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This paper reports the development and application of a low-cost multifunctional webcam spectrophotometer for the conduct of molecular absorption and fluorometric measurements. The equipment, which...

In this work, we present a computational investigation on the photoexcitation of indigo carmine (IC). Physical insights regarding IC photoexcitation and photolysis were obtained from a fundamental perspective through quantum chemistry computations. Density functional theory (DFT) was used to investigate the ground state while its time-dependent formalism (TD-DFT) was used for probing excited state properties, such as vertical excitation energies, generalized oscillator strengths (GOS), and structures. All the computations were undertaken using two different approaches: M06-2X/6-311+G(d,p) and CAM-B3LYP/6-311+G(d,p), in water. Results determined using both methods are in systematic agreement. For instance, the first singlet excited state was found at 2.28 eV (with GOS = 0.4730) and 2.19 eV (GOS = 0.4695) at the TD-DFT/CAM-B3LYP/6-311+G(d,p) and TD-DFT/M06-2X/6-311+G(d,p) levels of theory, respectively. Excellent agreement was observed between the computed and the corresponding experimental UV-Vis spectra. Moreover, results suggest IC undergoes photodecomposition through excited state chemical reaction rather than via a direct photolysis path. To the best of our knowledge, this work is the first to tackle the photoexcitation, and its potential connections to photodegradation, of IC from a fundamental chemical perspective, being presented with expectations to motivate further studies.

In this study, we report an electrochemical study based on nanocellulose (NC) and single-walled carbon nanohorns (SWCNH). SWCNH and NC ensure large surface area, good conductivity, high porosity and chemical stability, becoming attractive for electrodes. The materials were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Scanning Electron Micrograph (SEM), Transmission electron microscopy (TEM), dynamic light scattering (DLS) and zeta potential. Using XRD and FTIR it was possible to observe particular characteristics of NC and SWCNH. The presence of dahlia-like assemblies on the NC surface was observed by MEV and TEM. Then, we investigated the electrochemical behavior of NC-SWCNH, which showed the excellent results when it was used guanine and adenine, as proof of concept, by using cyclic and linear sweep voltammetry (LSV). LSV was also employed for simultaneous detection resulting in limits of detection of 1.7 × 10−7 mol L−1 and 1.4 × 10−6 mol L−1, for guanine and adenine, respectively. In addition, the proposed electrode was applied for determination of both bases in synthetic human serum and fish sperm. We demonstrate that it is possible to use NC, a renewable material, in conducting thin films with SWCNH, and due to simplicity in the preparation and high conductivity, this new thin film could be extended for others electrochemical purposes such as sensing and biosensing.

A new architecture for a sensor and a voltammetric procedure were proposed, using a glassy carbon electrode modified with nanodiamonds and dihexadecyl phosphate for determination of codeine (COD) in pharmaceutical and biological fluid samples. Square-wave voltammetry (SWV) was used and the relevant experimental parameters were optimized. Under optimal experimental conditions, the analytical curve presented a linear concentration range from 0.299 to 10.8 μmol L −1 , and a limit of detection of 54.5 nmol L − 1 . The proposed voltammetric method was used for COD determination in commercial pharmaceutical and biological fluid samples such as urine and human serum with satisfactory results.

Abastract Levodopa analysis is important to monitor progress of patients in Parkinson's disease, as well as to determine the treatment directions. In this way, the development of an electrochemical sensor based on a glassy carbon electrode modified with gold nanoparticles supported in activated charcoal with an epichlorohydrin-reticulated chitosan film was carried out under the assistance of a Doehlert matrix design experiment. The resulting electrode was subjected to a series of characterization techniques, including scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, for morphological analysis, as well as electrochemical impedance spectroscopy and cyclic voltammetry for electrochemical characterization. The active surface presented response for electrocatalytic oxidation of levodopa with high current response at reduced potential, which was applied, along with a square-wave adsorptive anodic stripping voltammetric methodology, for analysis of levodopa in different samples, presenting a three order of magnitude linear concentration range (50.0 nmol L−1 to 10.0 µmol L−1), low detection limit of 8.2 nmol L−1, good recovery analysis of spiked samples with low signal deviation under the presence of interfering species, and good accuracy front a comparative methodology.

Melatonin is a hormone that affects sleep-wake cycles and plays a role in the understanding of neuronal disorders and has excellent potential for therapeutical applications in infectious diseases, becoming an important target of chemical analysis. In this context, we report the development of an electrochemical device comprising a self-adhesive electrode based on a graphite-automotive varnish (Gr-AV) mixture as a conductive material to produce a printable ink applied over a paper adhesive easily transferred to a polyethylene terephthalate substrate. The Gr-AV electrode presented a high electrochemically active surface area which showed to be suitable for melatonin oxidation. The association of the device alongside a square-wave voltammetry method offered a linear behavior in the concentration range from 10.0 to 100.0 µmol L−1, a limit of detection of 0.49 µmol L−1, as well as presenting exciting recovery and relative standard deviation over samples analysis. The results showed the valid application of the device for the determination of melatonin in biological samples, pharmaceutical formulations, and its potential for point-of-care analysis.

