Microfluidic Monitoring of Copper Ion Binding to and Oxidation of Phospholipid Bilayers

Restricted (Penn State Only)
- Author:
- Greenberger, Virginia
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 03, 2019
- Committee Members:
- Paul Cremer, Chair & Dissertation Advisor
David Boehr, Major Field Member
Tae-Hee Lee, Major Field Member
Joyce Jose, Outside Unit & Field Member
Philip Bevilacqua, Program Head/Chair - Keywords:
- Microfluidics
Lipid Bilayers
Transition Metals
Oxidation
Copper
Chemistry
Fluorescence - Abstract:
- Microfluidic devices provide an efficient, cost-effective platform for small scale experiments. The lab-on-a-chip phenomenon gained momentum in the 1990s when polydimethyl-siloxane (PDMS) was introduced as a polymer mold. PDMS allows for easy, affordable, biocompatible device fabrication. The polymer is cured above a mold with raised channels formed in the desired pattern. The channels are then left as an imprint in the hardened PDMS. In order to produce microfluidic devices, a hard pattern with micron-sized features must be made. Traditional techniques for producing these masters are oftentimes expensive and require complicated infrastructure and the use of dangerous etchants. We have developed a technique for rapid, inexpensive 3D printing of microfluidic patterns and implemented it in an undergraduate laboratory class. Supported lipid bilayers (SLB) can be formed in microfluidic devices and act as a model for cell membranes and interactions that may occur at their surface. Lipids are of interest when considering neurological diseases as the double bonds in their hydrocarbon tails are particularly vulnerable to oxidative damage. Brain slices from patients who have suffered from neurodegenerative disorders show damaged lipid products and excess amounts of metal ions. We used model systems to determine the affinities of metals for different lipid headgroups and the electrostatic forces that drive the binding. Some of the metal ions that bind to phospholipids in the cell membrane are redox active and able to produce reactive oxygen species (ROS). We hypothesized that if these metals are bound and adjacent to the membrane, more ROS will be generated near vulnerable lipid tails. To test this, the kinetics of Cu2+ catalyzed oxidation of POPE and POPS bilayers were measured using a new lipid–linked fluorophore. Additionally, mass spectrometry was used to probe the damage to lipid tails with high degrees of unsaturation. Combining model lipid systems with microfluidic devices provides a platform by which we can study the physical interactions at phospholipid surfaces. Herein, we demonstrate that we can generate affordable microfluidic patterns and implement them in both a research and teaching lab. These devices were used to measure how changing the surface potential of a bilayer changes the binding of Cu2+. We were able to quantify and visualize the oxidative damage that is catalyzed by Cu2+ to phospholipid membranes modeling potential interactions occurring at neuron surfaces.