Angiotensin II involvement in the development and persistence of amphetamine-induced sensitization: Striatal dopamine reuptake implications.

Amphetamine (AMPH) exposure induces behavioural and neurochemical sensitization observed in rodents as hyperlocomotion and increased dopamine release in response to a subsequent dose. Brain Angiotensin II modulates dopaminergic neurotransmission through its AT1 receptors (AT1-R), positively regulating striatal dopamine synthesis and release. This work aims to evaluate the AT1-R role in the development and maintenance of AMPH-induced sensitization. Also, the AT1-R involvement in striatal dopamine reuptake was analysed. The sensitization protocol consisted of daily AMPH administration for 5 days and tested 21 days after withdrawal. An AT1-R antagonist, candesartan, was administered before or after AMPH exposure to evaluate the participation of AT1-R in the development and maintenance of sensitization, respectively. Sensitization was evaluated by locomotor activity and c-Fos immunostaining. Changes in dopamine reuptake kinetics were evaluated 1 day after AT1-R blockade withdrawal treatment, with or without the addition of AMPH in vitro. The social interaction test was performed as another behavioural output. Repeated AMPH exposure induced behavioural and neurochemical sensitization, which was prevented and reversed by candesartan. The AT1-R blockade increased the dopamine reuptake kinetics. Neither the AMPH administration nor the AT1-R blockade altered the performance of social interaction. Our results highlight the AT1-R's crucial role in AMPH sensitization. The enhancement of dopamine reuptake kinetics induced by the AT1-R blockade might attenuate the neuroadaptive changes that lead to AMPH sensitization and its self-perpetuation. Therefore, AT1-R is a prominent candidate as a target for pharmacological treatment of pathologies related to dopamine imbalance, including drug addiction and schizophrenia.

Two birds with one stone: integrating exfoliation and immunoaffinity properties in multi-walled carbon nanotubes by non-covalent functionalization with human immunoglobulin G.

An innovative strategy is proposed to simultaneously exfoliate multi-walled carbon nanotubes (MWCNTs) and generate MWCNTs with immunoaffinity properties. This strategy was based on the non-covalent functionalization of MWCNTs with human immunoglobulin G (IgG) by sonicating 2.5 mg mL-1 MWCNTs in 2.0 mg mL-1 IgG for 15 min with sonicator bath. Impedimetric experiments performed at glassy carbon electrodes (GCE) modified with the resulting MWCNT-IgG nanohybrid in the presence of anti-human immunoglobulin G antibody (Anti-IgG) demonstrated that the immunoglobulin retains their biorecognition properties even after the treatment during the MWCNT functionalization. We proposed, as proof-of-concept, two model electrochemical sensors, a voltammetric one for uric acid quantification by taking advantages of the exfoliated MWCNTs electroactivity (linear range, 5.0 × 10-7 M - 5.0 × 10-6 M; detection limit, 165 nM) and an impedimetric immunosensor for the detection of Anti-IgG through the use of the bioaffinity properties of the IgG present in the nanohybrid (linear range, 5-50 µg mL-1; detection limit, 2 µg mL-1).

Ultrasensitive multiwall carbon nanotube-mesoporous MCM-41 hybrid-based platform for the electrochemical detection of ascorbic acid.

This work presents for the first time the systematic preparation of a novel carbon nanotube-MCM-41 hybrid employing the mesoporous material MCM-41 as a successful dispersant for multiwall carbon nanotubes (MWCNTs). Relevant dispersion variables such as the amount of MWCNTs, MCM-41 concentration, and sonication time were optimized through a central composite design (CDD)/response surface methodology (RSM). Several solvents were evaluated and N,N-dimethylformamide (DMF) was selected because it allowed reaching stable dispersions with very good electrochemical response. The electrochemical performance of glassy carbon electrodes (GCE) modified with different hybrids was evaluated by cyclic voltammetry (CV) using ascorbic acid (AA) as redox marker, while their surface morphology was characterized by SEM microscopy. The optimal MWCNT-MCM-41 dispersion condition was 0.75 mg mL-1 MWCNTs, 0.25 mg mL-1 MCM-41, and 30 min sonication. Both, electrochemical results and SEM images correlate with a percolation behavior from MWCNT-MCM-41 hybrid. Electrooxidation of AA at GCE modified with the optimal hybrid occurred under diffusion control and exhibited an enhanced current response (65 µA) and a lower overvoltage (-0.005 V) compared to bare GCE (ip = 22 µA, Ep = 0.255 V). The amperometric response of AA at GCE/MWCNT-MCM-41 exhibited remarkable figures of merit, including an ultralow detection limit (1.5 nM), high sensitivity (45.4 × 103 µA M-1), excellent short- and long-term stability, and very good anti-interference ability for AA detection. The analytical applicability of the developed electrochemical sensor was evaluated by sensing AA in several real samples, showing excellent correlation with the values reported by manufacturers in both pharmaceutical and food samples.