Bentazon (BTZ) is a post-emergence herbicide widely applied in different cultures. It is characterized by low adsorption and high solubility in water, which facilitates its penetration and contamination of aquatic environments. Human exposure to BTZ is responsible for numerous toxic effects and, therefore, it is of great importance to develop simple and efficient analytical methods capable of accurately detecting the presence of this herbicide in environmental samples. The present paper reports the development and application of a glassy carbon electrode modified with carbon nanosphere-based cross-linked chitosan film for the voltammetric determination of BTZ herbicide. The incorporation of cetyltrimethylammonium bromide surfactant into the supporting electrolyte solution helped enhance the voltammetric signal and the sensor repeatability. The use of chitosan film crosslinked with epicholorohydrin contributed toward improving the properties of the carbon nanospheres, including the electron transfer rate. A set of assays were conducted aiming optimizing the experimental parameters related to the supporting electrolyte composition (pH and surfactant concentration) and the square-wave voltammetry technique. Under optimized conditions and based on the application of the method proposed in the study, a linear concentration range of 1.99 to 65.4 μ mol L−1 was obtained, with limit of detection of 1.4 μ mol L−1 and sensitivity of 6.22 A mol−1 L cm−2. The modified electrode presented good intra- (2.8%, n = 10 ) and inter-day (1.4%, n = 5 ) repeatability and high selectivity for bentazon. The optimized electroanalytical technique was successfully applied for the quantification of bentazon in environmental water samples (recoveries close to 100%).

A novel flow injection spectrophotometric determination of ranitidine in pharmaceuticals is reported. The method is based on a compound formed in a reaction using ranitidine with and potassium permanganate in neutral media, which can be monitored at 430 nm. Under optimal conditions, an analytical curve was constructed, which was linear in the range between 5.0 × 10−5 and 1.0 × 10−3 mol L−1 with a detection limit of 1.0 × 10−5 mol L−1. In addition, the sample throughput was 60 h−1 and the obtained results for commercial formulation samples by applying the proposed method were in good agreement with labeled values and those obtained by a reference method at a 95% confidence level.

A carbon paste electrode (CPE) was modified with graphite oxide (GrO) and β-cyclodextrin (CD) to obtain a sensor for simultaneous voltammetric determination of levodopa (LD), piroxicam (PRX), ofloxacin (OFX) and methocarbamol (MCB). The morphology, structure and electrochemical properties of the functionalized GrO were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, contact angle measurements and cyclic voltammetry. Under the optimal experimental conditions, the sensor is capable of detecting LD, PRX, OFX and MCB by square wave voltammetry (SWV) at working potentials of +0.40, +0.60, +1.03 and + 1.27 V (versus Ag/AgCl), respectively. Response is linear from 1.0 to 20 μM for LD, from 1.0 to 15 μM for PRX, from 1.0 to 20 μM for OFX, and from 1.0 to 50 μM for MCB. The respective limits of detection are 65, 105, 89 and 400 nM. The method was successfully applied to the simultaneous determination of LD, PRX, OFX and MCB in (spiked) real river water and synthetic urine samples, and the results were in agreement with those obtained using a spectrophotometric method, with recoveries close to 100%. Graphical abstract Schematic presentation of a novel electroanalytical method employing a carbon paste electrode modified with graphite oxide and β-cyclodextrin for the simultaneous determination of levodopa, piroxicam, ofloxacin and methocarbamol in urine and river water samples by square wave voltammetry.

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(-5)molL(-1) with a detection limit of 1.7×10(-7)molL(-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.

A glassy carbon electrode (GCE) modified with carbon Printex 6L (Printex6L/GCE) as a novel sensor is proposed. A morphological study was carried out using scanning electron microscopy, and an electrochemical characterization of the proposed electrode was performed by cyclic voltammetry (CV) using [Fe(CN)6]4− as a redox probe. With the incorporation of the carbon Printex 6L film onto the GCE surface, the [Fe(CN)6]4− analytical signal was substantially increased and the difference between the oxidation and reduction potentials (ΔE p) decreased, a characteristic of the electrocatalytic effect. Furthermore, the use of carbon Printex 6L film resulted in an 84 % increase in the oxidation current and a 123 % increase in the reduction current. Faster charge transfer was observed at the proposed electrode/electrolyte interface during CV when compared with GCE. The Printex6L/GCE was tested for ranitidine (RNT) sensing and showed a decrease in the working potential and an increase in the analytical signal, when compared with GCE, again demonstrating an electrocatalytic effect. Under optimized experimental conditions, the developed square-wave adsorptive anodic stripping voltammetry (SWAdASV) method presented an analytical curve that was linear in RNT concentration range from 1.98 × 10−6 to 2.88 × 10−5 mol L−1 with a detection limit of 2.44 × 10−7 mol L−1. The developed Printex6L/GCE was successfully applied to the determination of RNT concentrations in human body fluid samples (urine and serum).

