Bioelectrocatalysis is an interdisciplinary research field combining biocatalysis and electrocatalysis via the utilization of materials derived from biological systems as catalysts to catalyze the redox reactions occurring at an electrode. Bioelectrocatalysis synergistically couples the merits of both biocatalysis and electrocatalysis. The advantages of biocatalysis include high activity, high selectivity, wide substrate scope, and mild reaction conditions. The advantages of electrocatalysis include the possible utilization of renewable electricity as an electron source and high energy conversion efficiency. These properties are integrated to achieve selective biosensing, efficient energy conversion, and the production of diverse products. This review seeks to systematically and comprehensively detail the fundamentals, analyze the existing problems, summarize the development status and applications, and look toward the future development directions of bioelectrocatalysis. First, the structure, function, and modification of bioelectrocatalysts are discussed. Second, the essentials of bioelectrocatalytic systems, including electron transfer mechanisms, electrode materials, and reaction medium, are described. Third, the application of bioelectrocatalysis in the fields of biosensors, fuel cells, solar cells, catalytic mechanism studies, and bioelectrosyntheses of high-value chemicals are systematically summarized. Finally, future developments and a perspective on bioelectrocatalysis are suggested.

SignificanceQuorum sensing is a communication system that allows bacteria to coordinate their activities, and these systems are critical for virulence in several bacteria, including Pseudomonas aeruginosa. There is a significant gap in knowledge about how quorum sensing proceeds during infection, particularly how spatial organization of the infecting microbial community impacts signaling. Using a model that recapitulates the biogeographical properties of P. aeruginosa infection of the cystic fibrosis lung, we discovered that communication primarily occurs within P. aeruginosa aggregates and that communication between aggregates is only observed for very large aggregates containing ≥5,000 cells. This study identifies a critical role for spatial distribution and bacterial phenotypic heterogeneity in bacterial signaling during infection, and provides a platform for future ecological and evolutionary studies.

Here, we use a recently developed electrochemical sensing platform of transparent carbon ultramicroelectrode arrays (T-CUAs) for the in vitro detection of phenazine metabolites from the opportunistic human pathogen Pseudomonas aeruginosa. Specifically, redox-active metabolites pyocyanin (PYO), 5-methylphenazine-1-carboxylic acid (5-MCA), and 1hydroxyphenazine (OHPHZ) are produced by P. aeruginosa, which is commonly found in chronic wound infections and in the lungs of cystic fibrosis patients. As highly diffusible chemicals, PYO and other metabolites are extremely toxic to surrounding host cells and other competing microorganisms, thus their detection is of great importance as it could provide insights regarding P. aeruginosa virulence mechanisms. Phenazine metabolites are known to play important roles in cellular functions; however, very little is known about how their concentrations fluctuate and influence cellular behaviors over the course of infection and growth. Herein we report the use of easily assembled, low-cost electrochemical sensors that provide rapid response times, enhanced sensitivity, and high reproducibility. As such, these T-CUAs enable real-time electrochemical monitoring of PYO and another extremely reactive and distinct redox-active phenazine metabolite, 5-methylphenazine-1-carboxylic acid (5-MCA), from a highly virulent laboratory P. aeruginosa strain, PA14. In addition to quantifying phenazine metabolite concentrations, changes in phenazine dynamics are observed in the biosynthetic route for the production of PYO. Our quantitative results, over a 48-h period, show increasing PYO concentrations during the first 21 h of bacterial growth, after which PYO levels plateau and then slightly decrease. Additionally, we explore environmental effects on phenazine dynamics and PYO concentrations in two growth media, tryptic soy broth (TSB) and lysogeny broth (LB). The maximum concentrations of cellular PYO were determined to be 190 ± 5 μM and 150 ± 1 μM in TSB and LB, respectively. Finally, using desorption electrospray ionization (DESI) and nanoelectrospray ionization (nano-ESI) mass spectrometry we confirm the detection and identification of reactive phenazine metabolites.

