Effect of ionic liquids as mobile phase additives on retention behaviors of G-quadruplexes in reversed-phase high performance liquid chromatography

G-quadruplexes (G4s) play an important role in a variety of biological processes and have extensive application prospects. Due to the significance of G4s in physiology and biosensing, studies on G4s have attracted much attention, stimulating the development or improvement of methods for G4 structures and polymorphism analysis. In this work, ionic liquids (ILs) were involved as mobile phase additives in reversed-phase high performance liquid chromatography (RP-HPLC) to analyse G4s with various conformations for the first time. How ILs affected the retention behaviors of G4s was investigated comprehensively. It was found that the addition of ILs markedly enhanced G4 retention, along with obvious amelioration on chromatographic peak shapes and separation. The influence of pH of mobile phase and types of ILs were also included in order to acquire an in-depth understanding. It appeared that the effect of ILs on G4 retention behaviors was the result of a combination of various interactions between G4s with the hydrophobic stationary phase and with the IL-containing mobile phase, where ion pair mechanism and enhanced hydrophobic interaction dominated. The findings of this work revealed that ILs could effectively improve the separation of G4s in RP-HPLC, which was conducive to G4 structural analysis, especially for G4s polymorphism elucidation.

Magnetic Ti3C2 MXene Nanosheets Prepared for Enrichment of Phosphopeptides

MXenes have received lots of attention since discovered and have been applied in various fields. In this work, Ti₃C₂-Fe₃O₄ composites with exposed non-modified Ti₃C₂ MXene nanosheets were designed and prepared by an in situ growth strategy and then applied in the enrichment of phosphopeptides. The two-dimensional composites could interact with the phosphopeptides through a metal oxide affinity chromatography mechanism provided by Ti-O and Fe-O bonds and a hydrophilic interaction chromatography mechanism by surface hydroxyl groups. This magnetic nanomaterial with a specific surface area of 66.1 m²·g^-1 had high sensitivity to phosphopeptides (0.5 nmol·L^-1) and high selectivity (1:1000 of the molar ratio of β-casein to bovine serum albumin). Non-fat milk was adopted as a real sample to preliminarily examine the applicability of the Ti₃C₂-Fe₃O₄-based protocol. Subsequently, Qingkailing injection, a kind of traditional Chinese medicine injection, was introduced to further explore the suitability of the nanocomposites for phosphopeptide enrichment from more complex matrices and satisfactory results were obtained.

A novel particulate matter sampling and cell exposure strategy based on agar membrane for cytotoxicity study

Laboratories use different strategies to sample and extract atmospheric particulate matter (PM), some of which can be very complicated. Due to the absence of a standard protocol, it is difficult to compare the results of PM toxicity assessment across different laboratories. Here, we proposed a novel PM sampling and cell exposure strategy based on agar membrane. The agar membrane, prepared by a simple freeze-drying method, has a relatively flat surface and porous interior. We demonstrated that the agar membrane was a reliable substitute material for PM sampling. Then the PM on the agar membranes was directly extracted with the culture medium by vortex method, and the PM on the polytetrafluoroethylene (PTFE) filters was extracted with water by the traditional ultrasonic method for comparison. The extraction efficiency was evaluated and in vitro cytotoxicity assays were carried out to investigate the toxic effects of PM extracted with two strategies on macrophage cells. The results showed that the PM extracted from agar membranes induced higher cytotoxicity and more differentially expressed proteins. Overall, the novel PM sampling-cell exposure strategy based on the agar membrane is easy to operate, biocompatible and comparable, and has low disturbance, could be an alternative sampling and extraction method for PM toxicity assessment.

A combination approach using two functionalized magnetic nanoparticles for speciation analysis of inorganic arsenic

