Comprehensive Analysis of Electrostatic Gating in Nanofluidic Systems

Abstract

Molecular transport in nanofluidic systems exhibits properties that are unique to the nanoscale. Here, the electrostatic and steric interactions between particle and surfaces become dominant in determining particle transport. At the solid–liquid interface of charged surfaces an electric double layer (EDL) forms due to electrostatic interactions between surfaces and charged particles. In these systems, tunable charge-selective nanochannels can be generated by manipulating electrostatic gating via co-ions exclusion and counterions enrichment of the EDL at the solid–liquid interface. In this context, electrostatic gating has been used to modulate the selectivity of nanofluidic membranes for drug delivery, nanofluidic transistors, and FlowFET, among other applications. While an extensive body of literature investigating nanofluidic systems exists, there is a lack of a comprehensive analysis accounting for all major parameters involved in these systems. Here we performed an all-encompassing modeling investigation corroborated by experimental analysis to assess the influence of nanochannel size, electrolyte properties, surface chemistry, gate voltage, dielectric properties, and molecular charge and size on the exclusion and enrichment of charged analytes in nanochannels. We found that the leakage current in electrostatic gating, often overlooked, plays a dominant role in molecular exclusion. Importantly, by independently considering all ionic species, we found that counterions compete for EDL formation at the surface proximity, resulting in concentration distributions that are nearly impossible to predict with analytical models. Achieving a deeper understanding of these nanofluidic phenomena will help the development of innovative miniaturized systems for both medical and industrial applications.

All-Atom Molecular Dynamics Simulations of Communication Between Nanochannel Arrays

“…Nanochannels with tunable size and properties are the basis for many applications such as power generation, , desalination, , DNA sequencing, , biomolecule preconcentration, , drug delivery, , ionic logic gates, , and circuits. , The use of nanochannels for ion and molecule transport shows great flexibility in controlling transport characteristics inside the channel confinements. − In general, the nanochannels are exposed to external environments such as reservoirs or microchannels to study their transport characteristics. In this case, the nanochannels may be considered as single or stacked to form an array of nanochannels depending upon the point of applications.…”

Ionic Transistors

“…Besides, a more comprehensive analysis of how the gate voltage affects the surface potential of ion channels with different dielectric properties and surface chemistry was reported in recent years. 156 The simulation was applied on a similar ionic FET model with a SiO 2 ion channel, which demonstrates different dielectric properties by various thicknesses and generates different surface charges by various site densities (Θ s ). The results show that the absence of silanol sites (Θ s = 0, represents an ideal surface with no initial surface charge) exhibits a symmetric surface potential change response to the applied V G from −10 to 10 V (Figure 5d).…”

“…(d) The effect of V G on surface potential (ψ d ) of SiO 2 nanochannel with different thickness and different binding site densities (Θ s = 0). Reprinted with permission 156. Copyright 2022, American Chemical Society.…”

Multiscale simulations of nanofluidics: Recent progress and perspective

“…Kubeil and Bund 290 found that the conical pores with small half‐cone angles and small pore radii have the strongest rectification ability. Combined with model analysis and experimental verification, Trani et al 49 performed a comprehensive investigation to understand the influence of several parameters (nanochannel size, electrolyte properties, surface chemistry, gate voltage, dielectric properties, and molecular charge and size) on the enrichment and depletion of charged analytes in nanofluidics with electrostatic gating. They proved the importance of ionic size and dielectric leakage current in nanofluidics diffusion model.…”

“…Such new flow phenomena of fluid occur within the nano-confinement channel bring out novel applications of nanofluidics and promote industrial innovation in many fields, include desalination, [32][33][34][35][36][37][38] energy harvesting, [39][40][41][42][43][44][45][46][47][48] nanofluidic iontronics, [49][50][51][52][53][54][55] gas separation, [56][57][58][59][60] heat exchanger, [61][62][63][64][65][66] biological analyses, 3,4,[67][68][69] and so on, as shown in Figure 1. The size of nanochannels is often a key factor affecting their applications.…”