Silver nanoparticles decorated ZnO-CuO core-shell nanowire arrays with low water adhesion and high antibacterial activity.

Nanostructured surfaces based on silver nanoparticles decorated ZnO-CuO core-shell nanowire arrays, which can assure protection against various environmental factors such as water and bacteria were developed by combining dry preparation techniques namely thermal oxidation in air, radio frequency (RF) magnetron sputtering and thermal vacuum evaporation. Thus, high-aspect-ratio ZnO nanowire arrays were grown directly on zinc foils by thermal oxidation in air. Further ZnO nanowires were coated with a CuO layer by RF magnetron sputtering, the obtained ZnO-CuO core-shell nanowires being decorated with Ag nanoparticles by thermal vacuum evaporation. The prepared samples were comprehensively assessed from morphological, compositional, structural, optical, surface chemistry, wetting and antibacterial activity point of view. The wettability studies show that native Zn foil and ZnO nanowire arrays grown on it are featured by a high water droplet adhesion while ZnO-CuO core-shell nanowire arrays (before and after decoration with Ag nanoparticles) reveal a low water droplet adhesion. The antibacterial tests carried on Escherichia coli (a Gram-negative bacterium) and Staphylococcus aureus (a Gram-positive bacterium) emphasize that the nanostructured surfaces based on nanowire arrays present excellent antibacterial activity against both type of bacteria. This study proves that functional surfaces obtained by relatively simple and highly reproducible preparation techniques that can be easily scaled to large area are very attractive in the field of water repellent coatings with enhanced antibacterial function.

Quantifiable Relationship Between Antibacterial Efficacy and Electro-Mechanical Intervention on Nanowire Arrays.

Physical disruption is an important antibacterial means as it is lethal to bacteria without spurring antimicrobial resistance. However, it is very challenging to establish a quantifiable relationship between antibacterial efficacy and physical interactions such as mechanical and electrical forces. Herein, titanium nitride (TN) nanowires with adjustable orientations and capacitances are prepared to exert gradient electro-mechanical forces on bacteria. While vertical nanowires show the strongest mechanical force resulting in an antibacterial efficiency of 0.62 log reduction (vs 0.22 for tiled and 0.36 for inclined nanowires, respectively), the addition of electrical charges maximizes the electro-mechanical interactions and elevates the antibacterial efficacy to more than 3 log reduction. Biophysical and biochemical analyses indicate that electrostatic attraction by electrical charge narrows the interface. The electro-mechanical intervention more easily stiffens and rips the bacteria membrane, disturbing the electron balance and generating intracellular oxidative stress. The antibacterial ability is maintained in vivo and bacteria-challenged rats are protected from serious infection. The physical bacteria-killing process demonstrated here can be controlled by adjusting the electro-mechanical interactions. Overall, these results revealed important principles for rationally designing high-performance antibacterial interfaces for clinical applications.

Microbial nanowires: type IV pili or cytochrome filaments?

A dynamic field of study has emerged involving long-range electron transport by extracellular filaments in anaerobic bacteria, with Geobacter sulfurreducens being used as a model system. The interest in this topic stems from the potential uses of such systems in bioremediation, energy generation, and new bio-based nanotechnology for electronic devices. These conductive extracellular filaments were originally thought, based upon low-resolution observations of dried samples, to be type IV pili (T4P). However, the recently published atomic structure for the T4P from G. sulfurreducens, obtained by cryo-electron microscopy (cryo-EM), is incompatible with the numerous models that have been put forward for electron conduction. As with all high-resolution structures of T4P, the G. sulfurreducens T4P structure shows a partial melting of the α-helix that substantially impacts the aromatic residue positions such that they are incompatible with conductivity. Furthermore, new work using high-resolution cryo-EM shows that conductive filaments thought to be T4P are actually polymerized cytochromes, with stacked heme groups forming a continuous conductive wire, or extracellular DNA. Recent atomic structures of three different cytochrome filaments from G. sulfurreducens suggest that such polymers evolved independently on multiple occasions. The expectation is that such polymerized cytochromes may be found emanating from other anaerobic organisms.

