Synthesis of Polyethylenimine Functionalized Mesoporous Silica for In-Pipet-Tip Phosphopeptide Enrichment

Superhydrophilic nanocomposite adsorbents modified via nitrogen-rich phosphonate-functionalized ionic liquid linkers: enhanced phosphopeptide enrichment and phosphoproteome analysis of tau phosphorylation in the hippocampal lysate of Alzheimer's transgenic mice

In this study, new graphene-based IMAC nanocomposites for phosphopeptide enrichment were prepared according to the guideline of our new design strategy. Superhydrophilic polyethyleneimine (PEI) was introduced, to which a phosphonate-functionalized ionic liquid (PFIL) was covalently bound, to form superhydrophilic and cationic surface layers with high densities of nitrogen atoms, phosphonate functional groups, and high-loading metal ions. Due to the combined features of superhydrophilicity, flexibility, highly dense metal binding sites, large surface area and excellent size-exclusion effect, the fabricated nanocomposite G@mSiO₂@PEI-PFIL-Ti⁴⁺ exhibits superior detection sensitivity to enrich phosphopeptides (tryptic β-casein digest, 0.1 fmol), and extraordinary enrichment specificity to enrich phosphopeptides from a digest mixture of β-casein and bovine serum albumin (BSA) (molar ratio, 1 : 12 000). The excellent size-exclusion effect was also observed, and 27 endogenous phosphopeptides were identified in human saliva. All these results could be attributed to the unique superhydrophilic nanocomposite structure with a high density of a cationic linker modified with phosphonate functionality. Moreover, G@mSiO₂@PEI-PFIL-Ti⁴⁺ adsorbents were used to extract phosphopeptides from the tryptic digests of hippocampal lysates for quantitative phosphoproteome analysis. The preliminary results indicate that 1649 phosphoproteins, 3286 phosphopeptides and 4075 phosphorylation sites were identified. A total of 13 Alzheimer's disease (AD)-related phosphopeptides within tau proteins were detected with a wide coverage from p-Thr111 to p-Ser404, in which the amounts of some phoshopeptides at certain sites in AD transgenic mice were found statistically higher than those in wild type littermates. Besides, phosphorylated neurofilament heavy chains, a potential biomarker for amyotrophic lateral sclerosis and traumatic brain injury, were also identified. Finally, the adsorbent was applied to human cerebrospinal fluid (CSF) and blood samples. 5 unique phosphopeptides of neuroendocrine specific VGF were identified in the CSF, while many phosphopeptides originated from the nervous system were found in the blood sample. All these results suggest that our new IMAC materials exhibit unbiased enrichment ability with superior detection sensitivity and specificity, allowing the global phosphoproteome analysis of complicated biological samples more convincible and indicating the potential use in disease diagnosis.

Determination of free fatty acids in Antarctic krill meals based on matrix solid phase dispersion

Amino-modified mesoporous silicawas prepared by modifying mesoporous silica with 3-aminopropyltriethoxysilane and used as adsorbents in matrix solid-phase dispersion (MSPD) to analyze free fatty acids (FFAs) in krill meals for the first time. The adsorption-desorption experiments and Fourier-transform infrared spectroscopy showed amino-modified mesoporous silica with ordered mesoporous structure was successfully synthesized. The adsorption experiments including static and dynamic adsorption showed thatabsorption capacity of amino-modified mesoporous silica towards FFAs was better than that of aminated silicon microspheres at all concentrations. Under optimal extraction conditions, outstanding linearity (0.1-12000 nmol g^-1), low LODs (0.05-1.25 nmol g^-1), satisfactory recoveries (82.17-96.43%) and precisions (0.19-5.26%) were obtained. Moreover, the application of MSPD for FFAs analysis avoided complicated lipid extraction procedures and accomplished the homogenization, crushing, extraction and cleaning of the samples in one step. Consequently, this approach provides an alternative choice to the existing approach for analyzing FFAs in solid and semi-solid samples.

