Size-controllable synthesis of large-size spherical 3D covalent organic frameworks as efficient on-line solid-phase extraction sorbents coupled to HPLC.

BACKGROUND: Covalent organic frameworks (COFs) have found promising applications in separation fields due to their large surface area and high adsorption capacity, but the exiting COFs can not be directly used as the packing materials of on-line solid-phase extraction (SPE) coupled to HPLC and HPLC because their nano/submicron size or irregular shapes might cause ultrahigh column back pressure and low column efficiency. To synthesize the large-size spherical COFs larger than 3 µm as sorbents might be able to address these problems, however it is still a great challenge till now. RESULTS: In this work, two large-size spherical 3D COFs (COF-320 and COF-300) were size-controllably synthesized within 10-90 µm via a two-step strategy. These two spherical COFs showed large surface area, fine crystallinity, good chemical/mechanical stability, and good reproducibility. As an application case, when used as the on-line SPE sorbents coupled to HPLC, the large-size spherical COF-320 displayed high binding capacity for bisphenol F (Qmax of 452.49 mg/g), low column back pressure (6-8 psi at flow rate of 1 mL/min), and good reusability (at least 30 cycles). The developed on-line-SPE-HPLC-UV method presented good analytical performance with enrichment factor of 667 folds, linear range of 1.0-400 ng/mL, limit of detection (LOD, S/N = 3) of 0.3 ng/mL, limit of quantification (LOQ, S/N = 10) of 1.0 ng/mL, and recoveries of 100.3-103.2 % (RSDs of 2.0-3.5 %) and 95.2-97.0 % (RSDs of 4.3-5.6 %) for tap water and lake water samples, respectively. SIGNIFICANCE: This is the first case to synthesize the large-size spherical COFs within 10-90 µm, and this work made it possible to directly use COFs as the filling materials of on-line SPE coupled to HPLC and HPLC. The developed analytical method can be potentially applied to the rapid and sensitive detection of trace bisphenol F in environmental water samples.

Large-size porous spherical 3D covalent organic framework for preconcentration of bisphenol F in water samples and orange juice.

Large-size spherical sorbents with particle size of 10-50 µm are widely applied in separation fields, however it is still a great challenge to synthesize such large-size spherical covalent organic framework (COF). In this work, a type of large-size porous 3D COF was size-controablly synthesized via a two-step strategy, in which a large-size porous 3D spherical polymer was prepared first through a Pickering emulsion polymerization using nano silica as the stabilizer, and subsequently it was converted into porous spherical 3D COF by a solvothermal method. The as-prepared porous spherical COF (COF-320 as a model) showed size-controllable uniform spherical morphology within 15-45 µm, large specific surface area, fine crystalline structure, and good chemical stability. When used as the sorbent for dispersive solid-phase extraction (d-SPE) of bisphenol F (BPF), the porous spherical COF-320 (15 µm) displayed high adsorption capacity (Qmax = 335.6 mg/g), high enrichment factor (80 folds), and good reusability (at least five cycles). By coupling the d-SPE method to HPLC, a new analytical approach was developed and successfully applied to the determination of trace BPF in two water samples, an orange juice and a standard sample with recoveries of 96.0-102.2 % (RSD = 1.1-1.5 %), 95.7-97.4 % (RSD = 1.4-4.4 %) and 98.7 % (RSD = 2.3 %), respectively. The limit of detection (S/N = 3) and limit of quantification (S/N = 10) were 0.1 and 0.3 ng/mL, respectively. The new synthesis strategy opens a viable way to prepare large-size porous spherical COFs, and the developed analytical method can be potentially applied to sensitively detect the trace BPF in water samples and beverages.

Piezocatalysis for Chemical-Mechanical Polishing of SiC: Dual Roles of t-BaTiO3 as a Piezocatalyst and an Abrasive.

Chemical mechanical polishing (CMP) offers a promising pathway to smooth third-generation semiconductors. However, it is still a challenge to reduce the use of additional oxidants or/and energy in current CMP processes. Here, a new and green atomically smoothing method: Piezocatalytic-CMP (Piezo-CMP) is reported. Investigation shows that the Piezo-CMP based on tetragonal BaTiO3 (t-BT) can polish the rough surface of a reaction sintering SiC (RS-SiC) to the ultra-smooth surface with an average surface roughness (Ra) of 0.45 nm and the rough surface of a single-crystal 4H-SiC to the atomic planarization Si and C surfaces with Ra of 0.120 and 0.157 nm, respectively. In these processes, t-BT plays a dual role of piezocatalyst and abrasive. That is, it piezo-catalytically generates in-situ active oxygen species to selectively oxidize protruding sites of SiC surface, yielding soft SiO2 , and subsequently, it acts as a usual abrasive to mechanically remove these SiO2 . This mechanism is further confirmed by density functional theory (DFT) calculation and molecular simulation. In this process, piezocatalytic oxidation is driven only by the original pressure and friction force of a conventional polishing process, thus, the piezo-CMP process do not require any additional oxidant and energy, being a green and effective polishing method.

