Amino acid analysis using disposable copper nanoparticle plated electrodes

Synthesis of 3D Dendritic Gold Nanostructures Assisted by a Templated Growth Process: Application to the Detection of Traces of Molecules

Complex architectures like 3D gold dendritic nanostructures were synthesized by an in situ templated growth method using a thin film of a block copolymer [polystyrene-b-poly(4-vinylpyridine)] deposited onto silicon substrates. The overall study has demonstrated the strong link between the morphology, size, and distribution of the structures and the synthetic physicochemical parameters, such as pH, reaction temperature, concentration, and nature of reactants. A nonequilibirum state of the medium has been required to create a fractal growth of the gold structures onto a prepatterned gold-seeded surface and has led to a better control of the structures' surface coverage rate. Those as-prepared nanodendrites have also exhibited high electrocatalytic activity toward a significant enhancement factor, as well as important sensitivity, thanks to tip effects. The electrochemical experiment results have demonstrated efficient adsorption and quantification of very low traces of specific molecules like glutathione or hexadecanethiol.

Single amino acid utilization for bacterial categorization

Despite great advancement in genetic typing, phenotyping is still an indispensable tool for categorization of bacteria. Certain amino acids may be essential for bacterial survival, growth, pathogenicity or toxin production, which prompts the idea that the intrinsic ability to utilize single amino acid under live-or-die situation could be a basis for differentiation of bacteria species. In this study, we determined the single amino acid consumption profiles of 7 bacterial species, and demonstrated that most bacteria have species-specific pattern of amino acid consumption. We also discovered that bacterial strains from different hosts, toxigenicity, and antibiotic-resistance presented distinct preference for certain amino acids. Taken altogether, the amino acid consumption profiles showed potential to be a novel tool complementary to study not only bacterial categorization but also biochemical characteristics of the bacteria such that its phenotyping can be used to uncover strategies for nutritional, pharmaceutical, taxonomic, and evolutionary aspects of bacterial researches.

Screen-Printed Electrodes Modified with Metal Nanoparticles for Small Molecule Sensing

Recent progress in the field of electroanalysis with metal nanoparticle (NP)-based screen-printed electrodes (SPEs) is discussed, focusing on the methods employed to perform the electrode surface functionalization, and the final application achieved with different types of metallic NPs. The ink mixing approach, electrochemical deposition, and drop casting are the usual methodologies used for SPEs' modification purposes to obtain nanoparticulated sensing phases with suitable tailor-made functionalities. Among these, applications on inorganic and organic molecule sensing with several NPs of transition metals, bimetallic alloys, and metal oxides should be highlighted.

Optimal Conditions for the Direct RP-HPLC Determination of Underivatized Amino Acids with Online Multiple Detection

The combined use of a dual-UV detector as well as a fluorimetric and a multielectrode electrochemical detector (equipped with a dual electrode, consisting of a conventional size 3 mm diameter glassy carbon electrode (GCE) and of a pair of 30 μm thick carbon microfibers) is proposed for the detection of the following 15 underivatized amino acids: L-histidine (His), L-cysteine (Cys), creatine (Crn), S-methyl-L-cysteine (Me-Cys), DL-homocysteine (Hcy), L-methionine (Met), beta-(3,4-dihydroxyphenyl)-L-alanine (DOPA), L-tyrosine (Tyr), DL-m-tyrosine (m-Tyr), L-a-methyl-DOPA (Me-DOPA), L-phenylalanine (Phe), DL-alpha-methyltyrosine (Me-Tyr), 5-hydroxy-tryptophan (5-HTP), 3-nitro-L-tyrosine (NO₂Tyr), and L-tryptophan (Trp), as well as of 2 dipeptides L-cystathionine (Cysta) and L-carnosine (Car), and of creatinine (Cre). A multilinear solvent (acetonitrile) gradient elution program, determined by a simple optimization algorithm, is required for the efficient reversed-phase separation of the above mixture of 18 solutes within 27 min at a flow rate of 1.0 mL/min and at 25 °C.

