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A novel microplate-compatible chemiluminescence (CL) immunoassay has been developed for the determination of human immunoglobulin G (IgG) based on the luminol–AgNO3–gold nanoparticles CL system. Polystyrene microtiter plates were used for both immunoreactions and CL measurements. The primary antibody, goat-anti-human IgG, was first immobilized on polystyrene microwells. Then the antigen (human IgG) and the gold-labeled second antibody were connected to the microwells successively to form a sandwich-type immunocomplex. The gold label could trigger the reaction between luminol and AgNO3, accompanied by light emission. Under the optimized conditions, the CL intensity of the system was linear with the logarithm of the concentration of human IgG in the range from 25 to 5000 ng mL−1, with a detection limit of 12.8 ng mL−1(∼80 pM) at a signal to noise ratio of three (S/N= 3). Compared with other reported CL immunoassay method based on gold labels, the proposed CL protocol avoids a strict stripping procedure or difficult to control synthesis processes, making the method more simple, time-saving and easily automated. The present CL method is promising for the determination of clinically important bioactive analytes. [ABSTRACT FROM AUTHOR]

Low-molecular-weight (LMW) thiols are important small molecules that regulate or maintain redox homeostasis in physiological and pathological processes. Assessing the concentrations of LMW thiols in biological systems may provide valuable information regarding physiological processes and the early diagnosis of some diseases. Here, we developed a method to simultaneously determine the concentrations of multiple LWM thiols in single cells by chemical derivatization assisted liquid chromatography-mass spectrometry (LC-MS). In this method, we synthesized a pair of stable isotope reagents, N-(acridin-9-yl)-2-bromoacetamide (AYBA) and N-(1,2,3,4-[2H4]-acridin-9-yl)-2-bromoacetamide ([2H4]AYBA). AYBA was used to derivatize LWM thiols in human cervical cancer (HeLa) cells, while [2H4]AYBA was used to derivatize standard LWM thiols to prepare internal standards for the LC-MS method development. The proposed AYBA derivatization greatly enhanced the detection sensitivity of LWM thiols by LC-MS, and thereby achieved the simultaneous detection of multiple LWM thiols by LC-MS in ∼1000 HeLa cells. Finally, the developed method was successfully utilized for the quantitative analysis of multiple LWM thiols in a single HeLa cell and the content changes of LWM thiols in a single HeLa cell before and after oxidative stress treatment. Accordingly, six LMW thiols were detected, including cysteamine, cysteine, glutathione, homocysteine, hydrogen sulfide, and pantetheine. [ABSTRACT FROM AUTHOR]

Determination of low-molecular-weight compounds by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) has been a great challenge in the analytical research field. Here we developed a universal peptide-based derivatization (peptidylation) strategy for the sensitive analysis of low-molecular-weight compounds by MALDI-TOF-MS. Upon peptidylation, the molecular weights of target analytes increase, thus avoiding serious matrix ion interference in the low-molecular-weight region in MALDI-TOF-MS. Since peptides typically exhibit good signal response during MALDI-TOF-MS analysis, peptidylation endows high detection sensitivities of low-molecular-weight analytes. As a proof-of-concept, we analyzed low-molecular-weight compounds of aldehydes and thiols by the developed peptidylation strategy. Our results showed that aldehydes and thiols can be readily determined upon peptidylation, thus realizing the sensitive and efficient determination of low-molecular-weight compounds by MALDI-TOF-MS. Moreover, target analytes also can be unambiguously detected in biological samples using the peptidylation strategy. The established peptidylation strategy is a universal strategy and can be extended to the sensitive analysis of various low-molecular-weight compounds by MALDI-TOF-MS, which may be potentially used in areas such as metabolomics. [ABSTRACT FROM AUTHOR]

