Modeling of protein electrophoresis in silica colloidal crystals having brush layers of polyacrylamide

Comparison of separation modes for microchip electrophoresis of proteins

Separation of a set of model proteins was tested on a microchip electrophoresis analytical platform capable of sample injection by two different electrokinetic mechanisms. A range of separation modes-microchip capillary zone electrophoresis, microchip micellar electrokinetic chromatography, and nanoparticle-based sieving-was tested on glass and polydimethylsiloxane/glass microchips and with silica-nanoparticle colloidal arrays. The model proteins calmodulin (18 kiloDalton), bovine serum albumin (66 kDa), and concanavalin (106 kDa) were labeled with Alexa Fluor 647 for laser-induced fluorescence detection. The best separation and resolution were obtained in a silica-nanoparticle colloidal array chip.

Well-Defined Materials for High-Performance Chromatographic Separation

Chromatographic separation has been widely applied in various fields, such as chemical engineering, precision medicine, energy, and biology. Because chromatographic separation is based on differential partitioning between the mobile phase and stationary phase and affected by band dispersion and mass transfer resistance from these two phases, the materials used as the stationary phase play a decisive role in separation performance. In this review, we discuss the design of separation materials to achieve the separation with high efficiency and high resolution and highlight the well-defined materials with uniform pore structure and unique properties. The achievements, recent developments, challenges, and future trends of such materials are discussed. Furthermore, the surface functionalization of separation ma-terials for further improvement of separation performance is reviewed. Finally, future research directions and the challenges of chromatographic separation are presented.

Electrophoresis of megaDalton proteins inside colloidal silica

With the growth of the biopharmaceutical industry, there is a need for rapid size-analysis of proteins on the megaDalton scale. The large pore sizes needed for such separations cannot be easily reached by pushing the current limits of size-exclusion chromatography or gel electrophoresis. The concept detailed here is the formation of arbitrarily wide pores by packing nonporous colloidal silica in capillaries. This method can be called packed-capillary electrophoresis, or "pCE". Electrophoresis of protein standards (11-155 kDa) by pCE, using 345 nm diameter particles in 100 μm diameter capillaries, gives 2x higher resolution than a typical PAGE gel in 1/6 of the time. The electropherograms show that pCE is highly efficient, with half-micrometer plate heights for all seven standards, giving 105 plates for a 50 mm length. The large pore radius of 65 nm enables baseline resolution of proteins of 0.72, 1.048 and 1.236 MDa in less than 15 min. The short separation time of pCE is attributed to the absence of small pores that restrict protein migration in gels. The pCE separation is applied to the analysis of a stressed pharmaceutical-grade IgG4 sample, giving unprecedented baseline resolution of monomer, dimer, trimer and tetramer in less than 10 min.

Nanofluidic crystals: nanofluidics in a close-packed nanoparticle array

With various promising applications demonstrated, nanofluidics has been of broad research interest in the past decade. As nanofluidics matures from a proof of concept towards practical applications, it faces two major barriers: expensive nanofabrication and ultra-low throughput. To date, the only material that enables nanofabrication-free, high-throughput, yet precisely controllable nanofluidic systems is the close-packed nanoparticle array, i.e. nanofluidic crystals. Recently, significant progress in nanofluidics has been made using nanofluidic crystals, including high-current ionic diodes, high-power energy harvesters, efficient biomolecular separation, and facile biosensors. Nanofluidic crystals are seen as a key to applying nanofluidic concepts to real-world applications. In this review, we introduce the key concepts and models in nanofluidic crystals, summarize the fabrication methods, and discuss the various applications of nanofluidic crystals in depth, highlighting their advantages in terms of simple fabrication, low cost, flexibility, and high throughput. Finally, we provide our perspectives on the future of nanofluidic crystals and their potential impacts.

Submicrometer particles and slip flow in liquid chromatography

Smaller particles have progressively led to higher efficiency in liquid chromatography, particularly for proteins, due to smaller diffusion distances. Particle diameter has recently entered the submicrometer region, with the back-pressure requirements alleviated by slip flow.

Silica colloidal crystals as emerging materials for high-throughput protein electrophoresis

Silica colloidal crystals are a new type of media for protein electrophoresis, and they are assessed for their promise in rapidly measuring aggregation of monoclonal antibodies. The nature of silica colloidal crystals is described in the context of the need for a high-throughput separation tool for optimizing the formulations of protein drugs for minimal aggregation. The fundamental relations between molecular weight and mobility in electrophoresis are used to make a theoretical comparison of selectivity between gels and colloidal crystals. The results show that the selectivity is similar for these media, but slightly higher, 10%, for gels, and the velocity is inherently lower than that for gels due to the smaller free volume fraction. These factors are more than compensated for by lower broadening in colloidal crystals. These new media give plate heights of only 0.15 μm for the antibody monomer and 0.42 μm for the antibody dimer. The monoclonal antibody is separated from its dimer in 72 s over a distance of only 6.5 mm. This is five times faster than size-exclusion chromatography, with more than tenfold miniaturization, and amenable to parallel separations, all of which are promising for the design of high-throughput devices for optimizing protein drug formulations.

Polyacrylamide brush layer for hydrophilic interaction liquid chromatography of intact glycoproteins

A chromatographic column of nonporous silica particles with a bonded phase of linear polyacrylamide chains is evaluated for hydrophilic interaction liquid chromatography (HILIC) of intact glycoproteins. The column is shown to retain glycoproteins significantly more strongly than non-glycoproteins. A particle diameter of 700nm gives two-fold higher resolution than does a 1.4μm particle diameter, and the column efficiency is found to be mostly limited by packing heterogeneity. LCMS is able to resolve the five glycoforms of ribonuclease B and give high quality mass spectra, but there is loss of resolution of the isomers of glycoforms due to the lower amount of TFA. Compared to two leading commercial HILIC columns operated at 60°C, the polyacrylamide column operated at 30°C provided at least two-fold higher resolution for intact ribonuclease B, and showed peaks for glycoforms of prostate specific antigen, although not resolved.