Protein-Selective Coacervation with Hyaluronic Acid

Selective coacervation with hyaluronic acid (HA), a biocompatible and injectable anionic polysaccharide, was used to isolate a target protein, bovine serum albumin (BSA), with 90% purity from a 1:1 mixture with a second protein of similar pI, β-lactoglobulin (BLG). This separation was attributed to the higher HA-affinity of BSA, arising from its more concentrated positive domain. The values of pH corresponding respectively to the onset of complex formation, coacervation, precipitation, and redissolution (pH_c, pH_ϕ, pH_p, and pH_d) were determined as a function of ionic strength <i>I</i>. These pH values were related to critical values of protein charge, <i>Z</i>, and their dependence on <i>I</i> provided some insights into the mechanisms of these transitions. The higher polyanion binding affinity of BSA, deduced from its higher values of pH_c, was confirmed by isothermal titration calorimetry (ITC). Confocal laser microscopy clearly showed time-dependent coalescence of vesicular droplets into a continuous film. Comparisons with prior results for the polycation poly­(diallyldimethylammonium chloride) (PDADMAC) show reversal of protein selectivity due to reversal of the polyelectrolyte charge. Stronger binding of both proteins to PDADMAC established by ITC may be related to the higher chain flexibility and effective linear charge density of this polycation

Glucose Sensing Using Functionalized Amorphous In–Ga–Zn–O Field-Effect Transistors

Recent advances in glucose sensing have focused on the integration of sensors into contact lenses to allow noninvasive continuous glucose monitoring. Current technologies focus primarily on enzyme-based electrochemical sensing which requires multiple nontransparent electrodes to be integrated. Herein, we leverage amorphous indium gallium zinc oxide (IGZO) field-effect transistors (FETs), which have found use in a wide range of display applications and can be made fully transparent. Bottom-gated IGZO-FETs can have significant changes in electrical characteristics when the back-channel is exposed to different environments. We have functionalized the back-channel of IGZO-FETs with aminosilane groups that are cross-linked to glucose oxidase and have demonstrated that these devices have high sensitivity to changes in glucose concentrations. Glucose sensing occurs through the decrease in pH during glucose oxidation, which modulates the positive charge of the aminosilane groups attached to the IGZO surface. The change in charge affects the number of acceptor-like surface states which can deplete electron density in the n-type IGZO semiconductor. Increasing glucose concentrations leads to an increase in acceptor states and a decrease in drain-source conductance due to a positive shift in the turn-on voltage. The functionalized IGZO-FET devices are effective in minimizing detection of interfering compounds including acetaminophen and ascorbic acid. These studies suggest that IGZO FETs can be effective for monitoring glucose concentrations in a variety of environments, including those where fully transparent sensing elements may be of interest