Single-Layer Hexagonal Boron Nitride Nanopores as High-Performance Ionic Gradient Power Generators.

Atomically thin two-dimensional (2D) materials have emerged as promising candidates for efficient energy harvesting from ionic gradients. However, the exploration of robust 2D atomically thin nanopore membranes, which hold sufficient ionic selectivity and high ion permeability, remains challenging. Here, the single-layer hexagonal boron nitride (hBN) nanopores are demonstrated as various high-performance ion-gradient nanopower harvesters. Benefiting from the ultrathin atomic thickness and large surface charge (also a large Dukhin number), the hBN nanopore can realize fast proton transport while maintaining excellent cation selectivity even in highly acidic environments. Therefore, a single hBN nanopore achieves the pure osmosis-driven proton-gradient power up to ≈3 nW under 1000-fold ionic gradient. In addition, the robustness of hBN membranes in extreme pH conditions allows the ionic gradient power generation from acid-base neutralization. Utilizing 1 m HCl/KOH, the generated power can be promoted to an extraordinarily high level of ≈4.5 nW, over one magnitude higher than all existing ionic gradient power generators. The synergistic effects of ultrathin thickness, large surface charge, and excellent chemical inertness of 2D single-layer hBN render it a promising membrane candidate for harvesting ionic gradient powers, even under extreme pH conditions.

Spin-Polarized Photocatalytic CO2 Reduction of Mn-Doped Perovskite Nanoplates.

"Spin" has been recently reported as an important degree of electronic freedom to improve the performance of electrocatalysts and photocatalysts. This work demonstrates the manipulations of spin-polarized electrons in CsPbBr3 halide perovskite nanoplates (NPLs) to boost the photocatalytic CO2 reduction reaction (CO2RR) efficiencies by doping manganese cations (Mn2+) and applying an external magnetic field. Mn-doped CsPbBr3 (Mn-CsPbBr3) NPLs exhibit an outstanding photocatalytic CO2RR compared to pristine CsPbBr3 NPLs due to creating spin-polarized electrons after Mn doping. Notably, the photocatalytic CO2RR of Mn-CsPbBr3 NPLs is significantly enhanced by applying an external magnetic field. Mn-CsPbBr3 NPLs exhibit 5.7 times improved performance of photocatalytic CO2RR under a magnetic field of 300 mT with a permanent magnet compared to pristine CsPbBr3 NPLs. The corresponding mechanism is systematically investigated by magnetic circular dichroism spectroscopy, ultrafast transient absorption spectroscopy, and density functional theory simulation. The origin of enhanced photocatalytic CO2RR efficiencies of Mn-CsPbBr3 NPLs is due to the increased number of spin-polarized photoexcited carriers by synergistic doping of the magnetic elements and applying a magnetic field, resulting in prolonged carrier lifetime and suppressed charge recombination. Our result shows that manipulating spin-polarized electrons in photocatalytic semiconductors provides an effective strategy to boost photocatalytic CO2RR efficiencies.

Antibiotic Susceptibility Test with Surface-Enhanced Raman Scattering in a Microfluidic System.

Antibiotic susceptibility test (AST) is essential in clinical diagnosis of serious bacterial infection, such as sepsis, while it typically takes 2-5 days for sample culture, antibiotic treatment, and reading result. Detecting metabolites secreted from bacteria with surface-enhanced Raman scattering (SERS) enables rapid determination of antibiotic susceptibility, reducing the AST time to 1-2 days. However, it still requires 1 day of culture time to obtain sufficient quantity of bacteria for sample washing, bacterial extraction, and antibiotic treatment. Additionally, the whole procedure, manually performed in open environment, often suffers from contamination and human error. To address the above problems, a microfluidic system integrating membrane filtration and the SERS-active substrate (MF-SERS) was developed to perform on-chip bacterial enrichment, metabolite collection, and in situ SERS measurements for antibiotic susceptibility test. Using Escherichia coli as the prototype bacterium, the lowest SERS detection limit of bacterial concentration of the MF-SERS system is 103 CFU/mL, which is 4 orders of magnitude lower than that using centrifugation-purification procedure, significantly shortening the bacterial culture time. The bacteria and secreted metabolites are enclosed during bacterial trapping, metabolite filtration, and SERS detection, thus minimizing possible contamination and human errors. Finally, the successful demonstration of AST on E. coli with a concentration of 103 CFU/mL is presented. Overall, the MF-SERS system with a miniature size and well-confined microenvironment allows the integration of multiple bacteria processes for bacterial enrichment, culture, and determination of AST.

Highly Efficient Transfer of 7TM Membrane Protein from Native Membrane to Covalently Circularized Nanodisc.