Mercapto- and amino-functionalized magnetic nanoparticles, Fe₃O₄@SiO₂@MPTMS (SMNPs-MPTMS) and Fe₃O₄@SiO₂@APTES (SMNPs-APTES), have been applied as magnetic solid-phase extraction (MSPE) sorbents to directly extract arsenite (As(III)) and arsenate (As(V)) respectively, followed by inductively coupled plasma-mass spectrometry (ICP-MS) detection. Various MSPE parameters were optimized including dose of magnetic adsorbent, pH of sample solution, loading and elution conditions of analytes, adsorption capacity and reusability of SMNPs-MPTMS and SMNPs-APTES for As(III) and As(V) respectively. Under the optimized MSPE conditions, this combined scheme possesses excellent selectivity and strong anti-interference ability without any oxidation or reduction prior to capture of these two species. It is found that with a 25-fold enrichment factor, the limits of detection of As(III) and As(V) were 23.5 and 10.5 ng L^-1, respectively. To verify the reliability of the proposed protocol, a certified reference material of environmental water was analyzed, and the results for inorganic arsenic species were in close agreement with the certified values. The applicability of the combination strategy for speciation analysis of inorganic arsenic was evaluated in spiked tap, river, lake and rain water samples. Good recoveries of 89%-96% and 90%-102% were achieved for As(III) and As(V), respectively, with the relative standard deviation ranges of 3.2%-8.0% and 2.5%-7.6%. Through the characterization of functionalized magnetic nanoparticles and the optimization of MSPE experiment, it is confirmed that the existence of mercapto and amino groups on SMNPs-MPTMS and SMNPs-APTES sorbents are responsible for the extraction of As(III) and As(V), respectively, via coordination and electrostatic interactions.

Tetrasulfonate calix[4]arene modified large pore mesoporous silica microspheres: Synthesis, characterization, and application in protein separation

Effective protein adsorption by solid matrices from complex biological samples has attracted attention for broad application in biomedical field. Immobilization of calixarenes to solid supports is an essential process for their application in protein separation and purification. Silica is the most widely used support material in calixarene immobilization. With high concentration of polymer microspheres as templates, the large pore mesoporous silica microspheres with controllable, uniform size and structure were successfully synthesized and the resulting large pore mesoporous silica microspheres were modified with water-soluble tetrasulfonate calix[4]arene of unique hollow cavity-shaped structure. The tetrasulfonate calix[4]arene modified large pore mesoporous silica microspheres (SCLX4@LPMS) were characterized by diverse analytical techniques and their protein adsorption performance were also investigated. The obtained SCLX4@LPMS gave rise to an adsorption efficiency of >90% for cytochrome c and lysozyme within a wide pH range of 3.0-10.0 and possessed remarkably high adsorption capacity of cytochrome c (363.64 mg g^-1) and lysozyme (166.11 mg g^-1). The retained cytochrome c and lysozyme can be readily eluted by using phosphate buffer solution containing NaCl as a stripping reagent with the recoveries of 81% and 86% after 5 times enrichment, respectively. The SCLX4@LPMS microspheres have been applied for the selective adsorption of proteins in real samples and had the application potential in protein adsorption, drug delivery, biosensors, and other biomedical fields.

Preparation of a novel amino functionalized ion-imprinted hybrid monolithic column for the selective extraction of trace copper followed by ICP-MS detection

In this work, a novel amino functionalized Cu(II) ion-imprinted organic-inorganic hybrid monolithic column (Cu(II)-IIHMC) was prepared via one-pot co-condensation and the combination of sol-gel and ion-imprinting techniques in a fused capillary. The Cu(II)-IIHMC was used as solid phase microextraction (SPME) matrix followed by inductively coupled plasma-mass spectrometry (ICP-MS) for the analysis of trace Cu(II). The prepared Cu(II)-IIHMC has good mechanical strength, stable imprinting sites and homogeneous structure of network skeleton with large flow-through pores by optimizing the synthesis process. Under the optimized conditions, the Cu(II)-IIHMC can selectively adsorb Cu(II) with the adsorption capacity of 3.13 mg g^-1. With enrichment factor of 10-fold, the calibration curve was established in the range of 0.05-50 μg L^-1 with r² of 0.9992 and the detection limit was 0.008 μg L^-1 for Cu(II). Compared with the non-imprinted hybrid monolithic column (Cu(II)-NIHMC), the Cu(II)-IIHMC possesses better selectivity, anti-interference ability and adsorption capacity. The Cu(II)-IIHMC can specifically capture the target ion in the presence of competitive ions, with the selectivity coefficients exceeding 39.4. The protocol was validated by analyzing Certified Reference Materials of standard sediment, soil and iron ore, and the results were in good agreement with certified values. Moreover, the proposed in-tube SPME procedure can not only preconcentrate trace Cu(II), but also effectively reduce the matrix effect and powerfully eliminate the interference from the main metals in real samples. Therefore, the developed SPME-ICP-MS method with facile preparation, specific selectivity, high sensitivity and efficient analysis, was applied in the determination of trace Cu(II) in environmental and mineral samples with the recoveries of 89.8-111.8% in all spiked samples.