A miniaturized analytical method based on molecularly imprinted absorbents for selective extraction of (S)-1,1'-binaphthyl-2,2'-diamine and combinatorial screening of polymer precursors by computational simulation

Chiral resolution of binaphthylamine is often a toilful conundrum in the field of analytical chemistry and biomedicine. The work puts forward a selective, sensitive, and miniaturized analytical method based on molecularly imprinted polymers (MIPs) as adsorbent for miniaturized tip solid-phase extraction (MTSPE) in the separation of binaphthylamine enantiomer. This method combines the advantages of MIPs (high selectivity), MTSPE (low consumption), and high-performance liquid chromatography (HPLC, high sensitivity). A simple synthesis methodology of MIP (P2) was conducted through bulk polymerization with (S)-(-)-1,1'-binaphthyl-2,2'-diamine (S-DABN) as template together with methacrylic acid monomer, and ethylene glycol dimethacrylate as cross-linker in proper porogen, realizing a selective recognition and efficient enrichment for S-DABN. The method exhibited appreciable linearity (0.06-1.00 mg ml^-1 ), low quantification limit (0.056 mg ml^-1 ), good absolute recoveries (45.70%-69.29%), and high precision (relative standard deviations ≤ 3.54%), along with low consumption (0.50 ml sample solution and 25.0 mg adsorbent). Based on the density functional theory, computational simulation was used to make a preliminary prediction for rational design of MIPs and gave a reasonable elaboration involving the potential mechanism of templates interacting with functional monomers. The adsorption kinetics and thermodynamics were investigated to evaluate the recombination process of substrates. In addition, the selectivity of MIPs for S-DABN was obtained by MIP-MTSPE coupled with HPLC, which supports the feasibility of this convenient design process. The proposed method was employed for selective extraction of S-DABN and exhibited promising potential in the application of chiral analysis.

Removal of adsorption sites on the external surface of mesoporous adsorbent for eliminating the interference of proteins in enrichment of phosphopeptides/nucleotides

Various mesoporous adsorbents are of great promise for enriching small molecules from biological samples based on the size-exclusion effect. At present, the mesoporous adsorbents have adsorption sites distributed uniformly on the internal and external surfaces of mesopores. However, the adsorption sites on the external surface can adsorb proteins, interfering with the enrichment of small molecules. Herein, a novel immobilized-Ti⁴⁺ magnetic mesoporous adsorbent removing the adsorption sites on the external surface was facile prepared via the coupling chemistry of isocyanate with amine and consequent hydrolysis of urea linkage by urease. The adsorbent enables fast and selective enrichment of phosphopeptides and nucleotides from biological samples. In addition, sensitive detection methods for phosphopeptides and nucleotides in human serum are developed by coupling the magnetic solid-phase extraction with matrix-assisted laser desorption/ionization time of flight mass spectrometry and liquid chromatography-mass spectrometer, respectively. Under optimal conditions, response is linear (R² ≥ 0.9923), limits of detection are low (0.41-9.48 ng mL^-1), and reproducibility is acceptable (inter- and intra-day assay RSDs of≤15.0%) for six nucleotides. The developed strategy offers an effective method to eliminate the interference of proteins in the enrichment of small molecules from real biological samples.

Metal-Organic Framework-Derived Hollow and Hierarchical Porous Multivariate Metal-Oxide Microspheres for Efficient Phosphoproteomics Analysis

Pre-enrichment of the biological samples is a crucial step in phosphoproteomics research. At present, metal-oxide affinity chromatography (MOAC) is one of the most recognized enrichment strategy. Therefore, the design and preparation of a MOAC-based affinity material with better enrichment properties will be of great significance for the phosphoproteomics study. In this work, we obtained a novel multivariate metal-oxide microsphere (NiFe₂O₄@C@TiO₂) with a hollow and hierarchical porous structure through pyrolysis of TiO_2-modified Fe/Ni-based metal-organic frameworks (MOFs). After pyrolysis, the carbon matrix derived from the MOFs provided support and porous properties. Meanwhile, multivariate metal oxides endowed the microspheres with an excellent magnetic response property and superior enrichment performance for phosphorylated biomolecules. The unique hollow and hierarchical porous structure greatly enhanced the diffusion of phosphorylated biomolecules. Therefore, the microspheres exhibited excellent enrichment performance for phosphorylated biomolecules: a large adsorption capacity (124 μmol g^-1), excellent selectivity (α-casein/BSA, 1:5000, m/m), perfect size-exclusion performance (α-casein digests/α-casein/BSA, 1:500:500), and extremely low detection limit (2 fmol). Furthermore, the microspheres showed excellent enrichment performance in a series of real biological samples, such as nonfat milk, serum, saliva, rat brain tissue, and plasma exosomes of patients with esophageal cancer, which further demonstrated its huge application potential in MS-based phosphoproteomics research.

