Coupling Strong Anion-Exchange Monolithic Capillary with MALDI-TOF MS for Sensitive Detection of Phosphopeptides in Protein Digest

One-step online analysis of antibiotics in highly saline seawater by nano-based slug-flow microextraction

The transition to mass spectrometry (MS) in the analysis of antibiotics in the marine environment is highly desirable, particularly in the enhancement of sensitivity for high-salinity (3.5 wt%) seawater samples. However, the persistence of complex operational procedures poses substantial challenges to this transition. In this study, a rapid method for the online analysis of antibiotics in seawater samples via nano-electrospray ionization (nESI) MS based on slug-flow microextraction (SFME) has been proposed. Comparisons with other methods, complex laboratory setups for sample processing are now seamlessly integrated into a single online step, completing the entire process, including desalination and detection, SFME-nESI-MS provides faster results in less than 2 min while maintaining sensitivity comparable to that of other detection methods. Using SFME-nESI, six antibiotics in high-salinity (3.5 wt%) seawater samples have been determined in both positive and negative ion modes. The proposed method successfully detected clarithromycin, ofloxacin, and sulfadimidine in seawater within a linear range of 1-1000 ng mL-1 and limit of detection (LOD) of 0.23, 0.06, and 0.28 ng mL-1, respectively. The method recovery was from 92.8% to 107.3%, and the relative standard deviation was less than 7.5%. In addition, the response intensity of SFME-nESI-treated high-salinity (3.5 wt%) samples surpassed that of untreated medium-salinity (0.35 wt%) samples by two to five orders of magnitude. This advancement provides an exceptionally simplified protocol for the online rapid, highly sensitive, and quantitative determination of antibiotics in high-salinity (3.5 wt%) seawater.

Simultaneous enrichment optimization of glycopeptides and phosphopeptides with the highly hydrophilic DZMOF-FDP

Protein glycosylation and phosphorylation play essential roles in biological systems. The crosstalk of both glycosylation and phosphorylation on one protein represents an unveiled biological function. To realize the analyses of both glycopeptides and phosphopeptides, a simultaneous enrichment method of N-glycopeptides, mono-phosphopeptides and multi-phosphopeptides was developed based on a multi-functional dual-metal centered zirconium metal-organic framework that provided multiple interactions for HILIC, IMAC, and MOAC for glycopeptides and phosphopeptides. Based on a careful optimization of sample loading and elution conditions for the simultaneous enrichment of glycopeptides and phosphopeptides with the zirconium metal-organic framework, a total of 1011 N-glycopeptides derived from 410 glycoproteins and 1996 phosphopeptides including 741 multi-phosphopeptides derived from 1189 phosphoproteins could be identified from a HeLa cell digest. The simultaneous enrichment approach for glycopeptides and mono-/multi-phosphopeptides demonstrates the great potential of the combined interactions for HILIC, IMAC, and MOAC in integrated post-translational modification proteomics research.

Monodisperse Ti4+-immobilized macroporous adsorbent resins with polymer brush for improved multi-phosphopeptides enrichment in milk

Enrichment of phosphopeptides before mass spectrometry (MS) analysis is essential due to the limitations of low abundance and poor ionization efficiency in complex biological samples. Immobilized metal affinity chromatography (IMAC), especially titanium ion (Ti⁴⁺)-IMAC, has become a popular strategy for enrichment of phosphopeptides due to high selectivity and sensitivity. Conventional Ti⁴⁺-immobilized macroporous adsorption resin (MAR) fabricated by monolayer modification can preferentially capture mono-phosphopeptide over multi-phosphopeptides, which takes on more functions in the regulation of cell behaviors of organism. In this paper, a kind of monodisperse MAR microsphere with functional polymer brush (Ti⁴⁺-Brush@MAR) was prepared and modified via surface-initiated atom transfer radical polymerization (SI-ATRP). Compared with common Ti⁴⁺-MAR without polymer brush, Ti⁴⁺-Brush@MAR exhibited high enrichment specificity not only for mono-phosphopeptides but also for multi-phosphopeptides in β-casein or milk digest samples. As a result, a total of 93 unique phosphopeptides mapped to 18 phosphoproteins were identified from 5 μL milk, and the limit of detection is 10 fmol. It is expected that Ti⁴⁺-Brush@MAR would be utilized to enrich both multi-phosphopeptides and mono-phosphopeptides in additional biological or food samples.

