Rapid biosynthesis of silver nanoparticles from Bacillus megaterium (NCIM 2326) and their antibacterial activity on multi drug resistant clinical pathogens

The notion to fight against multi drug resistant pathogens is a great deal in the field of nanomedicine. The identifiable antimicrobial action of metal bionanoparticles on many microorganisms is reported earlier. As silver bionanoparticles (Ag-BNPs) are known to have efficient antibacterial properties they are synthesized in ecofriendly and biocompatible way. The present study is focused on the extracellular biosynthesis of highly stable Ag-BNPs from bacterial strain Bacillus megaterium (NCIM 2326) by bio-reduction of silver ion using the culture supernatant, and to determine the antibacterial efficacy on multi drug resistant clinical pathogens such as Streptococcus pneumoniae and Salmonella typhi. The biosynthesis process is rapid and Ag-BNPs are formed within few minutes if AgNO(3) comes to contact with cell filtrate. Furthermore the synthesized Ag-BNPs are characterized by UV-vis spectroscopy, Atomic Force Microscopy (AFM), Thin Layer Chromatography (TLC) and Fourier Transform Infrared Spectroscopy (FTIR).     

Savinase action on bovine serum albumin (BSA) monolayers demonstrated with measurements at the air-water interface and liquid Atomic Force Microscopy (AFM) imaging

We studied the enzymatic action of Savinase on bovine serum albumin (BSA) organized in a monolayer spread at the air/water interface or adsorbed at the mica surface. We carried out two types of experiments. In the first one we followed the degradation of the protein monolayer by measuring the surface pressure and surface area decrease versus time. In the second approach we applied AFM imaging of the supported BSA monolayers adsorbed on mica solid supports and extracted information for the enzyme action by analyzing the obtained images of the surface topography in the course of enzyme action. In both cases we obtained an estimate for the turnover number (TON) of the enzyme reaction.     

Semi-crystalline poly(ε-caprolactone) brushes on gold substrate via “grafting from” method: New insights with AFM characterization

This paper is the first report about the morphology of semi-crystalline poly(ε-caprolactone) (PCL) brushes studied by Atomic Force Microscopy (AFM) in tapping mode. This represents a convenient way to observe how the growth of a polymer proceeds from a thiol monolayer on gold substrate in terms of grafting density and thiol monolayer stability. The synthesis of semi-crystalline PCL brushes was carried out by Ring-Opening Polymerization (ROP) of ε-caprolactone (ε-CL) from hydroxyl end-group of thiol monolayer on gold surface as catalyzed with tin octoate (Sn(Oct)₂) at 50 °C. Addition of a sacrificial initiator was also attempted in order to get a finer control over PCL crystals. For a sake of comparison, triazabicyclo[4.4.0]dec-5-ene (TBD) was also investigated as another ROP catalyst active at ambient temperature. The composition and the morphology of resulting semi-crystalline PCL brushes were characterized using X-ray Photoelectron Spectroscopy (XPS) and AFM. In the case of Sn(Oct)₂-promoted ROP of CL with or without free (sacrificial) initiator (i.e., benzyl alcohol), different types of morphologies were observed on the gold substrate, due to the thermal instability of thiol-gold bond under the experimental conditions. When TBD was used at ambient temperature, a regular and homogeneous crystalline morphology, i.e., compact PCL crystals, could be observed.     

Ultrarelativistic electron optics in a weak magnetic field

Within an unprecedented analytical formulation, we find an approximate relationship for the ultrarelativistic velocity of electrons in the presence of a weak, time-independent and uniform magnetic field acting perpendicularly to the trajectory of the electrons. We also determine the corresponding velocity quantum operator whose eigenvalues are also determined as well as their corresponding Landau states. In addition, the corresponding synchrotron radiation losses are calculated.     

Microscopy of non-birefringent transmissive phase samples using Sagnac laser interferometer

A cyclic interferometer, appropriately combined with a long working distance microscope objective, is adapted for quantitative phase microscopy. In such an arrangement, the sample information, in terms of the diffracted orders emerging from the sample, is carried by both the counter propagating beams within the cyclic interferometer. However, positioning the sample close to the input/output cube beam splitter and use of a suitably converging laser beam of light as the input to the interferometer ensure that only one of the counter propagating beams carries the object information to the objective while the other beam, which serves as the reference, allows only the undiffracted component to contribute to the process of image formation. Use of suitable polarization optics renders the interferometer its polarization phase shifting property. Using the proposed arrangement, the experimental results showing the quantitative 3D phase rendering of polystyrene microspheres and micro-wells etched in glass are presented.     