Ambient ionization techniques show good potential in rapid analysis of target compounds. However, a direct application of these ambient ionization techniques for the determination of analytes in a complex matrix is difficult due to the matrix interference and ion suppression. To resolve this problem, here we developed a strategy by coupling magnetic solid phase extraction (MSPE) with desorption corona beam ionization (DCBI)-mass spectrometry (MS). As a proof of concept, the pyrrole-coated Fe3O4 magnetic nanoparticles (Fe3O4@Ppy) were prepared and used for the extraction of antidepressants. After extraction, the Fe3O4@Ppy with trapped antidepressants was then directly subjected to DCBI-MS analysis with the aid of a homemade magnetic glass capillary. As the MSPE process is rapid and the direct DCBI-MS analysis does not need solvent desorption or chromatographic separation processes, the overall analysis can be completed within 3 min. The proposed MSPE-DCBI-MS method was then successfully used to determine antidepressants in human urine and plasma. The calibration curves were obtained in the range of 0.005–0.5 μg mL−1 for urine and 0.02–1 μg mL−1 for plasma with reasonable linearity (R2 ＞ 0.951). The limits of detection of three antidepressants were in the range of 0.2–1 ng mL−1 for urine and 2–5 ng mL−1 for plasma. Acceptable reproducibility for rapid analysis was achieved with relative standard deviations less than 19.1% and the relative recoveries were 85.2–118.7%. Taken together, the developed MSPE-DCBI-MS strategy offers a powerful capacity for rapid analysis of target compounds in a complex matrix, which would greatly expand the applications of ambient ionization techniques with plentiful magnetic sorbents. [ABSTRACT FROM AUTHOR]

We developed a strategy for non-targeted profiling of aldehyde-containing compounds by stable isotope labelling in combination with liquid chromatography–double neutral loss scan–mass spectrometry (SIL–LC–DNLS–MS) analysis. A pair of stable isotope labelling reagents (4-(2-(trimethylammonio)ethoxy)benzenaminium halide, 4-APC and d4-4-(2-(trimethylammonio)ethoxy)benzenaminium halide, 4-APC-d4) that can selectively label aldehyde-containing compounds were synthesized. The 4-APC and 4-APC-d4 labelled compounds were capable of generating two characteristic neutral fragments of 87 Da and 91 Da, respectively, under collision induced dissociation (CID). Therefore, double neutral loss scans were carried out simultaneously to record the signals of the potential aldehyde-containing compounds. In this respect, the aldehyde-containing compounds from two samples labelled with 4-APC and 4-APC-d4 were ionized at the same time but recorded separately by mass spectrometry. The peak pairs with characteristic mass differences (n× 4 Da) can be readily extracted from the DNLS spectra and assigned as potential aldehyde-containing candidates, which facilitates the identification of the target aldehydes. 4-APC and 4-APC-d4 labelling also dramatically increased detection sensitivities of the derivatives. Using the SIL–LC–DNLS–MS strategy, we successfully profiled the aldehyde-containing compounds in human urine and white wine. Our results showed that 16 and 19 potential aldehyde-containing compounds were discovered in human urine and white wine, respectively. In addition, 5 and 4 aldehyde-containing compounds in human urine and white wine were further identified by comparison with aldehyde standards. Altogether, SIL–LC–DNLS–MS demonstrated to be a promising approach in the identification and relative quantification of aldehyde-containing compounds from complex samples. [ABSTRACT FROM AUTHOR]

DNA methylation, catalyzed by methyltransferases, plays critical roles in various biological processes in both prokaryotes and eukaryotes. Bacterial DNA adenine methyltransferases (DAM) are associated with bacterial pathogenesis and essential for bacterial virulence and viability. Since mammals do not methylate DNA at adenine, bacterial DAM is considered to be a great candidate target for developing new therapeutics for diseases. In the current study, we developed a simple, rapid and highly sensitive fluorescence method for the detection of DAM based on exonuclease-aided signal amplification. In the proposed strategy, a liberated amplifier upon DAM methylation and Dpn I digestion of the substrate can hybridize with a reporter (FT) that contains a quencher (TAMRA) at the second base of the 3′ end and a fluorophore (FAM) at the fifth base. Upon hybridization, exonuclease III degrades the reporter in the formed duplex DNA from the 3′ end successively, releasing the fluorophore from the quencher and resulting in an intensive appearance of the fluorescent signal. The amplifier will hybridize with another reporter and enter a new cycle, which therefore can amplify the signal and dramatically increase the detection sensitivity even with an extremely low amount of amplifier. Using this strategy, the detection limit down to 0.0025 U mL−1 of DAM was achieved within a short assay time of 30 min. Furthermore, the assay was applied to evaluate endogenous DAM activity in E. coli cell at different growth stages as well as the effects of inhibitors on DAM activity. Given the attractive analytical performance, the sensing strategy may find many important applications in biomedical research and clinical diagnosis. [ABSTRACT FROM AUTHOR]