Dual antifungal activity against Candida albicans of copper metallic nanostructures and hierarchical copper oxide marigold-like nanostructures grown in situ in the culture medium.

AIMS: This study aimed to determine in vitro activity of copper nanoparticles and copper nanowires against Candida albicans strains and to assess their effects on morphology and submicron structure. METHODS AND RESULTS: The microdilution method determined the minimal inhibitory concentration (MIC) of copper nanoparticles (CuNPs) and copper nanowires (CuNWs) against three strains of C. albicans: ATCC 10231 and two clinical strains (C and E). Effects on the morphology and ultrastructure of C. albicans strains were examined by scanning electron microscopy and transmission electron microscopy. MIC for CuNPs was 129·7 µg ml-1 for strain ATCC 10231, 1037·5 µg ml-1 for strain C and 518·8 µg ml-1 for strain E. MIC for CuNWs was similar for all strains tested (260·3 µg ml-1 ). SEM and TEM studies showed alterations in morphology, cell wall and the complete collapse of the yeast after incubation with CuNPs. In contrast, most of the yeast cells maintained their structure with an intact cell wall, and only decreased the number and size of fimbriae when C. albicans was exposed to CuNWs. CuNPs and CuNWs formed hierarchical copper oxide nanostructures growing in situ in the culture medium. Results suggest a dual mechanism for antifungal activity: (i) free Cu2+ ions act as a biocide, (ii) sharp edges of marigold-like petal nanostructures could injure the cellular wall and membrane and cause the death of the yeast. CONCLUSIONS: CuNPs and CuNWs inhibited the growth of the three strains of C. albicans tested. Moreover, CuNPs disrupted cell wall with leakage of the cytoplasmic content. Each concentration of the series used for the determination of the activity of CuNPs and nanowires against C. albicans formed copper oxide marigold-like nanostructures. SIGNIFICANCE AND IMPACT OF THE STUDY: This study suggests that CuNPs and CuNWs are good candidates for formulating new therapeutic agents for candidiasis.

The blind men and the filament: Understanding structures and functions of microbial nanowires.

Extracellular electron transfer via filamentous protein appendages called 'microbial nanowires' has long been studied in Geobacter and other bacteria because of their crucial role in globally-important environmental processes and their applications for bioenergy, biofuels, and bioelectronics. Thousands of papers thought these nanowires as pili without direct evidence. Here, we summarize recent discoveries that could help resolve two decades of confounding observations. Using cryo-electron microscopy with multimodal functional imaging and a suite of electrical, biochemical, and physiological studies, we find that rather than pili, nanowires are composed of cytochromes OmcS and OmcZ that transport electrons via seamless stacking of hemes over micrometers. We discuss the physiological need for two different nanowires and their potential applications for sensing, synthesis, and energy production.

High-Performance Core/Shell of ZnO/TiO2 Nanowire with AgCl-Doped CdSe Quantum Dots Arrays as Electron Transport Layer for Perovskite Solar Cells.

Most previous studies of perovskite core/shell structures have been based on ZnO/TiO2 nanowires (NWs), which are not suitable for high photoelectric conversion efficiency. Here, core/shell ZnO/TiO2 NWs with AgCl-doped CdSe quantum dots were fabricated as an electron transport layer (ETL) for perovskite solar cells, based on ZnO/TiO2 arrays. We designed CdSe with AgCl dopants that were synthesized by a colloidal process. An improvement of the recombination barrier (Rct1), due to shell supplementation with AgCl-doped CdSe quantum dots, improved the open circuit voltage, the fill factor, and the adsorption capacity of CH3NH3PbI3 perovskite with NWs. The enhanced cell steady state was attributable to TiO2 with AgCl-doped CdSe QD supplementation. A maximum power conversion efficiency of 15.12% was attained in an atmospheric environment. The mechanism of the recombination and electron transport in the perovskite solar cells becoming the basis of ZnO/TiO2 core/shell arrays was investigated to represent the merit of ZnO/TiO2 core/shell arrays as an electron transport layer in effective devices. These results showed an uncomplicated approach for restraining non-radiative recombination loss in hetero-structure core/shell arrays to significantly improve perovskite solar cell performance and increase the effectiveness of photovoltaics.

