Porous Polymer Monoliths Research Articles

A novel polymeric monolith prepared with multi-acrylate crosslinker for retention-independent efficient separation of small molecules in capillary liquid chromatography

Low column efficiency for small molecules in reversed-phase chromatography is a major problem commonly encountered in polymer-based monoliths. Herein, a novel highly crosslinked porous polymeric monolith was in situ prepared by using a multi-acrylate monomer, dipentaerythritol penta-/hexa-acrylate (DPEPA), as crosslinker, which copolymerized with lauryl methacrylate (LMA) as functional monomer in a UV-transparent fused-silica capillary via photo-initiated free-radical polymerization within 5min. The mechanical stability and permeability of the resulting poly(LMA-co-DPEPA) monolith were characterized in detail. One series of highly crosslinked poly(LMA-co-DPEPA) columns were prepared with relatively higher content of crosslinker (63.3%) in the precursor. Although they exhibited lower permeability, high column efficiency for alkylbenzenes was acquired in cLC, and the minimum plate height (column B) was in the range of 6.04–9.00μm, corresponding to 111,000–165,000Nm−1. Meanwhile, another series of poly(LMA-co-DPEPA) columns prepared with relatively lower content of crosslinker (52.7%) in the precursor exhibited higher permeability, but the minimum plate height (column E) was relatively low in the range of 10.75–20.04μm for alkylbenzenes, corresponding to 50,000–93,000Nm−1. Compared with common poly(LMA-co-EDMA) columns previously reported, the highly crosslinked poly(LMA-co-DPEPA) columns using a multi-acrylate monomer as crosslinker possessed remarkably high column efficiency for small molecules in cLC. By plotting of plate height (H) of alkylbenzenes versus the linear velocity (u) of mobile phase, the results revealed a retention-independent efficient performance of small molecules in the isocratic elution, indicating that the use of multi-functional crosslinker possibly prevents the generation of gel-like micropores in the poly(LMA-co-DPEPA) monolith, reducing the mass transfer resistance (C-term).

Mesoporous monoliths of inverse bicontinuous cubic phases of block copolymer bilayers.

Solution self-assembly of block copolymers into inverse bicontinuous cubic mesophases is a promising new approach for creating porous polymer films and monoliths with highly organized bicontinuous mesoporous networks. Here we report the direct self-assembly of block copolymers with branched hydrophilic blocks into large monoliths consisting of the inverse bicontinuous cubic structures of the block copolymer bilayer. We suggest a facile and scalable method of solution self-assembly by diffusion of water to the block copolymer solution, which results in the unperturbed formation of mesoporous monoliths with large-pore (>25 nm diameter) networks weaved in crystalline lattices. The surface functional groups of the internal large-pore networks are freely accessible for large guest molecules such as protein complexes of which the molecular weight exceeded 100 kDa. The internal double-diamond (Pn3m) networks of large pores within the mesoporous monoliths could be replicated to self-supporting three-dimensional skeletal structures of crystalline titania and mesoporous silica.

In situ synthesis of metal-organic frameworks in a porous polymer monolith as the stationary phase for capillary liquid chromatography.

In this study, HKUST-1 was synthesized in situ on the porous polymer monolith as the stationary phase for capillary liquid chromatography (cLC). The unique carboxyl functionalized poly(methacrylic acid-co-ethylene dimethacrylate) (poly(MAA-co-EDMA)) monolith was used as a support to directly grow HKUST-1 by a controlled layer-by-layer self-assembly strategy. X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectrometry, and Fourier transform infrared spectroscopy of the resulting HKUST-1-poly(MAA-co-EDMA) monoliths indicated that HKUST-1 was successfully grafted onto the pore surface of the poly(MAA-co-EDMA) monolith. The column performance of HKUST-1-poly(MAA-co-EDMA) monoliths for the separation of various small molecules, such as benzenediols, xylenes, ethylbenzenes, and styrenes, was evaluated. The chromatographic performance was found to improve with increasing HKUST-1 density, and the column efficiencies and resolutions of HKUST-1-poly(MAA-co-EDMA) monoliths were 18 320-19 890 plates m(-1) and 1.62-6.42, respectively, for benzenediols. The HKUST-1-poly(MAA-co-EDMA) monolith displayed enhanced resolution for the separation of positional isomers when compared to the traditional C18 and HKUST-1 incorporated polymer monoliths. Hydrophobic, π-π, and hydrogen bonding interactions within the HKUST-1-poly(MAA-co-EDMA) monolith were observed in the separation of small molecules. The results showed that the HKUST-1-poly(MAA-co-EDMA) monoliths are promising stationary phases for cLC.

