Cationic Covalent Organic Framework as an Ion Exchange Material for Efficient Adsorptive Separation of Biomolecules

Although covalent organic frameworks (COFs) have earned significant interest in separation applications, the use of COFs in biomolecule separation remains unexplored. We examined the ionic COF Py-BPy²⁺-COF as an ion exchange material for biomolecule separation. After characterizing the properties of the synthesized COF with a variety of techniques, binding experiments with both large and small biomolecules were performed. High adsorption capacities of amino acids with different hydrophobicity and charge, as well as proteins of different isoelectric points and molecular weights, were determined in batch equilibrium experiments. Desorption experiments with mixtures of model proteins demonstrated an ability to successfully separate one protein from another with the selectivity hypothesized to be a combination of the isoelectric point, hydrophobicity, and ability to penetrate the crystalline material. Overall, the results demonstrated that Py-BPy²⁺-COF can be exploited as a robust crystalline anion exchange biomolecule separation material.

Cobalt-Iron Double Ion-Bovine Serum Albumin Chelation-Assisted Thermo-Sensitive Surface-Imprinted Nanocage with High Specificity

To develop multifunctional protein imprinted materials, a cobalt-iron double ion-BSA directional chelation-assisted thermo-sensitive surface-imprinted hollow nanocage (Co-Fe@CBMA-MIPs) with excellent specificity is developed on the surface of ZIF-67@Co-Fe in this study by synergizing the advantages of surface imprinting, metal ion chelation, anti-protein adsorption segments, and thermo-sensitive components. Beyond previous research, well-designed multifunctional protein-imprinted materials possess high binding capacity, fast adsorption kinetics, and outstanding selectivity. When the adsorption is carried out at 32 °C, the adsorption capacity of Co-Fe@CBMA-MIPs for BSA reaches 520.35 mg/g within 50 min. The imprinting factor is 8.55. The selectivity factors of Co-Fe@CBMA-MIPs for HSA, Bhb, OVA, and Lyz are 3.72, 6.09, 4.10, and 8.41, respectively. More significantly, Co-Fe@CBMA-MIPs could specifically recognize BSA from mixed proteins and actual samples and exhibit excellent repeated use stability. Based on the above advantages, the development of this research provides an effective means to improve the recognition specificity of molecularly imprinted polymers.

Preparation of Fe3O4@PMAA@Ni Microspheres towards the Efficient and Selective Enrichment of Histidine-Rich Proteins

Magnetic material is considered to as a major concern material for the enrichment of histidine-rich proteins (His-proteins) via metal-ion affinity. In this work, magnetic polymer microspheres with core-shell structure (Fe₃O₄@PMAA@Ni) were successfully prepared via reflux-precipitation polymerization followed by in situ reduction and growth of Ni²⁺. The obtained Ni nanofoams with flower-like structure and uniform pore size (3.34 nm) provided numerous binding sites for His-proteins. The adsorption performance of Fe₃O₄@PMAA@Ni microspheres for His-proteins was estimated via selectively separating bovine hemoglobin (BHb) and bovine serum albumin (BSA) from a matrix composed of BHb, BSA, and lysozyme (LYZ). The results indicated that Fe₃O₄@PMAA@Ni microspheres could efficiently and selectively separate His-proteins from the matrix, with a maximum adsorption capacity of ∼2660 mg/g for BHb. Moreover, Fe₃O₄@PMAA@Ni microspheres exhibited good stability and recyclability for BHb separation over seven cycles. Therefore, this work reported a novel and facile strategy to prepare core-shell Fe₃O₄@PMAA@Ni microspheres, which was promising for practical applications of His-protein separation and purification in proteomics.

A Simple Method for In-Depth Proteome Analysis of Mammalian Cell Culture Conditioned Media Containing Fetal Bovine Serum

A conditioned medium of a cell culture is widely used for various biological applications and frequently analyzed to characterize the functional proteins responsible for observed biological functions. However, a large number of abundant proteins in fetal bovine serum (FBS), usually included in the conditioned medium of a mammalian cell culture medium, hampers in-depth proteomic analysis by liquid chromatography–tandem mass spectrometry (LC-MS/MS). For a deep proteomic analysis of a conditioned medium by LC-MS/MS, we developed a simple albumin depletion approach coupled with data-independent acquisition (DIA)-mode LC-MS/MS for the conditioned medium of mammalian cells in this study. The results showed that this approach enabled the detection of more than 3700 cell-derived proteins in the cell culture supernatant containing FBS. We further demonstrated the potency of this approach by analyzing proteins in the conditioned media of HeLa cells with and without tumor necrosis factor (TNF) stimulation: >40 differentially accumulated proteins, including four cytokines, upon TNF stimulation were identified in the culture media, which were hardly detected by conventional proteome approaches in the literature.

Feasibility of Human Platelet Lysate as an Alternative to Foetal Bovine Serum for In Vitro Expansion of Chondrocytes

Osteoarthritis (OA) is a degenerative joint disease that affects a lot of people worldwide. Current treatment for OA mainly focuses on halting or slowing down the disease progress and to improve the patient’s quality of life and functionality. Autologous chondrocyte implantation (ACI) is a new treatment modality with the potential to promote regeneration of worn cartilage. Traditionally, foetal bovine serum (FBS) is used to expand the chondrocytes. However, the use of FBS is not ideal for the expansion of cells mean for clinical applications as it possesses the risk of animal pathogen transmission and animal protein transfer to host. Human platelet lysate (HPL) appears to be a suitable alternative to FBS as it is rich in biological factors that enhance cell proliferation. Thus far, HPL has been found to be superior in promoting chondrocyte proliferation compared to FBS. However, both HPL and FBS cannot prevent chondrocyte dedifferentiation. Discrepant results have been reported for the maintenance of chondrocyte redifferentiation potential by HPL. These differences are likely due to the diversity in the HPL preparation methods. In the future, more studies on HPL need to be performed to develop a standardized technique which is capable of producing HPL that can maintain the chondrocyte redifferentiation potential reproducibly. This review discusses the in vitro expansion of chondrocytes with FBS and HPL, focusing on its capability to promote the proliferation and maintain the chondrogenic characteristics of chondrocytes.

Probing protein rejection behavior of blended PES-based flat-sheet ultrafiltration membranes: A density functional theory (DFT) study

Membrane fouling is a common problem in membrane technology and causes detrimental effects for the applied membranes such as loss of integrity and productivity. Henceforward, we devoted this work to fabricate membranes that pose favored criteria in the direction of alleviating membrane fouling incidence. Herein, the fabricated membranes were traced via an assortment of both experimental and molecular modeling verifications to understand the mechanism of interaction. To do so, firstly, three different ultrafiltration (UF) membranes had been prepared via facile wet phase inversion method thru dipping a casting solution composed of polyethersulfone-polyvinyl pyrrolidone (PES-PVP) and polyethersulfone-Pluronic P31R1 (PES-P31R1) in a water coagulation bath. Regarding the practical-based data, the pristine PES membrane exhibited the highest rejection of bovine serum albumin (BSA) protein (model foulant) compared with the modified PES-based membranes. The membrane chemical compositions were elucidated with ATR-FTIR Spectroscopy. On the other hand, molecular modeling has been carried out via calculating thermodynamic parameters, level parametric method, and density functional theory (DFT). Thermodynamic parameters analysis indicated that the noticeable difference of BSA rejection may be ascribed to different entropy behavior for the fabricated membranes. In addition, the level parametric method (PM6) and density functional theory DFT: B3LYP with 6-31g (d,p) basis set models clarified the interaction manner of BSA molecules to membrane surfaces.