In this study, the performance of a glassy carbon electrode (GCE) modified with functionalized multi-walled carbon nanotubes (MWCNT) immobilized within a poly(allylamine hydrochloride) (PAH) film for the electrochemical determination of the catecholamines, levodopa (LD) and carbidopa (CD) is evaluated. The electrochemical behaviour of the MWCNT-PAH/GCE sensor was investigated via cyclic voltammetry. Under the optimum experimental conditions, the LD and CD analytes were determined by differential pulse voltammetry (DPV) using their oxidation redox processes at −24 mV and +490 mV (versus Ag/AgCl (3.0 mol L−1 KCl)), respectively. The obtained analytical curves were linear from 2.0 to 27 μmol L−1 for LD and from 2.0 to 23 μmol L−1 for CD, with limits of detection of 0.84 μmol L−1 for LD and 0.65 μmol L−1 for CD. The proposed DPV method was successfully employed for LD and CD determination in commercial pharmaceutical formulation samples, and the collected results were consistent with those obtained by the respective standard methods at a confidence level of 95%. In addition, the potentiality of the DPV method was tested for LD and CD quantification in human serum samples.

A new architecture for a biosensor is proposed using a glassy carbon electrode (GCE) modified with hemoglobin (Hb) and silver nanoparticles (AgNPs) encapsulated in poly(amidoamine) dendrimer (PAMAM). The biosensors were characterized using ultraviolet-visible spectroscopy, ζ-potential and cyclic voltammetry to investigate the interactions between Hb, AgNPs and the PAMAM film. The biosensor exhibited a well-defined cathodic peak attributed to reduction of the Fe(3+) present in the heme group in Hb, as revealed by cyclic voltammetry in the presence of O2. An apparent heterogeneous electron transfer rate of 4.1s(-1) was obtained. The Hb-AgNPs-PAMAM/GCE third generation biosensor was applied in the amperometric determination of hydrogen peroxide over the linear range from 6.0 × 10(-6) to 9.1 × 10(-5)mol L(-1) with a detection limit of 4.9 × 1 0(-6)mol L(-1). The proposed method can be extended to immobilize and evaluate the direct electron transfer of other redox enzymes.

An analytical procedure was developed for the simultaneous determination of acetaminophen (ACP) and tramadol (TRA) by flow injection analysis with multiple pulse amperometric detection (FIA–MPA) using a cathodically pretreated boron-doped diamond electrode (BDDE). The proposed method was applied to the simultaneous determination of ACP and TRA in pharmaceutical samples and synthetic biological fluids. The obtained results are in acceptable levels, the proposed method presents low RSD values (

a b s t r a c t A novel electrochemical method for the determination of rosuvastatin calcium (RC) using a compos- ite of vertically aligned carbon nanotubes and graphene oxide (VACNT-GO) as the electrode material is proposed. The VACNT-GO electrode was synthesized using a microwave-assisted chemical vapor deposition method followed by oxygen plasma treatment. The VACNT-GO electrode presented super- hydrophilic behavior and fast charge transfer, which are very attractive for electrochemical applications. The RC molecule presented an oxidation process at +1.26 V vs. Ag/AgCl (3.0 mol L −1 KCl) in phosphate buffer solution (pH 2), and this redox behavior was explored for its voltammetric determination. Using square-wave adsorptive anodic stripping voltammetry (SWAdASV) under optimized conditions, the ana- lytical curve was linear in RC concentration range from 0.48 to 46.72 mol L −1 with a limit of detection of 0.06 mol L−1. The developed SWAdASV method was applied for RC quantification in commercial pharmaceutical samples, and the results are consistent with those obtained by the comparative spec- trophotometric method at a confidence level of 95%. Moreover, RC was determined in human body fluid samples of urine and human serum. © 2015 Elsevier B.V. All rights reserved.

