In situ fabrication of covalent organic frameworks on solid-phase microextraction probes coupled with electrospray ionization mass spectrometry for enrichment and determination of androgens in biosamples.

Solid-phase microextraction (SPME) coupled with electrospray ionization mass spectrometry (ESI-MS) was developed for rapid and sensitive determination of endogenous androgens. The SPME probe is coated with covalent organic frameworks (COFs) synthesized by reacting 1,3,5-tri(4-aminophenyl)benzene (TPB) with 2,5-dioctyloxybenzaldehyde (C8PDA). This COFs-SPME probe offers several advantages, including enhanced extraction efficiency and stability. The analytical method exhibited wide linearity (0.1-100.0 µg L-1), low limits of detection (0.03-0.07 µg L-1), high enrichment factors (37-154), and satisfactory relative standard deviations (RSDs) for both within one probe (4.0-14.8%) and between different probes (3.4-12.7%). These remarkable performance characteristics highlight the reliability and precision of the COFs-SPME-ESI-MS method. The developed method was successfully applied to detect five kinds of endogenous androgens in female serum samples, indicating that the developed analytical method has great potential for application in preliminary clinical diagnosis.

Fluorescent Turn-On Probes for Visualizing GPx4 Levels in Live Cells and Predicting Drug Sensitivity.

Glutathione peroxidase 4 (GPx4) is the membrane peroxidase in mammals that is essential for protecting cells against oxidative damage and critical for ferroptosis. However, no live cell probe is currently available to specifically label GPx4. Herein, we report both inhibitory and noninhibitory fluorescent turn-on probes for specific labeling of GPx4 in live cells. With these probes, the GPx4 expression levels and degradation kinetics in live cells could be visualized, and their real-time responses to the cellular selenium availability were revealed. These probes could also potentially serve as staining reagents to predict the sensitivity of GPx4-related ferroptosis drugs. In view of these features, these GPx4-selective probes will offer opportunities for a deeper understanding of GPx4 function in natural habitats and hold great promise for biomedical applications.

Covalent organic framework film-based laser desorption/ionization mass spectrometry for rapid and sensitive quantification of homocysteine in human serum.

RATIONALE: Homocysteine (hcy) is a metabolite in the human body and an important determinant of cardiovascular health. To assist in the assessment of human cardiovascular safety, a rapid and accurate quantitative analysis method must be developed. Laser desorption/ionization mass spectrometry (LDI-MS) has been widely used in biological, chemical, and medical analyses due to its excellent characteristics of high throughput, low sample consumption, and high speed. Here, an LDI-MS method based on covalent organic framework (COF) film was developed for the rapid and sensitive determination of hcy in human serum using an isotope-labeled internal standard. METHODS: We tried to cultivate COFs on indium-tin oxide substrate at room temperature to form a thin film, which was used in LDI-MS. Compared with the traditional organic matrices, the COF film had a clean background and a high signal response for the detection of hcy. In addition, using COF film as the substrate, with a high signal intensity and a clean background, can be helpful to analyze a series of small molecules such as amino acids, bisphenols (Bps), estrogens, and drugs. We evaluated the limit of detection (LOD) and the reproducibility of this method. Finally, the calibration curve was constructed for the quantification of serum hcy using an isotope-labeled internal standard and was applied for the rapid determination of hcy in clinical human serum. RESULTS: COF film-assisted LDI-MS had a higher response signal and a cleaner background compared to four conventional organic matrices. The LOD of the method for hcy was 0.5 µmol/L, equivalent to 500 fmol. This method exhibited excellent performance for small-molecule compounds, including amino acids, Bps, drugs, and estrogens. The reproducibilities of this method for shot-to-shot and dot-to-dot were determined to be good. This method was applied for the rapid analysis of hcy in clinical human serum, showing good correlation with those obtained by hospital testing. CONCLUSION: The COF film-based LDI-MS method had simple sample preparation, short analysis time, clean background, and good reproducibility for hcy analysis. As an important indicator of human health, the detection of serum hcy is of great significance to human health.