Advances in phosphoproteomics and its application to COPD

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) was the third leading cause of global death in 2019, causing a huge economic burden to society. Therefore, it is urgent to identify specific phenotypes of COPD patients through early detection, and to promptly treat exacerbations. The field of phosphoproteomics has been a massive advancement, compelled by the developments in mass spectrometry, enrichment strategies, algorithms, and tools. Modern mass spectrometry-based phosphoproteomics allows understanding of disease pathobiology, biomarker discovery, and predicting new therapeutic modalities.

AREAS COVERED

In this article, we present an overview of phosphoproteomic research and strategies for enrichment and fractionation of phosphopeptides, identification of phosphorylation sites, chromatographic separation and mass spectrometry detection strategies, and the potential application of phosphorylated proteomic analysis in the diagnosis, treatment, and prognosis of COPD disease.

EXPERT OPINION

The role of phosphoproteomics in COPD is critical for understanding disease pathobiology, identifying potential biomarkers, and predicting new therapeutic approaches. However, the complexity of COPD requires the more comprehensive understanding that can be achieved through integrated multi-omics studies. Phosphoproteomics, as a part of these multi-omics approaches, can provide valuable insights into the underlying mechanisms of COPD.

Unique On-Site Spinning Sampling of Highly Water-Soluble Organics Using Functionalized Monolithic Sorbents

Water utilities encounter unpredictable odor issues that cannot be explained by routine water parameters during spring runoff, even in the summer and fall. Highly water-soluble organics (e.g., amino acids and saccharides) have been reported to form odorous disinfection byproducts during disinfection, but the lack of simple and practical on-site sampling techniques hampers their routine monitoring at trace levels in source water. Therefore, we have created two functionalized nested-in-sponge silica monoliths (NiS-SMs) using a one-pot synthesis method and demonstrated their application for extracting highly soluble organics in water. The NiS-SMs functionalized with the sulfonic group and phenylboronic moiety selectively extracted amino acids and monosaccharides, respectively. We further developed a spinning sampling technique using the composites and evaluated its robust performance under varying water conditions. The spinning sampling coupled to high-performance liquid chromatography tandem mass spectrometry analysis provided limits of detection for amino acids at 0.038-0.092 ng L^-1 and monosaccharides at 0.036-0.14 ng L^-1. Using the pre-equilibrium sampling-rate calibration, we demonstrated the applicability of the spinning sampling technique for on-site sampling and monitoring of amino acids and monosaccharides in river water. The new composite materials and rapid on-site sampling technique are unique and efficient tools for monitoring highly soluble organics in water sources.

A New Strategy for High-Efficient Tandem Enrichment and Simultaneous Profiling of N-Glycopeptides and Phosphopeptides in Lung Cancer Tissue

N-glycosylation and phosphorylation, two common posttranslational modifications, play important roles in various biological processes and are extensively studied for biomarker and drug target screening. Because of their low abundance, enrichment of N-glycopeptides and phosphopeptides prior to LC–MS/MS analysis is essential. However, simultaneous characterization of these two types of posttranslational modifications in complex biological samples is still challenging, especially for tiny amount of samples obtained in tissue biopsy. Here, we introduced a new strategy for the highly efficient tandem enrichment of N-glycopeptides and phosphopeptides using HILIC and TiO₂ microparticles. The N-glycopeptides and phosphosites obtained by tandem enrichment were 21%–377% and 22%–263% higher than those obtained by enriching the two PTM peptides separately, respectively, using 160–20 μg tryptic digested peptides as the starting material. Under the optimized conditions, 2798 N-glycopeptides from 434 N-glycoproteins and 5130 phosphosites from 1986 phosphoproteins were confidently identified from three technical replicates of HeLa cells by mass spectrometry analysis. Application of this tandem enrichment strategy in a lung cancer study led to simultaneous characterization of the two PTM peptides and discovery of hundreds of differentially expressed N-glycosylated and phosphorylated proteins between cancer and normal tissues, demonstrating the high sensitivity of this strategy for investigation of dysregulated PTMs using very limited clinical samples.

