Cysteine-functionalized metal–organic framework (MOF) was synthesized via a common and facile two-step method of in situ loading of Au nanoparticles on amino-derived MOF followed by l-cysteine (Cys) immobilization. Owing to the large specific surface area and ultrahigh hydrophilicity of this nanocomposite, excellent performance was observed in the enrichment of N-linked glycopeptides in both model glycoprotein and HeLa cell lysate. By using this nanocomposite, 16 and 31 glycopeptides were efficiently extracted from digest of horseradish peroxidase (HRP) and human serum immunoglobulin G (IgG), respectively. The short incubation time (5 min), large binding capacity (150 mg/g, IgG digest to material), good selectivity (1:50, molar ratio of IgG and bovine serum albumin (BSA) digest), high recovery (over 80%), and low detection limit (1 fmol) ensure the effectiveness and robustness of MIL-101(NH2)@Au-Cys in complex HeLa cell lysate. As a result, 1123 N-glycosylation sites corresponding to 1069 N-glycopeptides and 614 N-glycoproteins were identified from the lysate. Compared with those of previously reported hydrophilic methods, to our knowledge, it was the best result. This work paves a new way for fast functionalization of MOF and also provides a novel idea for material design in sample preparation, especially in glycoproteome and related analysis.Keywords: cell lysate; fast functionalization; glycopeptide enrichment; mass spectrometry; metal−organic framework;

A novel multifunctional composite comprising mesocrystalline SnO2 nanorods (NRs) vertically aligned on reduced graphene oxide (rGO) sheets was synthesized and developed for sequential capture of endogenous peptides and phosphopeptides. With the hydrophobicity of rGO and high affinity of SnO2 nanorods, sequential enrichment of endogenous peptides and phosphopeptides could be easily achieved through a modulation of elution buffer. With this multifunctional nanomaterial, 36 peptides were observed from diluted bovine serum albumin (BSA) tryptic digest and 4 phosphopeptides could be selectively captured from β-casein digest. The detection limit of tryptic digest of β-casein was low to 4 × 10–10 M, and the selectivity was up to 1:500 (molar ratio of β-casein and BSA digest). The effectiveness and robustness of rGO-SnO2 NRs in a complex biological system was also confirmed by using human serum as a real sample. Our work is promising for small peptide enrichment and identification especially in complicated biological sample preparation, which also opens a new perspective in the design of multifunctional affinity probes for proteome or peptidome.Keywords: endogenous peptides; mass spectrometry; multifunctional affinity probe; phosphopeptides; sequential enrichment;

A maltose-functionalized metal–organic framework (MOF), MIL-101(Cr)-maltose, was developed via a simple two step post-synthetic modification of MIL-101(Cr)-NH2. With the use of this nanomaterial, 33 glycopeptides were detected from the digest of human immunoglobulin G, demonstrating its high efficiency in glycoproteomic analysis. More importantly, the generic functionalization route from amino-derived MOFs opens a new perspective in material design in sample preparation.

Hydrazide functionalized monodispersed silica microspheres (HFMSM) were developed for the enrichment of phosphopeptides for the first time. With the aid of the tunable selectivity of HFMSM, global enrichment or fractionation of phosphopeptides with different numbers of phosphorylation sites could be realized by a simple modulation of the concentrations of formic acid in buffers.

A bifunctional affinity probe NiCoMnO4 was designed and prepared with controllable morphology and size using facile methods. It was observed that the probe could be applied in His-tagged proteins purification and phosphopeptides enrichment simply through the buffer modulation. NiCoMnO4 particles showed satisfactory cycling performance for His-tagged proteins purification and broad pH-tolerance of loading buffer for phosphopeptides affinity. Therefore, a high-throughput, cost-effective, and efficient protein/peptide purification method was developed within 10 min based on the novel bifunctional affinity probe.