Simultaneous Increase of Solvent Flux and Rejection of Thin-Film Composite Membranes by Incorporation of Dopamine-Modified Mesoporous Silica

Thin-film nanocomposite membranes have shown great promise in organic solvent nanofiltration. However, it is challenging to acquire high permeation flux without severe swelling, which might do harm to rejection and long-term stability. In this study, we introduced dopamine-modified mesoporous silica nanoparticles into the polyamide (PA) matrix via interfacial polymerization to fabricate a series of thin-film nanocomposite membranes. By using polyethyleneimine (PEI) as the aqueous monomer, the modified nanoparticles are designed to be cross-linked within the PA network, which allows the penetration of PEI into the mesopores, and therefore, the membranes show better resistance to solvent-induced swelling and pressure-induced densification. More importantly, the mesopores of nanoparticles provide additional fast channels for solvents, resulting in an unusual enhancement of solvent flux under reduced membrane swelling. Along with the permeation flux, the rejection performance of the nanocomposite membranes is simultaneously improved, thanks to the controlled swelling arising from the strong interfacial adhesion. Thin-film nanocomposite membranes with optimal filler concentration exhibit a high isopropanol permeance of 8.47 L m^-2 h^-1 bar^-1 as well as a quite low-molecular-weight cutoff of 281 Da.

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.

Phosphoproteomic strategies in cancer research: a minireview

Understanding the cellular processes is central to comprehend disease conditions and is also true for cancer research. Proteomic studies provide significant insight into cancer mechanisms and aid in the diagnosis and prognosis of the disease. Phosphoproteome is one of the most studied complements of the whole proteome given its importance in the understanding of cellular processes such as signaling and regulations. Over the last decade, several new methods have been developed for phosphoproteome analysis. A significant amount of these efforts pertains to cancer research. The current use of powerful analytical instruments in phosphoproteomic approaches has paved the way for deeper and sensitive investigations. However, these methods and techniques need further improvements to deal with challenges posed by the complexity of samples and scarcity of phosphoproteins in the whole proteome, throughput and reproducibility. This review aims to provide a comprehensive summary of the variety of steps used in phosphoproteomic methods applied in cancer research including the enrichment and fractionation strategies. This will allow researchers to evaluate and choose a better combination of steps for their phosphoproteome studies.

A molecularly imprinted polymer based monolith pipette tip for solid-phase extraction of 2,4-dichlorophenoxyacetic acid in an aqueous sample

This paper presents a simple approach for fabrication of a pipette tip solid-phase extraction (PT-SPE) device, which possesses a monolith structure with low back pressure and has high selectivity to 2,4-dichlorophenoxyacetic acid (2,4-D). Pipette tips were packed with molecularly imprinted polymers (MIPs) as a selective adsorbent and high-density polyethylene (HDPE) as a co-sintering agent, and then heated to form a monolith extraction device. The key factors including the particle size and amount of packing material, and the type and volume of elution solvent, which influence PT-SPE device performance were optimized. A packing material of 40 mg/0.20 mL in a ratio of 4/6 (MIPs/HDPE) and treatment temperature of 150 °C was selected. By the determination with high-performance liquid chromatography (HPLC-SPD), the extraction device was found to have a good extraction recovery for a 2,4-D lake water sample at a low concentration (0.006 mg L-1) with an enrichment factor about 50. The proposed method provided a simple approach for the fabrication of a PT-SPE monolith device with reduced back pressure and wall effect, which are very important for improving the extraction efficiency. And the device will have promising application in the extraction of a variety of analytes in complex samples.

Recent advancements in polyethyleneimine-based materials and their biomedical, biotechnology, and biomaterial applications

Precise-synthesis strategies and integration approaches of bioinspired PEI-based systems, and their biomedical, biotechnology and biomaterial applications.

PAMAM–PMAA brush-functionalized magnetic composite nanospheres: a smart nanoprobe with tunable selectivity for effective enrichment of mono-, multi-, or global phosphopeptides

A novel PAMAM–PMAA brush functionalized magnetic composite nanosphere was successfully prepared for selective enrichment of mono-, multi-, or global phosphopeptides by modulating buffer polarity and acidity.

