Any alternative device or simple tool to these devices to increase protein concentration for western blot? Taking into account, the maximum signal used and minimum lysis buffer used.
We'd need to know more about where your protein is coming from (cell cultures, tissues, bacteria?) and what you've been doing so far to get it out.
Generally, if low protein concentration really is the problem, acetone precipitation is a great way to concentrate it up to some ~20x. Western blot executed correctly can be incredibly sensitive though. Protein concentration should not usually be limiting. So it may pay to look for problems elsewhere too. For example, have you established the detection limit for your antigen using positive controls?
We'd need to know more about where your protein is coming from (cell cultures, tissues, bacteria?) and what you've been doing so far to get it out.
Generally, if low protein concentration really is the problem, acetone precipitation is a great way to concentrate it up to some ~20x. Western blot executed correctly can be incredibly sensitive though. Protein concentration should not usually be limiting. So it may pay to look for problems elsewhere too. For example, have you established the detection limit for your antigen using positive controls?
You can try a centricon centrifugal filter from Amicon with a molecular mass less than that of your desired protein. By this the total volume will reduce without loosing any protein. The process also will not denature the protein.
http://kirschner.med.harvard.edu/files/protocols/Millipore_Centricons.pdf
We too have met this problem with low concentration from cell culture. Sometimes you are able to improve harvesting (scraping without trypsinizing, lysis in the well) but other times you need to use the lysate you've got. A way to work around is adjusting your WB protocol.
You can load the sample twice if that helps. Apply sample into the well, run until the well gets nearly empty and apply a 2nd round. As long as the 2nd application keeps in touch with the first one, it will not affect the run. Run slowly at the beginning allowing the sample to focus at the top of the running gel.
There are also variations in WB equipment from various companies, allowing to load larger samples. Double thickness of the gel will increase sample volume as well.
We too have been using Millipore/Amicon filters with hell, but the volume of cell lysates from cultured cells can be too small.
I've found lysis buffers containing SDS produce stronger concentrations of rat brain homogentates. Also NOT heating the samples before loading the gel is much better for some proteins, in my case transmembrane subunit bands almost doubled in strength when I stopped boiling my samples and simply left them at RT for 30 minutes. I've also tried some spin cup filters to concentrate lysate above a cut-off molecular weight. They don't seem to work as well as advertised but they reduce the volume by half at least. Olaf's idea of adding more sample in behind the first batch while running at low voltage is fascinating. I will have to give that a try.
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