抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Recently a new, large family of two-dimensional (2D) early transition metal carbides and carbonitrides, called MXenes, was discovered. MXenes are produced by selective etching of the A element from the MAX phases, which are metallically conductive, layered solids connected by strong metallic, ionic, and covalent bonds, such as Ti2AlC, Ti3AlC2, and Ta4AlC3. MXenes ­combine the metallic conductivity of transition metal carbides with the hydrophilic nature of their hydroxyl or oxygen terminated surfaces. In essence, they behave as “conductive clays”. This article reviews progress—both ­experimental and theoretical—on their synthesis, structure, properties, intercalation, delamination, and potential applications. MXenes are expected to be good candidates for a host of applications. They have already shown promising performance in electrochemical energy storage systems. A detailed outlook for future research on MXenes is also presented.

25th Anniversary Article: MXenes: A New Family of Two‐Dimensional Materials

Core/Shell Nanoparticles: Classes, Properties, Synthesis Mechanisms, Characterization, and Applications

A nanopore-based device provides single-molecule detection and analytical capabilities that are achieved by electrophoretically driving molecules in solution through a nano-scale pore. The nanopore provides a highly confined space within which single nucleic acid polymers can be analyzed at high throughput by one of a variety of means, and the perfect processivity that can be enforced in a narrow pore ensures that the native order of the nucleobases in a polynucleotide is reflected in the sequence of signals that is detected. Kilobase length polymers (single-stranded genomic DNA or RNA) or small molecules (e.g., nucleosides) can be identified and characterized without amplification or labeling, a unique analytical capability that makes inexpensive, rapid DNA sequencing a possibility. Further research and development to overcome current challenges to nanopore identification of each successive nucleotide in a DNA strand offers the prospect of 'third generation' instruments that will sequence a diploid mammalian genome for ∼$1,000 in ∼24 h.

/pdf/the-potential-and-challenges-of-nanopore-sequencing-51qxscif85.pdf

The Potential and Challenges of Nanopore Sequencing

The passage of individual molecules through nanosized pores in membranes is central to many processes in biology. Previously, experiments have been restricted to naturally occurring nanopores, but advances in technology now allow artificial solid-state nanopores to be fabricated in insulating membranes. By monitoring ion currents and forces as molecules pass through a solid-state nanopore, it is possible to investigate a wide range of phenomena involving DNA, RNA and proteins. The solid-state nanopore proves to be a surprisingly versatile new single-molecule tool for biophysics and biotechnology.

Solid-state nanopores

Single nanometre-sized pores (nanopores) embedded in an insulating membrane are an exciting new class of nanosensors for rapid electrical detection and characterization of biomolecules. Notable examples include α-hemolysin protein nanopores in lipid membranes1,2 and solid-state nanopores3 in Si3N4. Here we report a new technique for fabricating silicon oxide nanopores with single-nanometre precision and direct visual feedback, using state-of-the-art silicon technology and transmission electron microscopy. First, a pore of 20 nm is opened in a silicon membrane by using electron-beam lithography and anisotropic etching. After thermal oxidation, the pore can be reduced to a single-nanometre when it is exposed to a high-energy electron beam. This fluidizes the silicon oxide leading to a shrinking of the small hole due to surface tension. When the electron beam is switched off, the material quenches and retains its shape. This technique dramatically increases the level of control in the fabrication of a wide range of nanodevices.

Fabrication of solid-state nanopores with single-nanometre precision.

We report experiments and modeling of translocation of double-strand DNA through a siliconoxide nanopore. Long DNA molecules with different lengths ranging from 6500 to 97000 base pairs have been electrophoretically driven through a 10 nm pore. We observe a power-law scaling of the translocation time with the length, with an exponent of 1.27. This nonlinear scaling is strikingly different from the well-studied linear behavior observed in similar experiments performed on protein pores. We present a theoretical model where hydrodynamic drag on the section of the polymer outside the pore is the dominant force counteracting the electrical driving force. We show that this applies to our experiments, and we derive a power-law scaling with an exponent of 1.22, in good agreement with the data.

/pdf/fast-dna-translocation-through-a-solid-state-nanopore-4pln0csitl.pdf

Fast DNA Translocation through a Solid-State Nanopore

We report double-strand DNA translocation experiments using silicon oxide nanopores with a diameter of about 10 nm . By monitoring the conductance of a voltage-biased pore, we detect molecules with a length ranging from 6557 to 48 500 base pairs. We find that the molecules can pass the pore both in a straight linear fashion and in a folded state. Experiments on circular DNA further support this picture. We sort the molecular events according to their folding state and estimate the folding position. As a proof-of-principle experiment, we show that a nanopore can be used to distinguish the lengths of DNA fragments present in a mixture. These experiments pave the way for quantitative analytical techniques with solid-state nanopores.

/pdf/translocation-of-double-strand-dna-through-a-silicon-oxide-rt7f0ts2f7.pdf

Translocation of double-strand DNA through a silicon oxide nanopore

Atomic-resolution electron microscopy reveals that pillarlike silicon double columns exist in the hardening nanoprecipitates of AlMgSi alloys, which vary in structure and composition. Upon annealing, the Si2 pillars provide the skeleton for the nanoparticles to evolve in composition, structure, and morphology. We show that they begin as tiny nuclei with a composition close to Mg2Si2Al7 and a minimal mismatch with the aluminum matrix. They subsequently undergo a one-dimensional growth in association with compositional change, becoming elongated particles. During the evolution toward the final Mg5Si6 particles, the compositional change is accompanied by a characteristic structural change. Our study explains the nanoscopic reasons that the alloys make excellent automotive materials.

https://science.sciencemag.org/content/sci/312/5772/416.full.pdf

Jianghua Chen

Papers

Fabrication of solid-state nanopores with single-nanometre precision.

Fast DNA Translocation through a Solid-State Nanopore

Translocation of double-strand DNA through a silicon oxide nanopore

Atomic pillar-based nanoprecipitates strengthen AlMgSi alloys.

Hot deformation behavior of 7150 aluminum alloy during compression at elevated temperature