The online combination of surface plasmon resonance (SPR) with mass spectrometry (MS) could be beneficial for accurately acquiring molecular interaction data simultaneously with their structural information at high throughputs. In this work, a novel SPR-MS interface was developed using a dielectric barrier discharge ionization (DBDI) source. The DBDI source was placed in front of the MS inlet, generating an ionization plasma jet. A spray tip was set between the DBDI source outlet and the MS inlet, nebulizing the SPR sample solution. Using this interface, samples could first be studied by SPR, then sprayed and ionized, finally analyzed by MS. By analyzing model samples containing small-molecule drugs dissolved in salt containing solutions, the practicability of this SPR-DBDI-MS interface was proved, observing the consistent change of SPR and MS signals. Compared with our previously developed direct analysis in real time (DART) based SPR-MS interface, this new interface exhibited a higher and better tolerance to non-volatile salts, and different ionization capabilities for various samples. These results indicated that the interface could find further utilization in SPR-MS studies especially when physiological conditions were needed.

•Recent applications of nanomaterials in sample preparation were summarized.•High specific area and activity facilitate nanomaterial based sample preparation.•Various compositions and morphologies diversify nanomaterials for sample preparation.•Distinct size and shape selectivity was present in nanoporous materials.Sample preparation is a key step for qualitative and quantitative analysis of trace analytes in complicated matrix. Along with the rapid development of nanotechnology in material science, numerous nanomaterials have been developed with particularly useful applications in analytical chemistry. Benefitting from their high specific areas, increased surface activities, and unprecedented physical/chemical properties, the potentials of nanomaterials for rapid and efficient sample preparation have been exploited extensively. In this review, recent progress of novel nanomaterials applied in sample preparation has been summarized and discussed. Both nanoparticles and nanoporous materials are evaluated for their unusual performance in sample preparation. Various compositions and functionalizations extended the applications of nanomaterials in sample preparations, and distinct size and shape selectivity was generated from the diversified pore structures of nanoporous materials. Such great variety make nanomaterials a kind of versatile tools in sample preparation for almost all categories of analytes.

The online coupling of surface plasmon resonance (SPR) with mass spectrometry (MS) has been highly desired for the complementary information provided by each of the two techniques. In this work, a novel interface for direct and online coupling of SPR to direct analysis in real time (DART) MS was developed. A spray tip connected with the outlet of the SPR flow solution was conducted as the sampling part of the DART-MS, with which the online coupling interface of SPR-MS was realized. Four model samples, acetaminophen, metronidazole, quinine, and hippuric acid, dissolved in three kinds of common buffers were used in the SPR-DART-MS experiments for performance evaluation of the interface and the optimization of DART conditions. The results showed consistent signal changes and high tolerance of nonvolatile salts of this SPR-MS system, demonstrating the feasibility of the interface for online coupling of SPR with MS and the potential application in the characterization of interaction under physiological conditions.

•A novel HPLC–QTOF MS technique was developed for intracellular pteridine detection.•Pteridine extraction from cell lysates was systematically examined.•Method performance was comparable to leading pteridine quantification methods.•Reported intracellular pteridine levels in A549 cells matched literature values.Pteridines are a diverse family of endogenous metabolites that may serve as useful diagnostic biomarkers for disease. While many preparative and analytical techniques have been described for analysis of selected pteridines in biological fluids, broad intracellular pteridine detection remains a significant analytical challenge. In this study, a novel, specific and sensitive extraction and high performance liquid chromatography–quadrupole time-of-flight mass spectrometry (HPLC–QTOF MS) method was developed to simultaneously quantify seven intracellular pteridines and monitor 18 additional, naturally-occurring intracellular pteridines. The newly developed method was validated through evaluation of spiked recoveries (84.5–109.4%), reproducibility (2.1–5.4% RSD), method detection limits (0.1–3.0 μg L−1) and limits of quantitation (0.1–1 μg L−1), and finally application to non-small cell lung cancer A549 cells. Twenty-three pteridine derivatives were successfully detected from cell lysates with an average RSD of 12% among culture replicates. Quantified intracellular pteridine levels ranged from 1 to 1000 nM in good agreement with previous studies. Finally, this technique may be applied to cellular studies to generate new biological hypotheses concerning pteridine physiological and pathological functions as well as to discovery new pteridine-based biomarkers.