高分辨和超分辨光学成像技术在空间和生物中的应用

大到天文光学望远镜观察浩瀚的宇宙, 小到光学显微镜探察细微的纳米世界, 光学成像技术在人类探索和发现未知世界奥秘的活动中扮演着至关重要的角色. 看得更远、看得更细、看得更清楚是人们不断追求的目标. 传统光学理论已证明所有经典光学系统都是一个衍射受限系统, 即光学系统空间分辨率的物理极限是由光的波长和系统的相对孔径(或数值孔径)决定的. 能否突破这个极限？能否不断提高光学系统的成像分辨率？围绕着这个问题, 本文综述了近年来开展的各种光学高分辨和超分辨成像技术, 及其在空间探测和生物领域中的应用.     

Stick-Slip Mechanisms at the Nanoscale

When two surfaces slide past each other, energy is mainly dissipated by stick-slip events. Macroscopic stick-slip is usually explained by asperities that come in and out of contact. Herein, we probe stick-slip at the nanoscale at interfaces and polymer coated interfaces by pulling single polymers covalently attached to an AFM cantilever tip laterally over solid substrates in liquid environment. We find two different stick mechanisms, namely desorption stick (DS) and cooperative stick (CS). While DS-slip resembles the velocity dependence of macroscopic stick-slip, CS-slip shows an increase in friction with velocity. For various reasons we anticipate that both stick mechanisms are necessary for a molecular understanding of stick-slip at the interface and interphase.     

Spectro-Microscopic Techniques for Studying Nanoplastics in the Environment and in Organisms

Nanoplastics (NPs), small (<1 μm) polymer particles formed from bulk plastics, are a potential threat to human health and the environment. Orders of magnitude smaller than microplastics (MPs), they might behave differently due to their larger surface area and small size, which allows them to diffuse through organic barriers. However, detecting NPs in the environment and organic matrices has proven to be difficult, as their chemical nature is similar to these matrices. Furthermore, as their size is smaller than the (spatial) detection limit of common analytical tools, they are hard to find and quantify. We highlight different micro-spectroscopic techniques utilized for NP detection and argue that an analysis procedure should involve both particle imaging and correlative or direct chemical characterization of the same particles or samples. Finally, we highlight methods that can do both simultaneously, but with the downside that large particle numbers and statistics cannot be obtained.     

Darobactins Exhibiting Superior Antibiotic Activity by Cryo-EM Structure Guided Biosynthetic Engineering**

Over recent decades, the pipeline of antibiotics acting against Gram-negative bacteria is running dry, as most discovered candidate antibiotics suffer from insufficient potency, pharmacokinetic properties, or toxicity. The darobactins, a promising new small peptide class of drug candidates, bind to novel antibiotic target BamA, an outer membrane protein. Previously, we reported that biosynthetic engineering in a heterologous host generated novel darobactins with enhanced antibacterial activity. Here we utilize an optimized purification method and present cryo-EM structures of the Bam complex with darobactin 9 (D9), which served as a blueprint for the biotechnological generation of twenty new darobactins including halogenated analogs. The newly engineered darobactin 22 binds more tightly to BamA and outperforms the favorable activity profile of D9 against clinically relevant pathogens such as carbapenem-resistant Acinetobacter baumannii up to 32-fold, without observing toxic effects.     

Single-entity Electrochemistry Unveils Dynamic Transformation during Tandem Catalysis of Cu2O and Co3O4 for Converting NO3− to NH3

Electrochemically converting nitrate to ammonia is an essential and sustainable approach to restoring the globally perturbed nitrogen cycle. The rational design of catalysts for the nitrate reduction reaction (NO₃RR) based on a detailed understanding of the reaction mechanism is of high significance. We report a Cu₂O+Co₃O₄ tandem catalyst which enhances the NH₃ production rate by ≈2.7-fold compared to Co₃O₄ and ≈7.5-fold compared with Cu₂O, respectively, however, most importantly, we precisely place single Cu₂O and Co₃O₄ cube-shaped nanoparticles individually and together on carbon nanoelectrodes provide insight into the mechanism of the tandem catalysis. The structural and phase evolution of the individual Cu₂O+Co₃O₄ nanocubes during NO₃RR is unveiled using identical location transmission electron microscopy. Combining single-entity electrochemistry with precise nano-placement sheds light on the dynamic transformation of single catalyst particles during tandem catalysis in a direct way.