The optical tweezers apparatus is now working well, so I'm off across town tomorrow to give it a try, with the expert help of my biophysicist collaborator. But can I remember what I had learned so far, and what the status of my DNA-on-beads preps is? No. So I'm glad I wrote some blog posts and kept a tolerably good notebook.
I can attach biotinylated DNA to streptavidin-coated polystyrene beads. The problem that the DNA caused the beads to clump together was resolved by agitating the beads better while they were incubating with the DNA (by putting the tubes on the roller in an orientation where they would be turned end-over-end). However this resulted in beads that were difficult to pellet for washing, a problem that hasn't been solved but can be circumented by washing the beads by filtration and then concentrating them with a disposable protein-concentrator (Amicon).
- I need to find the bead-DNA preps I made and take them home with me tonight.
- I will prepare some more coverslips and chambers before I go home tonight, and take them with me.
- But I suspect there may be contamination in the fridge stock of competence medium I use to wash the chambers and to wash and resuspend the cells in after thawing (to remove the glycerol antifreeze), so I should take some fresh stock with me and leave it in the -20 °C freezer rather than in the fridge.