We have studied ultrathin films of transition and noble metals on Mo(111) and W(111) using Auger spectroscopy, LEED, thermal desorption spectroscopy (TDS) and scanning tunneling microscopy (STM). The atomically rough, open bcc(111) surfaces are morphologically unstable when covered by films ≥ 1 monolayer thick of certain metals, i.e. they form faceted structures. For example, using a UHV STM to study Pd/W(111) , we find that the Pd-covered W(111) surface becomes completely faceted to three-sided {211} pyramids upon annealing, for Pd coverages greater than a critical coverage θc. Formation of pyramidal facets also occurs when W(111) or Mo(111) surfaces are dosed with Pt, Au, Ir, Rh, oxygen or sulfur. In contrast, monolayer films of Ti, Co, Ni, Cu, Ag and Gd do not induce massive reconstruction or faceting on W(111) and Mo(111) surfaces. The faceting appears to be thermodynamically driven but kinetically limited: faceting is caused by an increased anisotropy in surface free energy that occurs for the film-covered surfaces. An interesting correlation has been observed for both substrates: faceting occurs for overlayer elements having Pauling electronegativities greater than 2.0, suggesting that surface electronic effects are controlling the structural instability of both Mo(111) and W(111) . Structure sensitivity in a model catalytic reaction, n-butane hydrogenolysis, is observed over planar and faceted Pt/W(111) . We have also used soft x-ray photoemission spectrosocopy (SXPS) based on synchrotron radiation methods to characterize the bimetallic interface; for Pt, Pd and Au on W(111) , we find that substrate core level shift effects associated with interface formation are substantial, while those associated with faceting are rather subtle.
Background and Aims
Stool DNA testing is an emerging and attractive option for colorectal cancer (CRC) screening. We previously evaluated the feasibility of a stool DNA (sDNA) test of methylated SDC2 for CRC detection. The aim of this study was to assess its performance in a multicenter clinical trial setting.
Methods
Each participant was required to undergo a sDNA test and a reference colonoscopy. The sDNA test consists of quantitative assessment of methylation status of SDC2 promoter. Results of real-time quantitative methylation-specific PCR were dichotomized as positive and negative, and the main evaluation indexes were sensitivity, specificity, and kappa value. All sDNA tests were performed and analyzed independently of colonoscopy.
Results
Among the 1110 participants from three clinical sites analyzed, 359 and 38 were diagnosed, respectively, with CRC and advanced adenomas by colonoscopy. The sensitivity of the sDNA test was 301/359 (83.8%) for CRC, 16/38 (42.1%) for advanced adenomas, and 134/154 (87.0%) for early stage CRC (stage I–II). Detection rate did not vary significantly according to age, tumor location, differentiation, and TNM stage, except for gender. The follow-up testing of 40 postoperative patients with CRC returned negative results as their tumors had been surgically removed. The specificity of the sDNA test was 699/713 (98.0%), and unrelated cancers and diseases did not seem to interfere with the testing. The kappa value was 0.84, implying an excellent diagnostic consistency between the sDNA test and colonoscopy.
Conclusion
Noninvasive sDNA test using methylated SDC2 as the exclusive biomarker is a clinically viable and accurate CRC detection method.
Chinese Clinical Trial Registry
Chi-CTR-TRC-1900026409, retrospectively registered on October 8, 2019; http://www.chictr.org.cn/edit.aspx?pid=43888&htm=4.
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