Workbench for a Parabolic Trough Solar Collector with a Tracking System.

Solar energy found abundantly in nature is considered a renewable energy source. It is also of great interest as an option for energy generation and CO2 emissions reduction. Several technologies of solar concentrating systems, known internationally as CSP (concentrated solar power), are found in the industrial and scientific environment. One of the most mature and internationally known technologies is the parabolic trough solar collector (PTSC), which has several applications, such as electricity generation, desalination, steam generation, and refrigeration systems, among others. However, more research and development (R&D) has been done to improve its performance, using new materials, absorber tube geometries, solar tracking systems, and work (thermal oils, nanofluids). Thus, the present work describes the development of a low-cost PTSC for academic and research purposes. The PTSC was built with an edge angle of 120°, an opening area of 2.2 m2, and a copper absorber tube of 42 mm in outer diameter without a glass envelope. The gutter structure is composed of wooden sheets cut in a parabolic shape, where a 1.2 mm-thick galvanized steel sheet coated with a reflective film is supported, thus functioning as the reflective surface of the PTSC. The solar tracking system is one of the active types with two axes containing photoresistive sensors, which are used to determine the solar position and electric actuators to correct the positioning of the gutter. The monitoring system was developed through an interactive panel to visualize the operating parameters of the sensing elements, thermocouples that measure the inlet and outlet temperature in the absorber tube, and the flow sensor to measure the flow of the heat transport fluid. Laboratory tests were performed with deionized water as a transport fluid, establishing two testing conditions. The first test condition analyzed the efficiency of the collector at different temperatures. Thus, the inlet temperature varied, between 30 and 70°C, presenting a flow of 0.020 kg/s. The second one evaluated the collector efficiency for different flows, subjecting the collector to flows from 0.002 to 0.030 kg/s. Thus, the proposed collector obtained an efficiency as a function of the temperature represented by the expression η = 0.324-2.47443 c', where c' is a parameter that relates the inlet temperature to the ambient temperature as a function of the solar radiation available. Yet, the efficiency in function of the flow became optimal when the flow regime became turbulent. It was concluded that the proposed solar collector obtained lower efficiency when compared with other collectors in the literature, which was assumed to be due to the diffusion losses of the parabolic trough reflector and thermal losses by convection in the parabolic trough absorber tube (optical efficiency, removal factor, and heat loss coefficient).

Mesoscopic behaviour of multi-layered graphene: the meaning of supercapacitance revisited.

The electronic density of states and its contribution to the capacitance of graphene compounds (oxidized and reduced) were investigated using an electrochemical impedance-derived capacitance spectroscopic approach. It is clearly demonstrated that graphene oxide, which is known to exhibit semiconductor electronic characteristics, has little influence on the magnitude of the measured capacitance. Moreover, when graphene oxide is electrochemically reduced to graphene, the capacitance increases dramatically by about three orders of magnitude (from microfaradays to millifaradays). This increased capacitive effect has been interpreted as being directly associated with the electrochemical non-faradaic (super- or ultracapacitive) characteristics of the interface (i.e. associated with its electroactive area, for instance). The results obtained and interpretation made in this work demonstrate that the magnitude of the measured capacitance is a consequence of an electrochemical capacitive phenomenon (mesoscopic in essence; thus, the associated capacitance is equivalently termed mesoscopic capacitance) that energetically contains, in series, both electrostatic (geometrical) and quantum effects, thus being essentially different from those exclusively related to the amount of existing interfacial sites for ions (i.e. beyond those associated with pure double-layer capacitive effects). Conceptually, it is proposed that the mesoscopic capacitance of reduced graphene can be explained mainly through quantum chemical effects, ultimately following first-principles quantum mechanics supported on density functional theory, wherein the density of states is central.