Effects of negative and positive cooperative adsorption of proteins on hydrophobic interaction chromatography media

The adsorption behavior of the model proteins: alpha-Lactalbumin, Bovine Serum Albumin, Lysozyme, and a monoclonal antibody, in single component and in binary mixtures, was investigated on two different hydrophobic interaction chromatography resins using both static and dynamic methods. A kinetic model of the adsorption process was developed, which accounted for protein unfolding and intermolecular interactions in the adsorbed phase. The latter incorporated positive cooperative interactions, resulting from preferred and multilayer adsorption on the adsorbent surface, as well as negative cooperative interactions attributed to exclusion effects due to size exclusion and repulsion. Cooperative adsorption resulted in negative or positive deviations from the Langmuir model for both single and multicomponent isotherms. The model was used to assess possible contributions of different adsorption mechanisms of proteins and their structurally different forms to the overall adsorption pattern, as well as to simulate chromatographic band profiles under different loading conditions. For proteins with unstable structure, the overall adsorption isotherm was dominated by binding of unfolded species at low surface coverage and by positive cooperative adsorption at high surface coverage. Furthermore, regardless of structural stability, exclusion effects influenced strongly adsorption equilibrium, particularly at low surface coverages. In case of chromatographic elution, i.e. under dynamic conditions, unfolding, negative cooperative adsorption, and kinetic effects governed the retention behavior and determined peak shapes, whereas the effect of positive cooperative adsorption was negligible.

Temperature-Activated PEG Surface Segregation Controls the Protein Repellency of Polymers

Poly(ethylene glycol) (PEG) is widely used to modulate the hydration states of biomaterials and is often applied to produce nonfouling surfaces. Here, we present X-ray scattering data, which show that it is the surface segregation of PEG, not just its presence in the bulk, that makes this happen by influencing the hydrophilicity of PEG-containing substrates. We demonstrate a temperature-dependent trigger that transforms a PEG-containing substrate from a protein-adsorbing to a protein-repelling state. On films of poly(desaminotyrosyl-tyrosine-co-PEG carbonate) with high (20 wt %) PEG content, in which very little protein adsorption is expected, quartz crystal microbalance data showed significant adsorption of fibrinogen and bovine serum albumin at 8 °C. The surface became protein-repellent at 37.5 °C. When the same polymer was iodinated, the polymer was protein-adsorbent, even when 37 wt % PEG was incorporated into the polymer backbone. This demonstrates that high PEG content by itself is not sufficient to repel proteins. By inhibiting phase separation either with iodine or by lowering the temperature, we show that PEG must phase-separate and bloom to the surface to create an antifouling surface. These results suggest an opportunity to design materials with high PEG content that can be switched from a protein-attractant to a protein-repellent state by inducing phase separation through brief exposure to temperatures above their glass transition temperature.

Rapid Size-Based Protein Discrimination inside Hybrid Isoporous Membranes

Owing to their unique morphology, isoporous membranes derived from block copolymers (BCPs) have rapidly advanced the process of macromolecular separation. In such separations, fouling is the most daunting challenge, affecting both the permeability and selectivity of high-performance isoporous membranes. To overcome this, we increase the hydrophilicity of nanostructured BCP isoporous membranes by incorporating hydrophilic polymer-grafted graphene oxide nanosheets into them. Due to the synergy of these two highly functional components, the hybrid isoporous membranes show pH-responsive and alcohol-gating behaviors, along with improved bactericidal capabilities. Leveraging the high permeability and selectivity behavior of BCP isoporous membranes together with the antifouling capabilities imparted by the polymer-grafted graphene oxide nanosheets, we achieved the highest separation factor (33) ever obtained during the ultrafiltration of the common blood proteins bovine serum albumin and immunoglobulin. This was accompanied by a 60% enhanced flux compared to that of the pristine BCP membranes during this challenging size-based separation of a protein mixture. We surmise that such fouling-resistant hybrid isoporous membranes with rationally functionalized filler materials can be used to replace existing membranes for specific energy-efficient bioseparation applications with improved performance.

Urea-based porous organic polymer/graphene oxide hybrid as a new sorbent for highly efficient extraction of bovine serum albumin prior to its spectrophotometric determination

A 3D urea-based porous organic polymer (Urea-POP) was prepared via the reaction of tetrakis(4-aminophenyl)methane and 1,4-Phenylene diisocyanate. The polymer was subsequently reacted with 2D layered nanosheets of graphene oxide (GO) to prepare Urea-POP/GO as a novel and highly efficient sorbent for pre-concentration and extraction of serum albumin samples, prior to spectrophotometric determination. The hybrid material combines advantages of both POP and GO such as hydrophilicity, high dispersion stability, porosity, and having a large number of nitrogen- and oxygen-containing functional groups. Parameters which influence the extraction efficiency such as the amount of the adsorbent, pH of sample solution, ionic strength, adsorption and desorption time were investigated and optimized. For the method, detection limit of 0.068 mg L^-1 and determination coefficient (R²) of 0.9991 were obtained. The intra- and inter-day was calculated with five replicates in the same day and seven consecutive days, respectively. Intra-day and inter-day precisions were 1.7% and 5.9%, respectively. The maximum sorption capacity was 357.1 mg g^-1, which is higher than the other reported sorbents. The proposed method was demonstrated to be sensitive enough for determination of serum albumin from bio-samples.

A microfluidic chip with a staircase pH gradient generator, a packed column and a fraction collector for chromatofocusing of proteins

A microfluidic device for pH gradient chromatofocusing is presented, which performs creation of a micro-column, pH gradient generation, and fraction collection in a single device. Using a sieve micro-valve, anion exchange particles were packed into a microchannel in order to realize a solid-phase absorption column. To fractionate proteins according to their isoelectric points, elution buffer solutions with a stepwise pH gradient were prepared in 16 parallel mixing reactors and flowed through the micro-column, wherein a protein mixture was previously loaded. The volume of the column is only 20 nL, hence it allows extremely low sample consumption and fast analysis compared with a conventional system. We demonstrated separation of two proteins, albumin-fluorescein isothiocyanate conjugate (FITC-BSA) and R-Phycoerythrin (R-PE), by using a microcolumn of commercial charged polymeric particles (Source 15Q). The microfluidic device can be used as a rapid diagnostic tool to analyse crude mixtures of proteins or nucleic acids and determine adsorption/desorption characteristics of various biochemical products, which can be helpful for scientific fundamental understanding as well as instrumental in various industrial applications, especially in early stage screening and process development.