Evaluation of Metal Oxide Surface Catalysts for the Electrochemical Activation of Amino Acids

Electrochemical detection of amino acids is important due to their correlation with certain diseases; however, most amino acids require a catalyst to electrochemically activate. One common catalyst for electrochemical detection of amino acids are metal oxides. Metal oxide nanoparticles were electrodeposited onto glassy carbon and platinum working electrodes. Cyclic voltammetry (CV) experiments in a flow cell were performed to evaluate the sensors’ ability to detect arginine, alanine, serine, and valine at micromolar and nanomolar concentrations as high as 4 mM. Solutions were prepared in phosphate buffer saline (PBS) and then 100 mM NaOH. Specifically, NiO surfaces were responsive to amino acids but variable, especially when exposed to arginine. Polarization resistance experiments and scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) data indicated that arginine accelerated the corrosion of the NiO catalyst through the formation of a Schiff base complex.

One-pot electrochemical preparation of copper species immobilized poly(o-aminophenol)/MWCNT composite with excellent electrocatalytic activity for use as an H2O2 sensor

Redox activity of copper species immobilized poly(o-aminophenol)/multi-walled carbon nanotube for direct electrocatalysis towards detection of H₂O₂.

Utilising copper screen-printed electrodes (CuSPE) for the electroanalytical sensing of sulfide

A mediatorless sulfide electrochemical sensing platform utilising a novel nanocopper-oxide screen-printed electrodes (CuSPE) is reported for the first time.

Electrochemical flow injection analysis of hydrazine in an excess of an active pharmaceutical ingredient: achieving pharmaceutical detection limits electrochemically

The quantification of genotoxic impurities (GIs) such as hydrazine (HZ) is of critical importance in the pharmaceutical industry in order to uphold drug safety. HZ is a particularly intractable GI and its detection represents a significant technical challenge. Here, we present, for the first time, the use of electrochemical analysis to achieve the required detection limits by the pharmaceutical industry for the detection of HZ in the presence of a large excess of a common active pharmaceutical ingredient (API), acetaminophen (ACM) which itself is redox active, typical of many APIs. A flow injection analysis approach with electrochemical detection (FIA-EC) is utilized, in conjunction with a coplanar boron doped diamond (BDD) microband electrode, insulated in an insulating diamond platform for durability and integrated into a two piece flow cell. In order to separate the electrochemical signature for HZ such that it is not obscured by that of the ACM (present in excess), the BDD electrode is functionalized with Pt nanoparticles (NPs) to significantly shift the half wave potential for HZ oxidation to less positive potentials. Microstereolithography was used to fabricate flow cells with defined hydrodynamics which minimize dispersion of the analyte and optimize detection sensitivity. Importantly, the Pt NPs were shown to be stable under flow, and a limit of detection of 64.5 nM or 0.274 ppm for HZ with respect to the ACM, present in excess, was achieved. This represents the first electrochemical approach which surpasses the required detection limits set by the pharmaceutical industry for HZ detection in the presence of an API and paves the wave for online analysis and application to other GI and API systems.

A disposable alkaline phosphatase-based biosensor for vanadium chronoamperometric determination

A chronoamperometric method for vanadium ion determination, based on the inhibition of the enzyme alkaline phosphatase, is reported. Screen-printed carbon electrodes modified with gold nanoparticles were used as transducers for the immobilization of the enzyme. The enzymatic activity over 4-nitrophenyl phosphate sodium salt is affected by vanadium ions, which results in a decrease in the chronoamperometric current registered. The developed method has a detection limit of 0.39 ± 0.06 µM, a repeatability of 7.7% (n = 4) and a reproducibility of 8% (n = 3). A study of the possible interferences shows that the presence of Mo(VI), Cr(III), Ca(II) and W(VI), may affect vanadium determination at concentration higher than 1.0 mM. The method was successfully applied to the determination of vanadium in spiked tap water.

