Label-Free Direct Identification of MicroRNAs Based on a Narrow Constant-Inner-Diameter Emitter Mass Spectrometry Analysis

MicroRNAs (miRNAs) are a class of endogenous noncoding small RNAs that play important roles in various biological processes and diseases. Direct determination of miRNAs is a cost-efficient and accurate method for analysis. Herein, we established a novel method for the analysis of miRNAs based on a narrow constant-inner-diameter mass spectrometry emitter. We utilized the gravity-assisted sleeving etching method to prepare a constant-inner-diameter mass spectrometry emitter with a capillary inner diameter of 5.5 μm, coupled it with a high-voltage power supply and a high-resolution mass spectrometer, and used it for miRNA direct detection. The method showed high sensitivity and reproducibility for the analysis of four miRNAs, with a limit of detection of 100 nmol/L (170 amol) for the Hsa-miR-1290 analysis. Compared with commercial ion sources, our method achieved higher sensitivity for miRNA detection. In addition, we analyzed the total miRNAs in the A549 cells. The result indicated that both spiked and endogenous miRNAs could be quantified with high accuracy. As a result, this method offers a promising platform for highly sensitive and accurate miRNA analysis. Furthermore, this approach can be extended to the analysis of other small oligonucleotides and holds the potential for studying clinical samples and facilitating disease diagnosis.

Open tubular liquid chromatography: Recent advances and future trends

Nano-liquid chromatography (nanoLC) is gaining significant attention as a primary analytical technique across various scientific domains. Unlike conventional high-performance LC, nanoLC utilizes columns with inner diameters (i.ds.) usually ranging from 10 to 150 μm and operates at mobile phase flow rates between 10 and 1000 nl/min, offering improved chromatographic performance and detectability. Currently, most exploration of nanoLC has focused on particle-packed columns. Although open tubular LC (OTLC) can provide superior performance, optimized OTLC columns require very narrow i.ds. (< 10 μm) and demand challenging instrumentation. At the moment, these challenges have limited the success of OTLC. Nevertheless, remarkable progress has been made in developing and utilizing OTLC systems featuring narrow columns (< 2 μm). Additionally, significant efforts have been made to explore larger columns (10-75 μm i.d), demonstrating practical applicability in many situations. Due to their perceived advantages, interest in OTLC has resurged in the last two decades. This review provides an updated outlook on the latest developments in OTLC, focusing on instrumental challenges, achievements, and advancements in column technology. Moreover, it outlines selected applications that illustrate the potential of OTLC for performing targeted and untargeted studies.

Single-Cell Metabolomics-Based Strategy for Studying the Mechanisms of Drug Action

Studying the mechanisms of drug antitumor activity at the single-cell level can provide information about the responses of cell subpopulations to drug therapy, which is essential for the accurate treatment of cancer. Due to the small size of single cells and the low contents of metabolites, metabolomics-based approaches to studying the mechanisms of drug action at the single-cell level are lacking. Herein, we develop a label-free platform for studying the mechanisms of drug action based on single-cell metabolomics (sMDA-scM) by integrating intact living-cell electro-launching ionization mass spectrometry (ILCEI-MS) with metabolomics analysis. Using this platform, we reveal that non-small-cell lung cancer (NSCLC) cells treated by gefitinib can be clustered into two cell subpopulations with different metabolic responses. The glutathione metabolic pathway of the subpopulation containing 14.4% of the cells is not significantly affected by gefitinib, exhibiting certain resistance characteristics. The presence of these cells masked the judgment of whether cysteine and methionine metabolic pathway was remarkably influenced in the analysis of overall average results, revealing the heterogeneity of the response of single NSCLC cells to gefitinib treatment. The findings provide a basis for evaluating the early therapeutic effects of clinical medicines and insights for overcoming drug resistance in NSCLC subpopulations.

Application of Porous Layer Open Tubular Columns: Beyond Permanent Gases

Porous layer open tubular (PLOT) columns are traditionally built with particles that are adhered to the tubing walls. These columns have unique selectivity and provide a great alternative when gaseous samples need to be separated, but these columns also have been used to separate higher boiling point analytes. There are many different commercially available stationary phases of PLOT columns, including alumina-based columns, molecular sieves, and porous polymers. Alumina-based columns have an aluminum oxide stationary phase that is then deactivated with different salts. These columns have high capacity, superior loading ability, and produce symmetrical peaks. Molecular sieve columns are designed specifically for permanent gas separations because the columns have high retention. Porous polymer columns are highly hydrophobic, making them more applicable to analyzing a wider range of samples.

