Pollyana S. Castro

Amperometric determination of hydrogen peroxide using a copper microelectrode

The cathodic reduction of hydrogen peroxide at copper microelectrodes was investigated in phosphate buffer solutions. Following the optimization of the experimental conditions, the proposed sensor presented excellent analytical properties for the amperometric detection of hydrogen peroxide at −0.2 V vs. Ag/AgCl (saturated KCl). The usefulness of the fabricated electrochemical sensor was confirmed by the determination of hydrogen peroxide in commercial products and the values obtained by the proposed method agreed well with those found by using a standard method.

Hybrid magnetic scaffolds: The role of scaffolds charge on the cell proliferation and Ca2+ ions permeation

Magnetic scaffolds with different charge densities were prepared using magnetic nanoparticles (MNP) and xanthan gum (XG), a negatively charged polysaccharide, or hydroxypropyl methylcellulose (HPMC), an uncharged cellulose ether. XG chains were crosslinked with citric acid (cit), a triprotic acid, whereas HPMC chains were crosslinked either with cit or with oxalic acid (oxa), a diprotic acid. The scaffolds XG-cit, HPMC-cit and HPMC-oxa were characterized by scanning electron microscopy (SEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES), superconducting quantum interference device (SQUID) magnetometry, contact angle and zeta-potential measurements. In addition, the flux of Ca2+ ions through the scaffolds was monitored by using a potentiometric microsensor. The adhesion and proliferation of murine fibroblasts (NIH/3T3) on XG-cit, XG-cit-MNP, HPMC-cit, HPMC-cit-MNP, HPMC-oxa and HPMC-oxa-MNP were evaluated by MTT assay. The magnetic scaffolds presented low coercivity (<25Oe). The surface energy values determined for all scaffolds were similar, ranging from 43mJm-2 to 46mJm-2. However, the polar component decreased after MNP incorporation and the dispersive component of surface energy increased in average 1mJm-2 after MNP incorporation. The permeation of Ca2+ ions through XG-cit-MNP was significantly higher in comparison with that on XG-cit and HPMC-cit scaffolds, but through HPMC-cit-MNP, HPMC-oxa and HPMC-oxa-MNP scaffolds it was negligible within the timescale of the experiment. The adhesion and proliferation of fibroblasts on the scaffolds followed the trend: XG-cit-MNP>XG-cit>HPMC-cit, HPMC-cit-MNP, HPMC-oxa, HPMC-oxa-MNP. A model was proposed to explain the cell behavior stimulated by the scaffold charge, MNP and Ca2+ ions permeation.

Gold random microarrays: design, characterization and amperometric determination of ciclopirox olamine in pharmaceutical products

In this work, a disposable gold random microarray (GRM) sensor was developed and applied for the determination of ciclopirox olamine in 0.10 mol L−1 Britton Robinson buffer (pH 5.0). The GRM was fabricated by the deposition of two toner pattern masks, the first mask delimiting the disc area and the second one (with 90% of toner) defining the microarrays. Following the optimization of the experimental parameters, the proposed sensor presented excellent analytical properties for the amperometric detection of ciclopirox olamine at +0.85 V vs. Ag/AgCl(KClsat). The usefulness of the GRM sensor was confirmed by determining ciclopirox olamine in commercial products. The results obtained were in good agreement with those found by potentiometric titration and the labelled values. The proposed GRM platform can be produced with high throughput and is cost-effective and disposable, hence no pre-treatment is required between measurements.

Scanning Electrochemical Microscopy as a Tool for the Characterization of Dental Erosion

When the tooth is exposed to acidic environments, an irreversible loss of dental hard tissue occurs in a process called dental erosion. In this work, the scanning electrochemical microscopy (SECM) was used to probe the consumption of protons at the vicinity of a tooth surface with a platinum microelectrode fixed at −0.5 (V) versus Ag/AgCl/KCl(sat). SECM approach curves were recorded to assess the extent of diffusion in the solution close to the tooth substrate. SECM images clearly demonstrated that the acid erosion process is very fast at solution pH values in the range between 3 and 4.