Xiaosheng Han

Clinical pathogen diagnostics detect targets by qPCR (but with low sensitivity) or blood culturing (but time-consuming). Here we leverage a dual-stem-loop DNA amplifier to enhance non-specific collateral enzymatic cleavage of an oligonucleotide linker between a fluophore and its quencher by CRISPR-CasΦ, achieving ultrasensitive target detection. Specifically, the target pathogens are lysed to release DNA, which binds its complementary gRNA in CRISPR-CasΦ to activate the collateral DNA-cleavage capability of CasΦ, enabling CasΦ to cleave the stem-loops in the amplifier. The cleavage product binds its complementary gRNA in another CRISPR-CasΦ to activate more CasΦ. The activated CasΦ collaterally cleaves the linker, releasing the fluophore to recover its fluorescent signal. The cycle of stem-loop-cleavage/CasΦ-activation/fluorescence-recovery amplifies the detection signal. Our target amplification-free collateral-cleavage-enhancing CRISPR-CasΦ method (TCC), with a detection limit of 0.11 copies/μL, demonstrates enhanced sensitivity compared to qPCR. It can detect pathogenic bacteria as low as 1.2 CFU/mL in serum within 40 min.

This study reported a landslide hazard pattern considering the dependence of hazard components, with the example of Heilongjiang Province. The spatial and magnitude probabilities of landslides were first constructed to develop a potential link with the annual occurrence rate. Thereafter, landslide hazard considering component dependence was derived based on a modified Poisson model, and presented via the exceeding probability under the scenarios of combining two magnitudes (greater than or equal to 30,000 and 100,000 m3) and four periods (1, 3, 5 and 10 years). Results show that the Poisson model refined is not only a temporal probability function conditional on the magnitude and space, but can capture the hazard definition accurately. Moreover, the exceeding probability is related to the location of the raster, magnitude and the time interval of the landslide. Geographically, the areas with high exceeding probability are concentrated in the central and southeastern parts of the study area. Further, landslide probability dynamically varies with the magnitude and time interval, increasing gradually with the time interval, but decreasing with the landslide magnitude. This study is significant to resolve the conflict between the independence assumptions of the hazard calculation and the conditional attributes in the hazard definition.