Incorporating membrane proteins into membrane mimicking systems is an essential process for biophysical studies and structure determination. Monodisperse lipid nanodiscs have been found to be a suitable tool, as they provide a near-native lipid bilayer environment. Recently, a covalently circularized nanodisc (cND) assembled with a membrane scaffold protein (MSP) in circular form, instead of conventional linear form, has emerged. Covalently circularized nanodiscs have been shown to have improved stability, however the optimal strategies for the incorporation of membrane proteins, as well as the physicochemical properties of the membrane protein embedded in the cND, have not been studied. Bacteriorhodopsin (bR) is a seven-transmembrane helix (7TM) membrane protein, and it forms a two dimensional crystal consisting of trimeric bR on the purple membrane of halophilic archea. Here it is reported that the bR trimer in its active form can be directly incorporated into a cND from its native purple membrane. Furthermore, the assembly conditions of the native purple membrane nanodisc (PMND) were optimized to achieve homogeneity and high yield using a high sodium chloride concentration. Additionally, the native PMND was demonstrated to have the ability to assemble over a range of different pHs, suggesting flexibility in the preparation conditions. The native PMND was then found to not only preserve the trimeric structure of bR and most of the native lipids in the PM, but also maintained the photocycle function of bR. This suggests a promising potential for assembling a cND with a 7TM membrane protein, extracted directly from its native membrane environment, while preserving the protein conformation and lipid composition.

Optimization of the Production of Covalently Circularized Nanodiscs and Their Characterization in Physiological Conditions.

Lipid nanodiscs are widely used platforms for studying membrane proteins in a near-native environment. Lipid nanodiscs made with membrane scaffold proteins (MSPs) in the linear form have been well studied. Recently, a new kind of nanodisc made with MSPs in the circular form, referred to as covalently circularized nanodiscs (cNDs), has been reported to have some possible advantages in various applications. Given the potential of nanodisc technology, researchers in the field are very interested in learning more about this new kind of nanodisc, such as its reproducibility, production yield, and the possible pros and cons of using it. However, research on these issues is lacking. Here, we report a new study on nanodiscs made with circular MSPs, which are produced from a method different from the previously reported method. We show that our novel production method, detergent-assisted sortase-mediated ligation, can effectively avoid high-molecular-weight byproducts and also significantly improve the yield of the target proteins up to around 80% for larger circular MSP constructs. In terms of the application of circular MSPs, we demonstrate that they can be used to assemble nanodiscs using both synthetic lipids and native lipid extract as the source of lipids. We also show that bacteriorhodopsin can be successfully incorporated into this new kind of cND. Moreover, we found that cNDs have improved stability against both heat and high-concentration-induced aggregations, making them more beneficial for related applications.

Rapid detection of copper chlorophyll in vegetable oils based on surface-enhanced Raman spectroscopy.

The addition of copper chlorophyll and its derivatives (Cu-Chl) to vegetable oils to disguise them as more expensive oils, such as virgin olive oils, would not only create public confusion, but also disturb the olive oil market. Given that existing detection methods of Ch-Chl in oils, such as LC-MS are costly and time consuming, it is imperative to develop economical and fast analytical techniques to provide information quickly. This paper demonstrates a rapid analytical method based on surface-enhanced Raman spectroscopy (SERS) to detect Cu-Chl in vegetable oils; the spectroscopic markers of Cu-Chl are presented and a detection limit of 5 mg kg(-1) is demonstrated. The analysis of a series of commercial vegetable oils is undertaken with this method and the results verified by a government agency. This study shows that a SERS-based assessment method holds high potential for quickly pinpointing the addition of minute amounts of Cu-Chl in vegetable oils.

Label-free and culture-free microbe detection by three dimensional hot-junctions of flexible Raman-enhancing nanohybrid platelets.

Novel nanohybrid arrays of silver (Ag)-on-silicate platelets with flexibility and three-dimensional (3D) hot-junctions (particularly in z-direction) were discovered for improving the stability of free nanoparticles and the mobility of rigid (glass or silicon-based) substrates in surface-enhanced Raman scattering (SERS) detection technology. Since the Ag nanoparticles are adsorbed on both sides of few nanometer-thick silicate platelets (single-layer exfoliated clay), the geometric arrangement of Ag on both sides of the nanoplatelets (Ag/NSP) may induce strong hot-junctions (z-direction) in reference to the pristine montmorillonite clay (multi-layers) at the thickness of ∼20 nm, measured by small molecules (adenine of DNA) and bacteria (S. aureus). Enormous red-shifts (16 nm wavelength difference) were observed between single layer and multi-layer silicate platelets, showing that huge surface plasmon enhancement comes from hot junctions in the z-direction (∼7 times higher than 2D hot-junctions of traditional SERS biochips). Further, the Ag/NSP SERS substrate displays a free floating mobility and optical transparency (less background interference), which inherently increase the contacted surface-area between the substrate and microorganisms, to enhance the SERS sensitivity. The surface modulation with a surfactant could be complimentary towards a variety of microorganisms including hydrophobic microbes, irregular-shaped microorganisms and larger biological cells due to their mutual specific surface interactions. It was anticipated to apply in the rapid detection for varied microbes with label-free and culture-free characterizations.

A novel vertical fan-out platform based on an array of curved anodic alumina nanochannels.