Organized cryogel composites with 3D hierarchical porosity as an extraction adsorbent for nucleosides

Macroscopic monoliths are highly desirable in many fields of application. Herein, well organized organic-inorganic cryogel composite with a three-dimensional hierarchical meso- and macroporous structure are presented, which were produced by in situ copolymerization of mesoporous multifunctional silica (size: 1-20 μm; pore: 2-20 nm mostly) and monomers (hydroxyethyl methacrylate and diallyldimethylammonium chloride) in water below the freezing point. This copolymerization method effectively adjusted the macropores of the basic cryogel, and the nanosilica was more homogeneously dispersed in the basic cryogel. The specific surface area of the cryogel composite was increased 17 times versus than that of the basic cryogel. The abundant meso- and macroporous pores on the cryogel composite provided sufficient reactive sites favorable for the efficient mass transport of target compounds. When the cryogel composite, as solid phase extraction adsorbent, was coupled with high-performance liquid chromatography, an analytical tool, the nucleosides were quantified with good selectivity, lower detection limits (0.9-1.3 ng/mL) and satisfactory recoveries of greater than 80% from spiked human serum.

Yolk-shell magnetic mesoporous TiO2 microspheres with flowerlike NiO nanosheets for highly selective enrichment of phosphopeptides

In this work, we fabricated a yolk-shell magnetic composite that contains mesoporous TiO₂ as the inner shell and flowerlike NiO as the outer shell (denoted as Fe₃O₄@H-TiO₂@f-NiO) to reduce the limitations of single-component metal oxides in phosphopeptide enrichment. The NiO nanosheets play a synergistic role in phosphopeptide enrichment. And the unique flowerlike structure of NiO with sufficient space can facilitate the reversible insertion/extraction of peptides, which will have less impact on the enrichment process of the inner TiO₂ shell. The yolk-shell structure and two types of porous nanostructures endowed this composite with a high surface area (156.58 m² g^-1) and a large pore volume (0.37 cm³ g^-1). Owing to the high surface area and combined properties of TiO₂ and NiO, the Fe₃O₄@H-TiO₂@f-NiO microspheres showed a better performance for phosphopeptide enrichment than the same material without NiO nanosheets (Fe₃O₄@H-TiO₂). According to the LC-MS/MS results, 972 unique phosphopeptides were identified from HeLa cell extracts with a high selectivity (91.9%) by Fe₃O₄@H-TiO₂@f-NiO relative to 837 phosphopeptides (selectivity: 60.2%) by Fe₃O₄@H-TiO₂. The results demonstrated that, compared with single-component metal oxides, composite metal oxides could enhance the selectivity and sensitivity for phosphopeptide enrichment.

Pyridoxal 5'-phosphate mediated preparation of immobilized metal affinity material for highly selective and sensitive enrichment of phosphopeptides

Phosphorylation is a crucial post-translational modification, which plays pivotal roles in various biological processes. Analysis of phosphopeptides by mass spectrometry (MS) is intractable on account of their low stoichiometry and the ion suppression from non-phosphopeptides. Thus, enrichment of phosphopeptides before MS analysis is indispensable. In this work, we employed pyridoxal 5'-phosphate (PLP), as an immobilized metal affinity chromatography (IMAC) ligand for the enrichment of phosphopeptides. PLP was grafted onto several substrates such as silica (SiO₂), oxidized carbon nanotube (OCNT) and silica coated magnetic nanoparticles (Fe₃O₄@SiO₂). Then the metal ions Fe³⁺, Ga³⁺ and Ti⁴⁺ were incorporated for the selective enrichment of phosphopeptides. It is indicated that Fe₃O₄@SiO₂-PLP-Ti⁴⁺ has a superior selectivity towards phosphopeptides under as much as 1000-fold interferences of non-phosphopeptides. Further, Fe₃O₄@SiO₂-PLP-Ti⁴⁺ exhibited high efficiency in selective enrichments of phosphopeptides from complex biological samples, including human serum and tryptic digested non-fat milk. Finally, Fe₃O₄@SiO₂-PLP-Ti⁴⁺ was successfully employed in the sample pretreatment for profiling phosphopeptides in a tryptic digest of rat brain proteins. Our experimental results evidenced a great potential of this new chelator-based material in phosphoproteomics study.

A micro-solid phase extraction in glass pipette packed with amino-functionalized silica for rapid analysis of petroleum acids in crude oils

A convenient micro-SPE was designed for rapid analysis of petroleum acids in crude oils.