Permselectivity and Ionic Conductivity Study of Na+ and Br- Ions in Graphene Oxide-Based Membranes for Redox Flow Batteries.

Permselectivity of a membrane is central for the development of electrochemical energy storage devices with two redox couples, such as redox flow batteries (RFBs). In RFBs, Br3-/Br- couple is often used as a catholyte which can cross over to the anolyte, limiting the battery's lifetime. Naturally, the development of permselective membranes is essential to the success of RFBs since state-of-the-art perfluorosulfonic acid (PFSA) is too costly. This study investigates membranes of graphene oxide (GO), polyvinylpyrrolidone (PVP), and imidazole (Im) as binder and linker, respectively. The GO membranes are compared to a standard PFSA membrane in terms of ionic conductivity (Na+) and permselectivity (exclusion of Br-). The ionic conduction is evaluated from electrochemical impedance spectroscopy and the permselectivity from two-compartment diffusion cells in a four-electrode system. Our findings suggest that the GO membranes reach conductivity and permselectivity comparable with standard PFSA membranes.

Core-Shell Gold/Silver Nanoparticles for Localized Surface Plasmon Resonance-Based Naked-Eye Toxin Biosensing.

The localized surface plasmon resonance (LSPR) phenomenon provides a versatile property for biodetection. Herein, this unique feature was employed to build a homogeneous optical biosensor to detect staphylococcal enterotoxin A (SEA) in solution down to very low levels by naked-eye readout. If the initial position of the LSPR band is located in the cyan region, even a small red shift (∼2-3 nm) induced by a refractive index change close to the surface of nanoparticles (NPs) could make the light absorption transit from cyan to green and become visually detectable via a concomitant change in the complementary colors. In this work, we aimed at synthesizing two types of NPs based on compositionally complex core-shell NPs-Ag shells on AuNPs (Au@AgNPs) and Ag inside gold nanoshells (Ag@AuNPs). By controlling the thickness of the shells and their surface chemistry with anti-SEA antibody (Ab), the LSPR band was tuned to near 495 and 520 nm for Ag@AuNPs and Au@AgNPs, respectively. The two particle systems were subsequently applied to spectroscopically and visually detect anti-SEA Ab-SEA interactions. Upon the addition of SEA, large red shifts of the LSPR band were observed spectroscopically and the limits of detection (LODs) were estimated to be 0.2 and 0.4 nM for Au@AgNPs and Ag@AuNPs, respectively. Although the two sets of NPs gave almost identical LODs, the Ag@AuNPs whose initial position of the LSPR band was tuned in the cyan to green region (∼500 nm) displayed a substantially more distinct color change from orange to red, as revealed by the naked eye. We foresee significant potential to this strategy in medical diagnostics and environmental monitoring, especially when basic laboratory infrastructure is sparse or nonexistent.