Carboxyl-functionalized hybrid monolithic column prepared by "thiol-ene" click reaction for noninvasive speciation analysis of chromium with inductively coupled plasma-mass spectrometry

A novel carboxyl-functionalized hybrid monolithic column was developed based on "thiol-ene" click reaction via "one-pot" by choosing mercaptosuccinic acid, γ-methyl methacrylate trimethoxysilane and tetramethoxysilane as reaction monomers. The design of the hybrid monolithic column was assisted by the comparison in computational simulation with existing carboxyl-functionalized materials. The characterization by scanning electron microscopy, energy dispersive X-ray spectroscopy, N₂ adsorption-desorption measurement, Fourier-transform infrared spectroscopy and elemental analysis showed that the carboxyl-functionalized material has the advantages of good permeability and high mechanical strength. Then, we used the prepared carboxyl-hybrid monolith column as solid phase microextraction adsorbent for separation of trace inorganic chromium species. Under pH 4.5, the hybrid monolith column can selectively enrich Cr(III) without adsorbing Cr(VI) and afterwards, Cr(III) can be eluted by 1.0 mol L^-1 HCl. The chromium speciation separation method based on carboxyl-hybrid monolith column followed by inductively coupled plasma-mass spectrometry possessed the merits of facile preparation, low cost, simple and mild extraction condition, and sensitive detection, which has been successfully applied to the separation, enrichment and detection of inorganic chromium in environmental waters.

Insight into the hydrophilic interaction liquid chromatographic retention behaviors of hydrophilic compounds on different stationary phases

In this work, the correlations between retention behavior and lipophilicity of a large set of hydrophilic neutral and ionic analytes were studied based on three hydrophilic interaction liquid chromatography (HILIC) stationary phases, including zwitterionic, crosslinked diol and triazole stationary phases. It was found that HILIC, due to the diversity of retention mechanism, is a more complex chromatography separation mode than reversed-phase liquid chromatography (RPLC) which has been widely accepted for lipophilicity assessment. Because electrostatic interactions contributed to the overall retention of the charged solutes on all three stationary phases, ion-strength of the mobile phase kept the same during the whole experiment. After the correlations between retention factor log k and water volume fraction Φ were investigated, the mixed retention model was revealed to be more suitable for HILIC retention behavior than other single models including partitioning and adsorption model. Moreover, in order to bridge the relationship between HILIC log k and lipophilicity parameter log D, net charge n_e and Abraham solvation parameter were introduced in the quantitative structure-retention relationship (QSRR) model. Although the correlation coefficients between log D and log k were still moderate, the significant improvement in correlation has made HILIC a potential choice as the complement of RPLC for log D measurement.

Cytotoxicity and toxicoproteomic analyses of human lung epithelial cells exposed to extracts of atmospheric particulate matters on PTFE filters using acetone and water

Differences of cytotoxicity associated with exposure to different extracts of atmospheric particulate matters (PMs) are still not well characterized by in vitro toxicoproteomics. In this study, in vitro cytotoxicity assays and toxicoproteomic analyses were carried out to investigate toxic effects of PM collected using polytetrafluoroethylene (PTFE) filters extracted with acetone for PM_2.1 and water for PM_2.1 and PM₁₀ on A549 human lung epithelial cells. The cytotoxicity assays based on cell viability, cell apoptosis and reactive oxygen species generation indicated that PM_2.1 extracted with acetone had the highest toxicity. iTRAQ labeling and LC-MS/MS analyses indicated that the number of differentially expressed proteins in A549 cells affected by PM_2.1 extracted with acetone was noticeably higher than that of the other two groups. Hierarchical cluster analyses showed that the influences of the extracts of PM_2.1 and PM₁₀ using water on the proteome of A549 cells were similar, whereas significantly different from the effect of PM_2.1 extracted with acetone. Pathways analyses indicated that PM_2.1 extracted with acetone influenced the expression of proteins involved in 14 pathways including glycolysis/gluconeogenesis, pentose phosphate pathway, proteasome, etc. PM_2.1 extracted with water affected the expression of proteins involved in 3 pathways including non-homologous end-joining, ribosome and endocytosis. However, PM₁₀ extracted with water affected the expression of proteins involved in only spliceosome pathway. The extracts of PM using different extractants to detach PM from PTFE filters influenced the cytotoxic effects of PM and the proteome of A549 cells. Therefore, extractants should be assessed carefully before the investigations on cytotoxicity to improve the compatibility of experimental results among research teams.