A one-step and template-free method to prepare uniform SnO2 nanospheres with a mesoporous structure was developed for the applications in phosphopeptide enrichment. The as-synthesized mesoporous SnO2 nanospheres have a large surface area and highly active surfaces for the effective binding of phosphopeptides. Compared with the non-porous SnO2 and commercial TiO2, mesoporous SnO2 nanospheres represent superior performance in the specific trapping of phosphopeptides from both standard protein and complex nonfat milk digests for mass spectrometry-based phosphoproteomic analysis. The feasible synthetic approach and the excellent enrichment performance make the mesoporous SnO2 nanospheres promising in further phosphoproteomic research.

Bone-like GdF3 was synthesized and applied for phosphopeptide enrichment for the first time. As a new kind of efficient phosphopeptide affinity probe, GdF3 exhibits high efficiency in the mediation of the dephosphorylation reaction. In addition, DFT calculations were introduced to theoretically explain the unique property of GdF3 compared to GdPO4, which is promising and can be potentially significant in protein phosphorylation research.

Guanidyl-functionalized graphene (GFG) was designed and synthesized. By simple modulation of the loading buffer this novel bifunctional adsorbent provides two enriching functions, one for global phosphopeptides, and the other for multiphosphopeptides with consecutive phosphorylated residues. GFG provides a promising perspective for consecutive phosphorylated peptide enrichment in phosphor–proteomic research and related biological process studies.

We report a novel method for the synthesis of DNA-encoded libraries without the need for discrete DNA template. Reactant DNAs self-assemble to enable chemical reactions and photo-cleavage transfers the product to the DNA terminus, making it suitable for the subsequent affinity-based selection and hit deconvolution.

Mass spectrometry imaging (MSI) has been widely used in many research areas for the advantages of providing informative molecular distribution with high specificity. Among the recent progress, ambient MSI has attracted increasing interests owing to its characteristics of ambient, in situ, and nonpretreatment analysis. Here, we are presenting the ambient MSI for traditional Chinese medicines (TCMs) and authentication of work of art and documents using plasma assisted laser desorption ionization mass spectrometry (PALDI-MS). Compared with current ambient MSI methods, an excellent average resolution of 60 μm × 60 μm pixel size was achieved using this system. The feasibility of PALDI-based MSI was confirmed by seal imaging, and its authentication applications were demonstrated by imaging of printed Chinese characters. Imaging of the Radix Scutellariae slice showed that the two active components, baicalein and wogonin, mainly were distributed in the epidermis of the root, which proposed an approach for distinguishing TCMs’ origins and the distribution of active components of TCMs and exploring the environmental effects of plant growth. PALDI-MS imaging provides a strong complement for the MSI strategy with the enhanced spatial resolution, which is promising in many research fields, such as artwork identification, TCMs’ and botanic research, pharmaceutical applications, etc.

ZnSn(OH)6 and binary-component SnO2–ZnSn(OH)6 were introduced as affinity probes for phosphopeptide enrichment for the first time. Two strategies, either ZnSn(OH)6 and SnO2 serial enrichment or binary-component SnO2–ZnSn(OH)6 enrichment in a single run, were proposed to enhance multi-phosphopeptide enrichment and to significantly improve global phosphopeptide detection.

The online coupling of capillary electrophoresis with ambient direct analysis in real time mass spectrometry (DART-MS) was realized by a coaxial tip interface. The analytes eluted from capillary electrophoresis (CE) were directly ionized by the metastable helium flux produced by DART and transferred into MS for the detection, with which the online separation and simultaneous detection were achieved. The CE-DART-MS can tolerate higher concentrations of detergents and salts than traditional CE-electrospray ionization (ESI)-MS and avoided the difficulties of collecting CE effluent and cleaning the interface, which simplified the experimental procedures and shortened the analysis time. The performance of the technique was successfully verified by capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) using a mixture of 4-aminoantipyrine, zolmitriptan, and quinine. This online technique showed good repeatability with the relative standard deviations (RSDs; n = 5) of 0.56–1.23% for the retention times and 2.01–7.41% for the peak areas. The quantitative analysis of 4-aminoantipyrine was accomplished in the range of 0.01–0.50 mg/mL with the linear correlation coefficient of 0.9995 and limit of detection of 14.7 fmol. Compared with CE-ESI-MS, the ion suppression effects of nonvolatile salts and detergents were efficiently minimized. The signal intensity remained constant when the concentrations reached 100 mM for sodium borate and 30 mM for SDS (in 30 mM sodium borate buffer). In addition, the proposed method was successfully applied to the detection of the endogenous caffeine in Chinese white tea.

