Bio-Nanohybrid Cell Based Signal Amplification System for Electrochemical Sensing.

A signal amplification system for electrochemical sensing was established by bio-nanohybrid cells (BNC) based on bacterial self-assembly and biomineralization. The BNC was constructed by partially encapsulating a Shewanella oneidensis MR-1 cell with the self-biomineralized iron sulfide nanoparticles. The iron sulfide nanoparticle encapsulated BNCs showed high transmembrane electron transfer efficiency and was explored as a superior redox cycling module. Impressively, by integrating this BNC redox cycling module into the electrochemical sensing system, the output signal was amplified over 260 times compared to that without the BNC module. Uniquely, with this BNC redox cycling system, ultrasensitive detection of riboflavin with an extremely low LOD of 0.2 nM was achieved. This work demonstrated the power of BNC in the area of biosensing and provided a new possibility for the design of a whole cell redox cycling based signal amplification system.

Engineered cytochrome fused extracellular matrix enabled efficient extracellular electron transfer and improved performance of microbial fuel cell.

Microbial fuel cell (MFC) was a promising technology for energy harvesting from wastewater. However, inefficient bacterial extracellular electron transfer (EET) limited the performance as well as the applications of MFC. Here, a new strategy to reinforce the EET by engineering synthetic extracellular matrix (ECM) with cytochrome fused curli was developed. By genetically fusing a minimal cytochrome domain (MCD) with the curli protein CsgA and heterogeneously expressing in model exoelectrogen of Shewanella oneidensis MR-1, the cytochrome fused electroactive curli network was successfully constructed and assembled. Interestingly, the strain with the MCD fused synthetic ECM delivered about 2.4 times and 2.0 times higher voltage and power density output than these of wild type MR-1 in MFC. More impressively, electrochemical analysis suggested that this synthetic ECM not only introduced cytochrome of MCD, but also attracted more self-secreted electrochemically active substances, which might facilitate the EET and improve the MFC performance. This work demonstrated the possibility to manipulation the EET with ECM engineering, which opened up new path for exoelectrogen design and engineering.

Wastewater-powered high-value chemical synthesis in a hybrid bioelectrochemical system.

A microbial electrochemical system could potentially be applied as a biosynthesis platform by extracting wastewater energy while converting it to value-added chemicals. However, the unfavorable thermodynamics and sluggish kinetics of in vivo whole-cell cathodic catalysis largely limit product diversity and value. Herein, we convert the in vivo cathodic reaction to in vitro enzymatic catalysis and develop a microbe-enzyme hybrid bioelectrochemical system (BES), where microbes release the electricity from wastewater (anode) to power enzymatic catalysis (cathode). Three representative examples for the synthesis of pharmaceutically relevant compounds, including halofunctionalized oleic acid based on a cascade reaction, (4-chlorophenyl)-(pyridin-2-yl)-methanol based on electrochemical cofactor regeneration, and l-3,4-dihydroxyphenylalanine based on electrochemical reduction, were demonstrated. According to the techno-economic analysis, this system could deliver high system profit, opening an avenue to a potentially viable wastewater-to-profit process while shedding scientific light on hybrid BES mechanisms toward a sustainable reuse of wastewater.

Single cell electron collectors for highly efficient wiring-up electronic abiotic/biotic interfaces.

By electronically wiring-up living cells with abiotic conductive surfaces, bioelectrochemical systems (BES) harvest energy and synthesize electric-/solar-chemicals with unmatched thermodynamic efficiency. However, the establishment of an efficient electronic interface between living cells and abiotic surfaces is hindered due to the requirement of extremely close contact and high interfacial area, which is quite challenging for cell and material engineering. Herein, we propose a new concept of a single cell electron collector, which is in-situ built with an interconnected intact conductive layer on and cross the individual cell membrane. The single cell electron collector forms intimate contact with the cellular electron transfer machinery and maximizes the interfacial area, achieving record-high interfacial electron transfer efficiency and BES performance. Thus, this single cell electron collector provides a superior tool to wire living cells with abiotic surfaces at the single-cell level and adds new dimensions for abiotic/biotic interface engineering.

A mediator-free whole-cell electrochemical biosensing system for sensitive assessment of heavy metal toxicity in water.