In this work, a simple and highly selective voltammetric method was developed for the simultaneous determination of paracetamol (PCT) and codeine (COD) in pharmaceuticals and human body fluids employing a glassy carbon electrode modified with carbon black (CB) and nickel oxide nanoparticles (NiONPs) within a dihexadecylphosphate (DHP) film. Using square-wave voltammetry (SWV), a separation of ca. 550 mV between the oxidation peak potentials of PCT and COD was obtained. The simultaneous determination of PCT and COD presented a linear concentration range from 3.0 to 47.8 µmol L−1 for PCT and from 0.83 to 38.3 µmol L−1 for COD.

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.

In this work, an alternative voltammetric procedure for the determination of Pb(II) was developed using a carbon nanotube paste electrode modified with crosslinked chitosan with glutaraldehyde (GA-CTS-CNTPE). Square-wave adsorptive stripping voltammetry (SWAdSV) was used and the relevant experimental parameters were optimized. Under optimal experimental conditions, the voltammetric response was linear in the range of 9.90 × 10 − 8 to 2.00 × 10 − 6 mol L − 1 with a detection limit of 5.70 × 10 − 8 mol L − 1 . The proposed voltammetric method showed good repeatability and low interference from other metallic species. It was successfully applied in the determination of Pb(II) in natural water samples and the results were in very close agreement with those obtained using a comparative method (inductively coupled plasma optical emission spectrometry (ICP-OES)).

Vertically aligned carbon nanotubes/graphene oxide nanocomposite (VACNT-GO) has been prepared and applied as electrode material. First, dense packets of VACNT were prepared in microwave chemical vapor deposition reactor, and then functionalized by oxygen plasma etching. We observed that oxygen plasma could exfoliate carbon nanotubes tips and provide oxygen group attachment on its surface, changing its wettability as well. This change in wettability of the VACNT is crucial for its electrochemical application, since as-grown VACNT is super-hydrophobic. After exfoliation and functionalization, the electrochemical tests were performed using potassium ferrocyanide. The cyclic voltammetry (CV) and impedance spectroscopy revealed fast electron transfer kinetics on this new material. The CV peak potential separation was 59 mV, suggesting ideal reversibility at the electrode. The Nyquist and Bode plots were well-fitted as modified Randles equivalent electrical circuits with non-charge transfer impedance. This new highly porous nanostructures have been intensively characterized by scanning electron microscopy, Brunauer–Emmett–Teller surface area, surface wettability, Raman and X-ray photoemission spectroscopy. Our results suggest this new material has a relevant potential for future applications in electrocatalysis and (bio)sensors.

A highly sensitive methodology is proposed utilizing a bismuth film modified electrode (BiFE) for the determination of methotrexate (MTX) based upon differential pulse adsorptive stripping voltammetry. The voltammetric behavior of MTX has been studied using cyclic voltammetry comparing the BiFE fabricated via electrodeposition onto a copper substrate, and as a control, a bare copper substrate electrode has also been compared. Additionally the optimum parameters have been explored using the electrochemical technique differential pulse adsorptive stripping voltammetry (DPAdSV) for the analysis of MTX. Analytical characteristics of the BiFE were explored with calibration curves which are found to be linear for MTX concentrations over the range from 12 nM to 1650 nM with the limit of detection of 0.9 nM. The proposed methodology for sensing MTX in pharmaceutical formulations via this novel approach was found to present a 95% confidence level when compared with high-performance liquid chromatography (HPLC). This work is of importance as it reports a simple analytical methodology that has the potential for field implementation and provides extremely low detection levels and analytical ranges which are analytically useful and is a valuable alternative to replace previously used mercury based electrodes.

In this report, we describe the individual determination of verapamil (VPM) and propranolol (PROP) in pharmaceutical formulations using square-wave adsorptive anodic stripping voltammetry (SWAdASV), differential-pulse adsorptive anodic stripping voltammetry (DPAdASV), and a glassy carbon electrode modified with functionalized multiwalled carbon nanotubes within a poly (allylamine hydrochloride) film. The anodic peak potential for VPM and PROP at this modified electrode was 1.09 V and 0.930 V (versus Ag/AgCl (3.0 mol L −1 KCl)), respectively, in a 0.25 mol L −1 H 2 SO 4 solution. Under optimized SWAdASV and DPAdASV conditions, the obtained analytical curves were linear for VPM concentrations ranging from 5.0 × 10 −9 to 1.1 × 10 −7 mol L −1 , and PROP concentrations ranging from 7.4 × 10 −8 to 1.0 × 10 −6 mol L −1 , with detection limits of 3.6 × 10 −9 mol L −1 and 2.6 × 10 −8 mol L −1 , respectively. Both of the proposed methods were successfully applied for the individual determination of VPM and PROP in several pharmaceutical formulations. The results were in a close agreement with a 95% confidence level for those obtained using official spectrophotometric methods.

