An electrochemical biosensor developed for the online monitoring of H2O2 based on the reduced graphene oxide-cerium dioxide nanocomposite

A biosensor was developed for monitoring H2O2 based on reduced Graphene Oxide-Cerium Oxide (rGO-CeO2) nanocomposite (NC). The NC shows catalytic effect on the electrochemical reduction of H2O2 at 0.3 V. The effect of the NC on the electrochemical reduction of H2O2 was studied by cyclic voltammetry and compared with bare glassy carbon (GC) and GC/r-GO. Moreover, to improve the signal a complex containing copper was incorporated in the dispersion of the nanocomposite which acts as a mediator. It was found that the electrochemical reduction of H2O2 takes place at less negative potential with increased peak current attitude at GC/r-GO-mediator. The developed sensor GC/r-GO-mediator, was applied for the continuous monitoring of H2O2 by chronoamperometry. The applied potential was 0.3 V which results in the enhanced sensitivity of the developed biosensor. The developed biosensor shows good stability, and reproducibility. The reproducibility of the developed electrode was evaluated by calculation of relative standard deviation value 6.77%. The linear range was found to be 3.4 - 23.48 g/ml. Furthermore, limit of detection and limit of quantification were 0.68 g/ml and 2.27 g/ml respectively

Bis(2,2-bipyridil)Copper(II) Chloride Complex: Tyrosinase Biomimetic Catalyst or Redox Mediator?

In this article, construction of amperometric sensor(s) based on screen-printed carbon electrodes covered by thin layers of two types of carbon nanomaterials serving as amplifiers, and containing [Cu(bipy)(2)Cl]Cl center dot 5H(2)O complex is reported. Their performance and biomimetic activity towards two selected neurotransmitters (dopamine and serotonin) was studied mainly using flow injection analysis (FIA). The important parameters of FIA such as working potential, flow rate, and pH were optimized. The mechanism of the catalytic activity is explained and experimentally confirmed. It reveals that presence of hydrogen peroxide plays a crucial role which leads to answer the title question: can presented complex really be considered as a tyrosinase biomimetic catalyst or only as a redox mediator

In situ investigation of the cytotoxic and interfacial characteristics of titanium when galvanically coupled with magnesium using scanning electrochemical microscopy

Recently, the cytotoxic properties of galvanically coupled Mg-Ti particles have been shown to different cells, although this cytotoxic effect has been attributed mainly to Mg due to its tendency to undergo activation when coupled with Ti forming a galvanic cell consisting of an anode (Mg) and a cathode (Ti). However, the role of the Ti cathode has been ignored in explaining the cytotoxic effect of Mg-Ti particles due to its high resistance to corrosion. In this work, the role of titanium (Ti) in the cytotoxic mechanism of galvanically coupled Mg-Ti particles was examined. A model galvanic cell was prepared to simulate the Mg-Ti particles. The electrochemical reactivity of the Ti sample and the pH change above it due to galvanic coupling with Mg were investigated using scanning electrochemical microscopy (SECM). It was observed that the Ti surface changed from passive to electrochemically active when coupled with Mg. Furthermore, after only 15 min galvanic coupling with Mg, the pH in the electrolyte volume adjacent to the Ti surface increased to an alkaline pH value. The effects of the galvanic coupling of Ti and Mg, as well as of the alkaline pH environment, on the viability of Hs27 fibroblast cells were investigated. It was shown that the viability of Hs27 cells significantly diminished when Mg and Ti were galvanically coupled compared to when the two metals were electrically disconnected. Next, the generation of reactive oxygen species (ROS) increased when the Ti and Mg were galvanically coupled. Thus, although Ti usually exhibited high corrosion resistance when exposed to physiological environments, an electrochemically active surface was observed when galvanically coupled with Mg, and this surface may participate in electron transfer reactions with chemical species in the neighboring environment; this participation resulted in the increased pH values above its surface and enhanced generation of ROS. These features contributed to the development of cytotoxic effects by galvanically coupled Mg-Ti particles

Correction: Sýs et al. Bis(2,2′-bipyridil)Copper(II) Chloride Complex: Tyrosinase Biomimetic Catalyst or Redox Mediator? <i>Materials</i> 2021, <i>14</i>, 113

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Total flavonoid content in plant derived beverages determined by extractive stripping voltammetry

The catechin (CAT)-equivalent of flavonoids content of plant derived-beverages (PDBs) was estimated by partial extraction into the bare carbon paste and subsequent determination by differential pulsed voltammetry (DPV). The selectivity of the method was investigated by determining in presence of the potential interferences. While the determination of CAT in the presence of some non-flavonoid interferences was not possible by direct voltammetry, there was no interfering effect observed in the developed method. The effect of various paste compositions was studied on the extraction of the CAT onto the paste, and it was found that the combination of expanded graphite with silicon oil provides the best paste for the extraction. The RSD of 3.93% confirms a good repeatability of the developed method when 5 repetitive measurements were carried out. The LOD and LOQ of the developed method were calculated to be 1.2 × 10−8 M and 3.9 × 10−8 M, respectively. The accuracy of the developed method was controlled by analysis of the spiked sample, where the recovery rate of 98% and 104% indicate the accuracy of the developed ex-situ method. Finally, the developed method was successfully used for the determination of CAT-equivalent of flavonoids in a green tea sample

A novel biocompatible titanium–gadolinium quantum dot as a bacterial detecting agent with high antibacterial activity

In this study, the titanium gadolinium quantum dots (TGQDs) were novel, first of its type to be synthesized, and fully characterized to date. Multiple physical characterization includes scanning electron microscopy (SEM), scanning electrochemical microscope (SCEM), x-ray fluorescence, spectrophotometry, and dynamic light scattering were carried out. The obtained results confirmed appropriate size and shape distributions in addition to processing optical features with high quantum yield. The synthesized TGQD was used as a fluorescent dye for bacterial detection and imaging by fluorescent microscopy and spectrophotometry, where TGQD stained only bacterial cells, but not human cells. The significant antibacterial activities of the TGQDs were found against a highly pathogenic bacterium (Staphylococcus aureus) and its antibiotic resistant strains (vancomycin and methicillin resistant Staphylococcus aureus) using growth curve analysis and determination of minimum inhibitory concentration (MIC) analysis. Live/dead cell imaging assay using phase-contrast microscope was performed for further confirmation of the antibacterial activity. Cell wall disruption and release of cell content was observed to be the prime mode of action with the reduction of cellular oxygen demand (OD)