Correlation of chromatographic performance with morphological features of organic polymer monoliths

Sequence-specific DNA solid-phase extraction in an on-chip monolith: Towards detection of antibiotic resistance genes

Antibiotic resistance of bacteria is a growing problem and presents a challenge for prompt treatment in patients with sepsis. Currently used methods rely on culturing or amplification; however, these steps are either time consuming or suffer from interference issues. A microfluidic device was made from black polypropylene, with a monolithic column modified with a capture oligonucleotide for sequence selective solid-phase extraction of a complementary target from a lysate sample. Porous properties of the monolith allow flow and hybridization of a target complementary to the probe immobilized on the column surface. Good flow-through properties enable extraction of a 100μL sample and elution of target DNA in 12min total time. Using a fluorescently labeled target oligonucleotide related to Verona Integron-Mediated Metallo-β-lactamase it was possible to extract and detect a 1pM sample with 83% recovery. Temperature-mediated elution by heating above the duplex melting point provides a clean extract without any agents that interfere with base pairing, allowing various labeling methods or further downstream processing of the eluent. Further integration of this extraction module with a system for isolation and lysis of bacteria from blood, as well as combining with single-molecule detection should allow rapid determination of antibiotic resistance.

Morphological Properties of Methacrylate-Based Polymer Monoliths: From Gel Porosity to Macroscopic Inhomogeneities

Shaping chemical interfaces of hard and soft matter materials into physical morphologies that guarantee excellent transport properties is of central importance for technologies relying on adsorption, separation, and reaction at the interface. Polymer monoliths with a hierarchically structured pore space, for example, are widely used in flow-driven processes, whose efficiency depends on the morphology of the support material over several length scales. Compared with alternative support structures, particularly silica monoliths, polymer monoliths yield lower efficiency, which suggests a suboptimal morphology. Based on physical reconstruction by serial block-face scanning electron microscopy we evaluate the structural features of a methacrylate-based polymer monolith from the pore scale to the column scale. The morphological data reveal a homogeneous polymer skeleton with a solute-impenetrable core-porous shell architecture and a heterogeneous macropore space that suffers from inhomogeneities at the short-range and the transcolumn scale. Although the morphology of the polymer phase is favorable to efficient mass transport, the performance of the polymer monolith is limited by severe transcolumn gradients in macroporosity and macropore size. We propose to overcome these morphological limitations by pursuing a preparation strategy that involves active rather than passive shaping of the macropore space, for example, by using silica monoliths as templating structures for polymer monolith preparation.

Methacrylate Polymer Monoliths for Separation Applications

This review summarizes the development of methacrylate-based polymer monoliths for separation science applications. An introduction to monoliths is presented, followed by the preparation methods and characteristics specific to methacrylate monoliths. Both traditional chemical based syntheses and emerging additive manufacturing methods are presented along with an analysis of the different types of functional groups, which have been utilized with methacrylate monoliths. The role of methacrylate based porous materials in separation science in industrially important chemical and biological separations are discussed, with particular attention given to the most recent developments and challenges associated with these materials. While these monoliths have been shown to be useful for a wide variety of applications, there is still scope for exerting better control over the porous architectures and chemistries obtained from the different fabrication routes. Conclusions regarding this previous work are drawn and an outlook towards future challenges and potential developments in this vibrant research area are presented. Discussed in particular are the potential of additive manufacturing for the preparation of monolithic structures with pre-defined multi-scale porous morphologies and for the optimization of surface reactive chemistries.

Larger voids in mechanically stable, loose packings of 1.3μm frictional, cohesive particles: Their reconstruction, statistical analysis, and impact on separation efficiency

Lateral transcolumn heterogeneities and the presence of larger voids in a packing (comparable to the particle size) can limit the preparation of efficient chromatographic columns. Optimizing and understanding the packing process provides keys to better packing structures and column performance. Here, we investigate the slurry-packing process for a set of capillary columns packed with C18-modified, 1.3μm bridged-ethyl hybrid porous silica particles. The slurry concentration used for packing 75μm i.d. fused-silica capillaries was increased gradually from 5 to 50mg/mL. An intermediate concentration (20mg/mL) resulted in the best separation efficiency. Three capillaries from the set representing low, intermediate, and high slurry concentrations were further used for three-dimensional bed reconstruction by confocal laser scanning microscopy and morphological analysis of the bed structure. Previous studies suggest increased slurry concentrations will result in higher column efficiency due to the suppression of transcolumn bed heterogeneities, but only up to a critical concentration. Too concentrated slurries favour the formation of larger packing voids (reaching the size of the average particle diameter). Especially large voids, which can accommodate particles from>90% of the particle size distribution, are responsible for a decrease in column efficiency at high slurry concentrations. Our work illuminates the increasing difficulty of achieving high bed densities with small, frictional, cohesive particles. As particle size decreases interparticle forces become increasingly important and hinder the ease of particle sliding during column packing. While an optimal slurry concentration is identified with respect to bed morphology and separation efficiency under conditions in this work, our results suggest adjustments of this concentration are required with regard to particle size, surface roughness, column dimensions, slurry liquid, and external effects utilized during the packing process (pressure protocol, ultrasound, electric fields).

Topological analysis of non-granular, disordered porous media: determination of pore connectivity, pore coordination, and geometric tortuosity in physically reconstructed silica monoliths

Different approaches are applied and compared, which are universally applicable to quantify pore coordination, pore and pore-throat connectivity, and geometric tortuosity.

Morphological Analysis of Physically Reconstructed Silica Monoliths with Submicrometer Macropores: Effect of Decreasing Domain Size on Structural Homogeneity

Silica monoliths are increasingly used as fixed-bed supports in separation and catalysis because their bimodal pore space architecture combines excellent mass transport properties with a large surface area. To optimize their performance, a quantitative relationship between morphology and transport characteristics has to be established, and synthesis conditions that lead to a desired morphology optimized for a targeted application must be identified. However, the effects of specific synthesis parameters on the structural properties of silica monoliths are still poorly understood. An important question is how far the macropore and domain size can be reduced without compromising the structural homogeneity. We address this question with quantitative morphological data derived for a set of eight macroporous-mesoporous silica monoliths with an average macropore size (d(macro)) of between 3.7 and 0.1 μm, prepared following an established route involving the sol-gel transition and phase separation. The macropore space of the silica monolith samples is reconstructed using focused ion beam scanning electron microscopy followed by a quantitative assessment of geometrical and topological properties based on chord length distributions (CLDs) and branch-node analysis of the pore network, respectively. We observe a significant increase in structural heterogeneity, indicated by a decrease in the parameter k derived from fitting a k-gamma function to the CLDs, when d(macro) reaches the submicrometer range. The compromised structural homogeneity of silica monoliths with submicrometer macropores could possibly originate from early structural freezing during the competitive processes of sol-gel transition and phase separation. It is therefore questionable if the common approach of reducing the morphological features of silica monoliths into the submicrometer regime by changing the point of sol-gel transition can be successful. Alternative strategies and a better understanding of the involved competitive processes should be the focus of future research.