Development of copper based drugs, radiopharmaceuticals and medical materials

Copper is one of the most interesting elements for various biomedical applications. Copper compounds show vast array of biological actions, including anti-inflammatory, anti-proliferative, biocidal and other. It also offers a selection of radioisotopes, suitable for nuclear imaging and radiotherapy. Quick progress in nanotechnology opened new possibilities for design of copper based drugs and medical materials. To date, copper has not found many uses in medicine, but number of ongoing research, as well as preclinical and clinical studies, will most likely lead to many novel applications of copper in the near future.

Optimal conditions for the direct RP-HPLC determination of underivatized amino acids with online multiple detection

The combined use of a dual-UV detector as well as a fluorimetric and a multielectrode electrochemical detector (equipped with a dual electrode, consisting of a conventional size 3 mm diameter glassy carbon electrode (GCE) and of a pair of 30 μm thick carbon microfibers) is proposed for the detection of the following 15 underivatized amino acids: L: -histidine (his), L: -cysteine (cys), creatine (crn), S-methyl-L: -cysteine (me-cys), DL: -homocysteine (hcy), L: -methionine (met), beta-(3,4-dihydroxyphenyl)-L: -alanine (dopa), L: -tyrosine (tyr), DL: -m-tyrosine (m-tyr), L: -a-methyl-dopa (me-dopa), L: -phenylanine (phe), DL: -alpha-methyltyrosine (me-tyr), 5-hydroxy-tryptophan (5htp), 3-nitro-L: -tyrosine (NO(2)Tyr) and L: -tryptophan (trp), as well as of two dipeptides: L: -cystathionine (cysta), L: -carnosine (car), and of creatinine (cre). A multilinear solvent (acetonitrile) gradient elution program, determined by a simple optimization algorithm, is required for the efficient reversed phase separation of the above mixture of 18 solutes within 27 min at a flow rate of 1.0 mL/min and at 25°C.

Direct RP-HPLC determination of underivatized amino acids with online dual UV absorbance, fluorescence, and multiple electrochemical detection

The combined use of a dual-UV detector, a fluorimetric one and of a multiple electrochemical (EC) detector equipped with a dual electrode, consisting of a conventional size 3 mm diameter glassy carbon electrode (GCE) and of a pair of 30 mum thick carbon microfibers, is proposed for the determination of 15 amino acids, two dipeptides and creatinine. This online coupling of the above detection modes could partially replace amino acid analysis by derivatization methods, since it solves problems concerning the direct detection of selected underivatized amino acids. Additionally, it was proved that the use of multiple-detection allows positive peak identification in a single chromatographic run, yields more information for free amino acids and solves in some cases the problem of chromatographic resolution. In order to optimize the detection conditions of the underivatized amino acids and related compounds by different detectors, their detection characteristics were determined by adequate preliminary experiments. The electro-oxidation characteristics of the underivatized compounds of interest were determined by hydrodynamic voltammetry using a flow cell with a macrodisc GCE and by ex-situ voltammetry using both a GCE of conventional size and a carbon fiber disk microelectrode. Important practical advantages of microfiber and microdisk electrodes with respect to macroelectrodes were demonstrated.

Fast differentiation of meats from fifteen animal species by liquid chromatography with electrochemical detection using copper nanoparticle plated electrodes

A simple, rapid and reliable method based on high-performance liquid chromatography with electrochemical detection was developed to routinely differentiate among meat products from fifteen food animal species. Samples from cattle, pigs, goats, deer, horses, chickens, ducks, ostriches, salmon, cod, shrimp, crabs, scallops, bullfrogs and alligators each exhibited unique electrochemical profiles. Species-specific markers exhibited reproducible peak retention times with coefficients of variation less then 6% across different runs, body regions and subjects. The method requires no derivatization or extraction steps and may be applicable to fresh or cooked meats. Incubation of fresh beef, pork or chicken at room temperature for 24h or repeated freezing and thawing changed the intensity but not the pattern of species-specific peaks. In conclusion, this method appears suitable for rapid differentiation of meats from various food animal species and demonstrates the utility of electrochemical detection to supplement existing immunochemical and molecular biological methods. The possibility of using this method to detect adulteration and degradative changes of meat proteins is discussed.