Facile synthesis of a conjugated microporous polymeric monolith via copper-free Sonogashira–Hagihara cross-coupling in water under aerobic conditions

Facile thiol–yne chemistry on a porous polymer monolith: the sulfur donors thus installed effectively take up Ag(i) ions, allowing for the catalysis of heterocyclization reaction in the solid phase.

Gold-nanoparticle, functionalized-porous-polymer monolith enclosed in capillary for on-column SERS detection

Gold nanoparticles functionalized porous polymer monoliths were developed via on-site synthesis method and enclosed in silica capillary as sensitive, uniform, and stable surface-enhanced Raman scattering (SERS) substrates.

Synergetic effect based gel-emulsions and their utilization for the template preparation of porous polymeric monoliths.

A polymerizable cholesteryl derivative (COA) was synthesized and used as a stabilizer for creating gel-emulsions with water in polymerizable monomers, of which they are styrene (ST), tert-butyl methacrylate (t-BMA), ethylene glycol dimethyl acrylate (EGDMA), and methyl methacrylate (MMA), etc. Interestingly, in addition to COA, the presence of a small amount of Span-80 is a necessity for the formation of the monomers containing gel-emulsions. Unlike conventional ones, the volume fraction of the dispersed phase in the gel-emulsions as created could be much lower than 74%, a critical value for routine gel-emulsions. Stabilization of these gel-emulsions as created has been attributed to the synergetic effect between COA, a typical low-molecular-mass gelator (LMMG), and Span-80, a surfactant, of which the former gels the continuous phase and the latter minimizes the interfacial energy of the continuous phase and the dispersed phase. SEM observation confirmed the network structures of COA in the gel-emulsions. Rheological tests demonstrated that the storage modulus, G', and the yield stress of the gel-emulsions decrease along with increasing the volume fraction of the dispersed phase, water, provided it is not greater than 74%-a result inconsistent with the theory explaining formation of routine gel-emulsions and in support of the conclusion that the systems under study follow a different mechanism. Furthermore, unlike LMMG-based stabilizers reported earlier, the gelator, COA, created in the present study has been functioning not only as a stabilizer but also a monomer. To illustrate the conceptual advantages, the gel-emulsions of water in ST/DVB/AIBN were polymerized. As expected, the densities and internal structures of the monoliths as prepared are highly adjustable, functionalization of the materials with cholesterol has been realized, and at the same time the problem of stabilizer leaking has been avoided. A preliminary test for gas adsorption demonstrated that the monoliths as prepared are good adsorbents for some volatile organic compounds (VOCs), in particular benzene, toluene, ethylbenzene, and xylene-the famous and toxic BTEX. It is believed that the findings reported in the present work provide not only a new strategy for creating novel gel-emulsions but also a new route for functionalizing porous polymeric monoliths.

Rapid identification of synthetic colorants in food samples by using indium oxide nanoparticle-functionalized porous polymer monolith coupled with HPLC-MS/MS.