A reactive matrix for in situ chemical derivatisation and specific detection of cis-diol compounds by matrix-assisted laser desorption/ionisation mass spectrometry.

Analysis of cis-diol compounds is essential, because they play important roles in cosmetics, food, pharmaceuticals, and living organisms. Herein, we describe the development of a matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS) method to analyse cis-diol compounds. In this method, a 6-borono-1-methylquinoline-1-ium (BMQI) reactive matrix was designed for in situ derivatisation of cis-diol compounds based on the boronate affinity interaction between boronic acid and cis-diol groups. Compared to traditional commercial matrices and other boronic acid reagents, BMQI can significantly accelerate the desorption/ionisation process, improve reproducibility, exhibit free background interference, and enhance signal intensity in the analysis of various cis-diol compounds even for amounts as low as 1 nmol. The BMQI-assisted laser desorption/ionisation mass spectrometry (LDI-MS) was successfully applied to the rapid screening and identification of sugar alcohols in different sugar-free foods. This work provides an alternative method to the LDI-MS analysis of cis-diol-containing molecules, and the method can be extended to other food samples and biofluids.

Spatial Metabolomics and Lipidomics Reveal the Mechanisms of the Enhanced Growth of Breast Cancer Cell Spheroids Exposed to Triclosan.

Triclosan (TCS), an antimicrobial compound, is known to have potential endocrine-disruptive properties, but the underlying toxic mechanisms at the metabolic level are not well understood. Here, we applied metabolomics and lipidomics combined with mass spectrometry imaging (MSI) to unveil the mechanisms of the enhanced growth of MCF-7 breast cancer cell spheroids (CCS) exposed to TCS. To obtain a wide coverage of metabolites and lipids by using MSI, we used techniques of matrix-assisted laser desorption/ionization (MALDI) and MALDI coupled with laser-postionization. The results showed that TCS and TCS sulfate penetrated into the entire area at 0-3 h and both localized in the inner area at 6 h. After 24 h, a portion of two compounds was released from CCS. Omic data indicated that TCS exposure induced alterations via several pathways, including energy metabolism and biosynthesis of glycerophospholipids and glycerolipids. Further MSI data revealed that the enhancement of energy supply in the peripheral area and the increase of energy storage in the inner area might contribute to the enhanced growth of MCF-7 breast CCS exposed to TCS. This study highlights the importance of integrating metabolite distributions and metabolic profiles to reveal the novel mechanisms of TCS-triggered endocrine disrupting effects.

Facile synthesis of spherical covalent organic frameworks for enrichment and quantification of aryl organophosphate esters in mouse serum and tissues.

Here, an imine-linked-based spherical covalent organic framework (COF) was prepared at room temperature. The as-synthesized spherical COF served as an adsorbent in dispersive solid-phase extraction (dSPE), by its virtue of great surface area (1542.68 m2 /g), regular distribution of pore size (2.95 nm), and excellent stability. Therefore, a simple and high-efficiency dispersive solid phase extraction method based on a spherical COF coupled with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was established to determine aryl organophosphate esters in biological samples. This approach displayed favorable linearity in the range of 10.0-1000.0 ng/L (r > 0.9989), a high signal enhancement factor (58.8-181.8 folds) with low limits of detection (0.3-3.3 ng/L). Moreover, it could effectively eliminate complex matrix interference to accurately extract seven aryl organophosphate esters from mouse serum and tissue samples with spiked recoveries of 82.0%-117.4%. The as-synthesized spherical COF has been successfully applied in sample preparation. The dSPE-HPLC-MS/MS method based on a spherical COF has potential application to study the pollutants' metabolism in vivo.

Facile synthesis of hollow microtubular COF as enrichment probe for quantitative detection of ultratrace quinones in mice plasma with APGC-MS/MS.

