Dihexadecylphosphate Film Research Articles

Antidiabetic Drug Metformin Oxidation and in situ Interaction with dsDNA Using a dsDNA‐electrochemical Biosensor

AbstractThe antidiabetic drug metformin (MET) is one of a group of emerging pharmaceutical drug contaminants in the wastewater treatment plants. The electrochemical behaviour of MET−Cu(II) complex by differential pulse and square wave voltammetry, in a wide pH range, at a glassy carbon electrode modified with a carbon black dihexadecylphosphate film (CB−DHP/GCE), was investigated. The MET−Cu(II) complex oxidation showed one pH‐dependent process, which leads to the formation of an oxidation product, being oxidized at a lower potential. The electroanalytical MET−Cu(II) complex detection limit, LOD=0.63 μM, and quantification limit, LOQ=2.09 μM, were obtained, and the MET−Cu(II) complex determination in wastewater samples collected from a senior residence effluent, using the CB−DHP/GCE, was achieved. Considering MET toxicity, the electrochemical evaluation of MET−dsDNA interaction, in incubated solutions and using dsDNA‐electrochemical biosensors, following the changes in the oxidation peaks of guanosine and adenosine residues electrochemical currents, was also investigated. The MET−dsDNA interaction mechanism, for shorter times, occurs by the binding of MET molecules in the minor grooves of the dsDNA, and for long times, the stabilization of the MET−dsDNA complex, causing a local distortion and/or unwinding of dsDNA morphology, is described. However, MET did not promote DNA oxidative damage.

A novel disposable self-adhesive inked paper device for electrochemical sensing of dopamine and serotonin neurotransmitters and biosensing of glucose

In this work, we detail the progress of a novel electrochemical disposable device, which has a relatively low cost and easy production, with a novel conductive ink, that consists of graphite and automotive varnish mixture, deposited over a self-adhesive paper, granting an easy production with relatively low cost. The electrode surface was characterized by scanning electron microscopy, X-ray powder diffraction and Fourier transforms infrared and Raman, cyclic voltammetry and electrochemical impedance spectroscopies. In addition, the proposed electrode was applied for individual electrochemical determination of dopamine and serotonin. The device achieved a linear response between 30 and 800 μmol L−1 and a limit of detection (LOD) of 0.13 μmol L−1, by square wave voltammetry for dopamine and a linear range from 6.0 to 100 μmol L−1, with a LOD of 0.39 μmol L−1, by differential pulse voltammetry for serotonin. Later, the working electrode was modified with glucose oxidase and dihexadecyl phosphate film in order to obtain a biosensor. At this stage, CV was applied to detect glucose in the range of 1.0–10 μmol L−1 and LOD of 0.21 μmol L−1. By three different techniques and analytes, the sensoring and biosensoring processes presented high reproducibility. The proposed adhesive electrode is easy to prepare, disposable, within non-restrictive nature, which allows an approach of a new device for electrochemical sensing and biosensing.

Effect of carbon black functionalization on the analytical performance of a tyrosinase biosensor based on glassy carbon electrode modified with dihexadecylphosphate film

Carbon Black (CB) has acquired a prominent position as a carbon nanomaterial for the development of electrochemical sensors and biosensors due to its low price and extraordinary electrochemical and physical properties. These properties are highly dependent on the surface chemistry and thus, the effect of functionalization has been widely studied for different applications. Meanwhile, the influence of CB functionalization over its properties for electroanalytical applications is still being poorly explored. In this study, we describe the use of chemically functionalized CB Vulcan XC 72R for the development of sensitive electrochemical biosensors. The chemical pre-treatment increased the material wettability by raising the concentration of surface oxygenated functional groups verified from elemental analysis and FTIR measurements. In addition, it was observed an enhancement of almost 100-fold on the electron transfer rate constant (k0) related to unfunctionalized CB, confirming a remarkable improvement of the electrocatalytic properties. Finally, we constructed a Tyrosinase (Tyr) biosensor based on functionalized CB and dihexadecylphosphate (DHP) for the determination of catechol in water samples. The resulting device displayed an excellent stability with a limit of detection of 8.7 × 10−8 mol L−1 and a sensitivity of 539 mA mol−1 L. Our results demonstrate that functionalized CB provides an excellent platform for biosensors development.