A synthetic protocol for the preparation of an indium oxide nanoparticle-functionalized poly(methacrylic acid-glycidyl methacrylate-ethylene dimethacrylate-ethanediamine) monolithic column is reported. Various techniques, including scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermal gravimetric analysis-derivative thermogravimetric analysis were employed to characterize the synthesized monolith. The modified monolithic column was coupled with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) for determining synthetic colorants in various food samples. Under optimized conditions, good linearity was obtained for all the targets with squared regression coefficients greater than 0.9982. The limits of detection (S/N = 3) for 12 synthetic colorants were in the range of 0.012-2.97 μg kg(-1). The intra-day and inter-day relative standard deviations, ranging from 2.7% to 8.5%, were within the acceptable range. The developed method was successfully applied to the determination of synthetic colorants in food samples (candy, milk, jelly, jam, canned food, juice, and carbonated drink). Target recoveries at different spiked levels ranged from 73.5% to 112.1% with relative standard deviations of less than 10.3%.

High-performance liquid chromatography on glass chips using precisely defined porous polymer monoliths as particle retaining elements

A stable and permanent integration of miniature packed bed separation columns into microfluidic systems is a major issue in nano liquid chromatography. Various approaches like differently shaped retaining elements or the use of key stone effect have been investigated. We show a flexible integration of miniature packed bed separation columns into microfluidic chips utilising common HPLC material achieved by laser-assisted generation of narrow, photopolymerised frits. The generated retaining elements serve as an in- and outlet frits for the columns. An optimised pre-polymeric solution, consisting of butyl acrylates and a porogen, allows a precise fabrication of frit-type structures with lengths of less than 100μm and the capability to withstand common slurry packing pressures of more than 250bar. The separation of seven polycyclic aromatic hydrocarbons by pressure-driven, reversed-phase chromatography proves the high quality of the created chromatographic column inside a glass chip. Plate heights down to 2.9 were achieved and extremely fast separations with sub-second peak widths were performed in isocratic and gradient elution modes on very short columns (≤25mm).

Preparation of a novel polymer monolith with functional polymer brushes by two-step atom-transfer radical polymerization for trypsin immobilization.

Novel porous polymer monoliths grafted with poly{oligo[(ethylene glycol) methacrylate]-co-glycidyl methacrylate} brushes were fabricated via two-step atom-transfer radical polymerization and used as a trypsin-based reactor in a continuous flow system. This is the first time that atom-transfer radical polymerization technique was utilized to design and construct polymer monolith bioreactor. The prepared monoliths possessed excellent permeability, providing fast mass transfer for enzymatic reaction. More importantly, surface properties, which were modulated via surface-initiated atom-transfer radical polymerization, were found to have a great effect on bioreactor activities based on Michaelis-Menten studies. Furthermore, three model proteins were digested by the monolith bioreactor to a larger degree within dramatically reduced time (50 s), about 900 times faster than that by free trypsin (12 h). The proposed method provided a platform to prepare porous monoliths with desired surface properties for immobilizing various enzymes.

Abstract 3494: Microfluidic platform for a protein-based thyroid cancer diagnostics

Abstract a) The current gold-standard of care in the management of patients with thyroid nodules is ultrasound-guided fine needle aspiration biopsy (FNAB) followed by microscopic examination of cell morphology by a trained cytopathologist. Due to the lack of distinguishing morphology, 10-25% of FNAs are termed “indeterminate” and required surgery. However, only 35% of them are found to have cancer. There is a need for a more accurate and minimally invasive cancer diagnostic technology. Our objective is to develop an inexpensive, point-of-care molecular diagnostic platform to isolate and detect thyroid specific proteins to enable real-world use of biomarkers to inform patient care. b) In this study, we engineer a miniature ion exchange column within a plastic (cyclic olefin polymer), disposable lab-on-a-chip platform for sample preparation and protein purification using microfluidic channels with a specialized porous polymer monolith (PPM)-based resin bed. We capitalized on the finding that cancer cells exhibit differential protein expressional patterns compared to normal thyroid cells by targeting thyroid transcription factor (TTF-1), a thyroid specific enhancer binding protein, as a biomarker for the diagnosis of thyroid cancer. The ability to capture and release TTF-1 from the papillary thyroid cancer (PTC) cell line was evaluated via western blot. We also tested various types of thyroid samples obtained from malignant and benign human thyroid nodules. c) We compared the efficiency of a small-scale protein prep using a commercial gravity column versus our lab-on-a-chip column. Our method showed TTF-1 protein was detectable from the lysate of 5x104 cultured BCPAP cancer cell line. In contrast, it was not detectable when purified by gravity ion-exchange column. We next showed that one can maximize the concentration of protein eluted from as fewer cells as possible. We found that by titrating the elution volume per fraction down to 10 µl, the final concentration of eluted protein can be increased, and hence increase the downstream LOD to 104 cells. Next, we evaluated our extraction and purification system by using 10 mg patient thyroid tissue samples. We tested 11 human thyroid specimens for TTF-1 protein capture. They were all found to be positive which correlated with the official histopathological findings. All tissue extracts had measurable levels of TTF-1 protein and the levels of the TTF-1 were variable in the tissue specimens. We also tested one negative thyroid specimen. No TTF-1 protein was found. d) Our microfluidic protein extraction and purification system is a platform technology that may allow for optimal use of low-volume sample preparation such as we see in thyroid biopsies. This manner, when combined with an on-chip ELISA assay, would be a simple, cost effective test that gives the doctor all the needed information quickly in a single test. When mature, the device can be applied to other type of cancer based on tailored assays for specific biomarkers. Citation Format: Shichu Huang, Siddhartha Sharma, Lena Liu, Andy Fan, Catherine Klapperich, Jennifer Rosen. Microfluidic platform for a protein-based thyroid cancer diagnostics. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3494. doi:10.1158/1538-7445.AM2014-3494