Presence of Fe-Al binary oxide adsorbent cake layer in ceramic membrane filtration and their impact for removal of HA and BSA

To enhance the removal of natural organic matter (NOM) in ceramic (Ce) membrane filtration, an iron-aluminum binary oxide (FAO) was applied to the ceramic membrane surface as the adsorbent cake layer, and it was compared with heated aluminum oxide (HAO) for the evaluation of the control of NOM. Both the HAO and FAO adsorbent cake layers efficiently removed the NOM regardless of NOM's hydrophobic/hydrophilic characteristics, and the dissolved organic carbon (DOC) removal in NOM for FAO was 1-1.12 times greater than that for HAO, which means FAO was more efficient in the removal of DOC in NOM. FAO (0.03 μm), which is smaller in size than HAO (0.4 μm), had greater flux reduction than HAO. The flux reduction increased as the filtration proceeded because most of the organic foulants (colloid/particles and soluble NOM) were captured by the adsorbent cake layer, which caused fouling between the membrane surface and the adsorbent cake layer. However, no chemically irreversible fouling was observed on the Ce membrane at the end of the FAO adsorbent cake layer filtration. This means that a stable adsorbent cake layer by FAO formed on the Ce membrane, and that the reduced pure water flux of the Ce membrane, resulting from the NOM fouling, can easily be recovered through physicochemical cleaning.

In vitro mouse spermatogenesis with an organ culture method in chemically defined medium

We previously reported the successful induction and completion of mouse spermatogenesis by culturing neonatal testis tissues. The culture medium consisted of α-minimum essential medium (α-MEM), supplemented with Knockout serum replacement (KSR) or AlbuMAX, neither of which were defined chemically. In this study, we formulated a chemically defined medium (CDM) that can induce mouse spermatogenesis under organ culture conditions. It was found that bovine serum albumin (BSA) purified through three different procedures had different effects on spermatogenesis. We also confirmed that retinoic acid (RA) played crucial roles in the onset of spermatogonial differentiation and meiotic initiation. The added lipids exhibited weak promoting effects on spermatogenesis. Lastly, luteinizing hormone (LH), follicle stimulating hormone (FSH), triiodothyronine (T3), and testosterone (T) combined together promoted spermatogenesis until round spermatid production. The CDM, however, was not able to produce elongated spermatids. It was also unable to induce spermatogenesis from the very early neonatal period, before 2 days postpartum, leaving certain factors necessary for spermatogenic induction in mice unidentified. Nonetheless, the present study provided important basic information on testis organ culture and spermatogenesis in vitro.

Bilirubin Removal from Albumin - Containing Solution by Adsorption on Polymer Resin

Adsorption equilibrium of bilirubin onto polymeric resins is studied. Solutions containing albumin are used in order to simulate the behavior of systems for removal of albumin-bound substances from blood, serum or dialysis fluids. The effect of albumin pre-loading on the resin is also analysed. Results are explained by a chemically based model that accounts for binding reaction between albumin and bilirubin in the liquid phase.

Thermodynamic equilibria and physical models are essential tools for designing adsorption columns aimed at detoxification treatments.

2-methoxyethylacrylate modified polysulfone membrane and its blood compatibility

Hydrophilic material 2-methoxyethylacrylate (MEA) was grafted onto polysulfone (PSF) membrane via Michael addition reaction. The ¹H nuclear magnetic resonance (¹H NMR), Attenuated total reflectance-Fourier transform infrared spectroscope (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) characterization of the modified membrane proved that MEA had been successfully grafted onto PSF membrane surface. The water contact angle of the membrane surface was tested. The results showed that the water contact angle changed from 76° to 59.5°, which means that the hydrophilicity of the modified membrane was improved. A series of blood compatibility tests including bovine serum protein adsorption, platelet adhesion, prothrombin time (PT), partial thromboplastin time (APTT) and thrombin time (TT) were carried out on PSF membrane and the modified PSF membrane with highest grafted density of MEA. All of the results indicate that MEA plays an important role in improving the blood compatibility of PSF membrane.

Using an FPLC to promote active learning of the principles of protein structure and purification

The concepts of protein purification are often taught in undergraduate biology and biochemistry lectures and reinforced during laboratory exercises; however, very few reported activities allow students to directly gain experience using modern protein purification instruments, such as Fast Protein Liquid Chromatography (FPLC). This laboratory exercise uses size exclusion chromatography (SEC) and ion exchange (IEX) chromatography to separate a mixture of four different proteins. Students use an SEC chromatogram and corresponding SDS-PAGE gel to understand how protein conformations change under different conditions (i.e. native and non-native). Students explore strategies to separate co-eluting proteins by IEX chromatography. Using either cation or anion exchange, one protein is bound to the column while the other is collected in the flow-through. In this exercise, undergraduate students gain hands-on experience with experimental design, buffer and sample preparation, and implementation of instrumentation that is commonly used by experienced researchers while learning and applying the fundamental concepts of protein structure, protein purification, and SDS-PAGE. © 2016 by The International Union of Biochemistry and Molecular Biology, 45(1):60-68, 2017.

Bioanalytical Application of Amino Acid Detection by Capillary Electrophoresis

This chapter illustrates the usefulness of capillary electrophoresis (CE) for the analysis of amino acids, and both normal and chiral separations are covered. In order to provide a general description of the main results and challenges in the biomedical field, some relevant applications and reviews on CE of amino acids are tabulated. Furthermore, some detailed experimental procedures are shown, regarding the CE analysis of amino acids in body fluids, in microdialysate, and released upon hydrolysis of proteins. In particular, the protocols will deal with the following compounds: (1) underivatized aminoacids in blood; (2) γ-Aminobutyric acid, glutamate, and L-Aspartate derivatized with Naphthalene-2,3-dicarboxaldehyde; (3) hydrolysate from bovine serum albumine derivatized with phenylisothiocyanate. By examining these applications on real matrices, the capillary electrophoresis efficiency as tool for Amino Acid analysis can be ascertained.

Tangential Flow Ultrafiltration Allows Purification and Concentration of Lauric Acid-/Albumin-Coated Particles for Improved Magnetic Treatment

Superparamagnetic iron oxide nanoparticles (SPIONs) are frequently used for drug targeting, hyperthermia and other biomedical purposes. Recently, we have reported the synthesis of lauric acid-/albumin-coated iron oxide nanoparticles SEON(LA-BSA), which were synthesized using excess albumin. For optimization of magnetic treatment applications, SPION suspensions need to be purified of excess surfactant and concentrated. Conventional methods for the purification and concentration of such ferrofluids often involve high shear stress and low purification rates for macromolecules, like albumin. In this work, removal of albumin by low shear stress tangential ultrafiltration and its influence on SEON(LA-BSA) particles was studied. Hydrodynamic size, surface properties and, consequently, colloidal stability of the nanoparticles remained unchanged by filtration or concentration up to four-fold (v/v). Thereby, the saturation magnetization of the suspension can be increased from 446.5 A/m up to 1667.9 A/m. In vitro analysis revealed that cellular uptake of SEON(LA-BSA) changed only marginally. The specific absorption rate (SAR) was not greatly affected by concentration. In contrast, the maximum temperature Tmax in magnetic hyperthermia is greatly enhanced from 44.4 °C up to 64.9 °C by the concentration of the particles up to 16.9 mg/mL total iron. Taken together, tangential ultrafiltration is feasible for purifying and concentrating complex hybrid coated SPION suspensions without negatively influencing specific particle characteristics. This enhances their potential for magnetic treatment.