In vitro inhalation bioaccessibility procedures for lead in PM2.5 size fraction of soil assessed and optimized by in vivo-in vitro correlation

In order to assess and optimize frequently used in vitro inhalation bioaccessibility procedures for heavy metals in the inhalation risk assessment, in vivo inhalation bioavailability of Pb in simulated atmosphere fine particles (PM_2.5) from aging soils spiked with lead compounds and field soils in lead-zinc mining areas was investigated via intranasally instilled experiments with these PM_2.5 suspensions to mice and Pb bioaccessibility was extracted by using four frequently used in vitro procedures (Gamble Solution, simulated lung fluid, simulated epithelial lung fluid and artificial lysosomal fluid). Mouse exposure experiments showed that Pb was mainly distributed in the liver, kidneys, blood and spleen. Based on the kidney model, in vitro inhalation bioaccessibility of Pb extracted with optimized Gamble Solution, in which solid to liquid ratio (S/L) was optimized to 1:1000 g ml^-1 and DTPA was proved to be the key effective component, showed a strong linear relationship with its in vivo inhalation bioavailability (y = 1.07x - 3.86, R² = 0.73). Moreover, in vitro bioaccessible and bioavailable fractions of Pb were mainly from acid exchangeable and reducible fractions of Pb in PM_2.5. Altogether, optimized Gamble Solution was suggested for the analysis of in vitro bioaccessibility for risk-based assessments.

One-pot preparation of zwitterionic sulfoalkylbetaine monolith for rapid and efficient separation of lysozyme from egg white

A porous zwitterionic monolithic column was prepared to rapidly and efficiently separate lysozyme from egg white. The monolith was synthesized in a stainless steel HPLC column (5 cm × 4.6 mm i.d.) by in-situ thermal initiated co-polymerization of N,N-dimethyl-N-methacryloxyethyl-N-(3-sulfopropyl) ammonium betaine (MSA) and ethylene dimethacrylate (EDMA). Due to the combination of quaternary ammonium and sulfonic groups on the monolithic matrix in one-pot process, the hydrophobic carbon chain and hydrophilic radical were obtained, which provided multiple driving forces for neutral, basic and acidic analytes, thus mix-mode chromatography mechanism contributed to the retention of different charged proteins. Properties such as composition, morphology and stability of the MSA-co-EDMA monolithic column were characterized by various analytical methods and the results showed that the monolith has large through-pores, good hydrophilicity and permeability. The effects of mobile phase pH and ionic strength on proteins were investigated, drawing the conclusion that the main adsorption and elution mechanism of lysozyme on MSA-co-EDMA monolith was electrostatic interaction, while those of other proteins included hydrophobic, hydrophilic and electrostatic interactions. Therefore, efficient separation of lysozyme and other proteins could be successfully achieved by switching the pH of mobile phase. Lysozyme can be adsorbed using 20 mmol/L phosphate buffer (pH 7.0) and eluted with 20 mmol/L phosphate buffer (pH 2.0). To prove the practicality of the monolithic column, it was also applied in the separation of lysozyme in egg white, which means the work has the potential for further development in proteome analysis of real biological samples.

Organic molecule-assisted synthesis of Fe3O4/graphene oxide nanocomposites for selective capture of low-abundance peptides and phosphopeptides

The iron oxide nanoparticles (Fe₃O₄) were prepared by organic molecule-assisted method in aqueous solution. The facile synthetic process of Fe₃O₄ nanoparticles was conducted only by mixing FeCl₂ and 2-methylimidazole (2-MIM) without any additives. A possible growth mechanism of the Fe₃O₄ nanocrystals was proposed for this mild reaction. Then, the Fe₃O₄ nanoparticles were anchored onto graphene oxide (GO) sheets in water by ultrasound-assisted method, forming an affinity probe with strong biocompatibility. Due to the hydroxy and carboxylic groups of GO sheets, Fe₃O₄/GO probe exhibits excellent performance for enriching low-abundance hydrophilic peptides, while the Fe₃O₄ nanoparticles endure the probe with specific affinity to phosphopeptides. The analytical protocol was developed for sequential enrichment of low-abundance peptides and phosphopeptides by the affinity probe. It exhibited the sequence coverage of 26% for capture of 17 low-abundance peptides from bovine serum albumin (BSA), as well as the selectivity of 1:1:100 for phosphopeptides from α-/β-casein/BSA, and low detectable concentration of 2.5 fmol and probe reusability of 5 times for capture of phosphopeptides from α-/β-casein. Consequently, the prepared Fe₃O₄/GO material possesses excellent feature as multifunctional affinity probe for low-abundance peptides including phosphopeptides from complex biological matrices detected by matrix-assisted laser desorption ionization time-of-flight mass spectrometry.