Development of an electrochemical sensor for the quantification of ascorbic acid and acetaminophen in pharmaceutical samples.

This work presents the modification of glassy carbon electrodes (GCE) by using a dispersion resulting from the non-covalent functionalization of multi-walled carbon nanotubes (MWCNT) with polyarginine (polyArg). MWCNT-polyArg is used for the quantification of ascorbic acid (AA) in the presence of acetaminophen (APAP) and viceversa. Since ascorbic acid and acetaminophen are strongly absorbed on GCE/MWCNT-polyArg, they can be detected in the presence of 4.0×10-5 M acetaminophen (and 3.0×10-5 M ascorbic acid) by using adsorptive stripping with media exchange and differential pulse voltammetry. Using water as the solvent for the MWCNT dispersion, the result was Z-potential of 0.053 ± 0.006 V. The developed sensor showed excellent specificity, sensitivity, stability and reproducibility compared to previously published sensors. The GCE/MWCNT-polyArg sensor shows a fast response time of ∼5 minutes, low limits of detection and quantification for AA (0.95 and 2.9 µM respectively) and APAP (0.27 and 0.82µM, respectively), high sensitivity of 0.0616 µA/M for AA or APAP 0.240µA/M. It was used to test its practicability by determining the concentration of AA or APAP (AA and APAP) in pharmaceutical samples. Finally, the simultaneous measurement of ascorbic acid and acetaminophen in pharmaceuticals showed a good correlation, with a maximum error and RSD of 4.5 and 5.1 %, respectively.

In situ or Ex situ Synthesis for Electrochemical Detection of Hydrogen Peroxide-An Evaluation of Co2SnO4/RGO Nanohybrids.

Nowadays, there is no doubt about the high electrocatalytic efficiency that is obtained when using hybrid materials between carbonaceous nanomaterials and transition metal oxides. However, the method to prepare them may involve differences in the observed analytical responses, making it necessary to evaluate them for each new material. The goal of this work was to obtain for the first time Co2SnO4 (CSO)/RGO nanohybrids via in situ and ex situ methods and to evaluate their performance in the amperometric detection of hydrogen peroxide. The electroanalytical response was evaluated in NaOH pH 12 solution using detection potentials of -0.400 V or 0.300 V for the reduction or oxidation of H2O2. The results show that for CSO there were no differences between the nanohybrids either by oxidation or by reduction, unlike what we previously observed with cobalt titanate hybrids, in which the in situ nanohybrid clearly had the best performance. On the other hand, no influence in the study of interferents and more stable signals were obtained when the reduction mode was used. In conclusion, for detecting hydrogen peroxide, any of the nanohybrids studied, i.e., in situ or ex situ, are suitable to be used, and more efficiency is obtained using the reduction mode.

Impedimetric and amperometric genosensors for the highly sensitive quantification of SARS-CoV-2 nucleic acid using an avidin-functionalized multi-walled carbon nanotubes biocapture platform.