Amperometric determination of ascorbic acid with a glassy carbon electrode modified with TiO2-gold nanoparticles integrated into carbon nanotubes

A glassy carbon electrode wasmodified with a TiO2-gold nanoparticle hybrid integrated with multi-walled carbon nanotubes in a dihexadecylphosphate film (TiO2-Au NP-MWCNT-DHP/GCE) and applied to amperometric determination of ascorbic acid (AA). The modified sensor displays fast charge transfer and shows an irreversible anodic behavior for AA by cyclic voltammetry. Under optimal experimental conditions and using amperometry at 0.4V, the analytical curve presented a statistical linear concentration range for AA from 5.0 to 51μmolL-1, with a limit of detection of 1.2μmolL-1. The electrode was successfully applied to the determination of AA in pharmaceutical and fruit juice without the need for major pretreatment of samples. Graphical abstract Schematicof a new sensing platform for ascorbic acid (AA). It is based on a glassy carbon electrode (GCE) modified with TiO2-Au nanoparticles integrated into carbon nanotubes in a dihexadecylphosphate film. The sensorwas applied to amperometric determination of AA in juice and pharmaceutical samples.

Carbon black supported Au–Pd core-shell nanoparticles within a dihexadecylphosphate film for the development of hydrazine electrochemical sensor

An amperometric method for the determination of hydrazine (HDZ) using a glassy carbon (GC) electrode modified with carbon black supported Au–Pd core–shell structured nanoparticles (Au@Pd/CB) within dihexadecylphosphate (DHP) film (Au@Pd/CB-DHP/GCE) is proposed. Au@Pd nanoparticles were synthesized by chemical reduction of AuCl3 and PdCl2 using ethylene glycol as a reducing agent, and the nanoparticles supported on CB were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction techniques. The proposed Au@Pd/CB-DHP/GCE and CB-DHP/GCE (without Au@Pd) electrodes were used to investigate the electrochemical behavior of HDZ using cyclic voltammetry. When the Au@Pd/CB-DHP/GCE was used, an electrocatalytic effect was observed, the analytical signal was substantially increased (87%) and the oxidation potential decreased, i.e. in 728mV. Additionally, the apparently heterogeneous electron-transfer rate constant (k0) obtained for the Au@Pd/CB-DHP/GCE (0.15cms−1) was about two orders of magnitude greater than that obtained using the CB-DHP/GCE (0.068cms−1). Under the optimized conditions for the amperometric technique, a linear analytical curve for HDZ was obtained in the range of 2.50–88.0μmolL−1, with a limit of detection of 0.23μmolL−1 (0.0074ppm). The proposed method was satisfactorily applied to determine the concentration of HDZ in natural lake and tap water samples.

A new and simple method for the simultaneous determination of amoxicillin and nimesulide using carbon black within a dihexadecylphosphate film as electrochemical sensor

The first electroanalytical method for the simultaneous determination of an important antibiotic (amoxicillin – AMX) and an anti-inflammatory drug (nimesulide –NIM), widely used in combination, is here proposed. In this method, a glassy carbon (GC) substrate modified with carbon black (CB) immobilized within a dihexadecylphosphate (DHP) film is used as electrochemical sensor (CB–DHP/GC). The electrochemical activity of this sensor was assessed (comparatively to that of GC) by electrochemical impedance spectroscopy, using the [Fe(CN)6]3–/4– redox couple, when two different active electron transfer regions were clearly characterized. Using square-wave voltammetry and a 0.2molL−1 phosphate buffer (pH 7.0) as supporting electrolyte, a separation of ca. 180mV between the oxidation peak potentials of AMX and NIM was obtained with the novel CB–DHP/GC sensor, and the obtained detection limits for AMX and NIM were 0.12μmolL−1 and 0.016μmolL−1, respectively. This new electroanalytical method was successfully applied in the simultaneous determination of AMX and NIM in biological urine and environmental samples. The here-proposed method is of great analytical interest, as it is faster and cheaper than the only other method (based on HPLC) reported in the literature for the simultaneous determination of these drugs.

A biosensor based on gold nanoparticles, dihexadecylphosphate, and tyrosinase for the determination of catechol in natural water

In this work, a biosensor using a glassy carbon electrode modified with gold nanoparticles (AuNPs) and tyrosinase (Tyr) within a dihexadecylphosphate film is proposed. Cystamine and glutaraldehyde crosslinking agents were used as a support for Tyr immobilization. The proposed biosensor was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and cyclic voltammetry in the presence of catechol. The determination of catechol was carried out by amperometry and presented a linear concentration range from 2.5×10−6 to 9.5×10−5molL−1 with a detection limit of 1.7×10−7molL−1. The developed biosensor showed good repeatability and stability. Moreover, this novel amperometric method was successfully applied in the determination of catechol in natural water samples. The results were in agreement with a 95% confidence level for those obtained using the official spectrophotometric method.

