A Green Chemical Approach for the Synthesis of Gold Nanoparticles: Characterization and Mechanistic Aspect

This IRCSET-EMPOWER (Irish Research Council for Science, Engineering and Technology Postdoctoral Research Grant) project aims to improve current methodology for the synthesis of metal nanoparticles (NPs). The development of efficient methodology for metal nanomaterials synthesis is an economical and environmental challenge. While the current methods for NPs synthesis are often energy-intensive and involve toxic chemicals, NPs biosynthesis can be carried on at circumneutral pH and mild temperature, resulting in low cost and environmental impact. Nanomaterial biosynthesis has been already observed in magnetotactic bacteria, diatoms, and S-layer bacteria, however, controlled NPs biosynthesis is a relatively new area of research with considerable potential for development. A thorough understanding of the biochemical mechanism involved in NPs biosynthesis is needed, before biosynthetic methods can be economically competitive. The analysis and identification of active species in the nucleation and growth of metal NPs is a daunting task, due to the complexity of the microbial system. This project work focuses on the controlled biosynthesis of gold NPs by fungal microorganisms and aims to determine the biochemical mechanism involved in nucleation and growth of the particles

Visible spectroelectrochemical characterization of geobacter sulfurreducens biofilms on optically transparent indium tin oxide electrode

We report visible spectroelectrochemical (SEC) characterization of cytochrome c552 (cyt c552) in viable Geobacter sulfurreducens biofilms on tin-doped indium oxide (ITO) electrodes poised at 0.24 V vs.. SHE. G. sulfurreducens biofilms were grown in minimal medium with acetate as electron donor (turnover conditions), followed by 24 hours incubation in electron donor-depleted medium (non-turnover conditions). The electronic absorption spectra of G. sulfurreducens biofilms showed the lowest energy absorption band in the reduced state at 552 nm, which indicated excess of cyt c552 in the biofilm. The spectra under non-turnover conditions displayed gradual reduction of the cyt c552, following the step-wise decrease of electrode potential from 0.0 V to -0.6 V vs.. standard calomel electrode (SCE). The spectral changes were fully reversible in both positive and negative direction of the scan potential, with average midpoint potential value of -0.42 V vs.. SCE. Confocal microscopy analysis revealed that the thickness of biofilms under turnover conditions and non-turnover conditions was approximately 35 and 3.5 µm, respectively. This is the first study to observe the reversible redox conversion of cyt c552 in viable G. sulfurreducens biofilms

Extracellular electron transfer mechanism in Shewanella loihica PV- 4 biofilms formed at indium tin oxide and graphite electrodes

Electroactive biofilms are capable of extracellular electron transfer to insoluble metal oxides and electrodes; such biofilms are relevant to biogeochemistry, bioremediation, and bioelectricity production. We investigated the extracellular electron transfer mechanisms in Shewanella loihica PV-4 viable biofilms grown at indium tin oxide (ITO) and graphite electrodes in potentiostat-controlled electrochemical cells poised at 0.2 V vs. Ag/AgCl. Chronoamperometry and confocal microscopy showed higher biofilm growth at graphite compared to the ITO electrode. Cyclic voltammetry, differential pulse voltammetry, along with fluorescence spectroscopy showed that direct electron transfer through outer membrane c type cytochromes (Omcs) prevailed at the biofilm/ITO interface, while biofilms formed at graphite electrode reduced the electrode also via secreted redox mediators, such as flavins and quinones. The biofilm age does not affect the prevalent transfer mechanism at ITO electrodes. On the other hand, secreted redox mediators accumulated at biofilm/graphite interface, thus increasing mediated electron transfer as the biofilm grows over five days. Our results showed that the electrode material determined the prevalent electron transfer mechanism and the dynamic of secreted redox mediators in S. loihica PV-4 biofilms. These observations have implications for the optimization of biofilm-based electrochemical systems, such as biosensors and microbial fuel cells

Sustainable Power Production in a Membrane-less and Mediator-less Wastewater Microbial Fuel Cell

Microbial fuel cells (MFCs) fed with wastewater are currently considered a feasible strategy for production of renewable electricity at low cost. A membrane-less MFC with biological cathode was built from a compact wastewater treatment reactor. When operated with an external resistance of 250 Ohm, the MFC produced a long-term power of approximately 70 mW/m2 for ten months. Denaturing Gradient Gel Electrophoresis (DGGE) analysis of the cathode biomass when the MFC was closed on a 2100 Ohm external resistance showed that the sequenced bands were affiliated with Firmicutes, -Proteobacteria, -Proteobacteria, -Proteobacteria, and Bacteroidetes groups. When the external resistance was varied between 250 and 2100 Ohm, sustainable resistance decreased from 900 to 750 Ohm, while sustainable power output decreased from 32 to 28 mW/m2. It is likely that these effects were caused by changes in the microbial ecology of anodic and cathodic biomass attached to the electrodes. Results suggest that cathodic biomass enrichment in “electroactive” bacteria may improve MFCs power output in a similar fashion to what has been already observed for anodic biomass

Mediator-free interaction of glucose oxidase, as model enzyme for immobilization, with Al-doped and undoped ZnO thin films laser-deposited on polycarbonate supports

