Xiao-Shui Li

A magnetite/oxidized carbon nanotube composite used as an adsorbent and a matrix of MALDI-TOF-MS for the determination of benzo[a]pyrene

A magnetite/oxidized carbon nanotube composite, Fe(3)O(4)@SiO(2)/OCNT, was fabricated in a simple way, and it was successfully used as a magnetic solid-phase extraction sorbent and a significant matrix of the matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) for the detection of benzo[a]pyrene (BaP).

Facile fabrication of reduced graphene oxide-encapsulated silica: A sorbent for solid-phase extraction

In this study, a facile hydrothermal reduction strategy was developed for the preparation of reduced graphene oxide-encapsulated silica (SiO2@rGO). Compared with other conventional methods for the synthesis of SiO2@rGO, the proposed strategy endowed the obtained SiO2@rGO with larger amount of immobilized rGO. The prepared functionalized silica shows remarkable adsorption capacity toward chlorophenols (CPs) and peptides. When it was used as solid-phase extraction (SPE) sorbent, a superior recovery could be obtained compared to commercial sorbents, such as C18 silica, graphitized carbon black and carbon nanotubes. Based on these, the prepared material was used as SPE sorbent for the enrichment of CPs, and a method for the analysis of CPs in water samples was established by coupling SPE with high performance liquid chromatography-ultra violet detection (SPE-HPLC/UV). In addition, the obtained SiO2@rGO was further successfully extended to the enrichment of peptides in bovine serum albumin (BSA) digests.

Preparation of magnetic poly(diethyl vinylphosphonate-co-ethylene glycol dimethacrylate) for the determination of chlorophenols in water samples.

In this work, a novel type of magnetic polymer particle, magnetic poly(diethyl vinylphosphonate-co-ethylene glycol dimethacrylate) [Fe(3)O(4)@p(DEVP-co-EDMA)], was successfully synthesized and applied for the extraction and determination of chlorophenols in water samples by coupling with high-performance liquid chromatography (HPLC). Fe(3)O(4)@p(DEVP-co-EDMA) was synthesized by a simple seeded radical polymerization method and exhibited well-defined core-shell structure and good magnetic response ability. In addition, the magnetic polymer had the advantages of abundant adsorption sites and high enrichment efficiency. Due to the presence of PO group in the skeleton of polymer, the magnetic polymer material displayed excellent extraction performance for chlorophenols, such as 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP). Hydrophobic skeleton of the magnetic polymer also provided strong interaction with the target analytes, especially pentachlorophenol (PCP) which is a kind of non-polar chlorophenol. Desorption solution, pH of water sample, extraction time and desorption time, the amount of adsorbent, and the volume of desorption solution were optimized. Under the optimized conditions, the linear ranges of four chlorophenols were 2-500 ng/mL with the limits of detection (S/N=3) ranging from 0.20 to 0.34 ng/mL. The repeatability was investigated by evaluating the intra- and inter-day precisions with relative standard deviations (RSDs) lower than 15.0%. The recoveries for real water samples were in the range of 92.7-108.0%. Collectively, the results indicated that the novel Fe(3)O(4)@p(DEVP-co-EDMA) was successfully applied in the extraction and detection of chlorophenols from water samples, and the magnetic polymer particle showed potential applications in the analysis of polar compounds.

Preparation of magnetic polymer material with phosphate group and its application to the enrichment of phosphopeptides.

As one of the most important post-translational modifications (PTM), reversible phosphorylation of protein is involved in many cellular processes. Enrichment and separation of phosphopeptides have become essential for large-scale identification of protein phosphorylation by mass spectrometry. In this work, five magnetic polymer materials with different numbers of phosphate groups were fabricated using a simple polymeric method and their abilities to enrich phosphopeptides were investigated. Our results showed that the enrichment efficiency is closely related to the number of phosphate groups attached to magnetic polymer sorbent. Under optimized condition (3% trifluoroacetic acid and 80% acetonitrile), magnetic polymer-particles with appropriate proportion of phosphate groups (Fe(3)O(4)@p(VPA-EDMA-1)-Zr(4+)) showed high performance for extracting phosphopeptides from complex peptides mixture of standard protein digestion. In this regard, a total of 988 unique phosphopeptides were successfully identified from proteolytic digestion of HeLa cell extracts by employing magnetic polymer-particles combined with nano-RPLC-MS/MS analysis.

Pseudomorphic synthesis of monodisperse magnetic mesoporous silica microspheres for selective enrichment of endogenous peptides

In this work, we describe a novel synthetic strategy of magnetic mesoporous silica spheres (Fe3O4@mSiO2) for the selective enrichment of endogenous peptides. Fe3O4 particles were coated with silica shell by a sol-gel method, followed by pseudomorphic synthesis to transform nonporous silica shell into ordered mesoporous silica shell. The core/shell structure and mesostructure were individually fabricated in two steps, which can be expedient to independently optimize the properties of monodispersion, magnetization and mesostructure. Actually, it was confirmed that the produced Fe3O4@mSiO2 particles possess good monodispersion, high magnetization, superparamagnetism, uniform accessible mesopores, and large surface area and pore volume. With these good properties, Fe3O4@mSiO2 spheres were applied to the rapid enrichment of peptides. Based on the size-exclusion mechanism and hydrophobic interaction with siloxane bridge group mainly on the surface of inside pores, Fe3O4@mSiO2 can selectively capture peptides and exclude high-MW proteins and salts. Furthermore, peptides in human plasma were successfully enriched by Fe3O4@mSiO2.

