Microbial nanowires with genetically modified peptide ligands to sustainably fabricate electronic sensing devices

Sensing devices fabricated with Escherichia coli expressing genetically tunable nanowires incorporated into a water-stable polymer

Electrically conductive, genetically tunable, pilin-based protein nanowires (ePNs) expressed in Escherichia coli grown on the biodiesel byproduct glycerol are a sustainable electronic material. They were previously shown to effectively function as sensing components for volatile analytes when deployed as thin films in electronic devices. However, thin-film devices are not suitable for analyzing components dissolved in water. To evaluate the possibility of fabricating a water-stable ePN matrix, ePNs purified from cells were mixed with polyvinyl butyral (PVB) to produce a transparent, electrically conductive, water-stable composite. ePN/PVB composite conductivity was tuned by changing the concentration of ePNs in the composite or genetically tailoring ePNs for different conductivities. Devices with an ePN/PVB sensing component rapidly responded in a linear fashion to changes in concentrations of dissolved ammonia or acetate. Genetically modifying nanowires to display an analyte-binding peptide on the ePN outer surface that was specific for ammonia or acetate increased sensing sensitivity and specificity. Composites comprised of whole cells of E. coli expressing ePNs and PVB were also electrically conductive. They functioned as sensing components whose sensitivity could also be tuned with the expression of ePNs displaying specific analyte-binding peptides. This approach avoids the laborious and time-consuming purification of protein nanowires from cells. The simplicity of sustainably fabricating an electronic sensing component with ePN-expressing E. coli mixed with a polymer, coupled with the potential of exquisitely tuning sensing specificity with facile 'plug and play' nanowire design, demonstrates the possibility of simply and inexpensively producing sensing devices for detecting a broad range of analytes.

Long-Distance Electron Transport in Unicellular Organisms and Biofilms

Electrical forces are widespread in single-celled organisms and underpin sophisticated communication systems. Bacterial biofilm colonies, for example, attract new members electrically. Bacteria also join together end to end and engage in long-distance electron transport along bacterial filaments over centimetres. This transport of electrons across around 10,000 cells separates life-essential redox reactions spatially and keeps "colleagues breathing" in otherwise challenging aquatic sediments.

Expression of filaments of the Geobacter extracellular cytochrome OmcS in Shewanella oneidensis

The physiological role of Geobacter sulfurreducens extracellular cytochrome filaments is a matter of debate and the development of proposed electronic device applications of cytochrome filaments awaits methods for large-scale cytochrome nanowire production. Functional studies in G. sulfurreducens are stymied by the broad diversity of redox-active proteins on the outer cell surface and the redundancy and plasticity of extracellular electron transport routes. G. sulfurreducens is a poor chassis for producing cytochrome nanowires for electronics because of its slow, low-yield, anaerobic growth. Here we report that filaments of the G. sulfurreducens cytochrome OmcS can be heterologously expressed in Shewanella oneidensis. Multiple lines of evidence demonstrated that a strain of S. oneidensis, expressing the G. sulfurreducens OmcS gene on a plasmid, localized OmcS on the outer cell surface. Atomic force microscopy revealed filaments with the unique morphology of OmcS filaments emanating from cells. Electron transfer to OmcS appeared to require a functional outer-membrane porin-cytochrome conduit. The results suggest that S. oneidensis, which grows rapidly to high culture densities under aerobic conditions, may be suitable for the development of a chassis for producing cytochrome nanowires for electronics applications and may also be a good model microbe for elucidating cytochrome filament function in anaerobic extracellular electron transfer.

