The use of exoelectrogens in microbial fuel cells (MFCs) has given a wide berth to the addition of artificial electron shuttles/conduits as they have the molecular machinery to transfer the electrons exogenously to the electrode surface or to soluble or insoluble electron acceptors. Exoelectrogens transfer the electrons either directly to the electrode surface (via c-Cyts or pili) and/or mediate them by secreting electron shuttles such as, flavins or pyocyanin. Such microorganisms form electroactive biofilms on the electrode surface. They produce cyclopropane fatty acids and exopolysaccahride matrix to modify surface charge, which also provides favorable anchoring points for the retention of c-type cytochromes (c-Cyts). The longer subunit of PilA plays a vital role in cell attachment in the case of a well-known exoelectrogen Geobacter sulfurreducens during biofilm formation. G. sulfurreducens relies on flavin molecules for mediated electron transfer (MET) during initial biofilm formation and on c-Cyts and pili for the direct electron transfer (DET) during the later phase of biofilm formation. A new protein, cbcl inner membrane multiheme c-Cyt has been revealed in G. sulfurreducens that participates in the electron transfer when electron acceptor with low reduction potential (below 0.1 V) is used in the MFCs. On the other hand, inner membrane c-type cytochrome ImcH is involved in the reduction of electron acceptors exhibiting the potential above 0.1 V. Shewanella oneidensis, another exoelectrogen expresses CheA-3 histidine protein kinase for chemotactic responses to electron acceptors. S. oneidensis do not produce pili and utilizes flavin-cytochrome complexes to regulate the electron transfer to the electrode surfaces. The inherent electron transfer rates can be increased in order to improve the MFC performance. Such strategies as the anode surface modification with nanoparticles, expression of the genes for flavin biosynthesis pathway in the exoelectrogens, and chemical treatment of the microbial membrane have shown to increase the current outputs in the MFCs. This article provides the latest information about the exoelectrogens and molecular drivers involved in extracellular electron transfer (EET) mechanisms, and also summarizes the important characteristics of electroactive biofilms. It also highlights the different approaches that have been employed to facilitate the EET mechanisms and some uncommon exoelectrogens used in the MFCs recently.

Exoelectrogens: Recent Advances in Molecular Drivers Involved in Extracellular Electron Transfer and Strategies used to Improve it for Microbial Fuel Cell Applications

Nanoparticle technology for heavy oil in-situ upgrading and recovery enhancement: Opportunities and challenges

Microbial fuel cell (MFC) harnesses the metabolic activities of microorganism to generate electricity from substrate oxidation. However, the power generated from the MFC is relatively low for practical applications, thus the urgent need for its improvement. In MFC, anode is a crucial component of the setup, both structurally and functionally. It provides support for bacterial attachment and simultaneously acts as a sink for electrons from substrate metabolism. Poor performance of anode electrode in MFC is still a major setback for its practical applications. Successful anode electrode modification is expected to enhance the MFC electricity generation efficiency. Materials such as carbon nanotube, stainless steel, conducting polymers, metal oxides, and electrolytes have been employed as anode electrode modifiers with varying degree of success. Henceforth, this communication highlights and discusses the latest research advances made in MFC anode electrode modification using the aforementioned materials. The importance of the modification methods and their consequences towards anode architecture, biocompatibility, and longevity to improve the overall MFC performance are discussed.

Mini-review: Anode modification for improved performance of microbial fuel cell

Conventional biological wastewater treatment processes are energy-intensive endeavors that yield little or no recovered resources and often require significant external chemical inputs. However, with embedded energy in both organic carbon and nutrients (N, P), wastewater has the potential for substantial energy recovery from a low-value (or no-value) feedstock. A paradigm shift is thus now underway that is transforming our understanding of necessary energy inputs, and potential energy or resource outputs, from wastewater treatment, and energy neutral or even energy positive treatment is increasingly emphasized in practice. As two energy sources in domestic wastewater, we argue that the most suitable way to maximize energy recovery from wastewater treatment is to separate carbon and nutrient (particularly N) removal processes. Innovative anaerobic treatment technologies and bioelectrochemical processes are now being developed as high efficiency methods for energy recovery from waste COD. Recently, energy savings or even generation from N removal has become a hotspot of research and development activity, and nitritation–anammox, the newly developed CANDO process, and microalgae cultivation are considered promising techniques. In this paper, we critically review these five emerging low energy or energy positive bioprocesses for sustainable wastewater treatment, with a particular focus on energy optimization in management of nitrogenous oxygen demand. Taken together, these technologies are now charting a path towards to a new paradigm of resource and energy recovery from wastewater.