Investigation of metformin hydrochloride–bovine serum albumin interaction by narrow-bore capillary zone electrophoresis

A narrow-bore capillary (inner diameter = 2 μm) zone electrophoresis method was developed to study the interaction between metformin hydrochloride and bovine serum albumin. Free metformin hydrochloride, free bovine serum...

Intact living-cell electrolaunching ionization mass spectrometry for single-cell metabolomics

A novel living-cell mass spectrometry method allows a whole cell to enter entirely into the MS inlet and ionize with almost no sample dilution and matrix interference, which greatly improves the sensitivity of single-cell metabolite detection.

Synthesis of a novel chiral DA-TD covalent organic framework for open-tubular capillary electrochromatography enantioseparation

Herein, a novel chiral covalent organic framework, DA-TD COF, with good chemical/thermal stability was synthesized and used as a chiral stationary phase for open-tubular capillary electrochromatography enantioseparation. The DA-TD COF coated capillary exhibited excellent enantioseparation efficiency and its separation efficiency did not show an obvious decrease over 200 runs. Furthermore, the enantioseparation mechanism was studied.

An overview of open tubular liquid chromatography with a focus on the coupling with mass spectrometry for the analysis of small molecules

Open tubular liquid chromatography (OT-LC) can provide superior chromatographic performance and more favorable mass spectrometry (MS) detection conditions. These features could provide enhanced sensitivity when coupled with electrospray ionization sources (ESI-) and lead to unprecedented detection capabilities if interfaced with a highly structural informative electron ionization (EI) source. In the past, the exploitation of OT columns in liquid chromatography evolved slowly. However, the recent instrumental developments in capillary/nanoLC-MS created new opportunities in developing and applying OT-LC-MS. Currently, the analytical advantages of OT-LC-MS are mainly exploited in the fields of proteomics and biosciences analysis. Nevertheless, under the right conditions, OT-LC-MS can also offer superior chromatographic performance and enhanced sensitivity in analyzing small molecules. This review will provide an overview of the latest developments in OT-LC-MS, focusing on the wide variety of employed separation mechanisms, innovative stationary phases, emerging column fabrication technologies, and new OT formats. In the same way, the OT-LC's opportunities and shortcomings coupled to both ESI and EI will be discussed, highlighting the complementary character of those two ionization modes to expand the LC's detection boundaries in the performance of targeted and untargeted studies.

A Performance-enhanced Electroosmotic Pump with Track-etched Polycarbonate Membrane by Allylhydridopolycarbosilane Coating

Nanochannel plastic membranes are excellent materials for electroosmotic pump (EOP) elements owing to their surface charge properties, flexibility and cost-effectiveness. However, the surface charge properties of plastics are inferior to those of silicate-based materials. This paper reports a performance-enhanced EOP equipped with a glassified track-etch polycarbonate membrane (PC), which has a nanochannel surface covered by allylhydridopolycarbosilane (AHPCS). The effects of applied voltage, pH and membrane pore size on the electroosmotic flow velocity, along with a comparative study of the EOP with coated and pure membranes were investigated. It was found that when low DC voltage (10 - 40 V) was applied to both ends of the pump, the magnitude of the electroosmotic flow was linearly proportional to the voltage when the pore size of the membrane was less than 600 nm. A higher flow rate was obtained with larger pore size membranes. Compared with the uncoated film, the coated one showed faster electroosmosis velocity, with higher stability under the same conditions. For pH 10.0 buffer solution, a flow rate of 89.13 μL/min was obtained in the modified membrane-based EOP with excellent repeatability and durability, while the flow rate was only 37.89 μL/min in the bare PC membrane under 20 V. In order to demonstrate the performance of the developed EOP, the EOP was used for microcomplexometric titration to determine actual tap water hardness. The measured results were highly consistent with the results of a conventional complexometric titration methed. The EOP with an AHPCS-coated plastic membrane expanded the application range to harsh condition solutions, such as high-concentration acids or bases.