Electrochemical Characterization of Protein Adsorption onto YNGRT-Au and VLGXE-Au Surfaces

The adsorption of the proteins CD13, mucin and bovine serum albumin on VLGXE-Au and YNGRT-Au interfaces was monitored by electrochemical impedance spectroscopy in the presence of [Fe(CN)₆]^3−/4−. The hydrophobicity of the Au surface was tailored using specific peptides, blocking agents and diluents. The combination of blocking agents (ethanolamine or n-butylamine) and diluents (hexanethiol or 2-mercaptoethanol) was used to prepare various peptide-modified Au surfaces. Protein adsorption onto the peptide-Au surfaces modified with the combination of n-butylamine and hexanethiol produced a dramatic decrease in the charge transfer resistance, R_ct, for all three proteins. In contrast, polar peptide-surfaces induced a minimal change in R_ct for all three proteins. Furthermore, an increase in R_ct was observed with CD13 (an aminopeptidase overexpressed in certain cancers) in comparison to the other proteins when the VLGXE-Au surface was modified with n-butylamine as a blocking agent. The electrochemical data indicated that protein adsorption may be modulated by tailoring the peptide sequence on Au surfaces and that blocking agents and diluents play a key role in promoting or preventing protein adsorption. The peptide-Au platform may also be used for targeting cancer biomarkers with designer peptides.

Formation and reshuffling of disulfide bonds in bovine serum albumin demonstrated using tandem mass spectrometry with collision-induced and electron-transfer dissociation

Thermolysin hydrolyzates of freshly isolated, extensively stored (6 years, 6 °C, dry) and heated (60 min, 90 °C, in excess water) bovine serum albumin (BSA) samples were analyzed with liquid chromatography (LC) electrospray ionization (ESI) tandem mass spectrometry (MS/MS) using alternating electron-transfer dissociation (ETD) and collision-induced dissociation (CID). The positions of disulfide bonds and free thiol groups in the different samples were compared to those deduced from the crystal structure of native BSA. Results revealed non-enzymatic posttranslational modifications of cysteine during isolation, extensive dry storage, and heating. Heat-induced extractability loss of BSA was linked to the impact of protein unfolding on the involvement of specific cysteine residues in intermolecular and intramolecular thiol-disulfide interchange and thiol oxidation reactions. The here developed approach holds promise for exploring disulfide bond formation and reshuffling in various proteins under conditions relevant for chemical, biochemical, pharmaceutical and food processing.

Sample preconcentration utilizing nanofractures generated by junction gap breakdown assisted by self-assembled monolayer of gold nanoparticles

The preconcentration of proteins with low concentrations can be used to increase the sensitivity and accuracy of detection. A nonlinear electrokinetic flow is induced in a nanofluidic channel due to the overlap of electrical double layers, resulting in the fast accumulation of proteins, referred to as the exclusion-enrichment effect. The proposed chip for protein preconcentration was fabricated using simple standard soft lithography with a polydimethylsiloxane replica. This study extends our previous paper, in which gold nanoparticles were manually deposited onto the surface of a protein preconcentrator. In the present work, nanofractures were formed by utilizing the self-assembly of gold-nanoparticle-assisted electric breakdown. This reliable method for nanofracture formation, involving self-assembled monolayers of nanoparticles at the junction gap between microchannels, also decreases the required electric breakdown voltage. The experimental results reveal that a high concentration factor of 1.5×10(4) for a protein sample with an extremely low concentration of 1 nM was achieved in 30 min by using the proposed chip, which is faster than our previously proposed chip at the same conditions. Moreover, an immunoassay of bovine serum albumin (BSA) and anti-BSA was carried out to demonstrate the applicability of the proposed chip.

Enhanced extraction of bovine serum albumin with aqueous biphasic systems of phosphonium- and ammonium-based ionic liquids

Novel aqueous biphasic systems (ABS) composed of phosphonium- or ammonium-based ionic liquids (ILs), combined with a buffered aqueous solution of potassium citrate/citric acid (pH=7.0), were investigated for the extraction of proteins. For that purpose, the phase diagrams, tie-lines and tie-line lengths were determined at 25 °C, and the performance of these ABS for the extraction of bovine serum albumin (BSA) was then evaluated. The obtained results reveal that, with the exception of the more hydrophobic ILs, most of the systems investigated allow the complete extraction of BSA for the IL-rich phase in a single-step. These remarkable extraction efficiencies are far superior to those afforded by more conventional extraction systems previously reported. The composition of the biphasic systems, i.e., the amount of phase-forming components, was also investigated aiming at reducing the overall costs of the process without losing efficiency on the protein extraction. It is shown that the extraction efficiencies of BSA are maintained at 100% up to high protein concentrations (at least up to 10 g L(-1)). The recovery of the BSA from the IL-rich phase by dialysis is also shown in addition to the demonstration of the IL recyclability and reusability, at least for 3 times. In the sequential three-step extractions (BSA recovery/IL reusability), the extraction efficiencies of BSA for the IL-rich phase were maintained at 100%. For the improved ABS, the preservation of the protein native conformation was confirmed by Size Exclusion High-Performance Liquid Chromatography (used also as the quantification method) and by Fourier Transform Infra-Red spectroscopy. According to the results herein reported, ABS composed of phosphonium- or ammonium-based ILs and a biodegradable organic salt represent an alternative and remarkable platform for the extraction of BSA and may be extended to other proteins of interest.

Nonfouling tunable βCD dextran polymer films for protein applications

Polymeric β-cyclodextrin (βCD) films tunable with respect to thickness and βCD content were prepared in order to develop a suitable platform, allowing for inclusion of nonpolar guest molecules in the βCD cavity, while suppressing nonspecific protein adsorption. The βCD films were synthesized from linear βCD dextran polymers, and grafted onto silicon oxide surfaces by "click" chemistry. Topographic and morphological characteristics are controllable by reaction conditions and polymer type, with average film heights from 2.5 to 12.5 nm. Reversible introduction of electrostatic charges in the βCD dextran by complex formation with 1-adamantanecarboxylic acid prior to surface grafting resulted in a thinner and denser film, presumably by decompaction of the polymers. Total internal reflection fluorescence spectroscopy (TIRF) was employed to evaluate the accessibility of βCD cavities to the fluorescent probe 2-anilinonaphthalene-6-sulfonic acid. Only a minor fraction of the βCD cavities was accessible in the thicker and less dense films; however, accessibility was largely improved with increased ionic strength using NaCl up to 1 M. Antifouling properties of the βCD dextran polymer films were assessed by TIRF real-time monitoring, using bovine serum albumin as a model protein, and showed a 5- to 10-fold reduction in nonspecific adsorption as compared to a bare quartz surface with the degree of reduction reflecting film thickness and interfacial polymer density.