We report two novel genosensors for the quantification of SARS-CoV-2 nucleic acid using glassy carbon electrodes modified with a biocapture nanoplatform made of multi-walled carbon nanotubes (MWCNTs) non-covalently functionalized with avidin (Av) as a support of the biotinylated-DNA probes. One of the genosensors was based on impedimetric transduction offering a non-labelled and non-amplified detection of SARS-CoV-2 nucleic acid through the increment of [Fe(CN)6]3-/4- charge transfer resistance. This biosensor presented an excellent analytical performance, with a linear range of 1.0 × 10-18 M - 1.0 × 10-11 M, a sensitivity of (5.8 ± 0.6) x 102 Ω M-1 (r2 = 0.994), detection and quantification limits of 0.33 aM and 1.0 aM, respectively; and reproducibilities of 5.4% for 1.0 × 10-15 M target using the same MWCNTs-Av-bDNAp nanoplatform, and 6.9% for 1.0 × 10-15 M target using 3 different nanoplatforms. The other genosensor was based on a sandwich hybridization scheme and amperometric transduction using the streptavidin(Strep)-biotinylated horseradish peroxidase (bHRP)/hydrogen peroxide/hydroquinone (HQ) system. This genosensor allowed an extremely sensitive quantification of the SARS-CoV-2 nucleic acid, with a linear range of 1.0 × 10-20 M - 1.0 × 10-17 M, detection limit at zM level, and a reproducibility of 11% for genosensors prepared with the same MWCNTs-Av-bDNAp1 nanoplatform. As a proof-of-concept, and considering the extremely high sensitivity, the genosensor was challenged with highly diluted samples obtained from SARS-CoV-2 RNA PCR amplification.

New trends in the development of electrochemical biosensors for the quantification of microRNAs.

MicroRNAs (miRNAs) are non-coding regulatory RNAs that play an important role in RNA silencing and post-transcriptional gene expression regulation. Since their dysregulation has been associated with Alzheimer disease, cardiovascular diseases and different types of cancer, among others, miRNAs can be used as biomarkers for early diagnosis and prognosis of these diseases. The methods commonly used to quantify miRNAs are, in general, complex, costly, with limited application for point-of-care devices or resource-limited facilities. Electrochemical biosensors, mainly those based on nanomaterials, have emerged as a promising alternative to the conventional miRNA detection methods and have paved the way to the development of sensitive, fast, and low-cost detection systems. This review is focused on the most relevant contributions performed in the field of electrochemical miRNAs biosensors between 2017 and the beginning of 2020. The main contribution of this article is the critical discussion of the different amplification strategies and the comparative analysis between amplified and non-amplified miRNA electrochemical biosensing and between the different amplification schemes. Particular emphasis was given to the importance of the nanostructures, enzymes, labelling molecules, and special sequences of nucleic acids or analogues on the organization of the different bioanalytical platforms, the transduction of the hybridization event and the generation the analytical signal.

Co2TiO4/Reduced Graphene Oxide Nanohybrids for Electrochemical Sensing Applications.

For the first time, the synthesis, characterization, and analytical application for hydrogen peroxide quantification of the hybrid materials of Co2TiO4 (CTO) and reduced graphene oxide (RGO) is reported, using in situ (CTO/RGO) and ex situ (CTO+RGO) preparations. This synthesis for obtaining nanostructured CTO is based on a one-step hydrothermal synthesis, with new precursors and low temperatures. The morphology, structure, and composition of the synthesized materials were examined using scanning electron microscopy, X-ray diffraction (XRD), neutron powder diffraction (NPD), and X-ray photoelectron spectroscopy (XPS). Rietveld refinements using neutron diffraction data were conducted to determine the cation distributions in CTO. Hybrid materials were also characterized by Brunauer-Emmett-Teller adsorption isotherms, Scanning Electron microscopy, and scanning electrochemical microscopy. From an analytical point of view, we evaluated the electrochemical reduction of hydrogen peroxide on glassy carbon electrodes modified with hybrid materials. The analytical detection of hydrogen peroxide using CTO/RGO showed 11 and 5 times greater sensitivity in the detection of hydrogen peroxide compared with that of pristine CTO and RGO, respectively, and a two-fold increase compared with that of the RGO+CTO modified electrode. These results demonstrate that there is a synergistic effect between CTO and RGO that is more significant when the hybrid is synthetized through in situ methodology.

Highly selective determination of dopamine in the presence of ascorbic acid and serotonin at glassy carbon electrodes modified with carbon nanotubes dispersed in polyethylenimine.

