Continuous Biomolecular Fractionation

Biomolecule analysis is often compared to finding "a needle in a haystack", so the importance of biosample fractionation cannot be exaggerated. Traditionally, Gel electrophoresis, gel-exclusion chromatography and other filtration techniques have been used for bioseparation. In addition to well-known drawbacks such as manual operation, slow separation rate, and need for large equipments, the science behind the molecular sieving and filtration is still yet to be fully clarified. One issue is that most molecular sieves (gels) are random nanoporous materials, making it difficult to control / optimize the separation process. In our group, patterned regular sieving structures and nanofilters have been sought as an alternative to conventional separation method: recent developments in micro nanofluidic sieves and filters have demonstrated superior performance for both analytical and preparative separation of various physiologically relevant macromolecules, including proteins.

A shortage of fresh water is one of the acute challenges facing the world today. An energy-efficient approach to converting sea water into fresh water could be of substantial benefit, but current desalination methods require high power consumption and operating costs or large-scale infrastructures, which make them difficult to implement in resource-limited settings or in disaster scenarios. Here, we report a process for converting sea water (salinity ~500 mM or ~30,000 mg/L) to fresh water (salinity <10 mM or <600 mg/L) in which a continuous stream of sea water is divided into desalted and concentrated streams by ion concentration polarization, a phenomenon that occurs when an ion current is passed through ion-selective membranes. During operation, both salts and larger particles (cells, viruses and microorganisms) are pushed away from the membrane (a nanochannel or nanoporous membrane), which significantly reduces the possibility of membrane fouling and salt accumulation, thus avoiding two problems that plague other membrane filtration methods. To implement this approach, a simple microfluidic device was fabricated and shown to be capable of continuous desalination of sea water (~99% salt rejection at 50% recovery rate) at a power consumption of less than 3.5 Wh/L, which is comparable to current state-of-the-art systems. Rather than competing with larger desalination plants, the method could be used to make small- or medium-scale systems, with the possibility of battery-powered operation.

Methods are described to achieve more efficient multidimensional protein separation in a microfluidic channel. The new methods couple isoelectric focusing (IEF) with high ionic strength electrophoretic separations by active microvalve control in a microchip. Chip based IEF with CE or CGE are successfully integrated and 2D protein separation on-chip is achieved in 20 minute.