Ana R. Guadalupe

Screen-printable surfactant-induced sol–gel graphite composites for electrochemical sensors

Abstract A novel procedure to prepare sol–gel graphite composite electrodes is presented. This procedure uses the surfactant bis(2-ethylhexyl) sulfosuccinate (AOT) and eliminates the need for a cosolvent, an acidic catalyst, a cellulose binder and thermal curing. Cobalt phthalocyanine (CoPC), diphenylthiocarbazone (DPT) and glucose oxidase (GOx)/ferrocene (Fc) were encapsulated during the surface preparation to study the utility of these composites as catalytic surfaces and biochemical sensors. The glucose sensor has a useful working range up to 30 mM with a 10 s response time. The DPT-modified electrode has been applied for lead determination based on a complexing/voltammetric strategy. The CoPC modified surface was catalytically active for reduced glutathione (GSH) reducing the onset potential for its oxidation by 400 mV. Fabrication of screen-printed electrodes by this method proved to be a simple approach for electroanalytical applications in aqueous and nonaqueous solvents.

Preconcentration and voltammetry of mercury on a functionalized sol-gel thin film modified glassy carbon electrode.

A functionalized sol-gel thin film modified glassy carbon electrode has been prepared for the determination of mercury. The tetrasulfide in the sol-gel matrix has a high affinity for mercury species. The chemically integrated functional groups in the sol-gel precursor ensure a high chemical and mechanical stability of the modified electrodes, and therefore a stable and reproducible analytical performance. By medium exchange anodic stripping voltammetry, this modified electrode allows reliable, low cost and interference-free determination of mercury.

Ruthenium complexes as redox mediators for malate and lactate dehydrogenases

Abstract Two ruthenium complexes [Ru(phendione) 3 ] 2+ and [Ru(tpy) (bpy)H 2 O] 2+ were tested as redox mediators for the electrocatalytic enzyme-coupled oxidation of malate and lactate with their respective dehydrogenase enzymes. Both complexes were capable of regenerating NAD + after its enzymatic reduction, but with varying current density as shown by cyclic voltammetry. Studies were performed at different concentrations of NAD + and the mediator and with different number of enzyme units. The best experimental conditions were used in experiments with different substrate concentrations. The results were fitted to the Michaelis-Menten equation giving the following K M and V max values in carbonate buffer at pH 9.3. Lactate dehydrogenase ( r = 0.9999): K M = 9.784 ± 1.163 mM; k cat = 3.819 ± 0.104 s −1 . Malate dehydrogenase ( r = 0.9999): K M = 3.934 ± 0.722 mM; k cat = 3.376 ± 0.171 s −1 .

Synthesis, characterization and use of Ru-Fc intercalation complex as an electrochemical label for the detection of pathogen-DNA

This report describes the synthesis of [Ru(Fe-Phen)2dppz](PF6)2 (Ru-Fe complex) for a label-free approach to detect DNA hybridization. The Ru-Fe complex showed oxidation signals at +608 mV and +1192 mV corresponding to the RuII/III and FeII/III centers, respectively. We used the Ru-Fe complex and the Ferrocene covalently attached to the target to monitor the hybridization event of a 70-mer oligo immobilized in 10.3KD NHS-PS-NHS. The lowest target detectable concentration for the DNA fragment was around 0.4 μM.

Transmission Electron Microscopy Characterization and Application of Sol-Gel Membranes.

: Using standard square mesh grids as supports, we have prepared sol-gel membranes from a functionalized silane precursor, bis[3-(triethoxysilyl)propyl]tetrasulfide in various organic solvents. These mesh-supported membranes allow direct characterization of their microstructure and morphology by transmission electron microscopy (TEM). Homogeneous membranes without prominent microstructural features (or featureless) at nanometer scale were obtained from dimethyl formamide (DMF), isopropanol, and butanol solutions. However, highly porous membranes were produced from DMF and ethylene glycol binary system. Heterogeneous membranes filled with nanoparticles were formed from dimethyl sulfoxide solution. The featureless sol-gel membranes with tunable performances provide a useful alternative as supporting films for TEM applications.

Synthesis and characterization of novel ferrocenyl chalcone ammonium and pyridinium salt derivatives

A novel series of ferrocenyl chalcone ammonium and pyridinium salt derivatives were synthesized in order to improve their solubility in aqueous media. Substituted ferrocenyl chalcones with amines and pyridines were synthesized using the base-catalyzed Claisen-Schmidt reaction, and their corresponding salts were prepared by a nucleophilic quaternization reaction at the nitrogen atom. Most of the synthesized ferrocenyl chalcone salts were soluble in water at room temperature. They were fully characterized by IR, NMR spectroscopy and HRMS spectrometry, and their electrochemistry was studied. The salt derivatives presented chemical reversibility, electrochemical quasi reversibility, and the slope of a plot of Log Ipc (or Ipa) versus Log v were almost 0.5 suggesting that their redox process was controlled by diffusion.