The development of rapid screening and identification techniques is of great importance for drug discovery, doping control, forensic identification, food safety and quality control. Ambient mass spectrometry (AMS) allows rapid and direct analysis of various samples in open air with little sample preparation. Recently, its applications in high-throughput screening have been in rapid progress. During the past decade, various ambient ionization techniques have been developed and applied in high-throughput screening. This review discusses typical applications of AMS, including DESI (desorption electrospray ionization), DART (direct analysis in real time), EESI (extractive electrospray ionization), etc., in high-throughput screening (HTS).

•First time study of graphene matrix effects in open air conditions.•Graphene acts as an excellent medium for energy transfer.•Graphene is general and effective matrix for ambient MS.In this work, the signal intensity of ambient plasma assisted laser desorption ionization mass spectrometry (PALDI-MS) was significantly increased with graphene as matrix. The graphene functions as a substrate to trap analytes, absorb energy from the visible laser irradiation and transfer energy to the analytes to facilitate the laser desorption process. The desorbed analytes are further ionized by helium plasma and analyzed by MS. Compared with a traditional organic matrix, α-cyano-4-hydroxycinnamic acid (CHCA), graphene exhibited much higher desorption efficiency for most of the compounds benefitting from the strong optical absorption at 532 nm. The performance has been confirmed by the facile analysis of more than forty compounds with various structures. Additionally, this method was successfully applied to distinguish three kinds of Chinese tea leaves by detecting the endogenous caffeine and theanine, which proved the utility, facility and convenience of this method for rapid screening of main components in real samples.Graphical abstractThe signal intensity of ambient plasma assisted laser desorption ionization mass spectrometry (PALDI-MS) was significantly increased with graphene as matrix. This method has been proved to be utility, facile and convenient for rapid screening of main components in real samples.

A novel plasma assisted multiwavelength (1064, 532, and 355 nm) laser desorption ionization mass spectrometry (PAMLDI-MS) system was fabricated and applied in the analysis of low molecular weight compounds through combination with thin layer chromatography (TLC). The TLC/PAMLDI-MS system successfully integrated TLC, the multiwavelength laser ablation, and the excitated state plasma from direct analysis in real time (DART) and was proved to be effective in the facile separation and selective identification of low molecular weight compounds. An automated three-dimensional platform was utilized to facilitate the analysis procedures with all the parameters of the TLC/PAMLDI-MS systematically optimized, and the desorption/ionization mechanisms were discussed. The successful combination of three-wavelength laser with DART based system extended the range of the analytes and provided broad possibilities for the compound desorption from the TLC. The experimental results clearly showed that the laser desorption was wavelength dependent. The PAMLDI-MS system was successfully applied in the detection of low molecular weight compounds from different kinds of samples separated on a normal-phase silica gel, such as dye mixtures, drug standards, and tea extract, with the detection level of 5 ng/mm2.

In this work, a new labeling reagent, 2-bromopyridine-5-boronic acid (BPBA), was introduced to derivatize brassinosteroids (BRs). The BPBA not only provided a very simple and rapid labeling procedure, but also remarkably increased the detection sensitivity of BRs. Based on this new labeling reaction, a rapid and sensitive method for BRs' analysis in Arabidopsis thaliana was established by using the ultra high performance liquid chromatography-electrospray ionization triple quadrupole mass spectrometry (UHPLC-ESI-QqQ-MS). The extraction and purification procedure of the plant sample was also simplified and improved in this work. Good linearities were obtained for three BRs with the determination coefficients (R2) about 0.9999. The limits of detection (S/N=3) for three BRs were found to be 2.00–8.00 ng/L while the limits of quantification (S/N=10) were 6.00–23.0 ng/L. The RSD % for all three samples are lower than 8.67% (n=5). The recoveries of three BRs spiked in A. thaliana samples were from 76.9% to 86.1%. Using this method, the endogenous 0.055 ng/g fresh weight (FW) 24-epiBR and 0.070 ng/g (FW) 28-epihomoBR were successfully detected from only 2 g A. thaliana plants.Highlights► A rapid and simple derivatization reaction of brassinosteroids (BRs) using BPBA. ► Sensitive analytical method of BRs with LOD lower to attomolar level. ► Endogenous 24-epiBR and 28-epihomoBR were detected from Arabidopsis thaliana.

