Preparation of graphene nanocomposites from aqueous silver nitrate using graphene oxide's peroxidase-like and carbocatalytic properties.

The present study evaluates the role of graphene oxide's (GO's) peroxidase-like and inherent/carbocatalytic properties in oxidising silver nitrate (AgNO3) to create graphene nanocomposites with silver nanoparticles (GO/Ag nanocomposite). Activation of peroxidase-like catalytic function of GO required hydrogen peroxide (H2O2) and ammonia (NH3) in pH 4.0 disodium hydrogen phosphate (Na2HPO4). Carbocatalytic abilities of GO were triggered in pH 4.0 deionised distilled water (ddH2O). Transmission electron microscope (TEM), scanning electron microscope (SEM), cyclic voltammetry (CV) and UV-Vis spectroscopy aided in qualitatively and quantitatively assessing GO/Ag nanocomposites. TEM and SEM analysis demonstrated the successful use of GO's peroxidase-like and carbocatalytic properties to produce GO/Ag nanocomposite. UV-Vis analysis indicated a higher yield in optical density values for GO/Ag nanocomposites created using GO's carbocatalytic ability rather than its peroxidase-like counterpart. Additionally, CV demonstrated that GO/Ag nanocomposite fabricated here is a product of an irreversible electrochemical reaction. Our study outcomes show new opportunities for GO as a standalone catalyst in biosensing. We demonstrate a sustainable approach to obtain graphene nanocomposites exclusive of harmful chemicals or physical methods.

Complete Genome Sequence of Fish Pathogen Flavobacterium columnare Strain B185, Originating from Finland.

We report a complete genome sequence of a Finnish isolate of the fish pathogen Flavobacterium columnare Using PacBio RS II sequencing technology, the complete circular genome of F. columnare strain B185 with 3,261,404 bp was obtained.

Cellulose nanofibrils prepared by gentle drying methods reveal the limits of helium ion microscopy imaging.

TEMPO-oxidized cellulose nanofibrils (TCNFs) have unique properties, which can be utilised in many application fields from printed electronics to packaging. Visual characterisation of TCNFs has been commonly performed using Scanning Electron Microscopy (SEM). However, a novel imaging technique, Helium Ion Microscopy (HIM), offers benefits over SEM, including higher resolution and the possibility of imaging non-conductive samples uncoated. HIM has not been widely utilized so far, and in this study the capability of HIM for imaging of TCNFs was evaluated. Freeze drying and critical point drying (CPD) techniques were applied to preserve the open fibril structure of the gel-like TCNFs. Both drying methods worked well, but CPD performed better resulting in the specific surface area of 386 m2 g-1 when compared to 172 m2 g-1 and 42 m2 g-1 of freeze dried samples frozen in propane and nitrogen, respectively. HIM imaging of TCNFs was successful but high magnification imaging was challenging because the ion beam tended to degrade the TCNFs. The effect of the imaging parameters on the degradation was studied and an ion dose as low as 0.9 ion per nm2 was required to prevent the damage. This study points out the differences between the gentle drying methods of TCNFs and demonstrates beam damage during imaging like none previously reported with HIM. The results can be utilized in future studies of cellulose or other biological materials as there is a growing interest for both the HIM technique and bio-based materials.

Imaging Bacterial Colonies and Phage-Bacterium Interaction at Sub-Nanometer Resolution Using Helium-Ion Microscopy.

Imaging of microbial interactions has so far been based on well-established electron microscopy methods. This study presents a new way to study bacterial colonies and interactions between bacteria and their viruses, bacteriophages (phages), in situ on agar plates using helium ion microscopy (HIM). In biological imaging, HIM has advantages over traditional scanning electron microscopy with its sub-nanometer resolution, increased surface sensitivity, and the possibility to image nonconductive samples. Furthermore, by controlling the He beam dose or by using heavier Ne ions, the HIM instrument provides the possibility to mill out material in the samples, allowing for subsurface imaging and in situ sectioning. Here, the first HIM-images of bacterial colonies and phage-bacterium interactions are presented at different stages of the infection as they occur on an agar culture. The feasibility of neon and helium milling is also demonstrated to reveal the subsurface structures of bacterial colonies on agar substrate, and in some cases also structure inside individual bacteria after cross-sectioning. The study concludes that HIM offers great opportunities to advance the studies of microbial imaging, in particular in the area of interaction of viruses with cells.