Aggregation and dissolution of engineering nano Ag and ZnO pretreated with natural organic matters in the simulated lung biological fluids

The increasing application of engineered nanoparticles such as silver nanoparticles (nAg) and zinc oxide nanoparticles (nZnO), results in their accumulation in environmental media. The environmental natural organic matter (NOM) adsorbed by these nanoparticles may have great effects on the aggregation and dissolution of metall ions, which are interesting and important for the assessment of the inhalation risks of these airborne suspended NOM-coated nanoparticles to humans. Therefore, the aggregation and dissolution of nAg and nZnO pretreated with citric acid (CA), tartaric acid (TA) and fulvic acid (FA) in simulated lung biological fluids (artificial lysosomal fluid (ALF) and Gamble Solution) were investigated. The surface properties, morphology and size of the NOM-treated ENPs changed, but the crystalline phase was relatively stable when observed using surface-enhanced Raman scattering, transmission electron microscope, and X-ray diffraction. NOM treatment had no significant influence on the particle size of NOM-treated nAg and nZnO except for a decrease in the size of CA-treated nAg, and it could not promote the aggregation of NOM-treated nAg and nZnO except for the aggregation of TA-treated nAg in Gamble Solution or TA-treated nZnO in ALF. CA- and FA-treatments promoted the release of Zn²⁺ and Ag⁺, respectively, while no promotion was observed after TA-treatment. Therefore, NOM affects the release of Zn²⁺ and Ag⁺ from NOM-treated nAg and nZnO but does not promote the aggregation of NOM-treated nAg and nZnO, which influences the inhalation risk-based assessment.

Speciation analysis of chromium by carboxylic group functionalized mesoporous silica with inductively coupled plasma mass spectrometry

Carboxyl-group functionalized mesoporous silica (CFMS) prepared by one-pot co-condensation method was employed for the solid phase extraction (SPE) of chromium species for the first time. A new approach of SPE coupled to inductively coupled plasma mass spectrometry (ICP-MS) was thus established for the speciation of chromium in environmental water samples. The influences of pH, volume of sample, extraction time, amount of adsorbent, elution conditions, co-existing ions and adsorption capacity were investigated on adsorption or elution of chromium species. Cr(VI) was not retained on the CFMS material in the pH range of 1.0-9.0, while Cr(III) was quantitatively adsorbed at pH 5.0-9.0. The captured Cr(III) was enriched by using 1.5 mol L^-1 HNO₃ as elution solvent and detected by ICP-MS. Under the optimized SPE conditions, the maximum adsorption capacity of the CFMS for Cr(III) was 57.67 mg g^-1 and the enrichment factor was 25, with the detection limit (LOD) of 0.02 μg L^-1. The proposed protocol has been successfully applied to chromium speciation in rain, lake and river water samples, which exhibited a prospect in field separation and enrichment of chromium species in environmental waters.

In vitro inhalation/ingestion bioaccessibility, health risks, and source appointment of airborne particle-bound elements trapped in room air conditioner filters

The airborne particle-bound elements (Ca, Fe, Al, Mg, K, Na, Zn, Mn, P, Pb, Cu, Sr, Ti, Ba, Cr, Ni, As, Sb, Cd, Co, and V) trapped in room air conditioners' filters (filter dusts) during recirculating indoor air from different types of rooms were analyzed, and the objectives of this study were to assess the potential sources of those elements and their potential health risks via inhalation/ingestion exposure. Main crustal elements such as Ca, Fe, Al, Mg, and K with an average value of 60.6, 17.9, 11.3, 7.58, and 6.90 mg g^-1, respectively, are the preponderant elements, and the mean values of main toxic elements were 2230, 344, 508, 85.7, 71.5, 36.0, 8.02, and 16.9 mg kg^-1 for Zn, Cu, Pb, Cr, Ni, As, Cd, and Sb, respectively. The enrichment factors indicated the significant enrichment of Cd, Pb, Cr, Cu, Sb, and Zn in the filter dusts. Four potential sources with the contributions of 33.5, 29.1, 22.6, and 14.8%, respectively, were identified by absolute principal component scores-multiple linear regression analysis (APCS-MLR). Enrichment factor and APCS-MLR model reveal the outdoor input of toxic elements. In vitro inhalation and ingestion bioaccessibility of toxic elements showed elemental and in vitro procedure dependence. There are potential carcinogenic risks via ingestion exposure and no non-carcinogenic risks to both children and adults based on bioaccessible contents of toxic elements. This study reveals the potential health risks posed by the particle-bound elements.