Blotting from PhastGel to Membranes by Ultrasound

Ultrasound based approach for enhanced protein blotting is proposed. Three minutes of ultrasound exposure (1 MHz, 2.5 W/cm(2)) was sufficient for a clear transfer of proteins from a polyacrylamide gel (PhastGel) to nitrocellulose or Nylon 66 Biotrans membrane. The proteins evaluated were prestained sodium dodecyl sulfate-polyacrylamide standards (18,500-106,000 Da) and 14C-labeled Rainbow protein molecular weight markers (14,300-200,000 Da).

Metal mesh device sensor immobilized with a trimethoxysilane-containing glycopolymer for label-free detection of proteins and bacteria

Biosensors for the detection of proteins and bacteria have been developed using glycopolymer-immobilized metal mesh devices. The trimethoxysilane-containing glycopolymer was immobilized onto a metal mesh device using the silane coupling reaction. The surface shape and transmittance properties of the original metal mesh device were maintained following the immobilization of the glycopolymer. The mannose-binding protein (concanavalin A) could be detected at concentrations in the range of 10(-9) to 10(-6) mol L(-1) using the glycopolymer-immobilized metal mesh device sensor, whereas another protein (bovine serum albumin) was not detected. A detection limit of 1 ng mm(-2) was achieved for the amount of adsorbed concanavalin A. The glycopolymer-immobilized metal mesh device sensor could also detect bacteria as well as protein. The mannose-binding strain of Escherichia coli was specifically detected by the glycopolymer-immobilized metal mesh device sensor. The glycopolymer-immobilized metal mesh device could therefore be used as a label-free biosensor showing high levels of selectivity and sensitivity toward proteins and bacteria.

Coating gigaporous polystyrene microspheres with cross-linked poly(vinyl alcohol) hydrogel as a rapid protein chromatography matrix

Gigaporous polystyrene (PS) microspheres were hydrophilized by in situ polymerization to give a stable cross-linked poly(vinyl alcohol) (PVA) hydrogel coating, which can shield proteins from the hydrophobic PS surface underneath. The amination of microspheres (PS-NH2) was first carried out through acetylization, oximation and reduction, and then 4,4'-azobis (4-cyanovaleric acid) (ACV), a polymerization initiator, was covalently immobilized on PS-NH2 through amide bond formation, and the cross-linked poly(vinyl acetate) (PVAc) was prepared by radical polymerization at the surfaces of ACV-immobilized PS microspheres (PS-ACV). Finally, the cross-linked PVA hydrogel coated gigaporous PS microspheres (PS-PVA) was easily achieved through alcoholysis of PVAc. Results suggested that the PS microspheres were effectively coated with cross-linked PVA hydrogel, where the gigaporrous structure remained under optimal conditions. After hydrophilic modification (PS-PVA), the protein-resistant ability of microspheres was greatly improved. The hydroxyl-rich PS-PVA surface can be easily derivatized by classical chemical methods. Performance advantages of the PS-PVA column in flow experiment include good permeability, low backpressure, and mechanical stability. These results indicated that PS-PVA should be promising in rapid protein chromatography.

Facile synthesis of magnetic mesoporous hollow carbon microspheres for rapid capture of low-concentration peptides

Mesoporous and hollow carbon microspheres embedded with magnetic nanoparticles (denoted as MHM) were prepared via a facile self-sacrificial method for rapid capture of low-abundant peptides from complex biological samples. The morphology, structure, surface property, and magnetism were well-characterized. The hollow magnetic carbon microspheres have a saturation magnetization value of 130.2 emu g(-1) at room temperature and a Brunauer-Emmett-Teller specific surface area of 48.8 m(2) g(-1) with an average pore size of 9.2 nm for the mesoporous carbon shell. The effectiveness of these MHM affinity microspheres for capture of low-concentration peptides was evaluated by standard peptides, complex protein digests, and real biological samples. These multifunctional hollow carbon microspheres can realize rapid capture and convenient separation of low-concentration peptides. They were validated to have better performance than magnetic mesoporous silica and commercial peptide-enrichment products. In addition, they can be easily recycled and present excellent reusability. Therefore, it is expected that this work may provide a promising tool for high-throughput discovery of peptide biomarkers from biological samples for disease diagnosis and other biomedical applications.

Microfluidic based immunosensor for detection and purification of carbonylated proteins

A microchip has been developed on the basis of immno-precipitation approach for fast and sensitive enrichment of low abundant carbonylated proteins. This microfluidic method could enrich molecular biomarkers, which could be further analyzed in the proteomic study of age-related diseases and therapeutic development. In this study, an immunoaffinity-based PDMS micro-device was designed, fabricated, and chemically modified to specifically trap DNP-labeled PTM proteins of low abundance from a complex protein mixture. Carbonylated protein is selected as a representative PTM protein to illustrate the wide application of this immuno-based microchip for other PTMs which could be readily labeled by different antibody groups. Surface characterization methods such as atomic force microscopy and fluorescence microscopy were used to evaluate the construction of glutaraldehyde- and antibody- terminated PDMS substrates in the device fabrication. Quantitative study was also applied to study the target protein capture and elution efficiency of the device. In a testing mixture consisting of smaller amount of test model-In Vitro oxidized cytochrome c and large blocking protein BSA, a high sensitivity and specificity for only carbonylated protein biomarkers was demonstrated using this on-chip immnuoaffinity based extraction/enrichment. For this highly dense 193-post arrays μ-chip, a low abundance of 159 ng of standard in vitro test model- cytochrome c was enriched at flow speed of 5 μL/min within 110 min. We demonstrated that this nascent micro-immunoprecipitation (μ-IP) method is capable for enrichment of biomarkers in protein post-translation modification related diseases and promise great advance in early disease detection.

Dielectrophoresis-enhanced plasmonic sensing with gold nanohole arrays

We experimentally demonstrate dielectrophoretic concentration of biological analytes on the surface of a gold nanohole array, which concurrently acts as a nanoplasmonic sensor and gradient force generator. The combination of nanohole-enhanced dielectrophoresis, electroosmosis, and extraordinary optical transmission through the periodic gold nanohole array enables real-time label-free detection of analyte molecules in a 5 μL droplet using concentrations as low as 1 pM within a few minutes, which is more than 1000 times faster than purely diffusion-based binding. The nanohole-based optofluidic platform demonstrated here is straightforward to construct, applicable to both charged and neutral molecules, and performs a novel function that cannot be accomplished using conventional surface plasmon resonance sensors.