A hollow microtubular covalent organic framework (denoted as TatDha-COF) was synthesized by solvothermal method for the enrichment and determination of quinones. The TatDha-COF showed large specific surface area (2057 m2 g-1), good crystal structure, ordered pore size distribution (2.3 nm), stable chemical properties and good reusability. Accordingly, a simple and efficient method based on dispersive solid-phase extraction (d-SPE) and atmospheric pressure gas chromatography tandem mass spectrometry (APGC-MS/MS) was developed for the determination of quinones in complex samples. The established method demonstrated a wide liner range, good linearity (r>0.9990), high enrichment factors (EFs, 24-69-folds) and low detection limits (LODs, 0.200-30.0 pg L-1, S/N≥3). On this basis, the suggested method was successfully applied to sensitively detect the eight ultratrace quinones in mice plasma. Overall, the established method has provided a powerful tool for the enrichment and detection of ultratrace quinones in complex samples, presenting the promising application of TatDha-COF in sample pretreatment.

Defined positive charge patterns created on DNA nanostructures determine cellular uptake efficiency.

We provide an effective method to create DNA nanostructures below 100 nm with defined charge patterns and explore whether the density and location of charges affect the cellular uptake efficiency of nanoparticles (NPs). To avoid spontaneous charge neutralization, the negatively charged polymer nanopatterns were first created by in situ polymerization using photoresponsive monomers on DNA origami. Subsequent irradiation generated positive charges on the immobilized polymers, achieving precise positively charged patterns on the negatively charged DNA surface. Via this method, we have discovered that the positive charges located on the edges of nanostructures facilitate more efficient cellular uptake in comparison to the central counterparts. In addition, the high-density positive charge decoration could also enhance particle penetration into 3D multicellular spheroids. This strategy paves a new way to construct elaborate charge-separated substructures on NP surfaces and holds great promise for a deeper understanding of the influence between the surface charge distribution and nano-bio interactions.

Fluoro-Functionalized Spherical Covalent Organic Frameworks as a Liquid Chromatographic Stationary Phase for the High-Resolution Separation of Organic Halides.

The development of novel stationary phases with specific functionality is of great importance in chromatographic separation. Herein, we fabricated fluoro-functionalized spherical covalent organic frameworks (SF-COFs) via a bottom-up strategy as stationary phases for high-performance liquid chromatography (HPLC). Benefiting from the significant monodispersity, narrow size distribution, and high fluorine content, the SF-COFs packed column showed high column efficiency and excellent resolution for the separation of the organic fluorides involving polyfluorobenzenes, polychlorobenzenes, polybromobenzenes, perfluoroalkyl methacrylates, and halogenated trifluorotoluenes, which cannot be separated on the fluorine-free spherical covalent organic frameworks packed column. Especially, the column efficiency of 20 100-38 500 plates/m was obtained for polyfluorobenzenes, and the relative standard deviations of the retention time for continuous 10 separations of polychlorobenzenes and polybromobenzenes were less than 0.98%. Furthermore, the prepared SF-COFs packed column showed overwhelming superiority in the separation of organic halides compared with commercial C18 and pentafluorophenyl (PFP) packed columns. In addition, the compounds with different hydrophobicity or aromatic ring structure were also successfully separated on the SF-COFs packed column. This work extended the application of spherical COFs and provided a new way to introduce specific functional groups into the COF-based stationary phase for HPLC.

4-Mercaptobenzoic acid-assisted laser desorption/ionization mass spectrometry for sensitive quantification of cesium and strontium in drinking water.

