With increasing demands from researchers on discovering novel drug targets and early disease markers, people found current proteomics technologies fall short on dealing with protein complexities and abundance variation. Since human proteome has more than 10,000 different proteins, with high abundant proteins having 109 higher concentrations than low abundant ones, identifying low abundant proteins (biomarkers) in complex mixtures is one of the major challenges in proteomics. As a result, before one can identify any target proteins, at least one separation step must be performed.

This project focuses on studying and applying the physiochemical nanofluidic channels (~40 nm). We have developed a nanofluidic preconcentrator that can concentrate biomolecular samples up to 10 million fold. Due to the electrical double layer overlapping, sub 100 nm nanochannels have preferential transfer over counterions (or counterion current). As a result, a well known phenomenon called concentration polarization can be observed. However, once a higher bias is applied, the system will be driven into the over-limiting current regime, where the charge neutrality in the bulk no longer exists and the extended space charge layer (SCL) is formed. The detail mechanism is not well understood so far. However, by coupling a tangential field across the SCL, we can have a fast accumulation of charged molecules in front of it. In short, this device collects charged biomolecules based on two features: (i) the energy barrier for charged biomolecules generated by the induced space charge layer near the nanofluidic filter; (ii) a faster nonlinear electroosmotic flow for sample deliveries. Currently, we are able to achieve more than a million fold enhancement factor in 30 mins. The preconcentration factors and collection speed are close to those of the PCR for nucleic acids, which is an essential step for many genomics researches. Applications included biomolecular preconcentration and fluid pumping using electroosmotic flow (EOF) of the 2nd kind.

Figure 1 Nanofluidic protein preconcentration device.

Figure 2 Preconcentration of 33 fM GFP in the nanofluidic device.

References

1. Wang, Y.-C., Stevens, A. & Han, J. "Million-fold preconcentration of proteins and peptides by nanofluidic filter," Analytical Chemistry 77, 4293-4299 (2005). (doi)
2. Wang, Y.-C., Tsau, C. H., Burg, T. P., Manalis, S. & Han, J. "Efficient biomolecule pre-concentration by nanofilter triggered electrokinetic trapping," Proceedings of the MicroTAS 2005 Symposium, Boston, MA, vol. 1, pp. 238-240. (poster presentation)
3. Wang, Y.-C. & Han, J. "Million-fold biomolecule preconcentration by nanofluidic electrokinetic trapping," MicroScale Bioseparation 2005 Symposium, New Orleans, LA. (oral presentation)