We report the highly selective and sensitive voltammetric dopamine quantification in the presence of ascorbic acid and serotonin by using glassy carbon electrodes modified with a dispersion of multi-wall carbon nanotubes (MWCNT) in polyethylenimine, PEI (GCE/MWCNT-PEI). The electrocatalytic activity of the MWCNT deposited on the glassy carbon electrode has allowed an important decrease in the overvoltages for the oxidation of ascorbic acid and dopamine, making possible a clear definition of dopamine, serotonin and ascorbic acid oxidation processes. The sensitivities for dopamine in the presence and absence of 1.0 mM ascorbic acid and serotonin were (2.18 +/- 0.03) x 10(5) microAM(-1) (r = 0.9998); and (2.10 +/- 0.07) x 10(5) miroAM(-1) (r=0.9985), respectively, demonstrating the excellent performance of the GCE/MWCNT-PEI. The detection limit for dopamine in the mixture was 9.2 x 10(-7) M. The R. S. D. for the determination of 50 microM dopamine using four different electrodes was 3.9% when modified with the same MWCNT/PEI dispersion, and 4.6% when using four different dispersions. The modified electrode has been successfully applied for recovery assays of dopamine in human blood serum. Therefore, the new sensor represents an interesting and promising alternative for the electrochemical quantification of neurotransmitters and other analytes of clinical interest.

Label-Free Graphene Oxide-Based Surface Plasmon Resonance Immunosensor for the Quantification of Galectin-3, a Novel Cardiac Biomarker.

We report the first optical biosensor for the novel and important cardiac biomarker, galectin-3 (Gal3), using the anti-Gal3 antibody as a biorecognition element and surface plasmon resonance (SPR) for transducing the bioaffinity event. The immunosensing platform was built at a thiolated Au surface modified by self-assembling four bilayers of poly(diallyldimethylammonium chloride) and graphene oxide (GO), followed by the covalent attachment of 3-aminephenylboronic acid (3ABA). The importance of GO, both as the anchoring point of the antibody and as a field enhancer for improving the biosensor sensitivity, was critically discussed. The advantages of using 3ABA to orientate the anti-Gal3 antibody through the selective link to the Fc region were also demonstrated. The new platform represents an interesting alternative for the label-free biosensing of Gal3 in the whole range of clinically relevant concentrations (linear range between 10.0 and 50.0 ng mL-1, detection limit of 2.0 ng mL-1) with successful application for Gal3 biosensing in enriched human serum samples.

Bioelectrochemical sensing of promethazine with bamboo-type multiwalled carbon nanotubes dispersed in calf-thymus double stranded DNA.

We report the quantification of promethazine (PMZ) using glassy carbon electrodes (GCE) modified with bamboo-like multi-walled carbon nanotubes (bCNT) dispersed in double stranded calf-thymus DNA (dsDNA) (GCE/bCNT-dsDNA). Cyclic voltammetry measurements demonstrated that PMZ presents a thin film-confined redox behavior at GCE/bCNT-dsDNA, opposite to the irreversibly-adsorbed behavior obtained at GCE modified with bCNT dispersed in ethanol (GCE/bCNT). Differential pulse voltammetry-adsorptive stripping with medium exchange experiments performed with GCE/bCNT-dsDNA and GCE modified with bCNTs dispersed in single-stranded calf-thymus DNA (ssDNA) confirmed that the interaction between PMZ and bCNT-dsDNA is mainly hydrophobic. These differences are due to the intercalation of PMZ within the dsDNA that supports the bCNTs, as evidenced from the bathochromic displacement of UV-Vis absorption spectra of PMZ and quantum dynamics calculations at DFTB level. The efficient accumulation of PMZ at GCE/bCNT-dsDNA made possible its sensitive quantification at nanomolar levels (sensitivity: (3.50±0.05)×10(8) µA·cm(-2)·M(-1) and detection limit: 23 nM). The biosensor was successfully used for the determination of PMZ in a pharmaceutical product with excellent correlation.

Supramolecular architecture based on the self-assembling of multiwall carbon nanotubes dispersed in polyhistidine and glucose oxidase: Characterization and analytical applications for glucose biosensing.

