Switching Anionic and Cationic Semi-Permeability in Partially Hydrolyzed Polyacrylonitrile:A pH-Tunable Ionic Rectifier

Membrane materials with semipermeability for anions or for cations are of interest in electrochemical and nanofluidic separation and purification technologies. In this study, partially hydrolyzed polyacrylonitrile (phPAN) is investigated as a pH-switchable anion/cation conductor. When switching from anionic to cationic semipermeability, also the ionic current rectification effect switches for phPAN materials deposited asymmetrically onto a 5, 10, 20, or 40 μm diameter microhole in a 6 μm thick polyethylene-terephthalate (PET) film substrate. Therefore, ionic rectifier behavior can be tuned and used to monitor and characterize semipermeability. Effects of electrolyte type and concentration and pH (relative to the zeta potential at approximately 3.1) are investigated by voltammetry, chronoamperometry, and impedance spectroscopy. A computational model provides good qualitative agreement with the observed electrolyte concentration data. High rectification effects are observed for both cations (pH > 3.1) and anions (pH < 3.1) but only at relatively low ionic strengths

Electrochemiluminescence reaction pathways in nanofluidic devices

Nanofluidic electrochemical devices confine the volume of chemical reactions to femtoliters. When employed for light generation by electrochemiluminescence (ECL), nanofluidic confinement yields enhanced intensity and robust luminescence. Here, we investigate different ECL pathways, namely coreactant and annihilation ECL in a single nanochannel and compare light emission profiles. By high-resolution imaging of electrode areas, we show that different reaction schemes produce very different emission profiles in the unique confined geometry of a nanochannel. The confrontation of experimental results with finite element simulation gives further insight into the exact reaction ECL pathways. We find that emission strongly depends on depletion, geometric exclusion, and recycling of reactants in the nanofluidic device

Facile fabrication of microperforated membranes with re-useable SU-8 molds for organs-on-chips

Microperforated membranes are essential components of various organ-on-a-chip (OOC) barrier models devel- oped to study transport of molecular compounds and cells across cell layers in e.g. the intestine and blood-brain barrier. These OOC membranes have two functions: 1) to support growth of cells on one or both sides, and 2) to act as a filter-like barrier to separate adjacent compartments. Thin, microperforated poly(dimethylsiloxane) (PDMS) membranes can be fabricated by micromolding from silicon molds comprising arrays of micropillars for the formation of micropores. However, these molds are made by deep reactive ion etching (DRIE) and are expensive to fabricate. We describe the micromolding of thin PDMS membranes with easier-to-make, SU-8 epoxy photoresist molds. With a multilayer, SU-8, pillar microarray mold, massively parallel arrays of micropores can be formed in a thin layer of PDMS, resulting in a flexible barrier membrane that can be easily incorporated and sealed between other layers making up the OOC device. The membranes we describe here have a 30-μm thickness, with 12-μm-diameter circular pores arranged at a 100-μm pitch in a square array. We show application of these membranes in gut-on-a-chip devices, and expect that the reported fabrication strategy will also be suitable for other membrane dimension