Titanium dioxide-functionalized dendritic mesoporous silica nanoparticles for highly selective isolation of phosphoproteins

Selective isolation of phosphoproteins is of great significance in biological applications. Herein, titanium dioxide-functionalized dendritic mesoporous silica nanoparticles are prepared via a post-grafting method for selective capture of phosphoproteins. The fabricated nanoparticles possess a unique central-radial pore structure with a surface area of 666.66 m² /g and a pore size of 22.2 nm. The high-binding affinity of TiO₂ with the phosphate groups facilitates the selective adsorption of phosphoproteins. Moreover, the open central-radial pore structure endows the dendritic mesoporous nanoparticles with better adsorption performance toward phosphoproteins with respect to the commercial titanium dioxide nanoparticles and titanium dioxide-functionalized conventional mesoporous silica nanoparticles by providing more accessible affinity sites. At pH 2, an adsorption capacity of 157.2 mg/g is derived for β-casein. The feasibility of the as-prepared dendritic material in real biological sample assay is demonstrated by the selective isolation of phosphoproteins from defatted milk, as illustrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis assay.

One-step preparation of carbonaceous spheres rich in phosphate groups via hydrothermal carbonization for effective phosphopeptides enrichment

A green strategy was developed to prepare carbonaceous spheres rich in phosphoric acid groups on the surface with D-Glucose 6-phosphate sodium salt (called G6PNa₂) as a sole carbon source through one-step hydrothermal carbonization method. The method is simple and facile and meets the standards of green chemistry as water is the sole solvent employed. Following the hydrothermal carbonization synthesis, the carbonaceous spheres were further functionalized with Ti⁴⁺. The main factors including reaction temperature, reaction time, and concentration of G6PNa₂ were systematically studied in order to obtain the desirable morphology and the optimum phosphopeptides enrichment, for the resulting Ti⁴⁺ functionalized carbonaceous spheres (CS-Ti⁴⁺). The performance evaluation of the CS-Ti⁴⁺ prepared under the optimum conditions demonstrated excellent selectivity (1:1000), low detection limit (1 fmol) and high recovery rate (85%) towards phosphopeptides. Furthermore, 24 low-abundance phosphopeptides were captured from human saliva using CS-Ti⁴⁺, indicating its great potential in mass spectrometry-based phosphoproteome studies.

Carnosine functionalized magnetic metal-organic framework nanocomposites for synergistic enrichment of phosphopeptides

Protein phosphorylation regulates the conformations and function of proteins, which plays an important part in organisms. However, systematic and in-depth analysis of phosphorylation often hinders on account of the low abundance and suppressed ionization of phosphopeptides. Various materials based on single enrichment mechanism show potential in phosphopeptides enrichment, but the enrichment performance is typically not satisfactory. Herein, we developed a carnosine (Car) functionalized magnetic metal organic framework designed as Fe₃O₄@NH₂@ZIF-90@Car. Benefiting from the multiple recognition groups of Car and massive metal ions site of ZIF-90, the as-fabricated Fe₃O₄@NH₂@ZIF-90@Car was utilized as a multifunctional material with synergistic effect for phosphopeptides enrichment. On the basis of combined immobilized metal ion affinity chromatography (IMAC) and amine-based affinity enrichment mechanism, Fe₃O₄@NH₂@ZIF-90@Car exhibited higher enrichment performance of phosphopeptides compared with Fe₃O₄@NH₂@ZIF-90 (single IMAC mechanism). Besides, the feasibility of Fe₃O₄@NH₂@ZIF-90@Car nanocomposites in complicated samples was further verified by enriching phosphopeptides from nonfat milk, human fluids such as serum and saliva, demonstrating its bright application prospects in phosphoproteomics analysis.