A bioelectrochemical sensing system (BES) based on electroactive bacteria (EAB) has been used as a new and promising tool for water toxicity assessment. However, most EAB can reduce heavy metals, which usually results in low toxicity response. Herein, a starvation pre-incubation strategy was developed which successfully avoided the metal reduction during the toxicity sensing period. By integrating this starvation pre-incubation procedure with the amperometric BES, a sensitive, robust and mediator-free biosensing method for heavy metal toxicity assessment was developed. Under the optimized conditions, the IC50 (half maximal inhibitory concentration) values for Cu2+, Ni2+, Cd2+, and Cr6+ obtained were 0.35, 3.49, 6.52, 2.48 mg L-1, respectively. The measurement with real water samples also suggested this method was reliable for practical application. This work demonstrates that it is feasible to use EAB for heavy metal toxicity assessment and provides a new tool for water toxicity warning.

Nano-spectroscopic imaging of proteins with near-field scanning optical microscopy (NSOM).

Understanding the hierarchical structure of proteins at their fundamental length scales is essential to get insights into their functions and roles in fundamental biological processes. Near-field scanning optical microscopy (NSOM), which overcomes the diffraction limits of conventional optics, provides a powerful analytical tool to image target proteins at nanoscale resolution. Especially, by combining NSOM with infrared (IR) or Raman spectroscopy, near-field nanospectroscopic imaging of a single protein is achieved. In this review, we present the recent technical progress of NSOM setup for nanospectroscopic imaging of proteins, and its application to nanospectroscopic analysis of protein structures is highlighted and critically reviewed. Finally, current challenges and perspectives on application of NSOM in emerging areas of industrial, environmental and medical biotechnology are discussed.

Bioelectrochemical biosensor for water toxicity detection: generation of dual signals for electrochemical assay confirmation.

Toxicity assessment of water is of great important to the safety of human health and to social security because of more and more toxic compounds that are spilled into the aquatic environment. Therefore, the development of fast and reliable toxicity assessment methods is of great interest and attracts much attention. In this study, by using the electrochemical activity of Shewanella oneidensis MR-1 cells as the toxicity indicator, 3,5-dichlorophenol (DCP) as the model toxic compound, a new biosensor for water toxicity assessment was developed. Strikingly, the presence of DCP in the water significantly inhibited the maximum current output of the S. oneidensis MR-1 in a three-electrode system and also retarded the current evolution by the cells. Under the optimized conditions, the maximum current output of the biosensor was proportional to the concentration of DCP up to 30 mg/L. The half maximal inhibitory concentration of DCP determined by this biosensor is about 14.5 mg/L. Furthermore, simultaneous monitoring of the retarded time (Δt) for current generation allowed the identification of another biosensor signal in response to DCP which could be employed to verify the electrochemical result by dual confirmation. Thus, the present study has provided a reliable and promising approach for water quality assessment and risk warning of water toxicity.

Amplification of electrochemical signal by a whole-cell redox reactivation module for ultrasensitive detection of pyocyanin.

A bioelectrochemical sensing system based on a novel whole-cell redox reactivation/cycling module for ultrasensitive detection of pyocyanin (the biomarker of Pseudomonas aeruginosa infections) was developed. The electroactive bacteria mediated redox reactivation module was constructed using Shewanella oneidensis MR-1 cells as the bioelectro-catalyst and lactate as the electron donor. It could regenerate reductive pyocyanin from its oxidative state, which enabled pyocyanin molecule repeatedly registered by the electrode. Uniquely, with this redox reactivation module, the electrochemical response of pyocyanin was amplified about 405 times (1.3 µA/nM vs. 3.2nA/nM). Thus, an ultrasensitive bioelectrochemical sensing system for pyocyanin quantification was developed by integrating the pyocyanin reactivation module with conventional electrochemical detection system. Remarkably, with this developed biosensing system, an extremely low LOD of 47±1pM was reached. Additionally, this biosensing system showed excellent resistance to interferences from human fluids or bacterial contamination. This work provided a simple, ultrasensitive and robust tool for pyocyanin detection, and more importantly, demonstrated a new dimension for electrochemical signal amplification in biosensing.