Fiber organic electrochemical transistors based on multi-walled carbon nanotube and polypyrrole composites for noninvasive lactate sensing.

Multi-walled carbon nanotubes (MWCNT) play a synergistic role with conducting polymer in practical applications such as biological sensing. In this paper, multi-walled carbon nanotube and polypyrrole (PPy) composites were prepared on a fiber surface for the first time, and their morphology and electrical properties were characterized. Compared with PPy-coated fiber, the presence of carbon nanotubes induced the growth of large areas of PPy nanowires. In addition, fiber organic electrochemical transistors (FECTs) based on PPy and MWCNT were assembled, showing a higher on/off ratio, better stability, and greater flexibility. The lactate biosensor based on FECTs exhibits high sensitivity, with a correlation coefficient of R = 0.9889, quick response time of 0.6-0.8 s, a wide linear response range of 1 nM-1 mM, and excellent selectivity for lactate. Furthermore, the lactate concentration in human sweat was successfully detected by a FECT-based sensor. The hybrid fibers can be easily woven and placed on fabric simply by stitching. This favorable performance of the FECT-based sensor makes it suitable for noninvasive sensing of lactate. Therefore, it provides a promising platform for future use in healthcare and detection applications. Graphical abstract.

Protein Nanowires: the Electrification of the Microbial World and Maybe Our Own.

Electrically conductive protein nanowires appear to be widespread in the microbial world and are a revolutionary "green" material for the fabrication of electronic devices. Electrically conductive pili (e-pili) assembled from type IV pilin monomers have independently evolved multiple times in microbial history as have electrically conductive archaella (e-archaella) assembled from homologous archaellin monomers. A role for e-pili in long-range (micrometer) extracellular electron transport has been demonstrated in some microbes. The surprising finding of e-pili in syntrophic bacteria and the role of e-pili as conduits for direct interspecies electron transfer have necessitated a reassessment of routes for electron flux in important methanogenic environments, such as anaerobic digesters and terrestrial wetlands. Pilin monomers similar to those found in e-pili may also be a major building block of the conductive "cables" that transport electrons over centimeter distances through continuous filaments of cable bacteria consisting of a thousand cells or more. Protein nanowires harvested from microbes have many functional and sustainability advantages over traditional nanowire materials and have already yielded novel electronic devices for sustainable electricity production, neuromorphic memory, and sensing. e-pili can be mass produced with an Escherichia coli chassis, providing a ready source of material for electronics as well as for studies on the basic mechanisms for long-range electron transport along protein nanowires. Continued exploration is required to better understand the electrification of microbial communities with microbial nanowires and to expand the "green toolbox" of sustainable materials for wiring and powering the emerging "Internet of things."

In-Situ Synthesis of Heterostructured Carbon-Coated Co/MnO Nanowire Arrays for High-Performance Anodes in Asymmetric Supercapacitors.

Structural design is often investigated to decrease the electron transfer depletion in/on the pseudocapacitive electrode for excellent capacitance performance. However, a simple way to improve the internal and external electron transfer efficiency is still challenging. In this work, we prepared a novel structure composed of cobalt (Co) nanoparticles (NPs) embedded MnO nanowires (NWs) with an N-doped carbon (NC) coating on carbon cloth (CC) by in situ thermal treatment of polydopamine (PDA) coated MnCo2O4.5 NWs in an inert atmosphere. The PDA coating was carbonized into the NC shell and simultaneously reduced the MnCo2O4.5 to Co NPs and MnO NWs, which greatly improve the surface and internal electron transfer ability on/in MnO boding well supercapacitive properties. The hybrid electrode shows a high specific capacitance of 747 F g-1 at 1 A g-1 and good cycling stability with 93% capacitance retention after 5,000 cycles at 10 A g-1. By coupling with vanadium nitride with an N-doped carbon coating (VN@NC) negative electrode, the asymmetric supercapacitor delivers a high energy density of 48.15 Wh kg-1 for a power density of 0.96 kW kg-1 as well as outstanding cycling performance with 82% retention after 2000 cycles at 10 A g-1. The electrode design and synthesis suggests large potential in the production of high-performance energy storage devices.

