(9) We indeed confirmed this when increasing the concentration of silver nitrate up to 0.04 mM. Mirkin and co-workers reported that silver ions drive the formation of single-crystal particles with high-index facets by adsorption on the particle surface. (11) Although these design considerations-kinetic- and surface-controlled growth-were established from single-crystalline nanoparticles, further experimental work is required to understand how twinned structures fit within this context. At high Ag + concentrations, seeded growth has been reported to lead to anisotropic shapes with high-index facets. As a result, particle growth slows down, affecting the final nanoparticle shape and crystalline structure.
UPD occurs under conditions of seed-mediated synthesis in which ascorbic acid (AA) cannot reduce Ag + in bulk, thereby facilitating the formation of a silver (sub)monolayer on a gold surface and hindering further deposition of Au atoms. Silver ions (Ag +) are known to bind preferentially onto certain gold facets, which can result in anisotropic crystal growth through the well-known underpotential deposition (UPD) mechanism. Selective surface passivation, on the other hand, involves the use of chemical additives. On the contrary, at slow reduction rates, thermodynamically more stable particles, which display low-index facets, emerge. (9, 10) Kinetic effects dominate at high rates of metal reduction and usually result in thermodynamically unstable products (displaying high-index facets). It is commonly agreed that reaction kinetics and selective surface passivation are the primary factors behind nanoparticle growth mechanisms. Thus, the need for further experimental advancement is more than justified, which will not only ensure generalization of the current growth models but also open up opportunities for new synthetic pathways and crystal diversity at the nanoscale. (8) Although the initial single-crystal particles used in their work were prepared by conventional surfactant-assisted methods, the emergence of twin planes originated from the photochemical reduction of silver in the presence of additives that are not commonly used in established methods. For example, Mirkin and co-workers showed that single-crystalline gold nanoparticles can develop twin defects during their growth with silver, to yield core–shell nanoparticles with a twinned structure. (1-7) Recently, experimental monitoring of twin emergence has attracted the attention of several research groups. Mutant allele levels were significantly higher in blood and buccal samples of patients with than in those without MEG/HMEG ( P = 1.5 × 10 −7) ( Figure 2b), further supporting previous observations that PIK3CA mutations are generally not detectable in blood or buccal samples of individuals with PROS, except in patients with MCAP syndrome.The mechanistic understanding of the emergence of twin planes is of great importance in nanoparticle synthesis because the presence of defects can alter the physical properties of nanostructures, thereby opening new avenues toward the design of novel systems.
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Consistent with this observation, mutant allele levels were found to be systematically lower in blood and buccal samples than in fresh skin and overgrown tissues for any given patient, regardless of the phenotype ( Supplementary Figure S1 online). As expected, we found that mutant allele levels were significantly higher in fresh skin and overgrown tissues than in blood and buccal samples when considering all patients (two-tailed P = 3.9 × 10 −25, Mann-Whitney U test) this observation was also true for cases without ( P = 3.0 × 10 −24) and with MEG/HMEG ( P = 5.6 × 10 −5) ( Figure 2b). Among the 13 cultured skin fibroblasts tested, the mutation was absent in three (23.1%), suggesting that cultured samples may not be ideal for PIK3CA mutation testing. PIK3CA mutations were detected in all fresh skin and overgrown tissues tested, with a median mutant allele fraction of 0.14 (range, 0.01 to 0.47) ( Figure 2a) 32.3 and 73.7% of these samples had a mutant allele fraction less than 0.1 and 0.2, respectively, thus highlighting the need for sensitive PIK3CA screening methods. The mutant allele fraction for each patient and tissue is provided in Supplementary Figure S1 online. We screened a total of 201 specimens, most of which were fresh skin or overgrown tissues ( n = 99) and blood samples ( n = 83) ( Figure 2a). To investigate levels of mosaicism by tissue, we performed ultradeep sequencing of mutations of interest in all available samples from the 108 patients with identified PIK3CA mutations.
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