Time-dependent response of A549 cells upon exposure to cadmium

Cadmium is considered one of the most harmful carcinogenic heavy metals in the human body. Although many scientists have performed research on cadmium toxicity mechanism, the toxicokinetic process of cadmium toxicity remains unclear. In the present study, the kinetic response of proteome in/and A549 cells to exposure of exogenous cadmium was profiled. A549 cells were treated with cadmium sulfate (CdSO₄ ) for different periods and expressions of proteins in cells were detected by two-dimensional gel electrophoresis. The kinetic expressions of proteins related to cadmium toxicity were further investigated by reverse transcription-polymerase chain reaction and western blotting. Intracellular cadmium accumulation and content fluctuation of several essential metals were observed after 0-24 hours of exposure by inductively coupled plasma mass spectrometry. Fifty-four protein spots showed significantly differential responses to CdSO₄ exposure at both 4.5 and 24 hours. From these proteins, four expression patterns were concluded. Their expressions always exhibited a maximum abundance ratio after CdSO₄ exposure for 24 hours. The expression of metallothionein-1 and ZIP-8, concentration of total protein, and contents of cadmium, zinc, copper, cobalt and manganese in cells also showed regular change. In synthesis, the replacement of the essential metals, the inhibition of the expression of metal storing protein and the activation of metal efflux system are involved in cadmium toxicity.

Monolithic alkylsilane column: A promising separation medium for oligonucleotides by ion-pair reversed-phase liquid chromatography

In this paper, a monolithic octadecylsilane column and particle-packed octadecylsilane columns were used to investigate the retention behaviors of oligonucleotides by ion-pair reversed-phase liquid chromatography (IP-RPLC). Results showed that, with same base composition, hairpin oligonucleotides always had weaker retention than corresponding random coil oligonucleotides on the monolithic column, but not on the particle-packed columns. In addition, the linear correlation between the retention factor k of oligonucleotides and the reciprocal of temperature (1/T), especially for hairpins, was relatively weaker on the particle-packed columns, as compared to the correlation on the monolithic column. The correlation between k and 1/T became weaker with decreasing particle size of the particle-packed columns. Moreover, results revealed that the overall retention order on the particle-packed column with small particles (3 μm) differed greatly from that on the monolithic column. In contrast, the retention order on the 10 μm particle-packed column was very close to that on the monolithic column. From the above, we inferred that oligonucleotides could keep their primary conformations unchanged when passing through the monolithic column, attributed to the special pore structures of the monolith. However, the conformations of oligonucleotides were suppressed or even destroyed when oligonucleotides passed through the particle-packed columns. This because the narrow and tortuous channels created by the stacked stationary phase particles could lead to more complex and unequable retention behaviors. Therefore, the monolithic column exhibited better retention regularity for oligonucleotides of secondary structure especially for hairpins than the particle-packed columns. It is noteworthy that the monolith-based IP-RPLC opens an intriguing prospect in accurately elucidating the retention behaviors of oligonucleotides.

Mechanism and application of halogen bond induced fluorescence enhancement and iodine molecule cleavage in solution

Halogen bonding between iodine and ciprofloxacin (I⋯N XB) induces I–I cleavage with fluorescence enhancement.

Aptamer-based thrombin assay on microfluidic platform

A facile and sensitive aptamer-based protocol has been developed for protein assay on microfluidic platform with fluorescence detection using an off-chip microarray scanner. Aptamer-functionalized magnetic beads were used to capture thrombin that binds to a second aptamer fluorescently labeled by Cy3. Experimental conditions, such as incubation time and temperature, washing time, interfering proteins, and aptamer, etc., were optimized for the microchip method. This work demonstrated there was a good relationship between fluorescence intensity and thrombin concentration in the range of 65-1000 ng/mL with the RSD less than 8%. Notably, an analysis only needs 1 μL volume of sample injection and this system can capture extremely tiny amount thrombin (0.4 fmol). This method has been successfully applied to assay of thrombin in human serum with the recovery of 79.74-95.94%.

Chromatographic method for quick estimation of DNA interaction potency of environmental pollutants

The DNA interaction potency of a chemical has been defined in the present study as the degree of a chemical's ability to interact with DNA. An estimation method of such a potency has been established based on the peak reduction of an oligonucleotide probe resulting from its interaction with chemicals based on high-performance liquid chromatography. A DNA interaction potency equivalency (PEQ) also has been proposed to evaluate the relative interaction potency of test chemicals against benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE). Five known direct DNA interaction chemicals were employed to demonstrate the method. Two known inactive chemicals were used as negative controls. Both the potency and PEQ(50) values (PEQ of testing chemical at 50% of the probe peak reduction) of these five chemicals were determined as BPDE > phenyl glycidyl ether (PGE) > tetrachlorohydroquinone (Cl4HQ) > methyl methanesulfonate (MMS) > styrene-7,8-oxide (SO). Among the reactive chemicals, MMS was found to break the oligonucleotide into smaller fragments, whereas BPDE, PGE, and SO form covalent adducts with the oligonucleotide. In the latter case, the formation of multi-chemical-oligonucleotide adducts also was observed by mass spectrometry. The method was employed to estimate the DNA interaction potency equivalency of diesel vehicle exhaust gas to demonstrate the applicability of this approach in evaluating the interaction potency of environmental pollutants in both gas and liquid phases.

