode in an overnight incubation. The monolayer was characterized by ellipsometric, impedance and cyclic voltammetry measurements (capacitance = 1.60 +/- 0.06 microF/cm2, and thickness 1.34 +/- 0.15 nm). A mixture of phospholipid liposomes containing free amino groups was placed on the monolayer and allowed to incubate overnight. The self-assembly of a phospholipid monolayer and allowed to incubate overnight. The onto the alkanethiol monolayer, resulted in the formation of a bilayer. The formation of bilayer was again characterized by impedance and cyclic voltammetry measurements (capacitance = 0.98 +/- 0.09 microF/cm2, and thickness = 1.85 +/- 0.22 nm). TCNQ has been incorporated into the liposomes before the formation of the bilayer. Glucose oxidase was cross-linked with the amino-groups of the phospholipids using bis [2-(sulphosuccinimiidooxicarbonyloxy) ethyl] sulphone. TCNQ which was incorporated in the bilayer acted as an efficient mediator to regenerate glucose oxidase. Cyclic voltammetry of the modified electrode and a response curve for the glucose sensor are reported.
Assuntos
Técnicas Biossensoriais , Glucose/análise , Bicamadas Lipídicas , Glucose Oxidase , Nitrilas , Fosfolipídeos , Reagentes de SulfidrilaRESUMO
A flow injection analysis sensor for the measurement of glucose/lactate/glutamate is reported. The glucose oxidase/glutamate oxidase/lactate oxidase was immobilized on silanized controlled pore glass particles and packed into a Teflon column (i.d., 1.2 mm; length, 40 mm) to give a bed for glucose/lactate/glutamate. The hydrogen peroxide formed by the enzymatic reaction in the packed bed was monitored by a horseradish peroxidase- and tetracyanoquinodimethane (TCNQ)- modified graphite paste electrode at 50 mV vs Ag/AgCl. The glucose oxidase/lactate oxidase/glutamate oxidase were regenerated in the packed bed, whereas peroxidase was regenerated in the TCNQ-mediated graphite paste electrode by the oxidation of TCNQ. The oxidized TCNQ was electrochemically reduced at 50 mV vs Ag/AgCl. The cathodic current obtained by the reduction of TCNQ determined the concentration of the injected analytes in the packed bed. The system showed very rapid response. Response curves for the analysis of peroxide, glucose, lactate, and glutamate are reported.
Assuntos
Técnicas Biossensoriais , Glucose/análise , Ácido Glutâmico/análise , Peroxidase do Rábano Silvestre/farmacologia , Lactatos/análise , Nitrilas/farmacologia , Eletrodos , Análise de Injeção de Fluxo , Ácido LácticoRESUMO
A flow injection analysis (FIA) sensor for the oxidation of NADH is reported. The system utilizes a graphite paste electrode modified with the electroactive material tetracyanoquinodimethane (TCNQ). TCNQ acts as an efficient mediator for the oxidation of NADH to biologically active NAD+. Alcohol dehydrogenase/lactate dehydrogenase and NAD+ were coimmobilized in TCNQ-modified graphite paste using polyethylenimine to develop a FIA sensor for ethanol/lactate. The system responded rapidly with wide linearity. Response curves for ethanol/lactate and NADH are reported.
Assuntos
Álcool Desidrogenase/metabolismo , Enzimas Imobilizadas/metabolismo , L-Lactato Desidrogenase/metabolismo , NAD/metabolismo , Eletroquímica/métodos , Etanol/análise , Indicadores e Reagentes , Cinética , NAD/análise , Nitrilas , Oxirredução , Marcadores de SpinRESUMO
A flow injection analysis (FIA) system for the detection of the compounds that intercalate within DNA is reported. A derivative of 9,10-anthraquinone has been used as the reference compound for photoelectrochemical detection. The sodium salts of 9,10-anthraquinone-2,6-disulfonic acid and 9,10-anthraquinone-2-sulfonic acid are photochemically activated and then reduced in the presence of an electron donor (glucose). The electrochemical signal is based on the measurement of the anodic current resulting from the oxidation of the reduced form of 9,10-anthraquinone. The reduced form of the 9,10-anthraquinone is oxidized through a mediated mechanism at the surface of a tetracyanoquinodimethane-(TCNQ)-modified graphite paste electrode covered by a Nucleopore membrane. TCNQ acts as an efficient mediator for the oxidation of reduced 9,10-anthraquinone. Cyclic voltammetry, photocyclic voltammetry, and the photoelectrochemical FIA response of 9,10-anthraquinone are reported. Experimental results show that these anthraquinones can be intercalated within the helix of double-stranded calf thymus DNA. The anthraquinone molecules that are intercalated within DNA cannot be oxidized due to their limited transport to the modified electrode surface. This results in a decrease in the anodic current at a constant concentration of anthraquinone after intercalation. There is a linear relation between the decrease in electrochemical response and the DNA concentration at a constant concentration of anthraquinone. The intercalated anthraquinone molecules can be completely replaced by another intercalating agent (i.e., ethidium bromide) that is more strongly intercalated within DNA, thereby regenerating the electrochemical response.(ABSTRACT TRUNCATED AT 250 WORDS)
Assuntos
DNA/análise , Substâncias Intercalantes , Animais , Antraquinonas , Bovinos , Eletroquímica , Análise de Injeção de Fluxo , FotoquímicaRESUMO
A biosensor system using flow injection analysis (FIA) has been developed for the analysis of glucose in human serum. The system consists of the enzyme glucose oxidase incorporated into graphite paste modified with the electroactive material tetracyanoquinodimethane (TCNQ). TCNQ acts as an efficient mediator for oxidation of the reduced enzyme at 200 mV vs Ag/AgCl. The flow injection assay described has detection limits of 2 mM glucose using a 100-microliters sample injection through a 250-microliters sample loop. Data are presented to show the effect of sample injection volume and flow rate on the response of the FIA sensor. The biosensor exhibited excellent reproducibility for 800 injections. The loss of response after 800 injections was due to leaching of TCNQ from the graphite paste. Each assay takes 3 min giving a sample throughput of 20 per hour at a flow rate of 30 ml/h. The sensor was applied to the determination of glucose in human serum. The glucose measurements are in good agreement with those of a commercially available spectrophotometric method. Data showing the effect of interfering substances, ascorbic acid and acetaminophen, on the response of the sensor are also reported.