Fernando H. Cincotto

Simultaneous determination of epinephrine and dopamine by electrochemical reduction on the hybrid material SiO2/graphene oxide decorated with Ag nanoparticles

This paper describes the synthesis, characterization and applications of a new hybrid material composed of mesoporous silica (SiO2) modified with graphene oxide (GO), SiO2/GO, obtained by the sol-gel process using HF as the catalyst. The hybrid material, SiO2/GO, was decorated with silver nanoparticles (AgNPs) with a size of less than 20 nanometres, prepared directly on the surface of the material using N,N-dimethylformamide (DMF) as the reducing agent. The resulting material was designated as AgNP/SiO2/GO. The Ag/SiO2/GO material was characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and high-resolution transmission electron microscopy (HR-TEM). A glassy carbon electrode modified with AgNP/SiO2/GO was used in the development of a sensitive electrochemical sensor for the simultaneous determination of epinephrine and dopamine employing electrocatalytic reduction using squarewave voltammetry. Well-defined and separate reduction peaks were observed in PBS buffer at pH 7. No significant interference was seen for primarily biological interferents such as uric acid and ascorbic acid in the detection of dopamine and epinephrine. Our study demonstrated that the resultant AgNP/SiO2/GO-modified electrode is highly sensitive for the simultaneous determination of dopamine and epinephrine, with the limits of detection being 0.26 and 0.27 μmol L(-1), respectively. The AgNP/SiO2/GO-modified electrode is highly selective and can be used to detect dopamine and epinephrine in a human urine sample.

Electrochemical immunosensor for ethinylestradiol using diazonium salt grafting onto silver nanoparticles-silica-graphene oxide hybrids

This work describes the preparation of an electrochemical immunosensor for ethinylestradiol (EE2) based on grafting of diazonium salt of 4-aminobenzoic acid onto a glassy carbon electrode modified with silver nanoparticles/SiO2/graphene oxide hybrid followed by covalent binding of anti-ethinylestradiol (anti-EE2) to activated carboxyl groups. A competitive immunoassay was developed for the determination of the hormone using peroxidase-labeled ethinylestradiol (HRP-EE2) and measurement of the amperometric response at -200mV in the presence of hydroquinone (HQ) as redox mediator. The calibration curve for EE2 exhibited a linear range between 0.1 and 50ng/mL (r(2)=0.996), with a detection limit of 65pg/mL. Interference studies with other hormones related with EE2 revealed the practical specificity of the developed method for the analyte. A good reproducibility, with RSD=4.5% (n=10) was also observed. The operating stability of a single bioelectrode modified with anti-EE2 was maintained at least for 15 days when it was stored at 4°C under humid conditions between measurements. The developed immunosensor was applied to the analysis of spiked urine with good results.

Graphene Nanosheets and Quantum Dots: A Smart Material for Electrochemical Applications

A novel material for the electrochemical determination of endocrine disruptors using a composite based on graphene oxide modified with cadmium telluride quantum dots has been evaluated. The morphology, structure and electrochemical performance of the composite electrodes were characterised by transmission electron microscopy, dynamic light scattering, UV-visible absorption spectra, fluorescence spectra, Raman spectra and cyclic voltammetry. The dynamic light scattering, transmission electronic microscopy and spectrophotometric measurements all showed good distribution of the quantum dots with a small particle size. The electrochemical measurements demonstrated the high performance of the composite response in the presence of a light source. Differential pulse voltammetry allowed the development of a method to determine 17β-estradiol levels in the range from 0.2 to 4.0 μmol L(-1) with a detection limit of 2.8 nmol L(-1) (0.76 μg L(-1)).

Efficient electrochemical biosensors for ethynylestradiol based on the laccase enzyme supported on single walled carbon nanotubes decorated with nanocrystalline carbon quantum dots

A new hybrid nanomaterial based on single-walled carbon nanotubes incorporating nanocrystalline carbon quantum dots (SWCNT/C-dots) was developed and characterized by means of high resolution transmission electron microscopy, atomic force microscopy, Raman spectroscopy and electrochemical techniques. A glassy carbon electrode modified with SWCNT/C-dots exhibited an enhanced electrocatalytic response for 17α-ethynylestradiol, reflecting an increase of the active area of the hybrid material, promoted by the C-dots. However, the best activity was observed for laccase immobilized on CGE/SWCNT/C-dots, suggesting that the nanocrystalline C-dots improve the electron transport between the substrate, SWCNTs and the copper ions in the enzyme active sites. Such an association provided a very efficient bioelectrochemical sensor for the 17α-ethynylestradiol endocrine interfering agent, with a detection limit of 4.0 nmol L−1 in real samples.