RATIONALE: Cesium ions (Cs+ ) and strontium ions (Sr2+ ), which enter the human body mainly through drinking water, are an important determinant of health. They are widely distributed on Earth and extremely soluble in water. In order to assist assessment of the drinking safety, it was essential to develop a rapid analytical method for quantification. We have established a 4-mercaptobenzoic acid (MBA)-based matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) method for the rapid detection and sensitive quantification of Cs+ and Sr2+ in the aqueous environment. METHODS: Using MBA as the matrix, the rapid detection and quantification for Cs+ and Sr2+ were conducted by MALDI-TOF-MS. At first, the concentration of MBA was optimized. Then, salt tolerance, detection limit and reproducibility of this method were evaluated by standard solutions. Finally, the calibration curves were constructed and applied to the rapid determination of Cs+ and Sr2+ in six commercially available bottled waters for drinking. RESULTS: For the MBA-assisted MALDI-TOF-MS method, the optimal concentration of MBA was 2 mg/mL. The signal-to-noise (S/N) ratio of Cs+ was up to 971 in 1000 mmol/mL NaCl solution. The detection limits of the method for Cs+ and Sr2+ were 3 pg/mL and 10 pg/mL, respectively. Furthermore, this developed method was applied to the rapid analysis of Cs+ and Sr2+ in six commercially available drinking waters, and the results correlated well with the results obtained from a validated inductively coupled plasma mass spectrometry (ICP-MS) method. CONCLUSIONS: The MBA-assisted MALDI-TOF-MS method has high sensitivity, fast detection speed, less background interference, and high reproducibility in the analysis of Cs+ and Sr2+ . Because of the physiological functions and general toxic effects, detection of Cs+ and Sr2+ in water is of major importance for drinking safety.

Covalent Organic Framework Nanofilm-Based Laser Desorption/Ionization Mass Spectrometry for 5-Fluorouracil Analysis and Tissue Imaging.

Although matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has become a ubiquitous and effective tool for macromolecules, direct analysis of small molecules by MALDI-MS using conventional organic matrices poses a challenge. Herein, a large-area, uniform, and stable covalent organic framework (COF) nanofilm prepared directly on indium-tin oxide (ITO) glass was first introduced as a substrate for LDI-MS, which showed enhanced sensitivity, no background interference, and high reproducibility in the analysis of diverse small molecules. Taking into account all these merits, an attractive approach of COF nanofilm-based LDI-MS was developed to quantitatively evaluate the pharmacokinetics of 5-fluorouracil (5-FU) in mouse plasma. A good linear relationship (10-20,000 ng/mL) and a low limit of detection (LOD) for 5-FU (∼100 pg/mL) were achieved. In view of the fact that the COF nanofilm was uniform and without the requirement of additional matrix spraying, it was further extended for LDI-MS imaging (LDI-MSI) to visualize the spatial distribution of 5-FU in mouse liver at different interval times after intravenous and intragastric administrations. The results indicated that the decay of 5-FU in mouse liver obtained with the COF nanofilm-based LDI-MSI was consistent with the tendency of 5-FU pharmacokinetics. This work not only offers an alternative solution for LDI-MS/MSI analysis of small molecules but also extends the application fields of COF nanofilm in MS research.

4-Mercaptobenzoic acid as a MALDI matrix for highly sensitive analysis of metals.

4-Mercaptobenzoic acid (MBA) is introduced as a matrix for laser desorption/ionization time-of-flight mass spectrometry (MS) analysis of metals, exhibiting matrix-interference-free background, greatly enhanced MS signal intensity, and excellent reproducibility. The developed method was successfully extended for the rapid screening and sensitive determination of ultratrace metals in fine particulate matter (PM2.5).

Thiol functionalized covalent organic framework for highly selective enrichment and detection of mercury by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