Magnetic nanowires in biomedical applications.

Magnetic nanostructures and nanomaterials play essential roles in modern bio medicine and technology. Proper surface functionalization of nanoparticles (NPs) allows the selective bonding thus application of magnetic forces to a vast range of cellular structures and biomolecules. However, the spherical geometry of NPs poises a series of limitations in various potential applications. Mostly, typical spherical core shell structure consists of magnetic and non-magnetic layers have little tunability in terms of magnetic responses, and their single surface functionality also limits chemical activity and selectivity. In comparison to spherical NPs, nanowires (NWs) possess more degrees of freedom in achieving magnetic and surface chemical tenability. In addition to adjustment of magnetic anisotropy and inter-layer interactions, another important feature of NWs is their ability to combine different components along their length, which can result in diverse bio-magnetic applications. Magnetic NWs have become the candidate material for biomedical applications owing to their high magnetization, cheapness and cost effective synthesis. With large magnetic moment, anisotropy, biocompatibility and low toxicity, magnetic NWs have been recently used in living cell manipulation, magnetic cell separation and magnetic hyperthermia. In this review, the basic concepts of magnetic characteristics of nanoscale objects and the influences of aspect ratio, composition and diameter on magnetic properties of NWs are addressed. Some underpinning physical principles of magnetic hyperthermia (MH), magnetic resonance imaging (MRI) and magnetic separation (MS) have been discussed. Finally, recent studies on magnetic NWs for the applications in MH, MRI and MS were discussed in detail.

Molecularly imprinted polyaniline for detection of horseradish peroxidase.

A new facile and fast approach to the synthesis of polyaniline (PANi) molecularly imprinted polymers (MIPs) based on aniline oxidative chemical polymerization was proposed for protein recognition. For the first time, a surface imprinting strategy was implemented for the synthesis of PANi MIPs on the inner surface of soft glass polycapillaries (PC) with a large (2237) number of individual microcapillaries. Two different PANi layers-(i) PANi film and (ii) protein imprinted PANi nanowires-were synthesized sequentially. Uniform and highly stable PANi film was synthesized by oxidative polymerization at pH< 1. The synthesis of PANi MIPs on the PANi film pre-coated surface improved the reproducibility of PANi MIP formation. PANi MIP nanowires were synthesized at "mild" conditions (pH > 4.5) to preserve the protein template activity. The binding of horseradish peroxidase (HRP) molecules on the PANi MIP selective sites was confirmed by photometry (TMB chromogenic reaction), SEM images, and FTIR spectroscopy. The developed PANi MIPs enable HRP determination with a limit of detection (LOD) as low as 1.00 and 0.07 ng mL-1 on the glass slips and PC, respectively. The PANi MIPs are characterized by high stability; they are reversible and selective to HRP. The proposed approach allows PANi MIPs to be obtained for proteins on different supports and to create new materials for separation and sensing. Graphical abstract.

Synthesis of a PEDOT-TiO2 heterostructure as a dual biosensing platform operating via photoelectrochemical and electrochemical transduction mode.

A new organic-inorganic heterostructure was prepared by the hydrothermal deposition of poly (3,4-dioxoethylthiophene) (PEDOT) on TiO2 nanowire arrays (TiONWs) to construct a biosensor that can simultaneously function as photoelectrochemical (PEC) and electrochemical (EC) sensor to detect lactate. In both cases, the PEDOT-TiONWs heterostructure not only acted as an immobilization platform for lactate dehydrogenase (LDH) and coenzyme NAD+, but also generated current signals, which were further amplified by the cyclic catalytic mechanism. Specifically, LDH catalytically converted lactate to pyruvate, meanwhile NAD+ was transformed to NADH. For PEC sensing, the photo-generated holes from PEDOT-TiONWs could oxidize NADH back to NAD+, fulfilling a catalytic cycle. Herein, PEDOT significantly promoted the separation of electron-hole pairs and enhanced PEC signals due to its well-matched energy levels with TiONWs, high conductivity and strong visible light absorption. A dynamic range of 0.5-300 µM was observed between the PEC signals and lactate concentration, based on which a sensitivity of 0.1386 ± 0.0053 µA µM-1 and a detection limit of 0.08 ± 0.0032 µM were estimated. For EC sensing, PEDOT-TiONWs could directly oxidize NADH to NAD+ at ~0.54 V to realize the cyclic amplification due to the high conductivity and strong electrocatalytic capability of the heterostructure. The EC biosensor displayed a similar performance upon PEC mode of operation, except the relatively poor selectivity due to the possible oxidation of the interferences at the potentials > 0.54 V.