Focused ion beam lithography and a two-step anodization have been combined to fabricate a vertical fan-out platform containing an array of unique probes. Each probe comprises three anodic alumina nanochannels with a fan-out arrangement. The lithography is used to pattern an aluminum sheet with a custom-designed array of triangular 'cells' whose apexes are composed of nanoholes. The nanoholes grow into straight nanochannels under proper voltage in the first-step anodization. The second step uses a doubled voltage to induce lateral repulsion among the nanochannels' growth fronts originating in the same cell. Therefore, the fronts fan out. The repulsion roots in the inter-front distance being shorter than the naturally favoured length, which increases with anodization voltage. The fan-out evolution continues until the growth fronts originating in all the cells evolve into a close-packed two-dimensional hexagonal lattice whose spacing is identical to the favoured one. The chemical and physical mechanisms behind the fan-out fabrication are discussed. This novel fan-out platform facilitates probing and handling of many signals from different areas on a sample's surface and is therefore promising for applications in detection and manipulation at the nanoscale level.

On-chip thin film Zernike phase plate for in-focus transmission electron microscopy imaging of organic materials.

Transmission electron microscopy (TEM) is a powerful tool for imaging nanostructures, yet its capability is limited with respect to the imaging of organic materials because of the intrinsic low contrast problem. TEM phase plates have been in development for decades, yet a reliable phase plate technique has not been available because the performance of TEM phase plates deteriorates too quickly. Such an obstacle prohibits in-focus TEM phase imaging to be routinely achievable, thus limiting the technique being used in practical applications. Here we present an on-chip thin film Zernike phase plate which can effectively release charging and allow reliable in-focus TEM images of organic materials with enhanced contrast to be routinely obtained. With this stable system, we were able to characterize many polymer solar cell specimens and consequently identified and verified the existence of an unexpected nanoparticle phase. Furthermore, we were also able to observe the fine structures of an Escherichia coli specimen, without staining, using this on-chip thin film phase plate. Our system, which can be installed on a commercial TEM, opens up exciting possibilities for TEM to characterize organic materials.

A TEM phase plate loading system with loading monitoring and nano-positioning functions.

We present a phase plate loading system developed for a commercial transmission electron microscope (TEM). Our system can be installed without modifying the optical design of the TEM. This system is equipped with a loading monitoring set that allows users to easily and safely locate the phase plate between the pole pieces, and also comes with an airlock that permits quick loading of a phase plate without the need to re-vent the TEM column. The system uses a home-made three-axis nano-positioner to precisely position the phase plate hole at the desired location. Our system has a precision of approximately 10nm, an improvement of one order of magnitude compared with the precision of a phase plate holder modified from an objective aperture. We demonstrate the successful installation and the use of the loading system to place a phase plate at the desired position. Our phase plate loading system can be used to accommodate various types of phase plates and thus provides a good way to greatly speed up the development of TEM phase plates.

Phase TEM for biological imaging utilizing a Boersch electrostatic phase plate: theory and practice.

A Boersch electrostatic phase plate (BEPP) used in a transmission electron microscope (TEM) system can provide tuneable phase shifts and overcome the low contrast problem for biological imaging. Theoretically, a pure phase image with a high phase contrast can be obtained using a BEPP. However, a currently available TEM system utilizing a BEPP cannot achieve sufficiently high phase efficiency for biological imaging, owing to the practical conditions. The low phase efficiency is a result of the blocking of partial unscattered electrons by BEPP, and the contribution of absorption contrast. The fraction of blocked unscattered beam is related to BEPP dimensions and to divergence of the illumination system of the TEM. These practical issues are discussed in this paper. Phase images of biological samples (negatively stained ferritin) obtained by utilizing a BEPP are reported, and the phase contrast was found to be enhanced by a factor of approximately 1.5, based on the calculation using the Rose contrast criterion. The low gain in phase contrast is consistent with the expectation from the current TEM/BEPP system. A new generation of phase TEM utilizing BEPP and designed for biological imaging with a high phase efficiency is proposed.

Study of mean absorptive potential using Lenz model: toward quantification of phase contrast from an electrostatic phase plate.

An electrostatic phase plate can provide better phase contrast, a fact that plays a promising role for the high-resolution observation of specimens containing light elements. However, in order to quantify the "phase" contrast from images recorded using the phase plate, the "absorption" (or scattering) contrast arising from electrons scattered elastically and inelastically outside of the phase-plate ring must be analyzed. Angular distributions of the elastic and inelastic scattering are predicted using the Lenz model. The mean absorptive potential, V(o) serving as an index for the contribution of "absorption" contrast, is calculated from the reciprocal mean free path of elastic and inelastic scattering, and is verified experimentally. The mean absorptive potential of a particular phase plate with inner and outer radii of 0.25microm (theta(1)=0.09mrad) and 1mum (theta(2)=0.4mrad), respectively, is approximately 0.11eV for carbon and is equivalent to that of an objective aperture of semiangle 17mrad (cutoff frequency 6.7nm(-1)).