A spherical thiol-functionalized covalent organic framework (COF-SH) was designed via a facile thiol-yne click reaction of a alkynyl-terminated COF and pentaerythritol tetra(3-mercaptopropionate). The COF-SH was explored as a new adsorbent for the selective enrichment of Hg2+. The as-prepared COF-SH exhibited a uniform mesoporous structure, a high abundance of binding sites, and good chemical stability, which endow it with great performance for the adsorption of Hg2+ and its corresponding maximum adsorption capacity was up to 617.3 mg g-1. Furthermore, the adsorption behavior of Hg2+ on the COF-SH wasin good agreement with the Langmuir and pseudo-second-order models. The influences of adsorbent dosage, pH, selectivity, and reusability of the COF-SH on Hg2+ adsorption were also investigated. Besides this, the COF-SH showed high selectivity towards Hg2+ even in the presence of a high concentration of K+, Na+, Ca2+, Mg2+ and Zn2+ metal ions. Using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), the corresponding limit of detection (LOD) of Hg2+ was determined at very low concentrations of 80 pg mL-1 (equal to 396 amoL µL-1). In addition, the COF-SH was successfully applied to rapidly enrich and sensitively detect Hg2+ in industrial sewage, with recoveries in the range of 101.8-103.4%, demonstrating the promising potential of COF-SH as an effective adsorbent for use in environmental sample pretreatment.

Ti4+-immobilized hierarchically porous zirconium-organic frameworks for highly efficient enrichment of phosphopeptides.

Ti4+-immobilized hierarchically porous zirconium-organic frameworks (denoted as THZr-MOFs) was prepared for phosphopeptide enrichment. The THZr-MOFs showed high specific surface area of 185.28 m2 g-1, wide pore-size distribution of 3 ~ 20 nm, good chemical stability and excellent hydrophilicity. Introduction of hierarchical pores in MOFs not only facilitated the accessibility of phosphopeptides to the internal metal affinity sites and reduce their mass transfer resistance, but also increased the exposure sites of metal affinity interaction and binding energies of Zr and Ti elements. Benefited from these advantages, the THZr-MOFs showed high adsorption capacity (79.8 µg mg-1) towards standard phosphopeptide. A low detection limit (0.05 fmol µL-1) and high enrichment selectivity (ß-casein/BSA with a molar ratio of 1:5000) were also obtained by MALDI-TOF MS. The THZr-MOFs were applied to analyze complex samples including nonfat milk, human serum, and HeLa cell lysate. In total, 1432 phosphopeptides derived from 762 phosphoproteins were identified from human HeLa cell lysate. Schematic representation of the application of Ti4+-immobilized hierarchically porous zirconium-organic frameworks (denoted as THZr-MOFs) in high-efficiency and selective enrichment of low-abundance phosphopeptides from the tryptic digest of human HeLa cell lysate.

Facile fabrication of magnetic covalent organic frameworks and their application in selective enrichment of polychlorinated naphthalenes from fine particulate matter.

Magnetic covalent organic frameworks (Fe3O4@TPPCl4) were synthesized via a one-pot process in which magnetic nanoparticles (Fe3O4@MNP) served as a magnetic core and 2,4,6-trihydroxy-1,3,5-benzenetricarbaldehyde (TP) and 2,2',5,5'-tetrachlorobenzidine (PCl4) as two building blocks to form a shell. The as-prepared Fe3O4@TPPCl4 nanoparticles have superior features, including large surface area (186.5 m2 g-1), high porosity, strong magnetic responsiveness (42.6 emu g-1), high chlorine content, and outstanding thermal stability, which make them an ideal adsorbent for highly selective enrichment of polychlorinated naphthalenes (PCNs). Combining with atmospheric pressure gas chromatography tandem mass spectrometry (APGC-MS/MS), a simple analytical method of Fe3O4@TPPCl4-based magnetic solid-phase extraction (MSPE)-APGC-MS/MS was developed, which exhibited good linearity (r ≥ 0.9991) for eight PCNs in the concentration range 0.1-100 ng L-1. Moreover, low detection limits (0.005-0.325 ng L-1), high enrichment factors (46.62-81.97-fold), and good relative standard deviations (RSDs) of inter-day (n = 3, 1.64 to 7.44%) and day-to-day (n = 3, 2.62 to 8.23%) were achieved. This method was successfully applied to the selective enrichment of PCNs in fine particulate matter (PM)2.5 samples, and ultra-trace PCNs were found in the range 1.56-3.75 ng kg-1 with satisfactory recoveries (93.11-105.81%). The successful application demonstrated the great potential of Fe3O4@TPPCl4 nanoparticles as an adsorbent for enrichment of halogenated compounds. Schematic presented one-pot synthesis of magnetic covalent organic framework nanocomposites (Fe3O4@TPPCl4) and their application in the selective enrichment of PCNs from PM2.5 prior to APGC-MS/MS analysis.

