The effect of the surface functionalization and the electrolyte concentration on the electrical conductance of silica nanochannels

Abstract

It is known that the conductance of nanochannels as a function of electrolyte concentration deviates from a linearly proportional relationship and approaches a value independent of the concentration as the electrolyte concentration is lowered. Most of the proposed models account for this behavior by considering a constant surface charge density and an ideal electrolyte solution. However, at low electrolyte concentrations, the ideal electrolyte approximation is no longer valid because the ions that result from the atmospheric carbon dioxide dissolution in water dominate the ionic concentration. In this paper, arrays of silica nanochannels were electrically characterized via conductance measurements. The conductance at low salt concentrations is modeled by a variable surface charge model that accounts for all ionic species in solution. This model was used to determine the variable surface charge of the bare silica nanochannels as well as of chemically modified nanochannels. The model correctly predicted the variation of the nanochannel conductance observed after silane (aminopropyldimethylethoxysilane) functionalization and single-strand DNA immobilization. Finally, pH modification of bulk KCl solutions was employed as an alternative method of changing the surface charge of silica nanochannels. Surface charge calculated from conductance measurements performed at different bulk pH values confirmed that the surface charge of the silica nanochannel walls is sensitive to the H(+) concentration.

Effects of non-Newtonian power law rheology on mass transport of a neutral solute for electro-osmotic flow in a porous microtube

“…It is well known that the electroosmotic flow in micro/nanochannels is significantly affected by the electrical properties of the channel walls. Altering the conductance of channels by surface functionalization is performed by Martins et al 36 A variable charge model was developed which predicted the surface conductance due to change in electrolyte concentration at dilute ranges, change in wall properties due to surface reactions and change in pH of the solution. These findings are important for label-free biosensing, where detailed knowhow of the interaction of surface properties with fluid composition is necessary.…”

Investigation of injection molding of orthogonal fluidic connector for microfluidic devices

“…[1][2][3] Functional integration is very beneficial for the development of microfluidic devices. 4,5 However, limited by the current manufacturing capability, it is still difficult to form various functional units in a single substrate. Thus, multilayered microfluidic devices formed by the connection of multiple substrates are still popular.…”

Fabrication of PMMA nanofluidic electrochemical chips with integrated microelectrodes

“…Benefitting from its high sensitivity, label-free detection and ease of miniaturization and integration, electrochemical detection has been becoming one of the most popular detection methods for microchip analyses, and has been integrated with nanofluidic chips (Karnik et al, 2005;Martins et al, 2013a;Mela et al, 2004;Stein et al, 2004;Wolfrum et al, 2008). Initially, external electrodes, such as Ag or Pt wires, were inserted into the reservoir of the chip for electrochemical detection (Karnik et al, 2005;Mela et al, 2004;Stein et al, 2004).…”

“…Initially, external electrodes, such as Ag or Pt wires, were inserted into the reservoir of the chip for electrochemical detection (Karnik et al, 2005;Mela et al, 2004;Stein et al, 2004). Recently, to improve the integration of chips or fulfill some special functions (e.g., redox cycling), microelectrodes have been integrated on the chip (Martins et al, 2013a;Regonda et al, 2013;Wolfrum et al, 2008).…”

“…Therefore, a nanofluidic electrochemical chip mainly consists of microchannels, nanochannels and microelectrodes. In most cases, to avoid the troublesome alignment during the chip bonding process, nanochannels and microelectrodes were fabricated on the same plate (Martins et al, 2013a(Martins et al, , 2013bWolfrum et al, 2008), while microchannels were made on another plate. However, unfortunately, most polymer nanochannel fabrication methods are not compatible with the microelectrode fabrication methods.…”