[Analysis of the secondary structure of linker histone H1 based on IR absorption spectra]

This work was carried out to compare the effectiveness of the methods of infrared spectroscopy in the amide I region and UV circular dichroism to the analyze the protein secondary structure by the example of linker histone H1 and bovine serum albumin (BSA). It has been shown that the application of a diamond ATR cell quantifies the proportion of α-helices and β-structures in a good agreement with UV circular dichroism spectroscopy. It has been shown that histone H1 is able to aggregate, which results in considerable changes in its secondary structure.

Gold-coated ordered nanoporous anodic alumina bilayers for future label-free interferometric biosensors

A cost-effective label-free optical biosensor based on gold-coated self-ordered nanoporous anodic alumina bilayers is presented. The structure is formed by two uniform nanoporous layers of different porosity (i.e., a top layer with large pores and a bottom layer with smaller pores). Each layer presents uniform pore size, regular pore distribution, and regular diameter along its pore length. To increase and improve the output sensing signals, a thin gold layer on the top surface was deposited. The gold layer increases the refractive index contrast between the nanoporous alumina layer and the analytical aqueous solution, and it results in a greater contrast in the interferometric spectrum and a higher sensitivity of the structure. From this structurally engineered architecture, the resulting reflectivity spectrum shows a complex series of Fabry-Pérot interference fringes, which was analyzed by the reflective interferometric Fourier transform spectroscopy (RIFTS) method. To determine the performance of this structure for biosensing applications, we tested bovine serum albumin (BSA) as the target protein. The results show a significant enhancement of the RIFTS peak intensity and position when a gold layer is on the top surface.

Combinatorial synthesis with high throughput discovery of protein-resistant membrane surfaces

Using combinatorial methods, we synthesized a series of new vinyl amide monomers and graft-polymerized them to light-sensitive poly(ether sulfone) (PES) porous films for protein resistance. To increase the discovery rate and statistical confidence, we developed high throughput surface modification methods (HTP) that allow synthesis, screening and selection of desirable monomers from a large library in a relatively short time (days). A series of amide monomers were synthesized by amidation of methacryloyl chloride with amines and grafted onto commercial poly(ether sulfone) (PES) membranes using irradiation from atmospheric pressure plasma (APP). The modified PES membrane surfaces were then tested and screened for static protein adhesion using HTP. Hydroxyl amide monomers N-(3-hydroxypropyl)methacrylamide (A3), N-(4-hydroxybutyl)methacrylamide (A4), and N-(4-hydroxybutyl)methacrylamide (A6), ethylene glycol (EG) monomer N-(3-methoxypropyl)methacrylamide (A7), and N-(2-(dimethylamino)ethyl)-N-methylmethacrylamide (A8), and N-(2-(diethylamino)ethyl)-N-methylmethacrylamide (A9) all terminated with tertiary amines and were shown to have protein resistance. The PES membranes modified with these monomers exhibited both low protein adhesion (i.e. membrane plugging or fouling) and high flux. Their performance is comparable with previously identified best performing PEG and zwitterionic monomers, i.e. the so-called gold-standard for protein resistance. Combining a Hansen solubility parameter (HSP) analysis of the amide monomers and the HTP filtration results, we conclude that monomer solubility in water correlates with protein-resistant surfaces, presumably through its effects on surface-water interactions.

Highly hydrophilic polyvinylidene fluoride (PVDF) ultrafiltration membranes via postfabrication grafting of surface-tailored silica nanoparticles

Polyvinylidene fluoride (PVDF) has drawn much attention as a predominant ultrafiltration (UF) membrane material due to its outstanding mechanical and physicochemical properties. However, current applications suffer from the low fouling resistance of the PVDF membrane due to the intrinsic hydrophobic property of the membrane. The present study demonstrates a novel approach for the fabrication of a highly hydrophilic PVDF UF membrane via postfabrication tethering of superhydrophilic silica nanoparticles (NPs) to the membrane surface. The pristine PVDF membrane was grafted with poly(methacrylic acid) (PMAA) by plasma induced graft copolymerization, providing sufficient carboxyl groups as anchor sites for the binding of silica NPs, which were surface-tailored with amine-terminated cationic ligands. The NP binding was achieved through a remarkably simple and effective dip-coating technique in the presence or absence of the N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) cross-linking process. The properties of the membrane prepared from the modification without EDC/NHS cross-linking were comparable to those for the membrane prepared with the EDC/NHS cross-linking. Both modifications almost doubled the surface energy of the functionalized membranes, which significantly improved the wettability of the membrane and converted the membrane surface from hydrophobic to highly hydrophilic. The irreversibly bound layer of superhydrophilic silica NPs endowed the membranes with strong antifouling performance as demonstrated by three sequential fouling filtration runs using bovine serum albumin (BSA) as a model organic foulant. The results suggest promising applications of the postfabrication surface modification technique in various membrane separation areas.

Spectroscopic and electrochemical characterization of nanostructured optically transparent carbon electrodes

The present paper describes the results related to the optical and electrochemical characterization of thin carbon films fabricated by spin coating and pyrolysis of AZ P4330-RS photoresist. The goal of this paper is to provide comprehensive information allowing for the rational selection of the conditions to fabricate optically transparent carbon electrodes (OTCE) with specific electrooptical properties. According to our results, these electrodes could be appropriate choices as electrochemical transducers to monitor electrophoretic separations. At the core of this manuscript is the development and critical evaluation of a new optical model to calculate the thickness of the OTCE by variable angle spectroscopic ellipsometry. Such data were complemented with topography and roughness (obtained by atomic force microscopy), electrochemical properties (obtained by cyclic voltammetry), electrical properties (obtained by electrochemical impedance spectroscopy), and structural composition (obtained by Raman spectroscopy). Although the described OTCE were used as substrates to investigate the effect of electrode potential on the real-time adsorption of proteins by ellipsometry, these results could enable the development of other biosensors that can be then integrated into various CE platforms.

Recorded scan times can limit the accuracy of sedimentation coefficients in analytical ultracentrifugation

We report systematic and large inaccuracies in the recorded elapsed time in data files from the analytical ultracentrifuge, leading to overestimates of the sedimentation coefficients of up to 10%. This far exceeds previously considered factors contributing to the uncertainty in this parameter and has significant ramifications for derived parameters such as hydrodynamic shape and molar mass estimates. The source of this error is currently unknown, but we found it to be quantitatively consistent across different instruments, increasing with rotor speed. Furthermore, its occurrence appears to correlate with the use of the latest data acquisition software from the manufacturer, in use in some of our laboratories for nearly 2 years. Many of the recently published sedimentation coefficients may need to be reexamined. The problem can be easily recognized by comparing the file timestamps provided by the operating system with the elapsed scan times recorded within the data files. Therefore, we implemented a routine in SEDFIT that can automatically examine the data files, alert the user to significant discrepancies, and correct the scan times accordingly. This eliminates errors in the recorded scan times.