Analytical applications of a carbon nanotubes composite modified with copper microparticles as detector in flow systems

In this work we report on the successful use of a composite prepared by dispersion of multi-wall carbon nanotubes (1-5 microm length, 20-50 nm diameter) and copper microparticles within mineral oil as detector for amino acids quantification in flow injection analysis and capillary electrophoresis. The resulting electrode displays a highly sensitive amperometric detection of amino acids, based on the copper dissolution facilitated by the strong activity of amino acids as ligands of Cu(II). The sensor makes possible the detection of amino acids, electroactive or not, at very low potentials (0.000 V) and physiological pH. A correlation between the sensitivity for the amino acids and the amount of copper within the composite is observed, demonstrating the importance of the metal in the sensor response. The best analytical performance is obtained for the electrode containing 12.0% (w/w) copper. The excellent results obtained with the carbon nanotube paste electrodes containing copper (CNTPE-Cu) as detector in flow systems makes them an interesting alternative for further analytical applications involving different bioanalytes.

The use of nanoparticles in electroanalysis: a review

Nanoparticles can display four unique advantages over macroelectrodes when used for electroanalysis: enhancement of mass transport, catalysis, high effective surface area and control over electrode microenvironment. Therefore, much work has been carried out into their formation, characterisation and employment for the detection of many electroactive species. This paper aims to give an overview of the investigations carried out in this field. Particular attention is paid to examples of the advantages and disadvantages nanoparticles show when compared to macroelectrodes and the advantages of one nanoparticle modification over another. Most work has been carried out using gold, silver and platinum metals. However, iron, nickel and copper are also reviewed with some examples of other metals such as iridium, ruthenium, cobalt, chromium and palladium. Some bimetallic nanoparticle modifications are also mentioned because they can cause unique catalysis through the mixing of the properties of both metals.

An Electrochemical Cell Coupled with Disposable Screen-Printed Electrodes for Use in Flow Injection Analysis

An electrochemical cell coupled with disposable screen-printed electrodes (SPEs) that is specifically designed for use in flow injection analysis (FIA) is described in this study. The cell is made of foldable polyoxymethylene (acetal) thick platelets with the bottom portion consisting of a cavity track to drag the SPEs in position and the top portion having predrilled T-like holes to arrange the Ag/AgCl reference electrode and stainless steel inlet & outlet. An "O ring" is suitably fixed on the top of the working electrode to form a thin-layer space where the electrochemical reaction can take place. Hydrodynamic characterization was validated by using a benchmark hexacyanoferrate redox couple. The results of practical analysis of glucose in human plasma clearly demonstrate the characteristics and applicability of the proposed wall-jet electrochemical cell in FIA.

The Detection of Nitrate Using in-situ Copper Nanoparticle Deposition at a Boron Doped Diamond Electrode

Electrochemical deposition from a 0.1 M sodium sulphate solution, containing Cu2+ (adjusted to pH 3 with hydrochloric acid) produced a well defined copper nanoparticle deposit on the surface of a boron doped diamond electrode. Changing conditions such as potential (-0.8, -1.0 and -1.2 V), time (5, 2 and 0.5 s) and concentration of Cu2+ (500, 250 and 100 microM) was found to give copper nanoparticles of varying size and particle density. The electrocatalytic properties of the copper surface towards nitrate reduction were explored. An in-situ copper nanoparticle production method was developed for the detection of nitrate; this involves electrodeposition, followed by linear sweep voltammetry for the reduction of nitrate and then application of a stripping potential to renew the electrode surface. The linear sweep was discovered to have homogenised the size of the nanoparticles but their number density was still dependant on the initial conditions of deposition. Some particles were still present at the surface after the stripping potential had been applied but repetitions of the procedure showed these did not have an effect on subsequent deposits. Optimisation of the method lead to applying a deposition potential of -0.8 V, at a BDD electrode for 5 s in a 0.1 M sodium sulphate solution (pH 3) containing 100 microM Cu2+ followed by a linear sweep at 1 V/s; this yielded a limit of detection of 1.5 microM nitrate. The analytical applicability of the technique was evaluated for nitrate detection in a natural mineral water sample and was found to agree well with that stated by the manufacturer.