Square-Wave Voltammetric Determination of Nanomolar Levels of Linuron in Environmental Water Samples Using a Glassy Carbon Electrode Modified with Platinum Nanoparticles within a Dihexadecyl Phosphate Film

A new sensitive method for linuron determination using a glassy carbon electrode modified with platinum nanoparticles within a dihexadecyl phosphate film (PtNPs-DHP/GCE) and square-wave voltammetry was proposed. The PtNPs-DHP/GCE was characterised by scanning electron microscopy and the diameter of the Pt nanoparticles was between 13 and 34 nm. The electrochemical behaviour of linuron was studied using cyclic voltammetry and an irreversible anodic peak was obtained at a potential of 1.2 V in 0.1 mol L–1 phosphate buffer (pH 3.0) solution. The analytical curve, obtained by square-wave voltammetry after accumulation, was linear in the linuron concentration range from 1.0 to 74.0 nmol L–1, with a detection limit of 0.61 nmol L–1. This sensitive analytical method was successfully applied for linuron determination in environmental water samples with results that showed good agreement with those obtained using a comparative HPLC method.

Simultaneous voltammetric determination of dopamine and epinephrine in human body fluid samples using a glassy carbon electrode modified with nickel oxide nanoparticles and carbon nanotubes within a dihexadecylphosphate film.

A simple and highly selective electrochemical method was developed for the single or simultaneous determination of dopamine (DA) and epinephrine (EP) in human body fluids using a glassy carbon electrode modified with nickel oxide nanoparticles and carbon nanotubes within a dihexadecylphosphate film using square-wave voltammetry (SWV) or differential-pulse voltammetry (DPV). Using DPV with the proposed electrode, a separation of ca. 360 mV between the peak reduction potentials of DA and EP present in binary mixtures was obtained. The analytical curves for the simultaneous determination of dopamine and epinephrine showed an excellent linear response, ranging from 7.0 × 10(-8) to 4.8 × 10(-6) and 3.0 × 10(-7) to 9.5 × 10(-6) mol L(-1) for DA and EP, respectively. The detection limits for the simultaneous determination of DA and EP were 5.0 × 10(-8) mol L(-1) and 8.2 × 10(-8) mol L(-1), respectively. The proposed method was successfully applied in the simultaneous determination of these analytes in human body fluid samples of cerebrospinal fluid, human serum and lung fluid.

Electrochemical determination of estradiol using a thin film containing reduced graphene oxide and dihexadecylphosphate

Graphene is a material that has attracted attention with regard to sensing and biosensing applications in recent years. Here, we report a novel treatment (using ultrasonic bath and ultrasonic tip) to obtain graphene oxide (GO) and a new stable conducting film using reduced graphene oxide (RGO) and dihexadecylphosphate film (DHP). The GO was obtained by chemical exfoliation and it was reduced using NaBH4. Subsequently, RGO–DHP dispersion was prepared and it was dropped onto a glassy carbon electrode by casting technique. The electrode was characterized by cyclic voltammetry and electrochemical spectroscopy impedance. The voltammetric behavior of the RGO–DHP/GC electrode in the presence of estradiol was studied, and the results reported an irreversible oxidation peak current at 0.6V. Under the optimal experimental conditions, using linear sweep adsorptive stripping voltammetry, the detection limit obtained for this hormone was 7.7×10−8molL−1. The proposed electrode can be attractive for applications as electrochemical sensors and biosensors.

Tyrosinase biosensor based on a glassy carbon electrode modified with multi-walled carbon nanotubes and 1-butyl-3-methylimidazolium chloride within a dihexadecylphosphate film

A glassy carbon electrode modified with functionalized multi-walled carbon nanotubes (MWCNT), 1-butyl-3-methylimidazolium chloride (ionic liquid=IL) and tyrosinase (Tyr) within a dihexadecylphosphate (DHP) film for the development of a biosensor is proposed. MWCNT, IL and Tyr were efficiently immobilized in the film using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS) as crosslinking agents, and which was characterized by cyclic voltammetry (CV) in the presence of catechol. The IL-MWCNT nanocomposite showed good conductivity and biocompatibility with Tyr enzyme, since the biosensor presented biocatalytic activity toward the oxidation of catechol to o-quinone which was electrochemically reduced to catechol at a potential of 0.04V. The analytical curve ranged from 4.9×10−6 to 1.1×10−3molL−1 with a detection limit of 5.8×10−7molL−1. The developed Tyr-IL-MWCNT-DHP/GCE biosensor showed a wide linear range, good reproducibility, sensitivity and stability and the biosensor was successfully applied to the determination of catechol in natural water samples, with satisfactory results compared with a spectrophotometric method, at the 95% confidence level.