A sensor based on glassy carbon electrode (GCE) modified within reduced graphene oxide (RGO) and carbon black (CB) in a chitosan film (CTS) is presented. The combination of the nanomaterials with CTS provided a stable dispersion and could be successfully used as electroactive layer. By using the Nicholson method and the results obtained by cyclic voltammetry with the proposed RGO-CB-CTS/GCE, the heterogeneous electron transfer rate constant ( k 0 ) of 5.6 × 10 − 3 cm s − 1 was obtained. The proposed electrode was applied for the simultaneous determination of dopamine (DA) and paracetamol (PAR). Employing square-wave voltammetry, DA presented an anodic peak at 0.25 V and PAR at 0.50 V vs. Ag/AgCl (3.0 mol L − 1 KCl). The analytical curves obtained were linear in the range from 3.2 × 10 − 6 to 3.2 × 10 − 5 mol L − 1 and from 2.8 × 10 − 6 to 1.9 × 10 − 5 mol L − 1 for DA and PAR, respectively, with detection limits of 2.0 × 10 − 7 for DA and 5.3 × 10 − 8 mol L − 1 for PAR. The developed sensor presented advantages such as simple preparation, low cost of the nanomaterials employed and a fast response. Besides, it could successfully apply in the determination of DA and PAR in biological samples.

New insights into the design of highly sensitive, carbon-based electrochemical sensors are presented in this work by exploring the interesting properties of graphene oxide (GO) and ionic liquids (ILs). An electrochemical sensor based on the carbon paste electrode (CPE) modified with GO and IL was developed for the sensitive detection of ofloxacin using square-wave adsorptive anodic stripping voltammetry (SWAdASV). GO sheets were obtained from the acid treatment of graphene and characterized by scanning and transmission electronic microscopy (SEM and TEM) and selected area electron diffraction (SAED), and the electrochemical behavior of the modified GO-IL/CPE was explored by electrochemical impedance spectroscopy studies. The CPE modification with GO and IL allowed an 8.2 fold increase in the analytical sensitivity for ofloxacin sensing compared to the unmodified CPE. Under the optimized experimental conditions using the SWAdASV technique, the GO-IL/CPE sensor provided an analytical curve for ofloxacin in the concentration range of 7.0×10−9 to 7.0×10−7 mol L−1, with a sensitivity of 7.7×106 μA L mol−1 and limit of detection of 2.8×10−10 mol L−1 (0.28 nmol L−1). The proposed sensor was successfully applied for the ofloxacin determination in human urine and ophthalmic samples, with recoveries near 100%. The results were similar those obtained by a spectrophotometric comparative method.

The modification of a glassy carbon electrode with multi-walled carbon nanotubes and gold nanoparticles within a poly(allylamine hydrochloride) film for the development of a biosensor is proposed. This approach provides an efficient method used to immobilize polyphenol oxidase (PPO) obtained from the crude extract of sweet potato (Ipomoea batatas (L.) Lam.). The principle of the analytical method is based on the inhibitory effect of sulfite on the activity of PPO, in the reduction reaction of o-quinone to catechol and/or the reaction of o-quinone with sulfite. Under the optimum experimental conditions using the differential pulse voltammetry technique, the analytical curve obtained was linear in the concentration of sulfite in the range from 0.5 to 22 μmol L−1 with a detection limit of 0.4 μmol L−1. The biosensor was applied for the determination of sulfite in white and red wine samples with results in close agreement with those results obtained using a reference iodometric method (at a 95% confidence level).

A flow injection spectrophotometric procedure with symmetric merging zones for dipyrone determination in pharmaceutical formulations is proposed. The determination is based on the formation of a blue complex (monitored at a wavelength of 642 nm) yield in the complexation reaction of dipyrone with Fe(III) in acid medium. Under optimum conditions, a calibration curve was obtained from 3.5 to 281 mg L−1 with a detection limit of 2.8 mg L−1 and the samples throughput was 80 h−1. The analytical results obtained for commercial formulation samples by applying the proposed method were in good agreement with labeled values and those obtained by a comparative procedure at a 95% confidence level.

A flow‐injection spectrophotometric procedure was developed for determining N‐acetylcysteine in pharmaceutical formulations. The sample was dissolved in deionized water and 400 µl of the solution was injected into a carrier stream of 1.0×10−2 mol l−1 sodium borate solution. The sample flowed through a column (70 mm length×2.0 mm i.d.) packed with Zn3(PO4)2 immobilized in a polymeric matrix of polyester resin and Zn(II) ions were released from the solid‐phase reactor because of the formation of the Zn(II) (N‐acetylcysteine)2 complex. The mixture merged with a stream of borate buffer solution (pH 9.0) containing 5.0×10−4 mol l−1 Alizarin red S and the Zn(II)Alizarin red complex formed was measured spectrophotometrically at 540 nm. The analytical curve was linear in the N‐acetylcysteine concentration range from 3.0×10−5 to 1.5×10−4 mol l−1 (4.9 to 24.5 µg ml−1) with a detections limit of 8.0×10−6 mol l−1 (1.3 µg ml−1). The relative standard deviations (RSDs) were smaller than 0.5% (n=10) for solutio...