Bioinspired bio-voltage memristors.

Memristive devices are promising candidates to emulate biological computing. However, the typical switching voltages (0.2-2 V) in previously described devices are much higher than the amplitude in biological counterparts. Here we demonstrate a type of diffusive memristor, fabricated from the protein nanowires harvested from the bacterium Geobacter sulfurreducens, that functions at the biological voltages of 40-100 mV. Memristive function at biological voltages is possible because the protein nanowires catalyze metallization. Artificial neurons built from these memristors not only function at biological action potentials (e.g., 100 mV, 1 ms) but also exhibit temporal integration close to that in biological neurons. The potential of using the memristor to directly process biosensing signals is also demonstrated.

Controlled Fabrication of Optical Signal Input/Output Sites on Plasmonic Nanowires.

Silver nanowires have attracted considerable attention as subdiffraction limited diameter waveguides in a variety of applications including cell endoscopy and photonic integrated circuitry. Optical signal transport occurs by coupling light into propagating surface plasmons, which scatter back into light further along the wire. However, these interconversions only occur efficiently at wire ends, or at defects along the wire, which are not controlled during synthesis. Here, we overcome this limitation, demonstrating the visible laser light-induced fabrication of gold nanostructures at desired positions on silver nanowires, and their utility as efficient in/out coupling points for light. The gold nanostructures grow via plasmon-induced reduction of Au(III) and are shown to be excellent "hotspots" for surface-enhanced Raman scattering.

Optical Transduction for Vertical Nanowire Resonators.

We describe an optical transduction mechanism to measure the flexural mode vibrations of vertically aligned nanowires on a flat substrate with high sensitivity, linearity, and ease of implementation. We demonstrate that the light reflected from the substrate when a laser beam strikes it parallel to the nanowires is modulated proportionally to their vibration, so that measuring such modulation provides a highly efficient resonance readout. This mechanism is applicable to single nanowires or arrays without specific requirements regarding their geometry or array pattern, and no fabrication process besides the nanowire generation is required. We show how to optimize the performance of this mechanism by characterizing the split flexural modes of vertical silicon nanowires in their full dynamic range and up to the fifth mode order. The presented transduction approach is relevant for any application of nanowire resonators, particularly for integrating nanomechanical sensing in functional substrates based on vertical nanowires for biological applications.

Ultraminiaturized Stretchable Strain Sensors Based on Single Silicon Nanowires for Imperceptible Electronic Skins.

Miniaturized stretchable strain sensors are key components in E-skins for applications such as personalized health-monitoring, body motion perception, and human-machine interfaces. However, it remains a big challenge to fabricate miniaturized stretchable strain sensors with high imperceptibility. Here, we reported for the first time novel ultraminiaturized stretchable strain sensors based on single centimeter-long silicon nanowires (cm-SiNWs). With the diameter of the active materials even smaller than that of spider silks, these sensors are highly imperceptible. They exhibit a large strain sensing range (>45%) and a high durability (>10 000 cycles). Their optimum strain sensing ranges could be modulated by controlling the prestrains of the stretchable cm-SiNWs. On the basis of this capability, sensors with appropriate sensing ranges were chosen to respectively monitor large and subtle human motions including joint motion, swallow, and touch. The strategy of applying single cm-SiNWs in stretchable sensors would open new doors to fabricate ultraminiaturized stretchable devices.

Carboxylic Acid-Functionalized, Graphitic Layer-Coated Three-Dimensional SERS Substrate for Label-Free Analysis of Alzheimer's Disease Biomarkers.