Separation of three water-soluble vitamins by poly(dimethylsiloxane) microchannel electrophoresis with electrochemical detection

A method for rapid separation and sensitive determination of three water-soluble vitamins, pyridoxine, ascorbic acid (VC), and p-aminobenzoic acid (PABA) has been developed by PDMS microchannel electrophoresis integrated with amperometric detection. After treatment of the microchip with oxygen plasma, the peak shapes of the three analytes were essentially improved. Pyridoxine, VC, and PABA were well separated within only 80 s in a running buffer of 20 mM borate solution (pH 8.5). Good linearity was obtained within the concentration range of 2-200 microM for the three water-soluble vitamins. The detection limits were 1.0 microM for pyridoxine and VC, and 1.5 microM for PABA. The proposed method has been successfully applied to real human urine sample, without solid phase extraction, with recoveries of 80-122% for the three water-soluble vitamins.

Comparison of various extraction methods for policosanol from rice bran wax and establishment of chromatographic fingerprint of policosanol

A capillary gas chromatographic (GC) method has been developed for the separation and determination of policosanol components extracted from rice bran wax. A Varian CP-sil 8 CB column was employed, and an oven temperature was programmed. Gas chromatography-mass spectrometry (GC-MS) was used to identify the composition of policosanol. Quantitative analysis was carried out by means of hydrogen flame ionization detector (FID) with dinonyl phthalate (DNP) as internal standard. The results indicated that the extract obtained by dry saponification has the highest contents of octacosanol and triacontanol among extracts by all used extraction methods including dry saponification, saponification in alcohol, saponification in water (neutralized and non-neutralized), and transesterification. Meanwhile, the GC-MS fingerprint of policosanol extracted by dry saponification has been established. Euclidean distance similarity calculation showed remarkable consistency of compositions and contents among 12 batches of policosanol from a rice bran wax variety. This protocol provided a rapid and feasible method for quality control of policosanol products.

Polycation coating poly(dimethylsiloxane) capillary electrophoresis microchip for rapid separation of ascorbic acid and uric acid

A novel method for rapid separation and determination of ascorbic acid and uric acid has been developed with a polycation-modified poly(dimethylsiloxane) (PDMS) microchip under a negative-separation electric field. Just by flushing the microchip with aqueous solutions of the polycations, poly(allylamine) hydrochloride, poly(diallyldimethylammonium chloride) or chitosan could be stably coated on the PDMS microchannel surface, which resulted in a reversed electroosmotic flow and thus the rapid and efficient separation of the two substrates. Factors influencing the separation, including polycation category, buffer solution, detection potential and separation voltage, were investigated and optimized. The cheapness, rapid analysis speed and the successful analysis of human urine make this microsystem attractive for application in clinics.

Determination of morphine and codeine in urine using poly(dimethylsiloxane) microchip electrophoresis with electrochemical detection

In this paper, a poly(dimethylsiloxane) (PDMS) microchip with electrochemical (EC) detection was developed for rapid separation and detection of morphine and codeine. It was found that morphine and codeine were well separated within 140 s in phosphate buffer solution (PBS) (pH 6.6, 40 mM)-beta-cyclodextrin (beta-CD) (20 mM)-acetonitrile (30%, v/v). The detection limit was 0.2 microM for morphine and 1 microM for codeine. The protocol was successfully applied to monitoring the amount of morphine and codeine in human urine. Compared with the conventional methods, the presented method had many advantages such as lower instrument cost, less reagent consumption and shorter analysis time.

Rapid separation of strychnine and brucine on a dynamically modified poly(dimethylsiloxane) microchip followed by electrochemical detection

A method has been developed for rapidly separating and detecting strychnine and brucine using a poly(dimethysiloxane) (PDMS) microchip and electrochemical (EC) detection. PDMS microchannels dynamically modified by Brij35 are shown to be more efficient than native ones. The two analytes are well separated within 90 s in 70 mmol/L acetate buffer (pH 5.5) containing 0.01% (v/v) Brij35. Detection limits were found to be 1.0 micromol/L for strychnine and 0.2 micromol/L for brucine at S/N = 3. The method was used to determine trace strychnine and brucine in rat serum, and the results obtained correlate well with those obtained via high-performance liquid chromatography (HPLC).