Simple, fast, and inexpensive electroanalytical procedures were developed for the determination of codeine (COD) solely and paracetamol (PCT) and COD simultaneously in pharmaceutical formulations and human body fluids. The methods involve the combination of square-wave voltammetry (SWV) with a cathodically pretreated boron-doped diamond electrode and a 0.2 mol L –1 acetate buffer (pH 4.0) solution as the supporting electrolyte. Significantly low limits of detection were obtained for COD solely or PCT and COD simultaneously: 1.19 or 18 and 14 nmol L –1 , respectively. The proposed SWV method was successfully applied in the simultaneous determination of PCT and COD in four samples of pharmaceutical tablets, with results similar (at 98% confidence level) to those obtained using a reference high-performance liquid chromatography (HPLC) method. Additionally, adequate results were obtained when concentrations of PCT and COD were determined in human urine or serum samples by addition-recovery. Clearly, the proposed method is an excellent option for the determination of COD solely or PCT and COD simultaneously.

A novel vertically aligned carbon nanotube/graphene oxide (VACNT-GO) electrode is proposed, and its ability to determine atorvastatin calcium (ATOR) in pharmaceutical and biological samples by differential pulse adsorptive stripping voltammetry (DPAdSV) is evaluated. VACNT films were prepared on a Ti substrate by a microwave plasma chemical vapour deposition method and then treated with oxygen plasma to produce the VACNT-GO electrode. The oxygen plasma treatment exfoliates the carbon nanotube tips exposing graphene foils and inserting oxygen functional groups, these effects improved the VACNT wettability (super-hydrophobic) which is crucial for its electrochemical application. The electrochemical behaviour of ATOR on the VACNT-GO electrode was studied by cyclic voltammetry, which showed that it underwent an irreversible oxidation process at a potential of +1.08 V in pHcond 2.0 (0.2 mol L(-1) buffer phosphate solution). By applying DPAdSV under optimized experimental conditions the analytical curve was found to be linear in the ATOR concentration range of 90 to 3.81 × 10(3) nmol L(-1) with a limit of detection of 9.4 nmol L(-1). The proposed DPAdSV method was successfully applied in the determination of ATOR in pharmaceutical and biological samples, and the results were in close agreement with those obtained by a comparative spectrophotometric method at a confidence level of 95%.

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.

Voltammetric studies have been carried out using a glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (MWCNTs) and the ionic liquid 1-butyl-3-methylimidazolium chloride (IL). Studies on the electrochemical properties of GCEs modified with MWCNTs and IL within different polymeric films (dihexadecylphosphate (DHP), Nafion, and chitosan (CTS)) were performed using a [Fe(CN)6](4-/3-) electrochemical probe. The modified GCE with different polymeric films was also tested for ciprofibrate (CPF) sensing in the presence and absence of IL in the film. The presence of IL and the MWCNTs improved the electrochemical response for CPF in all cases due to a synergic effect, and the IL-MWCNTs-DHP/GCE showed a great voltammetric profile for CPF detection. The IL-MWCNTs-DHP/GCE and differential pulse voltammetry (DPV) were used for the determination of CPF. An analytical curve was obtained for CPF in the concentration range of 2.50 × 10(-7) to 7.41 × 10(-6) mol L(-1) with a detection limit of 9.20 × 10(-8) mol L(-1). The proposed DPV method was successfully applied for CPF determination in pharmaceutical samples, and the results obtained agree with the results obtained using a spectrophotometric method at a confidence level of 95%.

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.

We report a novel electrode composite comprising zinc phosphate within a multiwalled carbon nanotube paste electrode matrix which is applied for the detection of trace amounts of captopril (CAP) via square-wave adsorptive anodic stripping voltammetry (SWAdASV); to the best of our knowledge this is the first report on such a composite electrode. Under optimum experimental conditions, the peak current of CAP was found to be linear over the concentration range from 3.7 to 67 μmol L−1 with a limit of detection of 0.1 μmol L−1. The proposed method was applied for the successful determination of CAP in commercial tablet excipients and biological samples using the electroanalytical protocol evaluated against the laboratory standard iodometric procedure. Excellent comparability between the two is found suggesting that the former can replace the latter within laboratory settings or can be applied to in-the-field applications.