Surface-enhanced Raman spectroscopy (SERS)-based protein analysis is a promising alternative to existing early stage diagnoses. However, SERS research conducted thus far accompanies challenges such as nonuniformity of plasmonic nanostructures, irregular coating of analytes, and denaturation of proteins, which seriously limit the practicability of suggested approaches. Here, we introduce a carboxylic acid-functionalized and graphitic nanolayer-coated three-dimensional SERS substrate (CGSS) fabricated by sequential nanotransfer printing. The substrate consists of well-defined, uniform gold nanowire arrays for effective Raman signal enhancement and a strong protein-immobilization layer. With an enhancement factor (EF) of 5.5 × 105, on par with the highest ever reported values, the CGSS allows the detection of protein conformational changes and the determination of protein concentration via Raman measurements. Exploiting the CGSS, we successfully measured the SERS spectra of Alzheimer's biomarkers, tau protein and amyloid ß, based on which secondary structural changes were analyzed quantitatively.

Structured silicon for revealing transient and integrated signal transductions in microbial systems.

Bacterial response to transient physical stress is critical to their homeostasis and survival in the dynamic natural environment. Because of the lack of biophysical tools capable of delivering precise and localized physical perturbations to a bacterial community, the underlying mechanism of microbial signal transduction has remained unexplored. Here, we developed multiscale and structured silicon (Si) materials as nongenetic optical transducers capable of modulating the activities of both single bacterial cells and biofilms at high spatiotemporal resolution. Upon optical stimulation, we capture a previously unidentified form of rapid, photothermal gradient-dependent, intercellular calcium signaling within the biofilm. We also found an unexpected coupling between calcium dynamics and biofilm mechanics, which could be of importance for biofilm resistance. Our results suggest that functional integration of Si materials and bacteria, and associated control of signal transduction, may lead to hybrid living matter toward future synthetic biology and adaptable materials.

Magneto-controlled enzyme reactions.

Various approaches to magneto-controlled biocatalytic enzyme reactions are discussed with specific example systems. Magnetic nano- and micro-size particles functionalized with enzymes or cofactors/electron transfer mediators have been used to translocate the components of the biocatalytic processes and to activate/inhibit their reactions. Magneto-induced deposition of the functionalized particles on an electrode surface resulted in activation of bioelectrocatalytic reactions. On the other hand, magneto-induced removal of the particles from the electrode surface resulted in the inhibition of the electrochemical reactions. Aggregation/disaggregation of enzyme-modified magnetic nanoparticles resulted in different mechanisms of biocatalytic cascades, changing them reversibly between substrate diffusion and substrate channeling processes. Magnetohydrodynamic activation of bioelectrocatalytic processes allowed enhancement of a biofuel cell operation. Overall, a large variety of possible magneto-controlled enzyme reactions is briefly discussed, particularly emphasizing their applications in different bioelectronic systems.

E-DNA biosensors of M. tuberculosis based on nanostructured polypyrrole.

The objective of this paper is to demonstrate the potential of nanostructured polypyrrole formed by template free as platform for amperometric detection of DNA. The nanowires of polypyrrole (nw-PPy) are formed through electrochemical polymerization and chemically modified by electrochemical oxidation of ethylene diamine or dendrimers PAMAM to obtain aminated surface. The DNA probe and ferrocenyl group, as redox reporter, were covalently linked to the surface of nw-PPy. The chemical structure of nanostructured platform was characterized through SEM, FT-IR and XPS and the electrochemical properties through cyclic voltammetry and electrochemical impedance spectroscopy (EIS). We show that the properties of nw-PPy such as, hydrophilic character and large surface area have large effect on the electronic properties. Thus, the electrochemical performance is increased compared to others nanomaterials considering the obtained value of the rate of electron transfer of 18 s-1. These properties allow enhanced DNA sensing where detection limit of 0.36 atomolar without any amplification step. The biosensor can be applied in detection of genomic DNA of Mycobacterium tuberculosis and the mutated one which present the resistance to rifampicin and large selectivity was demonstrated. We believe that nw-PPy modified with redox marker is a promising platform for electrochemical biosensors and can be applied for various diagnosis prospects.