Lack of physiological evidence for cytochrome filaments functioning as conduits for extracellular electron transfer

Extracellular cytochrome filaments are proposed to serve as conduits for long-range extracellular electron transfer. The primary functional physiological evidence has been the reported inhibition of Geobacter sulfurreducens Fe(III) oxide reduction when the gene for the filament-forming cytochrome OmcS is deleted. Here we report that the OmcS-deficient strain from that original report reduces Fe(III) oxide as well as the wild-type, as does a triple mutant in which the genes for the other known filament-forming cytochromes were also deleted. The triple cytochrome mutant displayed filaments with the same 3 nm diameter morphology and conductance as those produced by Escherichia coli heterologously expressing the G. sulfurreducens PilA pilin gene. Fe(III) oxide reduction was inhibited when the pilin gene in cytochrome-deficient mutants was modified to yield poorly conductive 3 nm diameter filaments. The results are consistent with the concept that 3 nm diameter electrically conductive pili (e-pili) are required for G. sulfurreducens long-range extracellular electron transfer. In contrast, rigorous physiological functional evidence is lacking for cytochrome filaments serving as conduits for long-range electron transport.

IMPORTANCE

Unraveling microbial extracellular electron transfer mechanisms has profound implications for environmental processes and advancing biological applications. This study on Geobacter sulfurreducens challenges prevailing beliefs on cytochrome filaments as crucial components thought to facilitate long-range electron transport. The discovery of an OmcS-deficient strain's unexpected effectiveness in Fe(III) oxide reduction prompted a reevaluation of the key conduits for extracellular electron transfer. By exploring the impact of genetic modifications on G. sulfurreducens' performance, this research sheds light on the importance of 3-nm diameter electrically conductive pili in Fe(III) oxide reduction. Reassessing these mechanisms is essential for uncovering the true drivers of extracellular electron transfer in microbial systems, offering insights that could revolutionize applications across diverse fields.

Generic Air-Gen Effect in Nanoporous Materials for Sustainable Energy Harvesting from Air Humidity

Air humidity is a vast, sustainable reservoir of energy that, unlike solar and wind, is continuously available. However, previously described technologies for harvesting energy from air humidity are either not continuous or require unique material synthesis or processing, which has stymied scalability and broad deployment. Here, a generic effect for continuous energy harvesting from air humidity is reported, which can be applied to a broad range of inorganic, organic, and biological materials. The common feature of these materials is that they are engineered with appropriate nanopores to allow air water to pass through and undergo dynamic adsorption-desorption exchange at the porous interface, resulting in surface charging. The top exposed interface experiences this dynamic interaction more than the bottom sealed interface in a thin-film device structure, yielding a spontaneous and sustained charging gradient for continuous electric output. Analyses of material properties and electric outputs lead to a "leaky capacitor" model that can describe how electricity is harvested and predict current behaviors consistent with experiments. Predictions from the model guide the fabrication of devices made from heterogeneous junctions of different materials to further expand the device category. The work opens a wide door for the broad exploration of sustainable electricity from air.

High-performance pyramid-SiNWs biosensor for NH3gas detection

NH3is widely existed in the environment and is closely associated with various health issues. Additionally, detecting the small amounts of NH3exhaled by patients with liver and kidney diseases offers potential opportunities for painless early disease diagnosis. Therefore, there is an urgent need for a convenient, rapid, and highly sensitive real-time NH3monitoring method. This work presents a high-performance NH3sensor based on olfactory receptor-derived peptides (ORPs) on a pyramid silicon nanowires (SiNWs) structure substrate. First, we successfully fabricated the pyramid-SiNWs structure on a silicon substrate using a chemical etching method. Subsequently, by dehydrative condensation reaction between the amino groups on APTES and the carboxyl groups of ORPs, ORPs were successfully immobilized onto the pyramid-SiNWs structure. This methodology allows the ORPs sensor on the pyramid-SiNWs substrate to detect NH3as low as 1 ppb, which was the reported lowest limit of detection, with a higher response rate compared to ORPs sensors on flat SiNWs substrates. The sensors also exhibit good sensitivity and stability for NH3gas detection. The results show the feasibility and potential applications of ORPs-pyramid-SiNWs structure sensors, in the fields of food safety, disease monitoring, and environmental protection, etc.