No trabalho descrito nesta tese foi sintetizado por metodologia sol-gel material misto de alfa hidróxido de níquel com 25 % de chumbo cuja fase foi verificada por difratomeria de raios-X. Esse material foi adaptado para o desenvolvimento de eletrodos modificados de FTO, pasta de carbono e folha de grafite, sendo estes últimos aqueles selecionados para o desenvolvimento das aplicações analíticas. Foi projetada e aprimorada uma cela eletroquímica BIA de 4 mL para eletrodos planos com a tampa adaptada para fixar a posição da ponteira da pipeta, os componentes da cela foram desenhados por modelagem 3D e impressos em polímero ABS em uma impressora do laboratório. O sistema apresentou boa reprodutibilidade (DPR 3,6%) e praticidade de uso, bem como frequência analítica de 120 /h. Os eletrodos de folha de grafite modificados acoplados à BIA foram utilizados para quantificação de levodopa nas condições de um teste de degradação forçada, permitindo o acompanhamento da proporção de degradação do analito com o tempo de exposição às condições estudadas. O sistema desenvolvido foi também utilizado para a quantificação de açúcares (representados por seu componente majoritário, a lactose) em amostras de leite comum e zero lactose obtendo resultados condizentes com as concentrações esperadas para as amostras avaliadas(resultados obtidos na faixa de 10,8 a 12,0 g 200 mL-1, em comparação com os valores de rótulo, entre 9,3 e 14 g 200 mL-1 ). O efeito da porcentagem de chumbo no material foi avaliada para proporções ente 5 e 25 % do metal no hidróxido. Todos os materiais apresentaram tamanho de partícula similares, atestando a reprodutibilidade do método de síntese e os perfis obtidos por difratometria de raios-X foram condizentes com a fase esperada dos materiais (α). Entretanto, a repetição dos difratogramas 10 meses de estocagem após as sínteses sugeriu que os materiais contendo mais de 15 % do metal apresentam mudança parcial de fase com o passar do tempo enquanto as proporções mais baixas se mantêm na fase alfa. Adicionalmente os materiais contendo 5 e 10% de chumbo apresentaram maior distância interplanar (12,0 e 12,6 Å em comparação com 8,9 Å do material de 25 %) e perfil voltamétrico superior ao dos demais materiais, com estabilização mais rápida das correntes de pico. Foi observado que a sensibilidade desses novos materiais à lactose, glicose e galactose é apenas levemente menor do que a obtida para o material contendo 25 % de chumbo, sugerindo vantagens do uso desses materiais para aplicações analíticas. In this work, a mixed alpha nickel hydroxide containing 25 % of lead was syntetized through a sol-gel method; its phase was confirmed by X-ray diffractometry. This material was adapted for the fabrication of modified FTO, carbon paste and graphite foil electrodes, these last were chosen for the development of analytical applications. A 4 mL BIA electrochemical cell for flat electrodes was designed and optimized whose lid was adapted for the fixation of the pipette tip and work electrode distance; the components of the cell were drawn in a 3D modeling software and printed in ABS polymer in one of the laboratorys printers. The system showed good reproducibility (RSD 3.5 %), its use was very practical and it also had a high analytical frequency of 120 /h. The modified graphite foil electrodes coupled with BIA were used for the quantification of L-DOPA, in the conditions of a forced degradation test, permitting the follow up of the proportion of analyte degraded over time as exposed to the studied conditions. The system developed was also used for the quantification of sugars (represented by their main component - lactose) in samples of milk from 2 varieties, common and zero lactose, showing results in accordance to those expected of such samples (found concentrations in the range between 10.8 and 12.0 g 200 mL-1 , in comparison to the range of 9.3 to 14 g 200 mL-1 from label). The effect of the lead percentage was evaluated for materials containing from 5 to 25 % of the metal. All materials showed similar particle size attesting to the reproducibility of the synthesis method and the diffractographic profiles were in accordance with the phase expected for the materials (α). However, the repetition of the X-ray diffractometry after 10 months of storage suggested the materials containing over 15 % of the metal had a partial phase conversion while the materials with lower proportions stayed on the alpha phase. Additionally, the materials containing 5 and 10 % of lead showed larger interlamelar distance (12,0 e 12,6 Å in comparison to 8,9 Å of the material with 25 % Pb) and a superior voltammetric profile compared to the other materials, with faster stabilization of peak currents. The sensitivity of the new materials for lactose, glucose and galactose was only slightly lower than that observed for the material containing 25% of lead, which suggests advantages to the use of these materials for analytical applications.