Al doped and undoped ZnO thin films were deposited by pulsed-laser deposition on polycarbonate sheets. The films were characterized by optical transmission, Hall effect measurement, XRD and SEM. Optical transmission and surface reflectometry studies showed good transparency with thicknesses ∼100 nm and surface roughness of 10 nm. Hall effect measurements showed that the sheet carrier concentration was −1.44 × 1015 cm−2 for AZO and −6 × 1014 cm−2 for ZnO. The films were then modified by drop-casting glucose oxidase (GOx) without the use of any mediators. Higher protein concentration was observed on ZnO as compared to AZO with higher specific activity for ZnO (0.042 U mg−1) compared to AZO (0.032 U mg−1), and was in agreement with cyclic voltemmetry (CV). X-ray photoelectron spectroscopy (XPS) suggested that the protein was bound by dipole interactions between AZO lattice oxygen and the amino group of the enzyme. Chronoamperometry showed sensitivity of 5.5 μA mM−1 cm−2 towards glucose for GOx/AZO and 2.2 μA mM−1 cm−2 for GOx/ZnO. The limit of detection (LoD) was 167 μM of glucose for GOx/AZO, as compared to 360 μM for GOx/ZnO. The linearity was 0.28–28 mM for GOx/AZO whereas it was 0.6–28 mM for GOx/ZnO with a response time of 10s. Possibly due to higher enzyme loading, the decrease of impedance in presence of glucose was larger for GOx/ZnO as compared to GOx/AZO in electrochemical impedance spectroscopy (EIS). Analyses with clinical blood serum samples showed that the systems had good reproducibility and accuracy. The characteristics of novel ZnO and AZO thin films with GOx as a model enzyme, should prove useful for the future fabrication of inexpensive, highly sensitive, disposable electrochemical biosensors for high throughput diagnostics

An Efficient Catalytic Method for Regioselective Sulfenylation of Electron-rich Aza-aromatics at RoomTtemperature

Electron-rich aza-aromatic compounds such as indoles and pyrroles represent systems of particular interest and importance in organic chemistry. An useful methodology for regioselective direct introduction of sulfenyl group on electron-rich aza-aromatics through S-alkyl and S-arylthiophthalimides as sulfenylating agents is described. Catalytic amounts of CeCl3.7H2O-NaI system are crucial to the promotion of this regioselective carbon-sulfur bond-forming Friedel-Crafts reaction. The reaction occurred in mild conditions and the products were obtained in good to excellent yields. Due to the large importance of functionalized indoles among natural compounds and pharmaceutical products, the methodology represents an efficient preparation of sulfenyl aza-aromatics, which are useful intermediates for important organic transformations

Pokušaji lociranja i uzorkovanja velike bijele psine, Carcharodon carcharias (Lamniformes: Lamnidae), uz talijansku obalu u Sredozemnom moru

Described in the present report are documented attempts to tag and sample the white shark, Carcharodon carcharias (Linnaeus, 1758), along Italian coasts in the Mediterranean Sea, which took place near the Lampedusa Island in the lower Tyrrhenian Channel of Sicily, off the coast of Rimini in the Adriatic Sea, and of Civitavecchia in the central Tyrrhenian Sea. The project, activated in 2015, was aimed at tagging and sampling specimens of the white shark in order to collect data useful to implement conservation strategies in the Mediterranean Sea. Despite four tagging attempts made in 2017, 2018, 2021, and 2022 with 288 total hours of baiting activity and the use of 1030 kg of chum, no white sharks or any other shark species were sighted.U radu su dokumentirani pokušaji označavanja i uzorkovanja velike bijele psine Carcharodon carcharias (Linnaeus, 1758) uz talijansku obalu u Sredozemnom moru. Istraživanje je obavljeno na području oko otoka Lampeduze, u sicilijanskom kanalu u južnom Tirenskom moru, ispred Riminija u Jadranskom moru te kod Civitavecchije u centralnom Tirenskom moru. Projekt, koji je započeo 2015. godine, bio je usmjeren na označavanje i uzorkovanje primjeraka velike bijele psine s ciljem prikupljanja podataka važnih za implementaciju mjera za očuvanje populacije ove vrste u Sredozemnom moru. Unatoč četiri pokušaja označavanja obavljena 2017., 2018., 2021. i 2022. godine, u ukupnom trajanju od 288 sati primamljivanja uz pomoć mamca te 1030 kg mamca, ni jedan primjerak velike bijele psine, ni drugih vrsta morskih pasa, nije primijećen

Anodic biofilms as the interphase for electroactive bacterial growth on carbon veil

© 2016 American Vacuum Society. The structure and activity of electrochemically active biofilms (EABs) are usually investigated on flat electrodes. However, real world applications such as wastewater treatment and bioelectrosynthesis require tridimensional electrodes to increase surface area and facilitate EAB attachment. The structure and activity of thick EABs grown on high surface area electrodes are difficult to characterize with electrochemical and microscopy methods. Here, the authors adopt a stacked electrode configuration to simulate the high surface and the tridimensional structure of an electrode for large-scale EAB applications. Each layer of the stacked electrode is independently characterized using confocal laser scanning microscopy (CLSM) and digital image processing. Shewanella oneidensis MR-1 biofilm on stacked carbon veil electrodes is grown under constant oxidative potentials (0, +200, and +400mV versus Ag/AgCl) until a stable current output is obtained. The textural, aerial, and volumetric parameters extracted from CLSM images allow tracking of the evolution of morphological properties within the stacked electrodes. The electrode layers facing the bulk liquid show higher biovolumes compared with the inner layer of the stack. The electrochemical performance of S. oneidensis MR-1 is directly linked to the overall biofilm volume as well as connectivity between cell clusters