Biomimetic synthesis and characterization of cobalt nanoparticles using apoferritin, and investigation of direct electron transfer of Co(NPs)–ferritin at modified glassy carbon electrode to design a novel nanobiosensor

Oxyhydroxy cobalt CoO(OH) nanoparticles (Co-NPs) were prepared in horse spleen apoferritin (HsAFr) cavity. Transmission electron microscopy revealed the particle size was 5.5-6 nm. Mineralization effect on HsAFr was investigated by fluorescence and far-UV circular dichroism (far-UV CD) spectroscopies. The far-UV CD experiments indicated an increase in the α-helical content after mineralization. Intrinsic fluorescence data showed that mineralization acts as a quencher of HsAFr. For the first time, direct electron transfer between Co(NPs)-HsAFr and a glassy carbon electrode in the thin film of dihexadecylphosphate (DHP) was investigated by cyclic voltammetry (CV) to design a biosensor. The anionic surfactant DHP was used to achieve direct electron-transfer between Co(NPs)-HsAFr molecules and the GC electrode surface. CV result showed clearly a pair of well-defined and quasi-reversible redox peaks arise from Co(NPs)-HsAFr embedded in DHP film. This novel biosensor can be used in medical and industrial fields to detect different analytes.

Direct electron transfer of glucose oxidase at glassy carbon electrode modified with functionalized carbon nanotubes within a dihexadecylphosphate film

A glassy carbon electrode modified with functionalized multiwalled carbon nanotubes (CNTs) immobilized by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS) in a dihexadecylphosphate film was prepared and characterized by cyclic voltammetry and scanning electron microscopy. It was used as a support for FAD or glucose oxidase (GOx) immobilization with EDC/NHS crosslinking agents. Cyclic voltammetry of GOx immobilized onto the surface of CNTs showed a pair of well-defined redox peaks, which correspond to the direct electron transfer of GOx, with a formal potential of −0.418 V vs. Ag/AgCl (3 M KCl) in 0.1 M phosphate buffer solution (pH 7.0). An apparent heterogeneous electron transfer rate constant of 1.69 s −1 was obtained. The dependence of half wave potential on pH indicated that the direct electron transfer reaction of GOx involves a two-electron, two-proton transfer. The determination of glucose was carried out by square wave voltammetry and the developed biosensor showed good reproducibility and stability. The proposed method could be easily extended to immobilize and evaluate the direct electron transfer of other redox enzymes or proteins.

Influence of Molecular Structure on the Aggregating Properties of Thiacarbocyanine Dyes Adsorbed to Langmuir Films at the Air−Water Interface

The influence of substituents on the adsorption and aggregation of the anionic 3,3‘-disulfopropyl-5,5‘-dichloro-9-ethylthiacarbocyanine (THIATS) and its cationic analogue 3,3‘-diethyl-5,5‘-dichloro-9-ethylthiacarbocyanine (TDC) was investigated in Langmuir films at the air−water interface. Dioctadecyldimethylammonium bromide (DODAB) and octadecylammonium chloride (ODACl) were used to adsorb THIATS. Arachidic acid (AA) and dihexadecyl phosphate (DHP) were used to adsorb TDC. J-aggregate formation has been observed for the four different combinations of dyes and surfactants. The absorption and emission spectra of THIATS at the air−water interface revealed one narrow intense J-band which was not influenced by the chemical structure of the amphiphiles or by the concentration of THIATS in the subphase. Fluorescence microscopy experiments suggest that, depending on the subphase dye concentration, aggregation of dye molecules leads either to a layer of J-aggregates distributed homogeneously on the scale of a few micrometers or to the observation of individual domains of J-aggregates. For TDC adsorbed to an AA film, the absorption and emission spectra revealed the formation of two J-bands that coexist at the interface. The absorption spectra of TDC adsorbed onto a DHP film showed only one J-band, whose maximum gradually shifted from an initial value of 646 nm to 637 nm and then to 652 nm. The flexible alkyl spacer chain between the localized negative charges of the sulfate groups and the nitrogen atoms of the benzthiazole units allows a packing of the THIATS molecules that is less dependent on the charge distribution in the oppositely charged lipid film than for TDC. Fluorescence micrographs of THIATS/DODAB and TDC/AA films reveal different spatial features. They confirm the predominant influence of the lipid on the TDC/AA film morphology, as concluded from the spectral data. The presented study offers substantial information that was still lacking in this field of research: the time-dependence adsorption of the dyes onto charged monolayers as well as an investigation of the influence of the substitution pattern and the role of the packing of the amphiphiles on the formation of a specific type of aggregate.