Visual and real-time imaging focusing for highly sensitive laser-induced fluorescence detection at yoctomole levels in nanocapillaries

We developed a highly sensitive laser-induced fluorescence detection system, involving visual and real-time imaging focusing instead of the use of fluorescent reagents, for the detection of analytes in nanocapillaries.

Recent advancements in open-tubular liquid chromatography and capillary electrochromatography during 2014-2018

This review critically discusses the developments on open-tubular liquid chromatography (OT-LC) and open-tubular capillary electrochromatography (OT-CEC) during 2014-2018. An appropriate Scopus search revealed 5 reviews, 4 theoretical papers on open-tubular format chromatography, 29 OT-LC articles, 68 OT-CEC articles and 4 OT-LC/OT-CEC articles, indicating a sustained interest in these areas. The open-tubular format typically uses a capillary column with inner walls that are coated with an ample layer or coating of solid stationary phase material. The ratio between the capillary internal diameter and coating thickness (CID/CT) is ideally ≤ 100 for appropriate chromatographic retention. We, therefore, approximated the CID/CT ratios and found that 22 OT-LC papers have CID/CT ratios ≤100. The other 7 OT-LC papers have CID/CT ratio >100 but have clearly demonstrated chromatographic retention. These 29 papers utilised reversed phase or ion exchange mechanisms using known or innovative solid stationary phase materials (e.g. metal organic frameworks), stationary pseudophases from ionic surfactants or porous supports. On the other hand, we found that 68 OT-CEC papers, 7 OT-LC papers and 4 OT-LC & OT-CEC papers have CID/CT ratios >100. Notably, 44 papers (42 OT-CEC and 2 OT-LC & OT-CEC) did not report the retention factor and/or effective electrophoretic mobility of analytes. Considering all covered papers, the most popular activity was on the development of new chromatographic materials as coatings. However, we encourage OT-CEC researchers to not only characterise changes in the electroosmotic flow but also verify the interaction of the analytes with the coating. In addition, the articles reported were largely driven by stationary phase or support development and not by practical applications.

Admicelles in open-tube capillaries for chromatography and electrochromatography

Surfactant bilayers or admicelles at the solid surface-liquid interface inside 50-200 μm inner diameter (i.d.) open-tube fused-silica capillaries were developed as 'soft' stationary pseudophases for the liquid chromatographic (LC) separations of neutral and charged analytes. Admicelles were formed in-situ from buffered aqueous mobile phases with cetytrimethylammonium bromide at concentrations between the critical surface aggregation concentration and critical micelle concentration, which were determined by electroosmotic flow measurements using capillary electrophoresis. There were no micelles in the mobile phase solution. Also, there was no solid phase that is classically required in LC. Pressure and voltage driven modes or open-tubular admicellar liquid chromatography (OT-AMLC) and electrochromatography, respectively were proposed based on the separation of neutral analytes. The parameters (i.e., pH, concentration of surfactant, salt, and methanol in the mobile phase and capillary i.d.) that affected the surprising chromatographic effect of admicelles at the interface were investigated. The analytical performance of OT-AMLC for small molecules were found acceptable. Applications to environmental water and biological (HepG cell line metabolism media) samples analysis with appropriate sample preparation procedures were also conducted. The use of pseudophases at the solid surface-liquid interface could be a viable solution to problems associated with the use of solid stationary or support materials in nano- and micro-liquid chromatography and electrochromatography.

Advancement of electroosmotic pump in microflow analysis: A review

This review (with 152 references) covers the progress made in the development and application of electroosmotic pumps in a period from 2009 through 2018 in microflow analysis. Following a short introduction, the review first categorizes various electroosmotic pumps into five subclasses based on the materials used for pumping: i) open channel EOP, 2) packed-column EOP, iii) porous monolith EOP, iv) porous membrane EOP, and v) other types of EOP. Pumps in each subclass are discussed. A next section covers EOP applications, primarily the applications of EOPs in micro flow analysis and micro/nano liquid chromatography. Other scattered applications are also examined. Perspectives, trends and challenges are discussed in the final section.

Recent advances in open tubular capillary liquid chromatography

This review covers advances and applications of open tubular capillary liquid chromatography (OT-LC) over the period 2007–2018.

Nano liquid chromatography columns

Nano liquid chromatography (nanoLC), with columns having an inner diameter (ID) of ≤100 μm, can provide enhanced sensitivity and enable analysis of limited samples.