Shape-anchored porous polymer monoliths for integrated online solid-phase extraction-microchip electrophoresis-electrospray ionization mass spectrometry.

We report a simple protocol for fabrication of shape-anchored porous polymer monoliths (PPMs) for on-chip SPE prior to online microchip electrophoresis (ME) separation and on-chip (ESI/MS). The chip design comprises a standard ME separation channel with simple cross injector and a fully integrated ESI emitter featuring coaxial sheath liquid channel. The monolith zone was prepared in situ at the injection cross by laser-initiated photopolymerization through the microchip cover layer. The use of high-power laser allowed not only maskless patterning of a precisely defined monolith zone, but also faster exposure time (here, 7 min) compared with flood exposure UV lamps. The size of the monolith pattern was defined by the diameter of the laser output (∅500 μm) and the porosity was geared toward high through-flow to allow electrokinetic actuation and thus avoid coupling to external pumps. Placing the monolith at the injection cross enabled firm anchoring based on its cross-shape so that no surface premodification with anchoring linkers was needed. In addition, sample loading and subsequent injection (elution) to the separation channel could be performed similar to standard ME setup. As a result, 15- to 23-fold enrichment factors were obtained already at loading (preconcentration) times as short as 25 s without sacrificing the throughput of ME analysis. The performance of the SPE-ME-ESI/MS chip was repeatable within 3.1% and 11.5% RSD (n = 3) in terms of migration time and peak height, respectively, and linear correlation was observed between the loading time and peak area.

A chitosan coated monolith for nucleic acid capture in a thermoplastic microfluidic chip.

A technique for microfluidic, pH modulated DNA capture and purification using chitosan functionalized glycidyl methacrylate monoliths is presented. Highly porous polymer monoliths are formed and subsequently functionalized off-chip in a batch process before insertion into thermoplastic microchannels prior to solvent bonding, simplifying the overall fabrication process by eliminating the need for on-chip surface modifications. The monolith anchoring method allows for the use of large cross-section monoliths enabling high flowrates and high DNA capture capacity with a minimum of added design complexity. Using monolith capture elements requiring less than 1 mm(2) of chip surface area, loading levels above 100 ng are demonstrated, with DNA capture and elution efficiency of 54.2% ± 14.2% achieved.

Coupling isotachophoresis with affinity chromatography for rapid and selective purification with high column utilization, part 2: experimental study.

