We report theoretical and experimental results of the influence of surface immobilized aptamers on ionic transport through nanochannels. The ionic transport in a polyelectrolyte functionalized nanochannel may be modified either by electrostatic mechanisms that involve changes in double layer formed near the pore walls or through steric hindrance of the surface chains on the transport of solution ions. Arrays of well-defined nanochannels are fabricated using two-step anodization process of aluminum on ITO coated glass substrate. The anodization voltage and electrolyte are chosen to achieve the desired nanochannel radius and distribution. The alumina nanochannels are functionalized with thrombin binding DNA aptamers (TBA) to enable the formation of monomolecular films of polyelectrolytes on the nanochannel surface. The functionalized nanochannel arrays are then exposed to different concentrations of α-thrombin and change in impedance across the nanochannel array are characterized in order to identify the influence of protein/aptamer binding on the ionic conduction in the nanochannels. Both DNA aptamers (specific to thrombin) and α-thrombin are charged species and their interactions produce modulation of surface charges and modify the net ionic conductance across the nanochannel. We also characterized changes in ionic conductance in presence of γ-thrombin, an uncharged protein that has similar physiological structure as α-thrombin but no affinity towards TBA. Ionic and solution transport in the nanochannel is modeled using coupled Poisson-Nernst-Planck equation and Navier-Stokes equations. The conformation and charge density of aptamer monomolecular films on the nanochannel surface was modeled based on molecular dynamics simulation results of aptamer and thrombin/aptamer complexes (Gosai et al., 2016). The predicted changes in ionic conductance are compared to experimental results to identify the influence of electrostatic and steric interactions on the ion transport in polyelectrolyte functionalized nanochannel. The results show that aptamer functionalized alumina nanochannel have potential to be used for the development of disposable and point of care devices by employing relatively facile and inexpensive fabrication methodologies.

Reference:

• Gosai, A., Ma, X., Balasubramanian, G., Shrotriya, P., 2016. Electrical Stimulus Controlled Binding/Unbinding of Human Thrombin-Aptamer Complex. Sci. Rep. 6, 37449. doi:10.1038/srep37449