Surface-enhanced laser desorption/ionization mass spectrometry for rapid analysis of organic environmental pollutants by using polydopamine nanospheres as a substrate.

Polydopamine nanospheres (PDA) were designed to serve as a new substrate for surface-enhanced desorption/ionization mass spectrometry (SELDI-MS). Compared with conventional organic matrices, the PDA substrate showed superior LDI performance for analyzing a wide variety of environmental pollutants, including polycyclic aromatic hydrocarbons, bisphenols, benzophenones, sulfonamides, perfluorinated compounds and estrogens. Benzoapyrene was used to evaluate the ability of quantitative analysis and its corresponding limit of detection (LOD) of as low as 0.1 ng was achieved. High sensitivity and good reproducibility of PDA-based SELDI-MS allowed us to determine ultratrace PAHs in airborne particulate matters (PM2.5), and the corresponding concentration of BaP in different PM2.5 were 5.32, 8.97 and 9.79 ng m-3. Significantly, PDA exhibits the characteristics of simple synthesis, low cost, non-toxicity and less matrix interference, which provides the possibility for the sensitive analysis of organic small molecule pollutants at low concentrations in complex environmental samples.

A spherical covalent-organic framework for enhancing laser desorption/ionization mass spectrometry for small molecule detection.

A spherical vinyl-functionalized covalent-organic framework (COF-V) was prepared at room temperature by a facile method and applied as a novel substrate for surface-enhanced laser desorption/ionization mass spectrometry (SELDI-MS). Compared with conventional organic matrices, the spherical COF-V with high crystallinity and good monodispersity exhibited high sensitivity, no matrix background interference, wide-range applicability, high salt tolerance and reproducibility in the characterization of small molecules. Considering these advantages, the applicability of the spherical COF-V-based SELDI-MS method was successfully demonstrated by determining trace amounts of glucose in diabetic urine, which would be a promising candidate for clinical diagnosis of diabetes. In addition, the morphological effect and the desorption/ionization mechanism of the COF-V were investigated in detail and the results indicated that the spherical COF-V substrate could greatly enhance the LDI process compared with the bulk COF-V. This work not only extends the application of COFs in MS, but also offers a promising alternative for small molecule identification and clinical diagnosis of diabetes.

High-throughput screening of bisphenols using magnetic covalent organic frameworks as a SELDI-TOF-MS probe.

