Microdialysis of proteins: Performance of the CMA/20 probe

Unlike all other currently available sampling techniques, microdialysis allows the continuous recovery of dialysed fluid from the interstitial space of living tissue. Microdialysis has been extensively used to study small molecules such as neurotransmitters, metabolites and drugs in the brain and other tissues. There has been increasing interest in measuring proteins using microdialysis. Optimizing protein recovery requires slow buffer flow rates, large pore membranes and osmotic balancing. An examination of a widely used commercially available large pore (100 kDa MWCO) polymeric microdialysis probe, the CMA/20 (polyethersulfone) over 6 days of continuous microdialysis showed that: (1) published molecular weight cut-off values may not predict the size of proteins that can be recovered. This membrane had an effective molecular weight cut-off values (MWCO) of about 29 kDa, (2) protein recoveries decrease over time, (3) small proteins are much less affected than larger ones and (4) there can be significant differences in the recovery of proteins similar in size perhaps due to reaching of a critical size, protein aggregation, shape, surface charge or hydrophobicity.