No abstract

Targeting specificity is an essential issue in the development of CRISPR-Cas technology. Using a luciferase activation assay, off-target cleavage activity of sgRNA was systematically investigated on single nucleotide-mismatched targets. In addition to confirming that PAM-proximal mismatches are less tolerated than PAM-distal mismatches, our study further identified a “core” sequence that is highly sensitive to target-mismatch. This sequence is of 4-nucleotide long, located at +4 to +7 position upstream of PAM, and positioned in a steric restriction region when assembled into Cas9 endonuclease. Our study also found that, single or multiple target mismatches at this region abolished off-target cleavage mediated by active sgRNAs, thus proposing a principle for gene-specific sgRNA design. Characterization of a mismatch sensitive “core” sequence not only enhances our understanding of how this elegant system functions, but also facilitates our efforts to improve targeting specificity of a sgRNA.

Ni-rich cathode materials have attracted wide attention on account of their high specific capacity. However, the poor cycle retention of Ni-rich cathode materials, especially at high voltage or high temperature, is recognized as the main obstacle for extensive commercialization. In this research, we propose a new strategy of doping NCM622 (LiNi 0.6 Co 0.2 Mn 0.2 O 2 ) with Ta 5+ to improve the structural stability due to the high Ta−O dissociation bond energy. XRD refinement results indicate that almost all Ta 5+ are located in Li sites to play a pillar role and cation mixing is inhibited. Electrochemical impedance spectroscopy results show that the increase of charge transfer impedance during the cycling process is controlled. Owing to the stable structure, NCM622 with 0.25% Ta doping exhibits a capacity of 148.1 mAh g −1 with retention reaching 83.6% at 1 C over 3.0−4.5 V after 100 cycles, whereas the bare NCM622 only delivers 143.4 mAh g −1 with a retention of 80.1%. The above results signify that moderate Ta doping is a facile yet effective strategy to develop high-performance Ni-rich cathode materials.