Graphene Oxide Mediated Broad-Spectrum Antibacterial Based on Bimodal Action of Photodynamic and Photothermal Effects.

Graphene oxide (GO) with their interesting properties including thermal and electrical conductivity and antibacterial characteristics have many promising applications in medicine. The prevalence of resistant bacteria is considered a public health problem worldwide, herein, GO has been used as a broad spectrum selective antibacterial agent based on the photothermal therapy (PTT)/photodynamic therapy (PDT) effect. The preparation, characterization, determination of photophysical properties of two different sizes of GO is described. In vitro light dose and concentration-dependent studies were performed using Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria based on the PTT/PDT effect used ultra-low doses (65 mW cm-2) of 630 nm light, to achieve efficient bacterial decontamination. The results show that GO and nanographene oxide (nGO) can sensitize the formation of 1O2 and allow a temperature rise of 55°C to 60°C together nGO and GO to exert combined PTT/PDT effect in the disinfection of gram-positive S. aureus and gram-negative E. coli bacteria. A complete elimination of S. aureus and E. coli bacteria based on GO and nGO is obtained by using a dose of 43-47 J cm-2 for high concentration used in this study, and a dose of around 70 J cm-2 for low dose of GO and nGO. The presence of high concentrations of GO allows the bacterial population of S. aureus and E. coli to be more sensitive to the use of PDT/PTT and the efficiency of S. aureus and E. coli bacteria disinfection in the presence of GO is similar to that of nGO. In human neonatal dermal fibroblast, HDFs, no significant alteration to cell viability was promoted by GO, but in nGO is observed a mild damage in the HDFs cells independent of nGO concentration and light exposure. The unique properties of GO and nGO may be useful for the clinical treatment of disinfection of broad-spectrum antimicrobials. The antibacterial results of PTT and PDT using GO in gram-positive and gram-negative bacteria, using low dose light, allow us to conclude that GO and nGO can be used in dermatologic infections, since the effect on human dermal fibroblasts of this treatment is low compared to the antibacterial effect.

Multifunctional catalytic platform for peroxidase mimicking, enzyme immobilization and biosensing.

A hybrid platform based on ionic liquid-based alkoxysilane functionalized mesoporous silica was applied for the synthesis of supported Pt nanoparticles with peroxidase-like catalytic activity. The positively charged groups (imidazolium) chemically bonded to the surface provide dual-functionality as ion-exchangers to the hybrid material, firstly used for the in situ synthesis of the highly dispersed Pt nanostructures and, secondly, for the immobilization of biological species aiming biosensing purposes. The peroxidase-like catalytic activity of the SiO2/Imi/Pt material was evaluated towards the H2O2-mediated oxidation of a chromogenic peroxidase substrate (TMB), allowing the colorimetric detection of H2O2. Finally, to further explore the practical application of this nanomaterial-based artificial system, glucose oxidase (GOx) was immobilized on the catalytic porous platform and a bioassay for the colorimetric determination of glucose was successfully conducted as a model system. The enzyme-like catalytic properties of the SiO2/Imi/Pt as well as its ability to immobilize and keep active biological entities on the porous structure indicate that this hybrid porous platform is potentially useful for the development of biosensing devices.

Development of a sensor for L-Dopa based on Co(DMG)(2)ClPy/multi-walled carbon nanotubes composite immobilized on basal plane pyrolytic graphite electrode.

L-Dopa is the immediate precursor of the neurotransmitter dopamine, being the most widely prescribed drug in the treatment of Parkinson's disease. A sensitive and selective method is presented for the voltammetric determination of L-Dopa in pharmaceutical formulations using a basal plane pyrolytic graphite (BPPG) electrode modified with chloro(pyridine)bis(dimethylglyoximato)cobalt(III) (Co(DMG)(2)ClPy) absorbed in a multi-walled carbon nanotube (MWCNT). Scanning Electron Microscopy and Fourier Transform Infrared Spectroscopy were used to characterize the materials. The electrocatalytical oxidation of L-Dopa using the Co(DMG)(2)ClPy/MWCNT/BPPG electrode was investigated by cyclic voltammetry and square wave voltammetry. The parameters that influence the electrode response (the amount of Co(DMG)(2)ClPy and of MWCNT, buffer solution, buffer concentration, buffer pH, frequency and potential pulse amplitude) were investigated. Voltammetric peak currents showed a linear response for L-Dopa concentration in the range of 3 to 100 µM, with a sensitivity of 4.43 µAcm(-2)/µM and a detection limit of 0.86 µM. The related standard deviation for 10 determinations of 50 µM L-Dopa was 1.6%. The results obtained for L-Dopa determination in pharmaceutical formulations (tablets) were in agreement with the compared official method. The sensor was successfully applied for L-Dopa selective determination in pharmaceutical formulations.

Electrooxidation of nitrite on a silica-cerium mixed oxide carbon paste electrode.

A silica-cerium mixed oxide (SiCe) was prepared by the sol-gel process, using tetraethylorthosilicate and cerium nitrate as precursors and obtained as an amorphous solid possessing a specific surface area of 459 m(2) g(-1). Infrared spectroscopy of the SiCe material showed the formation of the Si-O-Ce linkage in the mixed oxide. Scanning electron microscopy/energy dispersive spectroscopy indicated that the cerium oxide particles were homogenously dispersed on the matrix surface. X-ray diffraction and (29)Si solid-state nuclear magnetic resonance implied non-crystalline silica matrices with chemical environments that are typical for silica-based mixed oxides. X-ray photoelectron spectroscopy showed that Ce was present in approximately equal amounts of both the 3+ and 4+ oxidation states. Cyclic voltammetry data of electrode prepared from the silica-cerium mixed oxide showed a peak for oxidation of Ce(3+)/Ce(4+) at 0.76 V and electrochemical impedance spectroscopy equivalent circuit indicated a porous structure with low charge transfer resistance. In the presence of nitrite, the SiCe electrode shows an anodic oxidation peak at 0.76 V with a linear response as the concentration of the analyte increases from 3×10(-5) at 3.9×10(-3) mol L(-1).