Engineering Magnetic Guanidyl-Functionalized Supramolecular Organic Framework for Efficient Enrichment of Global Phosphopeptides

Comprehensive mass spectrometry-based proteomics analysis is currently available but remains challenging, especially for post-translational modifications of phosphorylated proteins. Herein, multifunctional magnetic pillar[5]arene supramolecular organic frameworks were fabricated and immobilized with arginine (mP5SOF-Arg) for highly effective enrichment of global phosphopeptides. The specific phosphate-P5/phosphate-guanidine affinities and large surface area with regular porosity contribute to the high enrichment capacity. By coupling with mass spectrometry, high detection sensitivity (0.1 fmol), excellent selectivity (1:5000 molar ratios of β-casein/cytochrome c), and high recyclability (seven cycles) were achieved for phosphopeptide analysis. mP5SOF-Arg can efficiently enrich phosphopeptides from practical samples, including defatted milk, egg yolk, and human saliva. Notably, a total of 450 phosphopeptides were explored for highly selective identification from A594 cells and 1445 phosphopeptides were identified from mouse liver tissue samples. mP5SOF-Arg exhibited great potential to serve as the basis for peptidomic research to identify phosphopeptides and provided insight for biomarker discovery.

Facile preparation of bifunctional adsorbents for efficiently enriching N-glycopeptides and phosphopeptides

In bottom-up strategy, specific enrichment of glycopeptides and phosphopeptides from complicated biological samples is a prerequisite for efficient identifying glycosylation and phosphorylation by mass spectrometry. Although there were a plethora of materials used as either hydrophilic interaction liquid chromatography (HILIC) or immobilized metal affinity chromatography (IMAC) adsorbents, even several bifunctional materials for simultaneous enrichment of glycopeptides and phosphopeptides, most of them are not easily commercialized as many other well-performing adsorbents due to the complicated preparation process. In our case, a one-step modification strategy was developed to prepare bifunctional adsorbents for HILIC and IMAC, employing O-phospho-l-serine as the modifier and poly(GMA-co-EDMA) microspheres, a kind of macroporous adsorption resin (MAR) with epoxy groups, as the matrix. The MARs were directly modified with O-phospho-l-serine under facile condition for HILIC strategy and further chelated with Ti⁴⁺ for IMAC strategy. A total of 522 unique N-glycopeptides and 442 unique N-glycosylation sites mapped to 275 N-glycoproteins was identified from HeLa cell proteins, showing excellent enrichment efficiency in HILIC. Additionally, 3141 unique phosphopeptides were unambiguously identified from 200 μg of digest of HeLa cell proteins, demonstrating great enrichment efficiency in IMAC. Moreover, these materials have been successfully applied in the analysis of multiple biological samples including human serum and milk, demonstrating their feasibility for real sample applications and potential business value.

Modification of Luffa Sponge for Enrichment of Phosphopeptides

The enrichment technique is crucial to the comprehensive analysis of protein phosphorylation. In this work, a facile, green and efficient synthetic method was set up for quaternization of luffa sponge. The resultant luffa sponge showed strong anion-exchange characteristics and a high adsorption ability for phosphate ions. Along with the unique physical properties, e.g., tenacity and porous texture, quaternized luffa sponge was demonstrated to be a well-suited solid-phase extraction (SPE) material. The quaternized luffa sponge-based SPE method was simple, cost-effective and convenient in operation, and was successfully applied to the capture of phosphopeptides from protein digests. The enrichment approach exhibited exceptionally high selectivity, sensitivity and strong anti-interference ability. Four phosphopeptides were still detected by using the digest mixture of β-casein and bovine serum albumin with a molar ratio of 1:100. 21 phosphopeptides were identified from the tryptic digest of non-fat milk.