A rapid analysis method by coupling carbon nanotube film (CNTF) microextraction with desorption corona beam ionization (DCBI) was developed for the determination of Sudan dyes (I–IV) and Rhodamine B in chilli oil samples. Typically, CNTF was immersed into the diluted solution of chilli oil for extraction, which was then placed directly under the visible plasma beam tip of the DCBI source for desorption and ionization. Under optimized conditions, five dyes were simultaneously determined using this method. Results showed that the analytes were enriched by the CNTF through the π–π interactions, and the proposed method could significantly improve the sensitivities of these compounds, compared to the direct analysis by DCBI-MS/MS. The method with a linear range of 0.08–12.8 μg g−1 and good linear relationships (R2 ＞ 0.93) in a multiple reaction monitoring (MRM) mode was developed. Satisfactory reproducibility was achieved. Relative standard deviations (RSDs) were less than 20.0%. The recoveries ranged from 80.0 to 110.0%, and the limits of detection (LODs) were in the range of 1.4–21 ng g−1. Finally, the feasibility of the method was further exhibited by the determination of five illegal dyes in chilli powder. These results demonstrate that the proposed method consumes less time and solvent than conventional HPLC-based methods and avoids the contamination of chromatographic column and ion source from non-volatile oil. With the help of a 72-well shaker, multiple samples could be treated simultaneously, which ensures high throughput for the entire pretreatment process. In conclusion, it provides a rapid and high-throughput approach for the determination of such illicit additions in chilli products. [ABSTRACT FROM AUTHOR]

A novel in-syringe dispersive solid phase extraction (dSPE) system using electrospun silica fibers as adsorbents has been developed in the current work. A few milligrams of electrospun silica fibers were incubated in sample solution in the barrel of a syringe for microextraction assisted by vortex. Due to the benefit of dispersion and the high mass transfer rate of the sub-microscale electrospun silica fibers, the extraction equilibrium was achieved in a very short time (less than 1 min). Moreover, thanks to the long fibrous properties of electrospun fibers, the separation of the adsorbent from sample solution was easily achieved by pushing out the sample solution which therefore simplified the sample pretreatment procedure. Besides, the analytical throughput was largely increased by using a multi-syringe plate to perform the extraction experiment. The performance of the in-syringe dSPE device was evaluated by extraction of endogenous cytokinins from plant tissue samples based on the hydrophilic interaction. Six endogenous cytokinins in 20 mg of Oryza sativa L. (O. sativa) leaves were successfully determined under optimized conditions using in-syringe dSPE combined with liquid chromatography-mass spectrometry analysis. The results demonstrated that the in-syringe dSPE method was a rapid and high-throughput strategy for the extraction of target compounds, which has great potential in microscale sample pretreatment using electrospun fibers. [ABSTRACT FROM AUTHOR]

A simple, rapid and sensitive method based on magnetic solid phase extraction (MSPE) coupled with in situ derivatization (ISD) was developed for the determination of endogenous acidic phytohormones in rice leaves by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) analysis. With this method, acidic phytohormones were extracted onto the surface of a TiO2/magnetic hollow mesoporous silica sphere (MHMSS) through hydrophilic interaction, and then in situ derivatization was performed by the subsequent addition of 3-bromoactonyltrimethylammonium bromide (BTA). Thus, the process integrated extraction, purification, and derivatization into one step. Additionally, the permanent positively charged moiety from BTA significantly improved the ionization efficiencies of the acidic phytohormones. Several parameters affecting the efficiencies of the extraction, derivatization, and desorption were evaluated. The signal intensities of acidic phytohormones increased by 2 to 481 fold after treatment with MSPE-ISD. Under the optimized conditions, several endogenous acidic phytohormones, including GA4, GA9, GA20, JA, IAA, and ABA, were identified and quantified in rice leaves by the MSPE-ISD method. The limits of detection (LODs) were in the range of 1.03–91.21 pg mL−1. The relative recoveries ranged from 71.6–112.8%, with the intra- and interday relative standard deviations (RSDs) being less than 14.9% and 16.2%, respectively. Taken together, the proposed method provides a novel approach of combining magnetic solid phase extraction and in situ derivatization for the highly sensitive determination of endogenous acidic phytohormones. [ABSTRACT FROM AUTHOR]

In the current study, we developed a facile strategy for the one-pot synthesis of an aptamer-based organic–silica hybrid monolithic capillary column. A 5′-SH-modified aptamer, specifically targeting doxorubicin, was covalently modified in the hybrid silica monolithic column by a sol–gel method combined with “thiol–ene” click reaction. The prepared monolithic column had good stability and permeability, large specific surface, and showed excellent selectivity towards chemotherapeutic anthracyclines of doxorubicin and epirubicin. In addition, the enantiomers of doxorubicin and epirubicin can be easily separated by aptamer-based affinity monolithic capillary liquid chromatography. Furthermore, doxorubicin and epirubicin spiked in serum and urine were also successfully determined, which suggested that the complex biological matrix had a negligible effect on the detection of doxorubicin and epirubicin. Finally, we quantified the concentration of epirubicin in the serum of breast cancer patients treated with epirubicin by intravenous injection. The developed analytical method is cost-effective and rapid, and biological samples can be directly analyzed without any tedious sample pretreatment, which is extremely useful for monitoring medicines in serum and urine for pharmacokinetic studies. [ABSTRACT FROM AUTHOR]