Towards energy neutral wastewater treatment: methodology and state of the art

The outbreak of the coronavirus disease (COVID-19) pandemic caused by the novel coronavirus (SARS-CoV-2) has been declared an international public health crisis. It is essential to develop diagnostic tests that can quickly identify infected individuals to limit the spread of the virus and assign treatment options. Herein, we report a proof-of-concept label-free electrochemical immunoassay for the rapid detection of SARS-CoV-2 virus via the spike surface protein. The assay consists of a graphene working electrode functionalized with anti-spike antibodies. The concept of the immunosensor is to detect the signal perturbation obtained from ferri/ferrocyanide measurements after binding of the antigen during 45 min of incubation with a sample. The absolute change in the [Fe(CN)6]3-/4- current upon increasing antigen concentrations on the immunosensor surface was used to determine the detection range of the spike protein. The sensor was able to detect a specific signal above 260 nM (20 µg/mL) of subunit 1 of recombinant spike protein. Additionally, it was able to detect SARS-CoV-2 at a concentration of 5.5 × 105 PFU/mL, which is within the physiologically relevant concentration range. The novel immunosensor has a significantly faster analysis time than the standard qPCR and is operated by a portable device which can enable on-site diagnosis of infection.

https://www.mdpi.com/1424-8220/21/2/390/pdf

Rapid SARS-CoV-2 Detection Using Electrochemical Immunosensor.

Nanomodification of the electrodes in microbial fuel cell: Impact of nanoparticle density on electricity production and microbial community

The ecotoxicity of platinum nanoparticles (PtNPs) widely used in for example automotive catalytic converters, is largely unknown. This study employs various characterization techniques and toxicity end points to investigate PtNP toxicity toward the green microalgae Pseudokirchneriella subcapitata and Chlamydomonas reinhardtii. Growth rate inhibition occurred in standard ISO tests (EC50 values of 15–200 mg Pt/L), but also in a double-vial setup, separating cells from PtNPs, thus demonstrating shading as an important artifact for PtNP toxicity. Negligible membrane damage, but substantial oxidative stress was detected at 0.1–80 mg Pt/L in both algal species using flow cytometry. PtNPs caused growth rate inhibition and oxidative stress in P. subcapitata, beyond what was accounted for by dissolved Pt, indicating NP-specific toxicity of PtNPs. Overall, P. subcapitata was found to be more sensitive toward PtNPs and higher body burdens were measured in this species, possibly due to a favored binding of Pt to the ...

/pdf/a-multimethod-approach-for-investigating-algal-toxicity-of-5ge7gqtv7v.pdf

A Multimethod Approach for Investigating Algal Toxicity of Platinum Nanoparticles

Pyocyanin is a virulence factor uniquely produced by the pathogen Pseudomonas aeruginosa. The fast and selective detection of pyocyanin in clinical samples can reveal important information about the presence of this microorganism in patients. Electrochemical sensing of the redox-active pyocyanin is a route to directly quantify pyocyanin in real time and in situ in hospitals and clinics. The selective quantification of pyocyanin is, however, limited by other redox-active compounds existing in human fluids and by other metabolites produced by pathogenic bacteria. Here we present a direct selective method to detect pyocyanin in a complex electroactive environment using commercially available electrodes. It is shown that cyclic voltammetry measurements between −1.0 V to 1.0 V reveal a potential detection window of pyocyanin of 0.58–0.82 V that is unaffected by other redox-active interferents. The linear quantification of pyocyanin has an R2 value of 0.991 across the clinically relevant concentration range of 2–100 µM. The proposed method was tested on human saliva showing a standard deviation of 2.5% ± 1% (n = 5) from the known added pyocyanin concentration to the samples. This inexpensive procedure is suggested for clinical use in monitoring the presence and state of P. aeruginosa infection in patients.

/pdf/fast-selective-detection-of-pyocyanin-using-cyclic-nwlb64c8ac.pdf

Fast Selective Detection of Pyocyanin Using Cyclic Voltammetry

/pdf/electrochemical-sensing-of-biomarker-for-diagnostics-of-be38omfq9k.pdf

Fatima AlZahraa Alatraktchi

Papers

Rapid SARS-CoV-2 Detection Using Electrochemical Immunosensor.

Nanomodification of the electrodes in microbial fuel cell: Impact of nanoparticle density on electricity production and microbial community

A Multimethod Approach for Investigating Algal Toxicity of Platinum Nanoparticles

Fast Selective Detection of Pyocyanin Using Cyclic Voltammetry

Electrochemical sensing of biomarker for diagnostics of bacteria-specific infections