Challenges and Advances in the Fabrication of Monolithic Bioseparation Materials and their Applications in Proteomics Research

High-performance liquid chromatography integrated with tandem mass spectrometry (HPLC-MS/MS) has become a powerful technique for proteomics research. Its performance heavily depends on the separation efficiency of HPLC, which in turn depends on the chromatographic material. As the "heart" of the HPLC system, the chromatographic material is required to achieve excellent column efficiency and fast analysis. Monolithic materials, fabricated as continuous supports with interconnected skeletal structure and flow-through pores, are regarded as an alternative to particle-packed columns. Such materials are featured with easy preparation, fast mass transfer, high porosity, low back pressure, and miniaturization, and are next-generation separation materials for high-throughput proteins and peptides analysis. Herein, the recent progress regarding the fabrication of various monolithic materials is reviewed. Special emphasis is placed on studies of the fabrication of monolithic capillary columns and their applications in separation of biomolecules by capillary liquid chromatography (cLC). The applications of monolithic materials in the digestion, enrichment, and separation of phosphopeptides and glycopeptides from biological samples are also considered. Finally, advances in comprehensive 2D HPLC separations using monolithic columns are also shown.

Epitope-imprinted mesoporous silica nanoparticles for specific recognition of tyrosine phosphorylation

Tyrosine phosphorylation regulates the upstream signaling pathway but accounts for less than 0.1% of total phosphorylation in human cells. Herein, molecularly imprinted mesoporous materials were first synthesized to recognize the phosphorylated tyrosine residue from other phosphorylated residues.

Monolith columns for liquid chromatographic separations of intact proteins: A review of recent advances and applications

In this article we survey 256 references (with an emphasis on the papers published in the past decade) on monolithic columns for intact protein separation. Protein enrichment and purification are included in the broadly defined separation. After a brief introduction, we describe the types of monolithic columns and modes of chromatographic separations employed for protein separations. While the majority of the work is still in the research and development phase, papers have been published toward utilizing monolithic columns for practical applications. We survey these papers as well in this review. Characteristics of selected methods along with their pros and cons will also be discussed.

PAMA–Arg brush-functionalized magnetic composite nanospheres for highly effective enrichment of phosphorylated biomolecules

A novel polymer brush-functionalized magnetic composite nanosphere was successfully prepared, exhibiting large enrichment capacity, extremely high detection sensitivity, and high enrichment recovery in phosphorylated biomolecule enrichment.

Facile Preparation of Titanium(IV)-Immobilized Hierarchically Porous Hybrid Monoliths

Hierarchically porous materials have become a key feature of biological materials and have been widely applied for adsorption or catalysis. Herein, we presented a new approach to directly prepare a phosphate-functionalized hierarchically porous hybrid monolith (HPHM), which simultaneously contained mesopores and macropores. The design was based on the copolymerization of polyhedral oligomeric vinylsilsesquioxanes (vinylPOSS) and vinylphosphonic acid (VPA) by adding degradable polycaprolactone (PCL) additive. The phosphate groups could be directly introduced into the hybrid monoliths. This approach was simple and time-saving, and overcame the defect of a rigorous, complex process for preparing traditional Ti⁴⁺-immobilized metal ion affinity chromatography (IMAC) materials. The specific surface area of an optimal hybrid monolith could reach 502 m²/g obtained by nitrogen adsorption/desorption measurements, which originated from the degradation of PCL. Meanwhile, the characterization of scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) also suggested that the macropores existed in the hybrid monoliths. The size of macropores could be controlled by the content of PCL in the polymerization mixture. The prepared Ti⁴⁺-IMAC HPHMs exhibited high adsorption capacity (63.6 mg/g for pyridocal 5'-phosphatemonohydrate), and excellent enrichment specificity (tryptic digest of β-casein/BSA at a molar ratio of 1:1000) and sensitivity (tryptic digest of 5 fmol of β-casein). Moreover, the Ti⁴⁺-IMAC HPHMs provided effective enrichment ability of low-abundance phosphopeptides from human serum and HeLa cell digests.

