i'm working as a diy bio. I'm finding a way to create a micro glass capillary for picking up single cells. I see this video on youtube and would like to know what is the minimum I/O diameter if I pull a capillary like this. Can it be 10-50 µm at least ?
It is very difficult to establish what kind of tip you will get from pulling a capillary on a Bunsen burner. There are many variables to consider, including the glass you are using, the temperature you reach before pulling, the pulling strenght, speed and time, whether you pull once or make multiple pulls etc.
If you do not want to invest into a micropipette puller (they are indeed VERY expensive) you could at least build some mechanism to obtain a constant pull in terms of time and force.
The following paper may be of help:
It seems you would need a fairly high speed (0.8-1 m/s) to get a tip size of <50um.
I could not really find a specific reference for pulling over a Bunsen.
Here is a reference for pulling quartz glass pipettes using a custom oxy hydrogen burner. Here is a video of a commercial burner based pipette puller. Not sure what the specs are. I guess if you can melt your glass using a filament it could be easier than using a torch (a lightbulb circuit is easier to control than flame). People move to flame when dealing with high melting point quartz.
You can get a micropipette puller from Sutter for $1500 off of Ebay. I'm not completely sure how they work mechanically, but I have used many models. Someday I'd like to look inside them (the true mechanism is underneath, inside the box). They use a metal "boxcar shaped" filament that fits around the cappilary, and this heats up when a current is passed through. Two pulleys pull at the pipette, attached to something below doing the actual pulling.
I think there might be a spring-loaded mechanism for achieving the pull, rather than a motorized linear stage moving so fast. Maybe a stage or other actuator below pre-stretches a spring so that it is pulled to different degrees during melt cycle?