We developed a novel method for non-targeted screening of metabolites by high performance liquid chromatography-mass spectrometry with paired homologous double neutral loss scan mode after in vitro isotope labelling (IL-HPLC-PHDNL-MS). As a proof of concept, we investigated the carboxylic acid metabolite profiling in plant samples by the IL-HPLC-PHDNL-MS method. To this end, N,N-dimethylaminobutylamine (DMBA) and d4-N,N-dimethylaminobutylamine (d4-DMBA) were synthesized and utilized to label carboxylic acids. Our results show the MS response of carboxylic acids was enhanced by 20- to 40-fold after labelling. As for the IL-HPLC-PHDNL-MS analysis, DMBA and d4-DMBA labelled samples were mixed equally before MS analysis. Because the isotope labelled moieties (dimethylamino moiety, Me2N) of DMBA and d4-DMBA are easily ruptured and lost as neutral fragments (NL 45 and NL 49) under collision induced dissociation (CID), two neutral loss scans can be carried out simultaneously to record the signals of DMBA and d4-DMBA labelled samples, respectively. In this respect, the metabolites from two samples labelled with different isotope reagents are ionized at the same time but recorded separately by mass spectrometry, which can eliminate the MS response fluctuation and mutual interference. Using this method, six potential biomarkers involved in wounded tomato leaves were identified, and their structures were further elucidated by product ion scan and high resolution mass spectrometry analysis. Taken together, the IL-HPLC-PHDNL-MS method demonstrated good performance on the identification as well as relative quantification of metabolites with a carboxyl group in biological samples. [ABSTRACT FROM AUTHOR]

SiO2–TiO2 composite fibers, prepared by electrospinning, were successfully applied to the rapid enrichment of phosphopeptides using a lab-in-syringe approach for the first time. Because of their large surface area, mesoporous structure, extraordinary length and appropriate Lewis acidity, the as-prepared SiO2–TiO2 composite fibers exhibited high selectivity and capacity in the enrichment of phosphopeptides from the digestion mixture of β-casein and bovine serum albumin (BSA), as well as human blood serum and nonfat milk. The targeted phosphopeptides could be easily enriched and detected even when the total amount of β-casein was decreased to only 10 fmol, indicating the high detection sensitivity of this method. In addition, the whole enrichment extraction procedure can be finished in less than 3 min, which can avoid or decrease the degradation of endogenous phosphoproteins by proteases released ex vivo during time-consuming treatments. The developed method is rapid, cost-effective, selective, sensitive, operationally simple, and does not require any harsh conditions and intricate equipment, providing an ideal candidate for the enrichment of phosphopeptides from complex biological samples either in the lab or in the field. [ABSTRACT FROM AUTHOR]

In order to quantitatively study the jasmonate biosynthetic pathway, we chemically synthesized a pair of isotope mass probes and established a labeling protocol. The pair of mass probes used in our work were ω-bromoacetonylpyridinium bromide (BPB) and d5-ω-bromoacetonylpyridinium bromide (d5-BPB), which contain carboxylic acid reactive groups, isotopically labeled groups and permanent positive charges. High performance liquid chromatography (HPLC) and electrospray ionization quadrupole-time of flight mass spectrometry (ESI-QTOF-MS) were used for the detection of labeled standard mixtures and plant samples. In comparison to negative mode electrospray ionization detection of unlabeled analytes, the ESI signal of reverse charge labeled compounds was shown to improve by 20- to 80-fold. Accurate relative quantification was achieved as no isotopic effects of the different isotope labeled phytohormones during RP/SCX mixed-mode liquid chromatographic separation were observed. A data analysis method was established for analyzing metabolic pathways using our labeling strategy. We then applied our method and examined the jasmonate biosynthetic pathway of rice under salt stress and the premature senescence mutant. Here we found that under salt stress conditions, rice showed up-regulation in (13S)-hydroperoxyoctadecatrienoic acid (HOPT), cis-(+)-12-oxophytodienoic acid (OPDA), 3-oxo-2-(2′-pentenyl)-cyclopentane-1-octanoic acid (OPC-8) and jasmonoyl-valine (JA-Val) levels, while α-linolenic acid (LA) and jasmonic acid (JA) showed down-regulation, and three components (HPOT, OPC-8 and JA-Val) were accumulated. The premature senescence mutant showed up-regulation in all major components of the jasmonate biosynthetic pathway with the exception of LA, and an accumulation of HPOT, OPC-6 and JA-Val. This study demonstrates that our chemical stable isotope labeling strategy can be used as a powerful tool for metabolic pathway analysis of phytohormones in plants. [ABSTRACT FROM AUTHOR]