Preparation of quaternized cellulose/chitosan microspheres for selective enrichment of phosphopeptides

As one of the most important posttranslational modifications, protein phosphorylation plays an important role in vital movement. However, an efficiency enrichment treatment prior to MS detection is still a crucial step to protein phosphorylation analysis. In this work, a novel hybrid microsphere for efficient phosphopeptide enrichment was prepared by reverse-phase suspension polymerization of cellulose derivative and chitosan. The microspheres bore different kinds of amine groups and the main enrichment mechanism was based on anion exchange. This approach exhibited high selectivity for phosphopeptides from β-casein, α-casein, and non-fat milk. Three phosphopeptides could still be detected when the amount of β-casein was as low as 10 fmol. This study demonstrated a new attractive solid-phase support for phosphopeptide enrichment to meet the increasing need of phosphoproteomics analysis.

Metal–organic framework incorporated monolithic capillary for selective enrichment of phosphopeptides

Protein phosphorylation is a major post-translational modification, which plays a central role in the cellular signaling of numerous biological processes.

Toward Analysis of Proteins in Single Cells: A Quantitative Approach Employing Isobaric Tags with MALDI Mass Spectrometry Realized with a Microfluidic Platform

Protein identification and quantification in individual cells is essential to understand biological processes such as those involved in cell apoptosis, cancer, biomarker discovery, disease diagnostics, pathology, or therapy. Compared with present single cell genome analysis, probing the protein content of single cells has been hampered by the lack of a protein amplification technique. Here, we report the development of a quantitative mass spectrometric approach combined with microfluidic technology reaching the detection sensitivity of high abundant proteins in single cells. A microfluidic platform with a series of chambers and valves, ensuring a set of defined wells for absolute quantification of targeted proteins, was developed and combined with isotopic labeling strategies employing isobaric tags for relative and absolute quantitation (iTRAQ)-labels. To this aim, we adapted iTRAQ labeling to an on-chip protocol. Simultaneous protein digestion and labeling performed on the microfluidic platform rendered the labeling strategy compatible with all necessary manipulation steps on-chip, including the matrix delivery for MALDI-TOF analysis. We demonstrate this approach with the apoptosis related protein Bcl-2 and quantitatively assess the number of Bcl-2 molecules detected. We anticipate that this approach will eventually allow quantification of protein expression on the single cell level.

Hydrazide functionalized monodispersed silica microspheres: a novel probe with tunable selectivity for a versatile enrichment of phosphopeptides with different numbers of phosphorylation sites in MS analysis

Hydrazide functionalized monodispersed silica microspheres (HFMSM) were developed for the enrichment of phosphopeptides for the first time.

ZrO2 Nanofiber as a Versatile Tool for Protein Analysis

Phosphorylation is one of the most important post-translational modifications in proteins. Their essential roles in the regulation of cellular processes and alteration of protein-protein interaction networks have been actively studied. However, phosphorylated proteins are present at low abundance in cells, and ionization of the modified peptides is often suppressed by the more abundant species in mass spectrometry. Effective enrichment techniques are needed to remove the unmodified peptides and concentrate the phosphorylated ones before their identification and quantification. Herein, we prepared ZrO2 nanofibers by electrospinning, a straightforward and easy fabrication technique, and applied them to enrich phosphorylated peptides and proteins. The fibers showed good size homogeneity and porosity and could specifically bind to the phosphorylated peptides and proteins, allowing their separation from the unmodified analogues when present in either simple protein digests or highly complex cell lysates. The enrichment performance was superior to that of the commercially available nanoparticles. Moreover, modifying the solution pH could lead to selective adsorption of proteins with different pI values, suggesting the fibers' potential applicability in charge-based protein fractionation. Our results support that the electrospun ZrO2 nanofibers can serve as a versatile tool for protein analysis with great ease in preparation and handling.