Os imunossensores eletroquímicos sem marcação baseados em eletrodos de carbono impressos por serigrafia são uma ferramenta promissora para a detecção rápida, simples e econômica de biomarcadores de câncer. Porém, apesar do potencial desses dispositivos, algumas limitações, tal como a sua baixa sensibilidade, precisam ser superadas antes de sua adoção como uma tecnologia para análises clínicas. Nesse sentido, neste trabalho foram propostas diferentes estratégias para modificar eletrodos impressos de carbono, visando melhorar o sinal analítico e a área superficial para a imobilização dos anticorpos, que são duas características essenciais para o ótimo desempenho analítico de imunossensores sem marcação. Planteou-se explorar o potencial de aplicação do carbon black e das nanopartículas de NiFe2O4, dois nanomateriais de baixo custo e excelentes propriedades eletroquímicas que permanecem relativamente inexplorados na construção de imunossensores eletroquímicos. Em uma primeira abordagem, foi desenvolvido um imunossensor para a detecção do antígeno CA 19-9 utilizando-se eletrodos modificados com filmes compósitos de carbon black e dos polieletrólitos polietilenoimina e ácido poliacrílico. O imunossensor apresentou um valor de limite de detecção de 0,07 U mL-1, além de excelente reprodutibilidade de fabricação, estabilidade e seletividade. O dispositivo proposto foi aplicado na determinação de CA 19-9 em amostras de sobrenadante de célula e soro de pacientes com câncer de pâncreas, mostrando boa correlação com imunoensaios comerciais. Na segunda parte deste trabalho, foi fabricado um imunosensor para a detecção da proteína tumoral p53 baseado em eletrodos modificados com filmes de polietilenoimina e nanopartículas de NiFe2O4. O dispositivo apresentou melhores parâmetros analíticos do que a maioria de imunossensores reportados na literatura para a detecção de p53, com um baixo limite de detecção de 5 fg mL-1 . Adicionalmente, o imunossensor apresentou excelente seletividade na detecção de p53 em amostras de soro fetal bovino, saliva e sobrenadante de célula. As plataformas propostas neste trabalho combinaram as inúmeras vantagens dos eletrodos impressos com as excelentes propriedades dos nanomateriais estudados, permitindo o desenvolvimento de testes descartáveis, de baixo custo (

Para o desenvolvimento dos sensores aqui descritos foram utilizados materiais inovadores considerando relatos atuais da literatura, materiais estes: óxido de grafeno, óxido de grafeno reduzido, nanocompósitos de grafeno e nanopartículas (ródio, antimônio e sílica mesoporosa desordenada), materiais híbridos a base de grafeno e quantum dots de CdTe, além de biossensores incorporando a enzima lacase. Estes materiais foram sintetizados utilizando metodologias específicas e caracterizados por diversas técnicas analíticas como microscopia eletrônica de transmissão de alta resolução, microscopia de força atômica, espectroscopia Raman, difração de raios-X, espectroscopias de UV-Vis e fotoluminescência, e técnicas eletroquímicas. Posteriormente, os materiais foram utilizados para modificação em eletrodos de carbono vítreo e utilizados na determinação de interferentes endócrinos (os hormônios estriol e 17β-estradiol) como sensores eletroquímicos em amostras ambientais e clínicas. Em essência, os eletrodos desenvolvidos apresentaram importantes vantagens, tais como alta sensibilidade, boa reprodutibilidade, simples instrumentação, fácil preparação e procedimentos analíticos rápidos, apresentando baixos limites de detecção, na ordem de picomolar e nanomolar, com baixa taxa de interferência de outras espécies na mesma matriz da amostra. Concluindo assim que as técnicas eletroquímicas podem ser facilmente aplicadas na determinação de interferentes endócrinos em amostras reais. For the development of the sensors described here innovators materials were used considering current literature reports, these materials: Graphene oxide, reduced graphene oxide, nanocomposites graphene and nanoparticles (rhodium and antimony), hybrid materials of graphene and CdTe quantum dots, and biosensors incorporating the laccase enzyme. These materials were synthesized using specific methodologies and characterized by several analytical techniques such as transmission electron microscopy, high resolution transmission electron microscopy, atomic force microscopy, Raman spectroscopy, X-ray diffraction, UV-Vis and photoluminescence spectroscopy and electrochemical techniques. Subsequently, the materials were used for modification of glassy carbon electrodes to the determination of endocrine disruptors (estriol and 17β-estradiol hormone) as electrochemical sensors for environmental and clinical samples. In essence, developed electrodes showed important advantages such as high sensitivity, good reproducibility, simple instrumentation, easy preparation and quick analytical procedures, with low detection limits in the range of picomolar and nanomolar, low interference rate of other species in same matrix sample. Finally, electrochemical techniques can be easily applied in the determination of endocrine disruptors in real samples.