Adulteration of herbal supplements with synthetic drugs is illegal. A rapid and reliable method which utilizes direct analysis in real time mass spectrometry (DART-MS) was developed for the identification of seven synthetic antidiabetic drugs used as adulterants in herbal dietary supplements. The supplement sample was simply extracted with methanol/water by manually shaking several times and directly analyzed using DART-MS. The presence of synthetic drug adulterants was confirmed through the accurate m/z values and MS/MS data obtained via quadruple time of flight mass spectrometry (QTOF MS). Parameters for the DART source were systematically optimized, and the limits of detection (LODs) in herbal supplement matrices were measured. This method was successfully applied to examine five commercial herbal dietary supplements, and two of them proved to be adulterated with metformin without labeling.

The fragmentation pathways of two isomers of brassinosteroids, 28-homobrassinolide (28-h-BL) and 28-epihomobrassinolide (28-eh-BL), have been investigated by tandem mass spectrometry (MSn, n = 1, 2, 3, 4) with the electrospray ionization (ESI) source. The ESI mass spectrometric fragmentation pathways of protonated 28-h-BL and 28-eh-BL were comprehensively elucidated, and the principles revealed in this investigation could potentially be used to identify and distinguish brassinosteroids and their isomers.

Hydrazide functionalized monodispersed silica microspheres (HFMSM) were developed for the enrichment of phosphopeptides for the first time. With the aid of the tunable selectivity of HFMSM, global enrichment or fractionation of phosphopeptides with different numbers of phosphorylation sites could be realized by a simple modulation of the concentrations of formic acid in buffers.

ZnSn(OH)6 and binary-component SnO2–ZnSn(OH)6 were introduced as affinity probes for phosphopeptide enrichment for the first time. Two strategies, either ZnSn(OH)6 and SnO2 serial enrichment or binary-component SnO2–ZnSn(OH)6 enrichment in a single run, were proposed to enhance multi-phosphopeptide enrichment and to significantly improve global phosphopeptide detection.

Guanidyl-functionalized graphene (GFG) was designed and synthesized. By simple modulation of the loading buffer this novel bifunctional adsorbent provides two enriching functions, one for global phosphopeptides, and the other for multiphosphopeptides with consecutive phosphorylated residues. GFG provides a promising perspective for consecutive phosphorylated peptide enrichment in phosphor–proteomic research and related biological process studies.

We report a novel method for the synthesis of DNA-encoded libraries without the need for discrete DNA template. Reactant DNAs self-assemble to enable chemical reactions and photo-cleavage transfers the product to the DNA terminus, making it suitable for the subsequent affinity-based selection and hit deconvolution.

A one-step and template-free method to prepare uniform SnO2 nanospheres with a mesoporous structure was developed for the applications in phosphopeptide enrichment. The as-synthesized mesoporous SnO2 nanospheres have a large surface area and highly active surfaces for the effective binding of phosphopeptides. Compared with the non-porous SnO2 and commercial TiO2, mesoporous SnO2 nanospheres represent superior performance in the specific trapping of phosphopeptides from both standard protein and complex nonfat milk digests for mass spectrometry-based phosphoproteomic analysis. The feasible synthetic approach and the excellent enrichment performance make the mesoporous SnO2 nanospheres promising in further phosphoproteomic research.

Bone-like GdF3 was synthesized and applied for phosphopeptide enrichment for the first time. As a new kind of efficient phosphopeptide affinity probe, GdF3 exhibits high efficiency in the mediation of the dephosphorylation reaction. In addition, DFT calculations were introduced to theoretically explain the unique property of GdF3 compared to GdPO4, which is promising and can be potentially significant in protein phosphorylation research.