Insight into selectivity of photocatalytic methane oxidation to formaldehyde on tungsten trioxide.

Tungsten trioxide (WO3) has been recognized as the most promising photocatalyst for highly selective oxidation of methane (CH4) to formaldehyde (HCHO), but the origin of catalytic activity and the reaction manner remain controversial. Here, we take {001} and {110} facets dominated WO3 as the model photocatalysts. Distinctly, {001} facet can readily achieve 100% selectivity of HCHO via the active site mechanism whereas {110} facet hardly guarantees a high selectivity of HCHO along with many intermediate products via the radical way. In situ diffuse reflectance infrared Fourier transform spectroscopy, electron paramagnetic resonance and theoretical calculations confirm that the competitive chemical adsorption between CH4 and H2O and the different CH4 activation routes on WO3 surface are responsible for diverse CH4 oxidation pathways. The microscopic mechanism elucidation provides the guidance for designing high performance photocatalysts for selective CH4 oxidation.

"DSN-mismatched CRISPR″sensor for highly selective and sensitive detection of under-expressed miR-let-7a.

Several microRNAs (miRNAs) are expressed at lower levels in specific tumors, e.g., miR-let-7a in non-small cell lung cancer (NSCLC). This makes it challenging to analyze their lower abundance versus specifically elevated miRNAs. Here, we describe a novel fluorescent biosensor for the highly selective and sensitive detection of miR-let-7a constructed by combining miRNA screening assisted by a duplex-specific nuclease (DSN) with CRISPR-Cas12a system signal amplification. We meticulously designed a mismatch in the first three to four bases at the 5'-end of the capture DNA to improve the signal-to-noise ratio of the CRISPR-Cas12a system. Within this "DSN-mismatched CRISPR" fluorescence strategy, miR-let-7a was accurately screened by DSN-assisted cleavage, and the mismatched capture DNA unbound to target miRNA could trigger the CRISPR-Cas12a system to produce a mass of trans-cleave fluorescence signals. This "turn-off" approach was suitable for detecting decreased levels of miRNAs. This approach can not only discriminate the single-base mismatched let-7 family but also reach a limit of detection at 64.17 fM as well as be quantified from 100 fM to 500 pM. The miR-let-7a levels were then measured in clinical serum samples from healthy volunteers and patients with NSCLC. This study holds promise for the development of a universal under-expressed miRNA assay for early diagnosis and treatment of cancers.