A MALDI-TOF mass spectrometric method for rapid screening of protein tyrosine kinase (PTK) inhibitors has been developed. To circumvent the ion suppression of phosphorylated substrate peptides caused by the presence of high abundant non-phosphorylated peptides in the enzymatic reaction mixtures, a separation and enrichment process of the phosphorylated peptides from complex mixtures was carried out by using an in-house fabricated TiO2nanoparticle-coated capillary column prior to the MS analysis. With a synthetic phosphopeptide (DAIpYAAPFAKKK), of which the sequence is similar to that of the substrate (EAIYAAPFAKKK) of the Abelson tyrosine kinase (Abl), as the internal standard, the signal ratio of the phosphorylated substrate to the standard detected by MALDI-TOF MS is linearly correlated with the molar ratio of the two phosphopeptides over the range of 0.3 to 3 with r2= 0.99. We validated the MS method by determining the IC50value of imatinib, an Abl inhibitor for clinical treatment of chronic myelogenous leukaemia (CML). The obtained IC50value (234 nM) is consistent with that determined by ELISA (291 nM). Then, six analogues of imatinib synthesized in our laboratory were screened using the method, giving rise to inhibitory potential results which are in good agreement with the docking analysis data. The developed method is sensitive, operationally simple, does not require isotope-labelling and is cost/time effective, providing an alterative method for rapid screening of PTK inhibitors as therapeutic agents for tumours. [ABSTRACT FROM AUTHOR]

A MALDI-TOF mass spectrometric method for rapid screening of protein tyrosine kinase (PTK) inhibitors has been developed. To circumvent the ion suppression of phosphorylated substrate peptides caused by the presence of high abundant non-phosphorylated peptides in the enzymatic reaction mixtures, a separation and enrichment process of the phosphorylated peptides from complex mixtures was carried out by using an in-house fabricated TiO2nanoparticle-coated capillary column prior to the MS analysis. With a synthetic phosphopeptide (DAIpYAAPFAKKK), of which the sequence is similar to that of the substrate (EAIYAAPFAKKK) of the Abelson tyrosine kinase (Abl), as the internal standard, the signal ratio of the phosphorylated substrate to the standard detected by MALDI-TOF MS is linearly correlated with the molar ratio of the two phosphopeptides over the range of 0.3 to 3 with r2= 0.99. We validated the MS method by determining the IC50value of imatinib, an Abl inhibitor for clinical treatment of chronic myelogenous leukaemia (CML). The obtained IC50value (234 nM) is consistent with that determined by ELISA (291 nM). Then, six analogues of imatinib synthesized in our laboratory were screened using the method, giving rise to inhibitory potential results which are in good agreement with the docking analysis data. The developed method is sensitive, operationally simple, does not require isotope-labelling and is cost/time effective, providing an alterative method for rapid screening of PTK inhibitors as therapeutic agents for tumours. [ABSTRACT FROM AUTHOR]

A novel boronate affinity monolith, poly(3-acrylamidophenylboronic acid-co-ethylene dimethacrylate) (AAPBA-co-EDMA), was prepared in 530 µm capillaries by a one-step in situpolymerization procedure using a pre-polymerization mixture consisting of functional monomer 3-acrylamidophenylboronic acid, cross-linker ethylene dimethacrylate, porogenic solvent methanol with added poly(ethylene glycol) 20 000 (PEG 20 000) and initiator azobisisobutyronitrile (AIBN). The preparation of the monolith was optimized by investigating the ratio of functional monomer to cross-linker and the effect of poly(ethylene glycol) molecular weight. The resulting boronate monolith was used as a sorbent for polymer monolith microextraction (PMME). Using nucleosides as the testing analyte, the extraction performance of this boronate monolith towards glycol-containing compounds was examined. Finally, the boronate monolith was applied for selective enrichment of glycopeptides and glycoproteins. [ABSTRACT FROM AUTHOR]