We present an experimental study of coupling of isotachophoresis (ITP) and affinity chromatography (AC) to effect rapid, selective purification with high column utilization and high resolution. We provide a detailed protocol for performing ITP-AC and describe the design of a buffer system to perform sequence specific separation of nucleic acids. We describe the synthesis and functionalization of our affinity substrate, poly(glycidyl methacrylate-co-ethylene dimethacrylate) porous polymer monolith (GMA-EDMA PPM). This substrate allows easy immobilization of affinity probes, is nonsieving (even to macromolecules), and exhibits negligible nonspecific binding. We demonstrate ITP-AC with 25 nt, Cy5 labeled DNA target and a DNA probe and study the spatiotemporal dynamics using epifluorescence imaging. We make qualitative and quantitative comparisons between these data and the model presented in the first part of this two-paper series. We vary the target concentration from 1 pg μL–1 to 100 pg μL–1 and ITP velocity over the range of 10–50 μm s–1, and thereby explore over 4 orders of magnitude of scaled target amount. We observe very good agreement between predictions and experimental data for the spatiotemporal behavior of the coupled ITP and affinity process, and for key figures of merit, including scaled capture length and maximum capture efficiency. Lastly, we demonstrate that the resolution of ITP-AC increases linearly with time and purify 25 nt target DNA from 10 000-fold higher abundance background (contaminating) genomic fish sperm DNA. We perform this capture from 200 μL of sample in under 1 mm column length and within <10 min.

Facile Fabrication of Polymeric Ionic Liquid Grafted Porous Polymer Monolith for Mixed‐Mode High Performance Liquid Chromatography

AbstractA novel polymeric ionic liquid grafted porous polymer monolith has been facilely fabricated for mixed‐mode chromatography. The column is prepared from poly (glycidyl methacrylate‐co‐ethylene dimethacrylate) monolith through hydrolyzation of the epoxy moieties into hydroxyl groups, followed by "grafting from" polymerization of ionic liquid of 1‐vinyl‐3‐butylimidazolium chloride. Successful modification is characterized by scanning electron microscope, infrared spectroscopy, elemental analysis and mercury intrusion porosimetry. The HPLC performance of developed column is evaluated by separating acidic vitamin B analytes, neutral steroids and basic aromatic amines in mixed‐mode chromatography on a single column, respectively. The ionic liquid affords the monolith with both enhanced separation ability and improved column efficiency.

Ex situ integration of multifunctional porous polymer monoliths into thermoplastic microfluidic chips

A unique method for incorporating functional porous polymer monolith elements into thermoplastic microfluidic chips is described. Monolith elements are formed in a microfabricated mold, rather than within the microchannels, and chemically functionalized off chip before insertion into solvent-softened thermoplastic microchannels during chip assembly. Because monoliths may be trimmed prior to final placement, control of their size, shape, and uniformity is greatly improved over in situ photopolymerization methods. A characteristic trapezoidal profile facilitates rapid insertion and enables complete mechanical anchoring of the monolith periphery, eliminating the need for chemical attachment to the microchannel walls. Off-chip processing allows the parallel preparation of monoliths of differing compositions and surface chemistries in large batches. Multifunctional flow-through arrays of multiple monolith elements are demonstrated using this approach through the creation of a fluorescent immunosensor with integrated controls, and a microfluidic bubble separator comprising a combination of integrated hydrophobic and hydrophilic monolith elements.

RAFT (Reversible addition-fragmentation chain transfer) crosslinking (co)polymerization of multi-olefinic monomers to form polymer networks

The use of reversible addition–fragmentation chain transfer (RAFT) crosslinking (co)polymerization of multi-olefinic monomers to produce three-dimensional polymer networks is reviewed. We give specific attention to differences between RAFT and conventional processes, differences between RAFT and other forms of reversible deactivation radical polymerization (such as atom transfer radical and nitroxide-mediated polymerizations) and the dependence of the polymerization process and network properties on RAFT agent structure. This knowledge is important in network optimization for applications as dynamic covalent polymers (in self-healing polymers), as porous polymer monoliths or gels (used as chromatographic media, flow reactors, controlled release media, drug delivery vehicles and in molecular imprinting) and as coatings. © 2014 Society of Chemical Industry

Impact of biomolecule solute size on the transport and performance characteristics of analytical porous polymer monoliths

