Updates about PEG treatment

In collaboration with Alex Shestopalov’s lab, I started working on liquid based PEG treatment on windowed sepcon chips. The treatment is a 3-day long protocol and involves multiple washing and drying steps with different reagents. Most of our sepcon chips broke down in first few steps itself. The initial wash consists of Nanostrip (sulfuric plus nitric acid) wash followed with HF. The membranes survived chemically, as their pore structure remained more or less intact as compared to the untreated ones as seen under SEM. The next step was treating with PCl5 followed with overnight incubation with Grignard reagent as a part of surface functionalization. Since all the windows got broken after day 1, I didn’t proceed along with any further steps. SEM of chips treated with G-reagent showed substantial damage to the pore structure. So it was decided NOT to proceed along the lines of liquid based PEG treatment.

The whole reason of using liquid based protocol was because, this protocol was developed for PEG used in Alex’s lab, which is 18 carbon long or more, and cannot be deposited using vapor based methods. Alex was skeptical about PEG from McGrath lab as that PEG is a smaller molecule (12 C), and as a rule of thumb, smaller the chain, lesser the crosslinking, and hence lower the density of PEG brush. However, Dean’s preliminary result showed that McGrath PEG too gave good results in terms of reduced BSA binding. So we decided to use vapor deposition method to deposit McGrath PEG on windowless chips as a starting point.

I couldn’t do any binding assays on the treated chip, as I lost most of the chips during handling or while using it on TECAN or ended up having the protein evaporated and crystallized on the surface. However Katia from Alex’s lab has agreed to do some contact angle measurements on a time-lapse basis to see for the efficacy of treatment. Anyways, I will be doing a ELISA assay for complement protein on Friday to see how the new batch of PEG treated samples behave.

Following are the different SEM images.

SEM images of windowless chips vapor deposited with McGrath PEG.