In vitro sampling and storage of proteins with an ultrafiltration collection device (UCD) and analysis with absorbance spectrometry and SELDI-TOF-MS

Frequent in vivo sampling of blood proteins is often stressful, making it difficult to obtain more than a few samples. As a result, only limited time-profiles can be made. We have developed an ultrafiltration collection device (UCD) for continuous sampling. The UCD consists of a hollow fiber, a coil and a flow creator. Hollow fiber membranes are often hydrophobic and this can result in adsorption of protein and/or peptides, leading to clogged membranes. Adsorption was tested with a hydrophobic and hydrophilic peptide and two biocompatible hollow fibers made from different materials. The hollow fiber made from poly(ethylene) coated with ethylenevinyl alcohol gave near 100% recovery for both peptides. This was in contrast to the poly(sulfone) hollow fiber when sampling the hydrophobic peptide. Filling the coil with various peptide concentrations gave good recovery and insignificant diffusion even after storage for 6 d at 37 °C. Continuous pulse-free sampling was tested by vacuum. An average flow rate of 423 ± 50 nl min−1 over a period of 4 d was created using S-Monovette. The flow rate gradually declined during this period by <5% every consecutive day. In addition, we also examined a complex sample—serum in the poly(ethylene) hollow fiber. Serum and ultrafiltrate were spotted onto a protein chip and analyzed by surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF-MS). Six proteins out of 64 were found to be significantly different between serum and the ultrafiltrate (p < 0.05). The UCD has the potential to be used for in vivo real-time monitoring.