Silicon (Si) nanostructures have received much attention for their use in electronic devices and solar energy conversion. We performed chemical etching of Si(100) covered with graphene oxide (GO). After immersing the sample in a mixture of HF and H2O2 for 4 h or longer, the Si underneath the GO sheets had dissolved more than that in the non-covered area, suggesting that the sheets can be a catalyst for etching reactions. Therefore, the wet chemical method without noble metal catalysts may be another facile and cost-effective method to design Si nanostructures.
Chemical etching of silicon assisted
by various types of carbon
materials is drawing much attention for the fabrication of silicon
micro/nanostructures. We developed a method of chemical etching of
silicon that utilizes graphene oxide (GO) sheets to promote the etching
reaction in a hydrofluoric acid–nitric acid (HF–HNO3) etchant. By using an optimized composition of the HF–HNO3 etchant, the etching rate under the GO sheets was 100 times
faster than that of our HF–H2O2 system
used in a previous report. Kinetic analyses showed that the activation
energy of the etching reaction was almost the same at both the bare
silicon and GO-covered areas. We propose that adsorption sites for
the reactant in the GO sheets enhance the reaction frequency, leading
to a deeper etching in the GO areas than the bare areas. Furthermore,
GO sheets with more defects were found to have higher catalytic activities.
This suggests that defects in the GO sheets function as adsorption
sites for the reactant, thereby enhancing the etching rate under the
sheets.
Chemical etching of silicon assisted by a number of catalysts
is
attracting increasing attention in the fabrication of silicon micro–nanostructures.
In practical applications, metal-free catalysts, including carbon
materials, have been focused on as alternative materials for the assisted
etching of silicon. Although this anisotropic etching process is suitable
for the fabrication of silicon micro–nanostructures due to
its simplicity and cost effectiveness, a number of challenges remain,
such as the formation of a
porous layer and peeling of the catalyst by the gases produced during
the etching process. We herein report vapor-phase etching assisted
by graphene oxide and its mechanism in terms of reaction kinetics.
By optimizing etching conditions, graphene oxide enhances the etching
reaction in the vapor phase without the formation of a porous layer.
We also demonstrated the formation of micrometer-sized pores in the
desired areas by combining the microcontact printing of graphene oxide
with silicon etching in the vapor phase.
Angiogenin 4 bearing ribonuclease activity is an endogenous antimicrobial protein expressed in small and large intestine. However, the crucial amino acid residues responsible for the antibacterial activity of Ang4 and its impact on gut microbiota remain unknown. Here, we report the contribution of critical amino acid residues in the functional regions of Ang4 to its activity against Salmonella typhimurium LT2 and the effect of Ang4 on gut microbiota in mice. We found that Ang4 binds S. typhimurium LT2 through two consecutive basic amino acid residues, K58 and K59, in the cell-binding segment and disrupts the bacterial membrane integrity at the N-terminal α-helix containing residues K7 and K30, as evidenced by the specific mutations of cationic residues of Ang4. We also found that the RNase activity of Ang4 was not involved in its bactericidal activity, as shown by the H12 mutant, which lacks RNase activity. In vivo administration of Ang4 through the mouse rectum and subsequent bacterial 16S rRNA gene sequencing analyses demonstrated that administration of Ang4 not only increased beneficial bacteria such as Lactobacillus, Akkermansia, Dubosiella, Coriobacteriaceae UCG-002, and Adlercreutzia, but also decreased certain pathogenic bacteria, including Alistipes and Enterohabdus, indicating that Ang4 regulates the shape of gut microbiota composition. We conclude that Ang4 kills bacteria by disrupting bacterial membrane integrity through critical basic amino acid residues with different functionalities rather than overall electrostatic interactions and potentially maintains gut microflora in vivo under physiological and pathophysiological conditions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.