We report for the first time the development of a sensitive and selective glucose biosensor based on the self-assembling of multiwall carbon nanotubes (MWCNTs) dispersed in polyhistidine (Polyhis) and glucose oxidase (GOx) on glassy carbon electrodes (GCE). The supramolecular architecture was characterized by SEM, FT-IR and electrochemical techniques. The optimum multistructure was obtained with five (MWCNT-Polyhis/GOx) bilayers and one layer of Nafion as anti-interferent barrier. The sensitivity at 0.700V was (1.94±0.03) mAM(-1) (r=0.9991), with a linear range between 0.25 and 5.00mM, a detection limit of 2.2µM and a quantification limit of 6.7µM with minimum interference from lactose (1.5%), maltose (5.7%), galactose (1.2%), ascorbic acid (1.0%), and uric acid (3.3%). The biocatalytic layer demonstrated to be highly reproducible since the R.S.D. for 10 successive amperometric calibrations using the same surface was 3.6%. The sensitivity of the biosensor after 15 day storage at 4°C remained at 90% of its original value. The combination of the excellent dispersing properties and polycationic nature of polyhistidine, the stability of the MWCNT-Polyhis dispersion, the electrocatalytic properties of MWCNTs, the biocatalytic specificity of GOx, and the permselective properties of Nafion have allowed building up a sensitive, selective, robust, reproducible and stable glucose amperometric biosensor for the quantification of glucose in milk samples.

Dispersion of bamboo type multi-wall carbon nanotubes in calf-thymus double stranded DNA.

We report for the first time the use of double stranded calf-thymus DNA (dsDNA) to successfully disperse bamboo-like multi-walled carbon nanotubes (bCNT). The dispersion and the modified electrodes were studied by different spectroscopic, microscopic and electrochemical techniques. The drastic treatment for dispersing the bCNT (45min sonication in a 50% (v/v) ethanol:water solution), produces a partial denaturation and a decrease in the length of dsDNA that facilitates the dispersion of CNT and makes possible an efficient electron transfer of guanine residues to the electrode. A critical analysis of the influence of different experimental conditions on the efficiency of the dispersion and on the performance of glassy carbon electrodes (GCE) modified with bCNT-dsDNA dispersion is also reported. The electron transfer of redox probes and guanine residues was more efficient at GCE modified with bCNT dispersed in dsDNA than at GCE modified with hollow CNT (hCNT) dispersed in dsDNA, demonstrating the importance of the presence of bCNT.

Characterization of a modified gold platform for the development of a label-free anti-thrombin aptasensor.

This work reports the characterization of a modified gold surface as a platform for the development of a label free aptasensor for thrombin detection. The biorecognition platform was obtained by the self-assembly of 4-mercaptobenzoic acid onto a gold surface, covalent attachment of streptavidin and further immobilization of the biotinylated anti-thrombin aptamer. The biosensing platform was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, surface plasmon resonance (SPR) and quartz crystal microbalance with dissipation monitoring. The biorecognition event aptamer-thrombin was detected from changes in the SPR angle produced as a consequence of the molecular interaction between the aptasensor and the target protein. The biosensing platform demonstrated to be highly selective for human thrombin even in the presence of large excess of bovine thrombin, bovine serum albumin, cytochrome C, lysozyme and myoglobin. The relationship between the changes in the SPR angle and thrombin concentration was linear up to 0.19 µmol L(-1) (R(2)=0.992) while the detection limit was of 12.0 nmol L(-1) (240 fmol in the sample). This new sensing approach represents an interesting and promising alternative for the SPR-based quantification of thrombin.

Dispersion of multi-wall carbon nanotubes in polyhistidine: characterization and analytical applications.