A multifunctional microfluidic droplet-array chip for analysis by electrospray ionization mass spectrometry

This paper describes a multifunctional semi-closed droplet-array chip coupled with electrospray ionization mass spectrometry (ESI-MS) detection for multiple sample pretreatment and analysis. A novel interfacing method for coupling droplet system with ESI-MS was proposed using a sampling probe-two-dimensional (2D) droplet-array strategy. The 2D droplet-array system was composed of an 8 × 8 microwell array chip for droplet storage and a layer of oil covering the droplets served as a "virtual wall" to avoid droplet evaporation or cross-contamination. An L-shaped capillary was adopted as the interface of the droplet array and ESI-MS, using its inlet end as a sampling probe for droplets and its outlet with a tip size of ~20 μm as an electrospray emitter, without the need for any droplet extraction device. The droplet analysis was performed by moving the droplet-array chip to allow the capillary sampling probe to sequentially enter into the droplets through the oil and introduce the sample solution into the capillary emitter for MS detection. The MS analysis time for each droplet sample was 40 s with a sample consumption of ca. 13 nL. A good repeatability of 5.7% (RSD, n = 9) was obtained for 10(-6) M reserpine droplet analysis. The uses of the semi-closed 2D droplet array and off-line interfacing mode provide the system with the substantial flexibility and controllability in droplet indexing, multi-step manipulating, and on-demand sampling for MS analysis. We applied the present system in multi-step pretreatment and identification of small amounts of proteomic samples of myoglobin and cytochrome C, including in-droplet protein reduction, alkylation, digestion, and purification based on solid-phase extraction, matrix modification, sample droplet introduction under flow injection mode, and ESI-MS detection.

Chemoselective nanoporous membranes via chemically directed assembly of nanoparticles and dendrimers

Chemoselective nanoporous membranes: tunably porous membranes with embedded functionalities are generated using a template-free, chemically directed nanoparticle-dendrimer (NP-Den) network assembly. This approach provides a direction in the design of post-functionalizable nanoporous membranes for distinguishing both organic molecules and proteins with excellent chemo- and bioselectivity.

Rapid protein concentration, efficient fluorescence labeling and purification on a micro/nanofluidics chip

Fluorescence analysis has proved to be a powerful detection technique for achieving single molecule analysis. However, it usually requires the labeling of targets with bright fluorescent tags since most chemicals and biomolecules lack fluorescence. Conventional fluorescence labeling methods require a considerable quantity of biomolecule samples, long reaction times and extensive chromatographic purification procedures. Herein, a micro/nanofluidics device integrating a nanochannel in a microfluidics chip has been designed and fabricated, which achieves rapid protein concentration, fluorescence labeling, and efficient purification of product in a miniaturized and continuous manner. As a demonstration, labeling of the proteins bovine serum albumin (BSA) and IgG with fluorescein isothiocyanate (FITC) is presented. Compared to conventional methods, the present micro/nanofluidics device performs about 10(4)-10(6) times faster BSA labeling with 1.6 times higher yields due to the efficient nanoconfinement effect, improved mass, and heat transfer in the chip device. The results demonstrate that the present micro/nanofluidics device promises rapid and facile fluorescence labeling of small amount of reagents such as proteins, nucleic acids and other biomolecules with high efficiency.

Optimizing the enrichment of cross-linked products for mass spectrometric protein analysis

RATIONALE

Chemical cross-linking in combination with a mass spectrometric analysis of the created cross-linked products is an area of growing interest for deriving low-resolution structural information of proteins and protein complexes. One of the greatest challenges is the complexity of the created cross-linking mixtures, which can be met by a charge-based enrichment of cross-linked peptides after proteolytic digestion using strong cation-exchange (SCX) chromatography.

METHODS

SCX chromatography was used for the enrichment of cross-linked peptides with the N-hydroxysuccinimide ester bis(sulfosuccinimidyl)succinate (BS(3)) prior to a mass spectrometric analysis by nano-HPLC/nano-ESI-LTQ-Orbitrap-MS/MS. Bovine serum albumin (BSA) and glutathione S-transferase (GST) were employed as model proteins.

RESULTS

Conditions for SCX enrichment were optimized for obtaining as many interpeptide cross-linked peptides as possible in order to maximize the amount of structural information from a single experiment. With an SCX-based enrichment step of cross-linked products within BSA using the cross-linker BS(3), 154 interpeptidal cross-linking products were identified during nano-HPLC/nano-ESI-MS/MS analyses, whereas analyses without a prior SCX enrichment allowed the identification of merely 20 cross-linked products. The application of the SCX enrichment strategy for the analysis of cross-linked products of GST with BS(3) allowed the identification of 26 interpeptidal cross-linked products compared with 16 without SCX enrichment.

CONCLUSIONS

For both proteins investigated herein, BSA and GST, the introduction of an SCX-based enrichment step prior to nano-HPLC/nano-ESI-MS/MS of cross-linked products led to a considerable gain in structural information.

Optical trapping of a single protein

We experimentally demonstrate the optical trapping of a single bovine serum albumin (BSA) molecule that has a hydrodynamic radius of 3.4 nm, using a double-nanohole in an Au film. The strong optical force in the trap not only stably traps the protein molecule but also unfolds it. The unfolding of the BSA is confirmed by experiments with changing optical power and with changing solution pH. The detection of the trapping event has a signal-to-noise ratio of 33, which shows that the setup is extremely sensitive to detect the presence of a protein, even at the single molecule level.

Silver staining techniques of polyacrylamide gels

Although the main application for polyacrylamide gels is the separation and subsequent blotting of proteins for immunodetection, there are tasks that need staining of proteins in the polyacrylamide gel. Several different staining techniques exist for protein staining in SDS gels that differ in their sensitivity, their expenditure of time, and other aspects. Still, silver staining is the most sensitive and reliable staining technique. Because this technique was developed in the 1970s, a huge number of variations exist. Therefore, we will provide herein three methods, which are robust and easy to perform.

Coomassie-Brilliant Blue staining of polyacrylamide gels

Over the past, a series of staining procedures for proteins were published. The most commonly used staining dye for proteins is still Coomassie-Brilliant Blue. The major reason is Coomassie-Brilliant Blue staining is simple, fast, and sensitive. As Coomassie-Brilliant Blue is almost insoluble in water, a series of procedures including colloidal aqueous procedures were described.

Microwave-assisted protein staining, destaining, and in-gel/in-solution digestion of proteins

Rapid evolution of state-of-the-art proteomic analyses has encompassed development of high-throughput analytical instrumentation and bioinformatic tools. However, recently, there has been a particular emphasis on increasing the throughput of sample preparation, which has become one of the rate-limiting steps in protein characterization workflows. Researchers have been investigating alternative methods to conventional convection oven incubations to try and reduce sample preparation time for protein characterization. Several protocols have appeared in the literature, which employ microwave irradiation as a tool for the preparation of biological samples for subsequent characterization by a variety of analytical techniques. In this chapter, techniques for microwave-assisted protein staining, destaining, and digestion are described. In general, the application of microwave-assisted technologies resulted in the drastic reduction of overall sample preparation time, though discrepancies in the reproducibility of several published digestion protocols still remain to be clarified.