Facile Preparation of Core-Shell Magnetic Metal-Organic Framework Nanoparticles for the Selective Capture of Phosphopeptides

In regard to the phosphoproteome, highly specific and efficient capture of heteroideous kinds of phosphopeptides from intricate biological sample attaches great significance to comprehensive and in-depth phosphorylated proteomics research. However, until now, it has been a challenge. In this study, a new-fashioned porous immobilized metal ion affinity chromatography (IMAC) material was designed and fabricated to promote the selectivity and detection limit for phosphopeptides by covering a metal-organic frameworks (MOFs) shell onto Fe3O4 nanoparticles, taking advantage of layer-by-layer method (the synthesized nanoparticle denoted as Fe3O4@MIL-100 (Fe)). The thick layer renders the nanoparticles with perfect hydrophilic character, super large surface area, large immobilization of the Fe(3+) ions and the special porous structure. Specifically, the as-synthesized MOF-decorated magnetic nanoparticles own an ultra large surface area which is up to 168.66 m(2) g(-1) as well as two appropriate pore sizes of 1.93 and 3.91 nm with a narrow grain-size distribution and rapid separation under the magnetic circumstance. The unique features vested the synthesized nanoparticles an excellent ability for phosphopeptides enrichment with high selectivity for β-casein (molar ratio of β-casein/BSA, 1:500), large enrichment capacity (60 mg g(-1)), low detection limit (0.5 fmol), excellent phosphopeptides recovery (above 84.47%), fine size-exclusion of high molecular weight proteins, good reusability, and desirable batch-to-batch repeatability. Furthermore, encouraged by the experimental results, we successfully performed the as-prepared porous IMAC nanoparticle in the specific capture of phosphopeptides from the human serum (both the healthy and unhealthy) and nonfat milk, which proves itself to be a good candidate for the enrichment and detection of the low-abundant phosphopeptides from complicated biological samples.

Development of magnetic LuPO4 microspheres for highly selective enrichment and identification of phosphopeptides for MALDI-TOF MS analysis

Lichee-like core–shell structured magnetic lutetium phosphate (Fe₃O₄@LuPO₄) affinity microspheres were synthesized, characterized and successfully applied to enrich phosphopeptides.

Ti4+-immobilized multilayer polysaccharide coated magnetic nanoparticles for highly selective enrichment of phosphopeptides

A novel magnetic polymer nanoparticle (Fe₃O₄@SiO₂@(HA/CS)₁₀–Ti⁴⁺ IMAC) was synthesized for the highly selective and efficient enrichment of phosphopeptides.

Guanidyl-functionalized graphene as a bifunctional adsorbent for selective enrichment of phosphopeptides

This novel bi-functional gfg provides two enriching performances, one is for global phosphopeptides, and the other is for multi-phosphopeptides with consecutive phosphorylated residues.

Dipyridyl-immobilized ionic liquid type hybrid silica monolith for hydrophilic interaction electrochromatography

A pyridinium-based immobilized ionic liquid type multifunctional hybrid silica monolith was prepared by the in situ polymerization of 3-chloropropyl-silica matrix and 4,4'-dipyridyl for hydrophilic interaction CEC. The obtained hybrid monolith possessed of high stable skeletal microstructures with obviously hydrophilic retention mechanism under ACN content >50% in the mobile phase. Strong and stable anodic EOF could be observed under a broad pH range from pH 3.0 to 9.0. Due to the immobilized dipyridyl groups bonded to the silica matrix surface, the resulting hydrophilic hybrid monolith possessed multiple separation interactions including hydrogen bond, π-π, and anion exchange. Excellent separations of various polar analytes including electroneutral phenols, charged acid nucleotides, and basic analytes were successfully achieved. The highest column efficiencies up to 120,000, 164,000, and 106,000 plates/m were obtained for nucleotides, nucleic acid bases, and nucleosides and nicotines, respectively. These results demonstrated that the dipyridyl-immobilized ionic liquid functionalized hybrid monolith possessed highly mechanical stability and good chromatographic performance for hydrophilic interaction electrochromatography.