Core-shell structured magnetic covalent organic framework (Fe3O4@COF) nanospheres were rapidly synthesized at room temperature using the monodisperse Fe3O4 nanoparticles (NPs) as magnetic core and benzene-1,3,5-tricarbaldehyde (BTA) and 3,3'-dihydroxybenzidine (DHBD) as two building blocks (denoted as Fe3O4@BTA-DHBD), respectively. They can serve as a mass spectrometry probe for rapid and high-throughput screening of bisphenols (BPs) from pharmaceuticals and personal care products (PPCPs) by surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF-MS). The Fe3O4@BTA-DHBD nanospheres showed some superior features involving average pore size distribution (2.82 nm), high magnetization values (42.5 emu g-1), high specific surface area (82.96 m2 g-1), and good chemical/thermal stability. It was used as both ideal adsorbent for enrichment of BPs and new substrate to assist ionization in SELDI-TOF-MS. The method exhibited good linearity in the range 0.05-4000 ng mL-1 with correlation coefficients (r) higher than 0.9920. Low limits of detection (LODs) (500 pg mL-1 for bisphenol A (BPA), 2 pg mL-1 for bisphenol B (BPB), 28 pg mL-1 for bisphenol C (BPC), 60 pg mL-1 for bisphenol F (BPF), 33 pg mL-1 for bisphenol AF (BPAF), 200 pg mL-1 for bisphenol BP (BPBP), 10 pg mL-1 for bisphenol S (BPS), 90 pg mL-1 for tetrabromobisphenol A (BPA(Br)4), and 380 pg mL-1 for tetrabromobisphenol S (BPS(Br)4)) and good recoveries (80.6-115%) of BPs in PPCPs were achieved. The relative standard deviations (RSDs) of spot-to-spot (n = 10) and sample-to-sample (n = 5) were in the ranges 5-11% and 5-12%, respectively. The dual-function platform was successfully applied to the quantitative determination of BPs in PPCPs. It not only expanded the scope of the application of COFs but also provided an alternative strategy for the determination of hazardous compounds in PPCPs. Graphical abstract Schematic representation of the synthesis of core-shell structured magnetic covalent organic framework nanospheres (Fe3O4@COFs) and its application in the analysis of bisphenols by using Fe3O4@BTA-DHBD nanospheres as a MS probe based on surface-enhanced laser desorption/ionization time-of-flight mass spectrometry.

Size-Controllable Synthesis of Uniform Spherical Covalent Organic Frameworks at Room Temperature for Highly Efficient and Selective Enrichment of Hydrophobic Peptides.

Covalent organic frameworks (COFs) represent a new class of porous crystalline polymers with a diversity of applications. However, synthesis of uniform spherical COFs poses a great challenge. Here, we present size-controllable synthesis of uniform spherical COFs from nanometer to micrometer scale by a facile approach at room temperature. The as-prepared spherical COFs with different sizes exhibited ultrahigh surface area, good crystallinity, and chemical/thermal stability. Multifarious microscopic and spectroscopic techniques were performed to understand the formation mechanism and influencing factors of the spherical COFs. Moreover, the general applicability for room-temperature synthesis of the spherical COFs was demonstrated by varying different building blocks. Spherical COFs, because of the advantageous nature of their surface area, hydrophobicity, and mesoporous microenvironment, serve as an attractive restricted-access adsorption material for highly selective and efficient enrichment of hydrophobic peptides and size exclusion of macromolecular proteins simultaneously. On this basis, the spherical COFs were successfully applied to the specific capture of ultratrace C-peptide from human serum and urine samples. This research provides a new strategy for room-temperature controllable synthesis of uniform spherical COFs with different sizes and extends the application of COFs as an attractive sample-enrichment probe for clinical analysis.

Negative ion laser desorption/ionization time-of-flight mass spectrometric analysis of small molecules by using nanostructured substrate as matrices.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is an excellent analytical technique for rapid and sensitive analysis of macromolecules such as polymers and proteins. However, the main drawback of MALDI-TOF MS is its difficulty to detect small molecules with mass below 700 Da because of the intensive interference from MALDI matrix in the low mass region. In recent years there has been considerable interest in developing matrix-free laser desorption/ionization by using nanostructured substrates to substitute the conventional organic matrices, which is often referred as surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF MS). Despite these attractive features, most of the current SALDI-TOF MS for the analysis of small molecules employ positive ion mode, which is subjected to produce multiple alkali metal adducts, and thus increases the complexity of the analysis. Different from the complicated adducts produced in positive ion mode, mass spectra obtained in negative ion mode are featured by deprotonated ion peaks without matrix interference, which simplifies the interpretation of mass spectra and detection of unknown. In this review, we critically survey recent advances in nanostructured substrates for negative ion LDI-TOF MS analysis of small molecules in the last 5 years. Special emphasis is placed on the preparation of the nanostructured substrates and the results achieved in negative ion SALDI-MS. In addition, a variety of promising applications including environmental, biological, and clinical analysis are introduced. The ionization mechanism of negative ionization is briefly discussed.