Pyocyanin is a virulence factor produced as a secondary metabolite by the opportunistic human pathogen, Pseudomonas aeruginosa. Fast and direct detection of pyocyanin is of importance as it could provide important insights regarding P. aeruginosa's virulence mechanisms. Here, we present an electrochemical sensing platform of redox-active pyocyanin using transparent carbon ultramicroelectrode arrays (T-CUAs), which were made using a previously reported simple fabrication process ( Duay et al. Anal. Chem. 2015 , 87 , 10109 ). Square-wave voltammetry was used to quantify pyocyanin concentrations on T-CUAs with and without chitosan gold nanoparticles (CS/GNP) and planar transparent macroelectrodes (T-Macro). The response time (RT), limit of detection (LOD), and linear dynamic range (LDR) differ for each electrode type due to subtle influences in how the detectable signal varies in relation to the charging time and resistive and capacitive noise. In general lower LODs can be achieved at the consequence of smaller LDRs. The LOD for T-Macro was 0.75 ± 0.09 μM with a LDR of 0.75-25 μM, and the LOD for the CS/GNP 1.54 T-CUA was determined to be 1.6 ± 0.2 μM with a LDR of 1-100 μM, respectively. The LOD for the 1.54T-CUA with a larger LDR of 1-250 μM was 1.0 ± 0.3 μM. These LODs and LDRs fall within the range of PYO concentrations for a variety of in vitro and in vivo cellular environments and offer promise of the application of T-CUAs for the quantitative study of biotoxins, quorum sensing, and pathogenesis. Finally, we demonstrate the successful use of T-CUAs for the electrochemical detection of pyocyanin secreted from P. aeruginosa strains while optically imaging the cells. The secreted pyocyanin levels from two bacterial strains, PA11 and PA14, were measured to have concentrations of 45 ± 5 and 3 ± 2 μM, respectively.

Electrochemical sensors designed for rapid diagnosis, detection and real-time monitoring of bacterial pathogens in hospital settings.

No abstract

Transparent carbon ultramicroelectrode arrays (T-CUAs) were made using a previously reported facile fabrication method (Duay et al. Anal. Chem. 2015, 87, 10109). Two modifications introduced to the T-CUAs were examined for their analytical response to nitric oxide (NO•). The first modification was the application of a cellulose acetate (CA) gas permeable membrane. Its selectivity to NO• was extensively characterized via chronoamperometry, electrochemical impedance spectroscopy (EIS), and atomic force microscopy (AFM). The thickness of the CA membrane was determined to be 100 nm and 88 ± 15 nm using AFM and EIS, respectively. Furthermore, the partition and diffusion coefficients of NO• within the CA membrane were determined to be 0.0500 and 2.44 × 10–13 m2/s using EIS measurements. The second modification to the 1.54T-CUA was the introduction of chitosan and gold nanoparticles (CS/GNPs) to enhance its catalytic activity, sensitivity, and limit of detection (LOD) to NO•. Square wave voltammetry was used to quantify the NO• concentration at the CA membrane covered 1.54T-CUA with and without CS/GNPs; the LODs were determined to be 0.2 ± 0.1 and 0.44 ± 0.02 μM (S/N = 3), with sensitivities of 9 ± 9 and 1.2 ± 0.4 nA/μM, respectively. Our results indicate that this modification to the arrays results in a significant catalytic enhancement to the electrochemical oxidation of NO•. Hence, these electrodes allow for the in situ mechanistic and kinetic characterization of electrochemical reactions with high electroanalytical sensitivity.

The development of electrochemical catalytic conversion of 5‐hydroxymethylfurfural (HMF) has recently gained attention as a potentially scalable approach for both oxidation and reduction processes yielding value‐added products. While the possibility of electrocatalytic HMF transformations has been demonstrated, this growing research area is in its initial stages. Additionally, its practical applications remain limited due to low catalytic activity and product selectivity. Understanding the catalytic processes and design of electrocatalysts are important in achieving a selective and complete conversion into the desired highly valuable products. In this Minireview, an overview of the most recent status, advances, and challenges of oxidation and reduction processes of HMF was provided. Discussion and summary of voltammetric studies and important reaction factors (e. g., catalyst type, electrode material) were included. Finally, biocatalysts (e. g., enzymes, whole cells) were introduced for HMF modification, and future opportunities to combine biocatalysts with electrochemical methods for the production of high‐value chemicals from HMF were discussed.