Preparation of titanium-grafted magnetic mesoporous silica for the enrichment of endogenous serum phosphopeptides

As one of the most important post-translational modifications, reversible phosphorylation of protein plays crucial roles in a large number of biological processes. Moreover, endogenous phosphopeptides are also associated with certain human diseases. An efficient enrichment and separation method is the premise for successful identification and quantification of phosphopeptides. In this work, titanium grafted magnetic mesoporous silica (Fe3O4@Ti-mSiO2) was developed and applied for the enrichment of endogenous phosphopeptides. Fe3O4@Ti-mSiO2 particles were prepared by grafting titanocene dichloride on the inner walls of magnetic mesoporous silica and then being calcined to remove cyclopentadienyl ligand. The physicochemical properties of the prepared materials were characterized by energy dispersive X-ray spectroscopy (EDX), nitrogen adsorption-desorption analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). For selective enrichment of phosphopeptides, the prepared Fe3O4@Ti-mSiO2 particles were applied for tryptic digests of β-casein, mixtures of β-casein and bovine serum albumin (BSA), and low-fat milk. Finally, Fe3O4@Ti-mSiO2 was successfully applied for the enrichment of endogenous phosphopeptides from human serum.

Application of liquid phase deposited titania nanoparticles on silica spheres to phosphopeptide enrichment and high performance liquid chromatography packings

A novel core-shell composite (SiO(2)-nLPD), consisting of micrometer-sized silica spheres as a core and nanometer titania particles as a surface coating, was prepared by liquid phase deposition (LPD). Here, we show the resulting core-shell composite to have better efficient and selective enrichment for mono- and multi-phosphopeptides than commercially available TiO(2) spheres without any enhancer. The material exhibited favorable characteristics for HPLC, which include narrow pore size distribution, high surface area and pore volume. We also show that the core-shell composite can efficiently separate adenosine phosphate compounds due to the Lewis acid-base interaction between titania and phosphate group when used as HPLC packings. After coating the silica sphere with titania by LPD, the silanol of silica spheres will be shielded and that the stationary phase, C(18) bonded SiO(2)-3LPD, could be used under extreme pH condition.

Preparation of mesoporous silica embedded pipette tips for rapid enrichment of endogenous peptides

Mesoporous silica embedded pipette tips (mSiO2-Tips) were successfully prepared by a simple method and applied to rapid enrichment of endogenous peptides for the first time. The prepared mSiO2-Tips showed low back pressure when solvent was pipetted up and down. As a result, mSiO2-Tip could selectively trap peptides and exclude high-MW proteins simultaneously based on size-exclusion mechanism due to the uniform mesopore structure of the sorbent bed. The in-pipette-tip SPE approach was proved to be easy-operation, sensitive and fast (less than 2 min) for the analysis of peptides, which was further successfully applied in the efficient enrichment of peptides from human plasma.

Titanium-containing magnetic mesoporous silica spheres: effective enrichment of peptides and simultaneous separation of nonphosphopeptides and phosphopeptides.

Protein phosphorylation is a common posttranslational modification, and involved in many cellular processes. Like endogenous peptides, endogenous phosphopeptides contain many biomarkers of preclinical screening and disease diagnosis. In this work, titanium-containing magnetic mesoporous silica spheres were synthesized and applied for effective enrichment of peptides from both tryptic digests of standard proteins and human serum. Besides, the enriched peptides can be further separated into nonphosphopeptides and phosphopeptides by a simple elution. First, titanium-containing magnetic mesoporous silica spheres were synthesized by a sol-gel method and found to have high surface area, narrow pore size distribution, and useful magnetic responsivity. Then, as the prepared material was used for selective capturing of phosphopeptides, it demonstrated to have higher selectivity than commercial titanium dioxide. Moreover, via combination of size-exclusion mechanism, hydrophobic interaction, and affinity chromatography, titanium-containing magnetic mesoporous silica spheres were successfully applied to simultaneously extract and separate nonphosphopeptides and phosphopeptides from standard protein digestion and human serum.

Perovskite for the highly selective enrichment of phosphopeptides

Selective and effective enrichment of phosphopeptides from complex samples is essential in phosphoproteome study by mass spectrometry (MS). In this work, we compared perovskites (MgTiO3, CaTiO3, SrTiO3, BaTiO3 and CaZrO3) with metal oxides (ZrO2 and TiO2) in their capability for the selective enrichment of phosphopeptides. It was found here that perovskites exhibited higher selectivity towards phosphopeptides than commonly used ZrO2 and TiO2, even though they all have high affinity to phosphopeptides. As for perovskites, CaTiO3 exhibited better selectivity for enrichment of phosphopeptides than SrTiO3, MgTiO3, BaTiO3 and CaZrO3, which might be ascribed to their crystal structures and electrophilic abilities. Moreover, to further confirm the performance of CaTiO3, CaTiO3 and TiO2 were applied to the enrichment of phosphopeptides from tryptic digest of proteins of human Jurkat-T cell lysate, respectively. The results showed CaTiO3 has much higher selectivity than TiO2 in the enrichment of phosphopeptides from the complex biological sample. Taken together, here we show that CaTiO3 is an excellent material for the highly selective enrichment of phosphopeptides and it could be potentially used in the large-scale phosphoproteome study.