Porous monolithic poly(styrene-co-divinylbenzene) stationary phases in 4.6mm ID analytical format have been investigated with respect to their transport properties probed by solutes of biological origin varying vastly in size. Elucidation of several properties of these benchmark and robust materials gave complementary insight. These are: (i) the porous polymers’ apparent dry-state microscopic appearance, (ii) the columns porosity probed by the biomolecules and modulated by mobile phase solvent composition, (iii) the impact of probe solute size on apparent retention at varying mobile phase solvent compositions, and (iv) the elution performance under both nonretained and retained elution conditions. By varying the volume percentage of acetonitrile in the mobile phase, it is demonstrated that the monolithic scaffold shows a variable porosity experienced in particular by the larger sized solutes, while the smaller solutes are gradually less affected. The nanoscale swelling and solvation of porous monolithic adsorbents resulting in gel porosity varied with mobile phase solvent composition was, therefore, indicated. The plate height curves for the solutes under nonretained conditions show a moderate increase at increased flow velocity while approaching plateau values. These plateau values were in conjunction with a trend of a decreased performance at an increased molecular weight of the solute. The systematic shape of the plate height curves at increased flow velocity indicates pre-asymptotic dispersion. This is because the column bed aspect ratio of length-to-diameter is equal or smaller than 10. Imposing retention on the solutes at a constant flow velocity deteriorates isocratic elution performance, more pronouncedly for the larger sized solutes at even weak retention. This is explained with slow pore fluid–gel interface diffusion. Additionally, the apparent retention factor for elution of the probe solutes becomes a function of flow rate, consequently a function of imposed pressure experienced by the scaffold.

Fabrication of interfacial functionalized porous polymer monolith and its adsorption properties of copper ions

The interfacial functionalized poly (glycidyl methacrylate) (PGMA) porous monolith was fabricated and applied as a novel porous adsorbent for copper ions (Cu2+). PGMA porous material with highly interconnected pore network was prepared by concentrated emulsion polymerization template. Then polyacrylic acid (PAA) was grafted onto the interface of the porous monolith by the reaction between the epoxy group on PGMA and a carboxyl group on PAA. Finally, the porous monolith was interfacial functionalized by rich amount of carboxyl groups and could adsorb copper ions effectively. The chemical structure and porous morphology of the porous monolith were measured by Fourier transform infrared spectroscopy and scanning electron microscopy. Moreover, the effects of pore size distribution, pH value, co-existing ions, contacting time, and initial concentrations of copper ions on the adsorption capacity of the porous adsorbents were studied.

Integration of monolithic porous polymer with droplet-based microfluidics on a chip for nano/picoliter volume sample analysis.

In this paper, a porous polymer nanostructure has been integrated with droplet-based microfluidics in a single planar format. Monolithic porous polymer (MPP) was formed selectively within a microfluidic channel. The resulting analyte bands were sequentially comartmentalised into droplets. This device reduces band broadening and the effects of post-column dead volume by the combination of the two techniques. Moreover it offers the precise control of nano/picoliter volume samples.

Strong and small: strong cation-exchange solid-phase extractions using porous polymer monoliths on a digital microfluidic platform

We present the first method for digital microfluidics-based strong cation-exchange solid-phase extractions. Digital microfluidics is a microscale fluid handling technique in which liquid droplets are actuated over an array of electrodes by electrodynamic forces. Strong cation exchange has gained considerable importance in the field of proteomics as a separation mode for protein and peptide extractions. The marriage of these two techniques is achieved by incorporating sulphonate-functionalised porous polymer monolith discs onto digital microfluidic chips. By manipulating sample and solvent droplets onto and off of these porous polymer monoliths, proteins and peptides are extracted by controlling solution pH and ionic strength. This novel microscale extraction method has efficiency comparable to commercially available strong cation-exchange ZipTips and is highly effective for sample cleanup. We anticipate that this digital microfluidic strong cation-exchange extraction technique will prove useful for microscale proteomic analyses and other applications requiring separation of cationic compounds.