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Electronic devices are becoming increasingly used in chemical- and bio-sensing applications and therefore understanding the silica-electrolyte interface at the atomic scale is becoming increasingly important. For example, field-effect biosensors (BioFETs) operate by measuring perturbations in the electric field produced by the electrical double layer due to biomolecules binding on the surface. In this paper, explicit-solvent atomistic calculations of this electric field are presented and the structure and dynamics of the interface are investigated in different ionic strengths using molecular dynamics simulations. Novel results from simulation of the addition of DNA molecules and divalent ions are also presented, the latter of particular importance in both physiological solutions and biosensing experiments. The simulations demonstrated evidence of charge inversion, which is known to occur experimentally for divalent electrolyte systems. A strong interaction between ions and DNA phosphate groups was demonstrated in mixed electrolyte solutions, which are relevant to experimental observations of device sensitivity in the literature. The bound DNA resulted in local changes to the electric field at the surface; however, the spatial- and temporal-mean electric field showed no significant change. This result is explained by strong screening resulting from a combination of strongly polarised water and a compact layer of counterions around the DNA and silica surface. This work suggests that the saturation of the Stern layer is an important factor in determining BioFET response to increased salt concentration and provides novel insight into the interplay between ions and the electrical double layer.

Single-walled carbon nanotubes (SWNTs) have many outstanding properties due to the unique 1-dimensional structure. Especially, fabrication of the high performance device utilizing the intriguing opt-electronic property is regarded as a very promising output. However, the opt-electronic property is decided by the helicity of graphene wrapping, which is defined as SWNTs chirality, making the chirality control of SWNTs a very critical issue. Towards this goal, many researches about the precise control of catalyst are reported and the effects of catalyst size [1] and crystal structure [2] are well studied. On the other hand, the correlation between catalyst surface condition and chirality is seldom being studied, and the details still remain unclear. In this study, systematic investigations are carried out aiming for the elucidation of the correlation between SWNTs chirality and catalyst surface condition.