The aqueous biomolecule-silica interface is a technically important component present in many biosensors. For example, Biologically-sensitive Field Effect Transistors (BioFETs) are a class of biosensors designed to sense extremely small changes in the electric field at this interface. Understanding the physical and chemical nature of this surface region is crucially important to improving design of these devices. There are two influences on the electric field at this interface: surface charge from charging of silanol groups; and the structure/dynamics of mixed valency electrolytes near the charged silanolate surface. Density Functional Theory methods were used to explore the proton transfer rate to/from the surface, revealing a new reaction mechanism and demonstrating that it is limited by the rate of reorientation of nearby water molecules. Dynamic silica-surface charging can be therefore be modelled as an activationless, diffusion-limited process. [1] Classical Molecular Dynamics simulations were used to investigate electrolyte structure and dynamics under physiological conditions. The model showed that water polarisation plays an important role in determining the electric field near the interface, particularly for mixed valency magnesium/sodium electrolytes. This atomistic simulation work highlights the complexity of the silica-water interface, and provides detail which cannot be adequately described using conventional mean-field models such as the Poisson-Boltzmann description of the electric double layer. [1] Lowe, B. M., Skylaris, C.-K. & Green, N. G. Journal of Colloid and Interface Science 451, 231–244 (2015). doi: 10.1016/j.jcis.2015.01.094

Charge dynamics at the silica-electrolyte interface

251st National Meeting (2016)

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