We report for the first time the use of polyhistidine (Polyhis) to efficiently disperse multiwall carbon nanotubes (MWCNTs). The optimum dispersion MWCNT-Polyhis was obtained by sonicating for 30 min 1.0 mg mL(-1) MWCNTs in 0.25 mg mL(-1) Polyhis solution prepared in 75:25 (v/v) ethanol/0.200 M acetate buffer solution pH 5.00. The dispersion was characterized by scanning electron microscopy, and by cyclic voltammetry and amperometry using ascorbic acid as redox marker. The modification of glassy carbon electrodes with MWCNT-Polyhis produces a drastic decrease in the overvoltage for the oxidation of ascorbic acid (580 mV) at variance with the response observed at glassy carbon electrodes modified just with Polyhis, where the charge transfer is more difficult due to the blocking effect of the polymer. The reproducibility for the sensitivities obtained after 10 successive calibration plots using the same surface was 6.3%. The MWCNT-modified glassy carbon electrode demonstrated to be highly stable since after 45 days storage at room temperature the response was 94.0% of the original. The glassy carbon electrode modified with MWCNT-Polyhis dispersion was successfully used to quantify dopamine or uric acid at nanomolar levels, even in the presence of large excess of ascorbic acid. Determinations of uric acid in human blood serum samples demonstrated a very good correlation with the value reported by Wienner laboratory.

Selective detection of dopamine in the presence of ascorbic acid using carbon nanotube modified screen-printed electrodes.

This work reports on the performance of carbon nanotube modified screen-printed electrodes (SPE-MWCNT) for the selective determination of dopamine (DA) in the presence of ascorbic acid (AA) by adsorptive stripping voltammetry (AdSV). Several operating conditions and parameters were examined including the electrochemical pre-treatment and the previous AA interaction and DA accumulation in the presence AA at physiological conditions. Under the chosen conditions, DA peak current of differential pulse voltammograms increases linearly with DA concentration in the range of 5.0 x 10(-8) to 1.0 x 10(-6) mol L(-1) with a limit of detection of 1.5 x 10(-8) mol L(-1) in connection with 600s accumulation time. The sensitivity obtained for DA was independent from the presence or absence of AA; therefore, the proposed method can be readily applied to detect DA in real samples. The proposed methodology was successfully used for the quantification of DA in urine samples.

Label-free electrochemical aptasensor for the detection of lysozyme.

This work reports the advantages of a label free electrochemical aptasensor for the detection of lysozyme. The biorecognition platform was obtained by the adsorption of the aptamer on the surface of a carbon paste electrode (CPE) previously blocked with mouse immunoglobulin under controlled-potential conditions. The recognition event was detected from the decrease in the guanine and adenine electro-oxidation signals produced as a consequence of the molecular interaction between the aptamer and lysozyme. The biosensing platform demonstrated to be highly selective even in the presence of large excess (9-fold) of bovine serum albumin, cytochrome C and myoglobin. The reproducibility for 10 repetitive determinations of 10.0 mg L(-1) lysozyme solution was 5.1% and 6.8% for guanine and adenine electro-oxidation signals, respectively. The detection limits of the aptasensor were 36.0 nmol L(-1) (if considering guanine signal) and 18.0 nmol L(-1) (if taking adenine oxidation current). This new sensing approach represents an interesting and promising alternative for the electrochemical quantification of lysozyme.

Electrochemical sensor for amino acids and albumin based on composites containing carbon nanotubes and copper microparticles.

This work reports on the analytical performance of composites obtained by dispersing copper microparticles and multi-wall carbon nanotubes within a mineral oil binder (CNTPE-Cu) for the determination of amino acids and albumin. The strong complexing activity of amino acids towards copper makes possible an important improvement in the sensitivity for the determination of amino acids and albumin. This new electrode permits the highly sensitive amperometric detection of amino acids, even the non-electroactive ones, at very low potentials (0.000V) and physiological pH (phosphate buffer solution pH 7.40). The response of the electrode is highly dependent on the amount of copper, demonstrating the crucial role of the metal in the analytical performance of the sensor. The best analytical performance is obtained for the electrode containing 6.0% (w/w) copper. The resulting sensor shows a fast response (7s) and a sensitivity that depends on the nature of the amino acid. The electrode surface demonstrates an excellent resistance to surface fouling, with R.S.D. of 4% for the sensitivities of 10 successive calibration plots. Albumin is determined with CNTPE-Cu using a protocol based on the accumulation of the protein for 10min at -0.100V, followed by the square-wave voltammetric analysis. The quantification of albumin concentration in lyophilized control serum gives excellent agreement with the classical spectrophotometric methodology and with the value informed for the supplier.