Separation of caffeine and theophylline in poly(dimethylsiloxane) microchannel electrophoresis with electrochemical detection

A method for the rapid separation and sensitive determination of caffeine and theophylline was presented in poly(dimethylsiloxane) (PDMS) microchannel electrophoresis integrated with electrochemical detection. By using methanol as an additive, the peak shape and resolution were essentially improved. The analytes were well separated within only 40s in the running buffer of 5.0mM borate solution (pH 9.2) containing 10% (v/v) methanol. The linear ranges were from 6microM to 0.6mM and the detection limits were 4microM for caffeine and theophylline, respectively. The proposed method has been successfully applied to determine caffeine and theophylline in rat serum and urine.

Retention behavior ofo-phthalic, 3-nitrophthalic, and 4-nitrophthalic acids in ion-suppression reversed-phase high performance liquid chromatography using acids instead of buffers as ion-suppressors

In reversed-phase high performance liquid chromatography, the logarithm of the retention factor, log k, is usually correlated with the logarithm of the octanol-water partition coefficient, log Kow. The k and Kow of an ionizable analyte are greatly influenced by the mobile phase pH. In this paper, log kw of diprotic o-phthalic, 3-nitrophthalic, and 4-nitrophthalic acids, are obtained by extrapolation to pure aqueous fraction of mobile phase in ion-suppression reversed-phase high performance liquid chromatography with acetic acid and perchloric acid as the ion-suppressors. The Kow values of the three analytes are calibrated according to the apparent octanol-water partition coefficient, Kow, under different pH conditions, and the log K"ow values show a much better correlation with log kw than do log Kow. The influences of two ion-suppressors, acetic and perchloric acids, on the retention behavior of these diprotic acids at different pH are contrasted. An abnormal trend is found in the k vs. pHw plot of the acetic acid system when the methanol content is low. A possible reason is that acetic acid is an even stronger organic modifier than methanol, besides being an ion-suppressor. The results make the selection of mobile phase for the separation of acidic compounds by ion-suppression reversed-phase high performance liquid chromatography direct, accurate, and practical.

Morin applied in speciation of aluminium in natural waters and biological samples by reversed-phase high-performance liquid chromatography with fluorescence detection

A reversed-phase high-performance liquid chromatographic method with fluorescence detection for the determination of labile monomeric aluminium has been developed through pre-column complexation using morin as the analytical reagent. The highly fluorescent aluminium-morin complex (excitation wavelength 418 nm, emission wavelength 490 nm) was separated on a Spherisorb ODS 2 column with an eluent consisting of 30% methanol and 70% water (pH 1.0 with perchloric acid). The most remarkable point of this protocol was that only the most toxic aluminium species, that is, free aqua-aluminium ion and its monomeric hydroxo complex ions, selectively respond among various aluminium complexes. This strategy has been successfully applied to direct fractionation of the toxic aluminium in natural waters and biological samples without any pretreatment.

Determination of aluminum in environmental and biological samples by reversed-phase high-performance liquid chromatography via pre-column complexation with morin

Morin was used as a pre-column reagent for the determination of aluminum by RP-HPLC with fluorescence detection. This method has been successfully applied to direct determination of trace Al in environmental and biological samples. The response was linear from 6 x 10(-9) to 6 x 10(-5) M with a detection limit of 2 x 10(-9) M. In addition, the different Al complexes with morin were separated by the proposed HPLC procedure and their coordination ratios were depicted by molar-ratio method. The results showed that 1:1 and 2:1 Al-morin complexes formed.

Simultaneous determination of oxalic, fumaric, maleic and succinic acids in tartaric and malic acids for pharmaceutical use by ion-suppression reversed-phase high performance liquid chromatography

A reliable method for the simultaneous determination of oxalic, fumaric, maleic, and succinic acids in tartaric and malic acids for pharmaceutical use by reversed-phase ion-suppression high performance liquid chromatography is presented. HPLC was achieved on a Nova-Pak C18 column by isocratic elution using water adjusted to pH 2.10-2.15 with perchloric acid, and detection was by UV adsorption at a wavelength of 210 nm. This method was found to be superior to previous liquid chromatography as well as other classical assay, and to be an attractive choice for the analysis of these compounds.