Effects of Atmospheric Plasma Corona Discharge on Agrobacterium tumefaciens Survival

Soil-borne pathogenic microorganisms are known to cause extensive crop losses. Agrobacterium tumefaciens, a member of the Proteobacteria, causes the neoplastic crown gall disease in plants. Plant protection is mainly based on toxic chemicals that are harmful to the environment. The use of cold atmospheric-pressure plasma is an attractive method for microbial eradication. Its antimicrobial mechanism includes the formation of large quantities of reactive oxygen species (ROS). The advantages of eradicating bacteria using cold plasma are not needed for chemicals, short treatment, and environmental temperatures. This study examined the impact of plasma corona discharge exposure on A. tumefaciens viability, membrane permeability, relative cell size, and ROS formation. The results showed that 90 s of plasma exposure led to a reduction by four orders of magnitude when the initial concentration was 1 × 107 CFU/mL and in a dry environment. When the initial concentration was 1 × 106 CFU/mL, 45 s of exposure resulted in total bacterial eradication. In a liquid environment, in an initial concentration of 2.02 × 106 CFU/mL, there was no complete bacterial eradication even at the most prolonged examined exposure (90 s). The influence of plasma treatment on the membrane permeability of A. tumefaciens, and their possible recovery, were analyzed using flow cytometer analysis using propidium iodide (PI). When the plasma-treated bacteria were suspended in Luria–Bertani (LB) (rich medium), the PI-positive count of the plasma-treated bacteria after two hours was 12 ± 3.9%. At the 24th hour, this percentage was only 1.74 ± 0.6%, as the control (0.7 ± 0.1%). These results may indicate the repair of the plasma-treated bacteria that were suspended in LB. At the 24th hour, the relative cell size of the treated bacteria shifted to the right, to ~3 × 104 forward side scatter (FSC), about 0.5-fold higher than the untreated cells. Measurement of the ROS showed that the intracellular fluorescence of the 90-s plasma-treated cells led to significant fluorescence formation of 32 relative fluorescence units (RFU)/cell (9 × 104 fold, compared to the nontreated cells). This study showed that cold plasma is a useful method for A. tumefaciens eradication. The eradication mechanism involves ROS generation, membrane permeability, and changes in cell size.

A EFFECT OF CeO2 DOPING ON THE MICROSTRUCTURE AND CORROSION BEHAVIOR OF CoCuNiTi HIGH-ENTROPY ALLOY COATINGS

CoCuNiTi high-entropy alloy coatings with an equal molar ratio were prepared on 45 steel substrates using the laser-cladding method. The effect of CeO2 doping on phase structure, microstructure and corrosion behavior of CoCuNiTi coatings were investigated by X-ray diffraction, optical microscope, scanning electron microscope, and electrochemical workstation. The results show that the phase structure of CoCuNiTi coating doped with 1 w/% CeO2 is transformed from the original dual-phase structure of FCC main phase and BCC phase to the dual-phase structure of BCC main phase and FCC phase, mainly because CeO2 addition helps to improve the temperature gradient and solidification rate during solidification, reduce the nucleation resistance and the diffusion distance of the alloying elements, and provide a liquid environment with longer time, lower viscosity and higher diffusion rate. The microstructure of the two coatings is composed of BCC-phase dendrite and FCC-phase interdendrite. The widths of the primary dendrites of the columnar dendrites in CoCuNiTi cladding layer before and after CeO2 doping are about 8.10 µm and 6.51 µm, respectively. The CoCuNiTi coating doped with 1 w/% CeO2 has the smallest corrosion current density, the largest capacitive reactance arc radius and polarization resistance, and the best corrosion resistance in 3.5 w/% NaCl solution, which is mainly due to making the alloy structure refined and the element distribution uniform after the CeO2 addition.

Extending applications of AFM to fluidic AFM in single living cell and extracellular vesicle studies

In this article, a review of the application of atomic force microscopy (AFM) for the analyses of extracellular vesicles is presented. This information is then extended to include fluidic Atomic Force Microscopy (fluidic AFM) applications. Fluidic AFM is an offshoot of AFM that combines a microfluidic cantilever with AFM and has enabled the research community to conduct biological, pathological, and pharmacological studies on cells at the single-cell level in a liquid environment. AFM applications involving single cell and extracellular vesicle studies, colloidal force spectroscopy, and single cell adhesion measurements are discussed. In this review, new results are offered, using fluidic AFM, to illustrate (1) the speed with which sequential measurements of adhesion using coated colloid beads can be done, (2) the ability to assess lateral binding forces (LBFs) of endothelial or epithelial cells in a confluent cell monolayer in appropriate physiological environment, and (3) the ease of measurement of vertical binding force (VBFs) of intercellular adhesion between heterogeneous cells. Finally, key applications are discussed that include extracellular vesicle absorption, manipulation of a single living cell by intracellular injection, sampling of cellular fluid from a single living cell, patch clamping, and mass measurements of a single living cell.