Preparation of guanidine group functionalized magnetic nanoparticles and the application in preconcentration and separation of acidic protein

Guanidine group (Gnd) functionalized magnetic nanoparticles (Fe3O4@SiO2@NH2-Gnd) were synthesized and characterized in this work for the first time. The characterization of Fe3O4@SiO2@ NH2-Gnd nanoparticles was demonstrated by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectra, vibration sample magnetometer, and zeta potential analyzer. The novel multifunctional nanoparticles were served as a solid-phase extraction sorbent for easy isolation and preconcentration of acidic protein from aqueous solution only using a magnet. Bovine serum albumin (BSA) was selected as a model protein and the main experimental parameters influencing the adsorption and desorption efficiency were investigated and optimized. Under the optimum conditions, the particles reached saturated adsorption within 20 min and exhibited significant specific recognition for the acidic proteins. Fifteen fold enrichment efficiency was achieved and the detection limits was 45 ng x mL(-1) for BSA by capillary electrophoresis (CE). The practical application of the novel nanoparticles as a sorbent for the isolation and preconcentration of acidic proteins from basic proteins was demonstrated by effective separation and enrichment of bovine serum albumin from lysozyme and cytochrome C mixture, which was assayed by CE.

Carboxymethylated dextran-coated magnetic iron oxide nanoparticles for regenerable bioseparation

Carboxymethylated dextran (CMD)-coated magnetic iron oxide nanoparticles (MNPs) were synthesized using a co-precipitation method. Compared to neutral dextran coated MNPs, the CMD coating provides good dispersity and colloidal stability to the CMD-MNPs. In particular, the carboxyl groups on the CMD can be readily activated for covalent attachment of antibody molecules. The superparamagnetic property of the antibody-covered CMD-MNPs enables the captured antigen to be separated from the sample solution and CMD coating significantly reduces the nonspecific binding of the nanoparticles. Regeneration of the anti-BSA antibody-covered CMD-MNPs with NaOH does not significantly decrease the antibody activity, and the repeated magnetic separation and washing steps cause only small loss of the starting materials. The method was found to be highly reproducible (RSDs for BSA adsorption and desorption are between 0.78% and 5.1%). The anti-BSA antibody-covered CMD-MNPs possess good selectivity and are able to capture protein antigens from real samples.

Ion-permeable membrane for on-chip preconcentration and separation of cancer marker proteins

Cancer marker proteins have been electrophoretically concentrated and then separated in a microfluidic device. On-chip preconcentration was achieved using an ion-permeable membrane, consisting of acrylamide, N,N'-methylene-bisacrylamide and 2-(acrylamido)-2-methylpropanesulfonate. This negatively charged membrane was photopolymerized in the microdevice near the injection intersection. Anionic proteins were excluded from the porous membrane based on both size and charge, which concentrated target components in the injection intersection prior to separation by microchip capillary electrophoresis (μ-CE). Bovine serum albumin was used in the initial characterization of the system and showed a 40-fold enrichment in the μ-CE peak with 4 min of preconcentration. Adjustment of buffer pH enabled baseline resolution of two cancer biomarkers, α-fetoprotein (AFP) and heat shock protein 90 (HSP90), while fine control over preconcentration time limited peak broadening. Our optimized preconcentration and μ-CE approach was applied to AFP and HSP90, where enrichment factors of >10-fold were achieved with just 1 min of preconcentration. Overall, the process was simple and rapid, providing a useful tool for improving detection in microscale systems.

Initial experimental characterization of a new ultra-high resolution FTICR cell with dynamic harmonization

A new Fourier transform ion cyclotron resonance (FTICR) cell based on completely new principles of formation of the effective electric potential distribution in Penning type traps, Boldin and Nikolaev (Proceedings of the 58th ASMS Conference, 2010), Boldin and Nikolaev (Rapid Commun Mass Spectrom 25:122-126, 2011) is constructed and tested experimentally. Its operation is based on the concept of electric potential space-averaging via charged particle cyclotron motion. Such an averaging process permits an effective electric force distribution in the entire volume of a cylindrical Penning trap to be equal to its distribution in the field created by hyperbolic electrodes in an ideal Penning trap. The excitation and detection electrodes of this new cell are shaped for generating a quadratic dependence on axial coordinates of an averaged (along cyclotron motion orbit) electric potential at any radius of the cyclotron motion. These electrodes together with the trapping segments form a cylindrical surface like in a conventional cylindrical cell. In excitation mode this cell being elongated behaves almost like an open cylindrical cell of the same length. It is more effective in ion motion harmonization at larger cyclotron radii than a Gabrielse et al.-type (Int J Mass Spectrom Ion Processes 88:319-332, 1989) cylindrical cell with four compensation sections. A mass resolving power of more than twenty millions of reserpine (m/z 609) and more than one million of highly charged BSA molecular ions (m/z 1357) has been obtained in a 7T magnetic field.

Electrophoretic transport of biomolecules through carbon nanotube membranes

Electrophoretic transport of proteins across electrochemically oxidized multi-walled carbon nanotube (MWCNT) membranes has been investigated. A small charged protein, lysozyme, was successfully pumped across MWCNT membranes by an electric field while rejecting larger bovine serum albumin (BSA). Transport of lysozome was reduced by a factor of about 30 in comparison to bulk mobility and consistent with the prediction for hindered transport. Mobilities between 0.33 and 1.4 × 10(-9) m(2) V(-1) s(-1) were observed and are approximately 10-fold faster than comparable ordered nanoporous membranes and consistent with continuum models. For mixtures of BSA and lysozyme, complete rejection of BSA is seen with electrophoretic separations.

[Solid phase extraction of BSA]

Silica with immobilized polyoxyethyle-neisooctylphenol (SiO2-TX) was investigated as an adsorbent for solid phase extraction of bovine serum albumin (BSA). It was shown that efficient BSA extraction (up to 96%) takes place on SiO2-TX from water solution in the form of its ionic associates with cationic (at pH = 8) and anionic (at pH = 1.5) surfactants.

The extraction of liquid, protein molecules and yeast cells from paper through surface acoustic wave atomization

Paper has been proposed as an inexpensive and versatile carrier for microfluidics devices with abilities well beyond simple capillary action for pregnancy tests and the like. Unlike standard microfluidics devices, extracting a fluid from the paper is a challenge and a drawback to its broader use. Here, we extract fluid from narrow paper strips using surface acoustic wave (SAW) irradiation that subsequently atomizes the extracted fluid into a monodisperse aerosol for use in mass spectroscopy, medical diagnostics, and drug delivery applications. Two protein molecules, ovalbumin and bovine serum albumin (BSA), have been preserved in paper and then extracted using atomized mist through SAW excitation; protein electrophoresis shows there is less than 1% degradation of either protein molecule in this process. Finally, a solution of live yeast cells was infused into paper, which was subsequently dried for preservation then remoistened to extract the cells via SAW atomization, yielding live cells at the completion of the process. The successful preservation and extraction of fluids, proteins and yeast cells significantly expands the usefulness of paper in microfluidics.