Gradient-free determination of isoelectric points of proteins on chip

Urszula Łapińska, Kadi L. Saar, Emma V. Yates, Therese W. Herling, Thomas Müller, Pavan K. Challa, Christopher M. Dobson and Tuomas P. J. Knowles

Phys Chem Chem Phys 2017;19;23060-23067

Lapinska et al. using a microfluidic system built in house design a new technique to determine a protein's isoelectric point (pI) based on microfluidic free-flow electrophoresis (μFFE). The approach exploits temporal rather than spatial pH gradients. To demonstrate the effectiveness of this method the pI of 7 different proteins of known pI were tested; β-lactoglobulin, ribonuclease A, ovalbumin, human transferrin, ubiquitin and myoglobin. The paper shows that this method is successful in determining the pI using this new technique without the requirement of generating and maintaining pH gradients which is often challenging for other techniques. The technique requires low voltages and low sample consumption. The paper also shows that using this technique it is possible to estimate the pI values for a wide range of proteins measuring at only two pH values, suggesting that this technique is rapid and accurate on small volume samples.

Fig1. shows a diagram of the microfluidic chip used to determine the pI of the target proteins without a spatial pH gradient and instead using a temporal gradient.