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Title:Dynamically tunable nanoporous gold for ionic and molecular separations
Author(s):McCurry, Daniel A
Director of Research:Bailey, Ryan C
Doctoral Committee Chair(s):Bailey, Ryan C
Doctoral Committee Member(s):Rodríguez-López, Joaquín; Murphy, Catherine J; Suslick, Kenneth S
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Nanoporous gold (NPG)
Free corrosion
Ion selectivity
Abstract:The analysis of biomolecules, including proteins and DNA, is rapidly moving towards lab-on-a-chip devices in an effort to minimize sample volume and sample loss. Pores with diameters in the tens of nanometers range have gained significant attention recently through their use as single-molecule detectors and current rectifiers. Such devices must be designed for specific targets and the use of single pores limits high throughput applications. A membrane with adjustable properties in situ would provide a simple means of performing biomolecular separations and sample pre-concentration in microfluidic devices. The goal of this work is to fabricate a dynamic membrane that can be externally modulated and therefore tuned for specific analytes by uniting traditional separation methods based on size-exclusion principles with charge-based separations techniques. Gold serves as an attractive membrane material due to its high corrosion resistance, facile surface modification, and inherent conductivity. In our approach, a simple 2-day free-corrosion de-alloying procedure in concentrated nitric acid removes less noble metals (e.g. Cu, Ni, Zn, Ag) from Au-containing alloys to form a three-dimensional nanoporous network with a very large (4.2 ± 0.8 m 2 g −1 ) surface area density. The random orientation and small channel size of the network nearly guarantees analyte interaction with the walls. Pore sizes of 50 ± 20 nm, as measured by scanning electron microscopy, have been attained, but adjusting de-alloying time, temperature, and pH are shown to extend this range. As a model system of dynamic control, UV-visible detection of anionic and cationic tracers transport across the nanoporous gold membrane has been monitored as a function of applied potential. Herein, surface area characterization of the bicontinuous porous structure with feature sizes on the nanometer scale was performed using the well-known Brunauer-Emmett-Teller gas adsorption isotherm, Pb underpotential deposition, and oxide stripping voltammetry. Gateable molecular and ionic transport through NPG was obtained by dynamic electrochemical modulation of the electrical double layer (EDL) within the pores. Application of a salt gradient across bare NPG was also used to impose an asymmetrical EDL thickness, whereas NPG coated with self-assembled monolayers altered the surface charge through the oxidation or reduction of surface moieties. Initial studies regarding protein and DNA transport through NPG have been performed. Lysozyme (Lys), bovine serum albumin (BSA), and bovine hemoglobin (BHb) served as model proteins due to differences in their isoelectric points (Lys: 11.4, BHb: 6.8, BSA: 4.7). Lys was shown to have a much stronger correlation to an applied transverse migration potential through the NPG, most likely due to its small size (~14.3 kDa) compared to that of BSA (~66.4 kDa) and BHb (~64.5 kDa). DNA flux through NPG was found to be entropically unfavored and therefore demonstrated much lower rates of transport. Finally, a microfabrication route is proposed in order to scale the NPG membrane to a microfluidic device.
Issue Date:2016-09-01
Rights Information:Copyright 2016 Daniel A McCurry
Date Available in IDEALS:2017-03-01
Date Deposited:2016-12

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