A Dual Approach of an Oil–Membrane Composite and Boron-Doped Diamond Electrode to Mitigate Biofluid Interferences

Electrochemical biosensors promise a simple method to measure analytes for both point-of-care diagnostics and continuous, wearable biomarker monitors. In a liquid environment, detecting the analyte of interest must compete with other solutes that impact the background current, such as redox-active molecules, conductivity changes in the biofluid, water electrolysis, and electrode fouling. Multiple methods exist to overcome a few of these challenges, but not a comprehensive solution. Presented here is a combined boron-doped diamond electrode and oil–membrane protection approach that broadly mitigates the impact of biofluid interferents without a biorecognition element. The oil–membrane blocks the majority of interferents in biofluids that are hydrophilic while permitting passage of important hydrophobic analytes such as hormones and drugs. The boron-doped diamond then suppresses water electrolysis current and maintains peak electrochemical performance due to the foulant-mitigation benefits of the oil–membrane protection. Results show up to a 365-fold reduction in detection limits using the boron-doped diamond electrode material alone compared with traditional gold in the buffer. Combining the boron-doped diamond material with the oil–membrane protection scheme maintained these detection limits while exposed to human serum for 18 h.

Modulation and Signal Detection for Diffusive-Drift Molecular Communication with a Mobile Receiver

Molecular communication (MC), which allows nanomachines to communicate with each other by using chemical molecules, is considered to be a promising method for communications in liquid environment. Available works on MC mainly focus on modulation and signal detection schemes for MC systems with fixed nanomachines, i.e., fixed molecular communication (FMC) systems. However, the more complex systems with mobile nanomachines (i.e., mobile molecular communication (MMC) systems) have been largely unexplored. This paper considers a MMC system with a fixed transmitter and a mobile receiver communicating over diffusive-drift channels of a limited boundary. We first propose a new modulation scheme to address the issue of misalignment in the signal detection of MMC systems by adopting three types of molecules in the signal modulation and modulating the transmitted signals into blocks with equal length to avoid the transferring of a signal error in the current block on the signal detection in other blocks. We then propose a new signal detection scheme of the MMC systems by calculating the distance between the transmitter and the receiver based on a distance prediction method and detecting signals at the receiver based on the decided adaptive concentration threshold in each time interval. To verify the efficiency of our proposed scheme, we then conducted extensive simulations by the Monte Carlo simulation, and comparisons are also made among our proposed schemes, a well-known fixed threshold signal detection scheme, the CATD scheme, the PAD scheme, and a low complexity signal detection scheme for MMC systems in terms of the BER (bit error rate). Results show that our proposed schemes can outperform these schemes regarding the BER.

Turbulence Intensity Characteristics of a Magnetoliquid Seal Interface in a Liquid Environment

In a liquid environment, the turbulence intensity of the interfacial layer between the magnetic and sealing medium fluids in magnetic liquid seals directly affects the layer stability. Reducing the maximum turbulence intensity of the fluid interface layer effectively improves the stability of the magnetic fluid rotary seal. In this study, we simulated magnetic fluid sealing devices with different structures in liquid environments using the FLUENT software. The simulation results were verified through experimental analyses of the turbulence intensity at the sealing interface. The maximum turbulence intensity of the liquid interface layer increased with increasing shaft speed. At the same speed, the turbulence intensity was maximized at the shaft interface before gradually decreasing in a multistage linear pattern along the radial direction. A magnetic liquid seal with an optimized structure (OS) in the liquid environment was designed based on these results. The maximum turbulence intensity of the liquid interface layer in the OS was independent of the rotation speed and was more than 20% lower than that that in the traditional structure. These results provide a reference for designing magnetic liquid sealing devices.

Revealing DNA Structure at Liquid/Solid Interfaces by AFM-Based High-Resolution Imaging and Molecular Spectroscopy

DNA covers the genetic information in all living organisms. Numerous intrinsic and extrinsic factors may influence the local structure of the DNA molecule or compromise its integrity. Detailed understanding of structural modifications of DNA resulting from interactions with other molecules and surrounding environment is of central importance for the future development of medicine and pharmacology. In this paper, we review the recent achievements in research on DNA structure at nanoscale. In particular, we focused on the molecular structure of DNA revealed by high-resolution AFM (Atomic Force Microscopy) imaging at liquid/solid interfaces. Such detailed structural studies were driven by the technical developments made in SPM (Scanning Probe Microscopy) techniques. Therefore, we describe here the working principles of AFM modes allowing high-resolution visualization of DNA structure under native (liquid) environment. While AFM provides well-resolved structure of molecules at nanoscale, it does not reveal the chemical structure and composition of studied samples. The simultaneous information combining the structural and chemical details of studied analyte allows achieve a comprehensive picture of investigated phenomenon. Therefore, we also summarize recent molecular spectroscopy studies, including Tip-Enhanced Raman Spectroscopy (TERS), on the DNA structure and its structural rearrangements.