Open tubular liquid chromatographic system for using columns with inner diameter of 2 µm. A tutorial.

We have recently demonstrated the remarkable performances of liquid chromatography (LC) using 2-µm-i.d. open tubular (OT) columns; peak capacities of 2000+ within less than three hours have been routinely obtained at an elution pressure of around 100 bar or less. However, only a small number of researchers have been involved in the research in this area; part of the reason is due to the issues associated with setting up open tubular liquid chromatography (OTLC) systems. While cautions should be taken here and there in carrying out separations, but none of the issues can inhibit us from performing OTLC separations. Therefore, we feel it desirable to write a tutorial on how to build an OTLC system. In this tutorial, we introduce the key components for the apparatus, how to construct/prepare them or where to purchase them, and how to assemble them together into a complete system. We further discuss the advantages and disadvantages of the system; we mention particularly the practical issues from using the narrow (2-µm-i.d.) columns and how to mitigate these issues.

Extension of hydrodynamic chromatography to DNA fragment sizing and quantitation.

Hydrodynamic chromatography (HDC) is a technique originally developed for separating particles. We have recently extended it to DNA fragment sizing and quantitation. In this review, we focus on this extension. After we briefly introduce the history of HDC, we present the evolution of open tubular HDC for DNA fragment sizing. We cover both the theoretical aspect and the experimental implementation of this technique. We describe various approaches to execute the separation, discuss its representative applications and provide a future perspective of this technique in the conclusion section of this review.

Thiol/methylthio-functionalized porous aromatic frameworks for simultaneous capture of aromatic pollutants and Hg(II) from water.

Simultaneously capturing organic pollutants and heavy metal can greatly reduce the water remediation time and cost, however it is still a great challenge presently. Herein, two novel thiol/methylthio-functionalized porous aromatic frameworks were synthesized as sorbents via the Sonogashira-Hagihara reaction of 1,3,5-triethynylbenzene and 1,3,5-tris(4-bromophenyl) benzene, the subsequent chloromethylation of the phenyl rings, and the final nucleophile substitution of -Cl groups by NaSH/NaSMe. These two sorbents were characterized by FT-IR spectra, energy dispersive X-ray spectra, scanning electron microscope, nitrogen adsorption analysis, thermo-gravimetric analysis, and elemental analyses. Adsorption experiments displayed that new sorbents had high uptake abilities and fast adsorption kinetics for aromatic pollutants and mercury (II) (Hg(II)). The maximum adsorption capacity (Qmax) of toluene and m-xylene on both new sorbents were 531.9-571.4 mg/g with the kinetic binding rate constants (kobs) of 0.00276-0.02422 g/mg/min, and the Qmax values of Hg(II) were 148.1-180.3 mg/g with kobs of 0.00592-0.01573 g/mg/min. Moreover, new sorbents indicated high simultaneous uptake abilities for these pollutants with good reusability, and finally they were successfully applied to the simultaneous remediation of these pollutants in two simulated sewages with high and low concentration, indicating their great practical application potential in wastewater remediation.

A multi-herb-combined remedy to overcome hyper-inflammatory response by reprogramming transcription factor profile and shaping monocyte subsets.

Traditional Chinese multi-herb-combined prescriptions usually show better performance than a single agent since a group of effective compounds interfere multiple disease-relevant targets simultaneously. Huang-Lian-Jie-Du decoction is a remedy made of four herbs that are widely used to treat oral ulcers, gingivitis, and periodontitis. However, the active ingredients and underlying mechanisms are not clear. To address these questions, we prepared a water extract solution of Huang-Lian-Jie-Du decoction (HLJDD), called it as WEH (Water Extract Solution of HLJDD), and used it to treat LPS-induced systemic inflammation in mice. We observed that WEH attenuated inflammatory responses including reducing production of cytokines, chemokines and interferons (IFNs), further attenuating emergency myelopoiesis, and preventing mice septic lethality. Upon LPS stimulation, mice pretreated with WEH increased circulating Ly6C- patrolling and splenic Ly6C+ inflammatory monocytes. The acute myelopoiesis related transcriptional factor profile was rearranged by WEH. Mechanistically we confirmed that WEH interrupted LPS/TLR4/CD14 signaling-mediated downstream signaling pathways through its nine principal ingredients, which blocked LPS stimulated divergent signaling cascades, such as activation of NF-κB, p38 MAPK, and ERK1/2. We conclude that the old remedy blunts LPS-induced "danger" signal recognition and transduction process at multiple sites. To translate our findings into clinical applications, we refined the crude extract into a pure multicomponent drug by directly mixing these nine chemical entities, which completely reproduced the effect of protecting mice from lethal septic shock. Finally, we reduced a large number of compounds within a multi-herb water extract to seven-chemical combination that exhibited superior therapeutic efficacy compared with WEH.

Liquid Chromatographic Separation Using a 2 µm i.d. Open Tubular Column at Elevated Temperature.

We have experimentally demonstrated the extraordinarily high resolving power of liquid chromatography (LC) using a narrow open tubular (OT) column. In this work, we show that we can further increase its efficiency, peak capacity, and separation speed by elevating the operation (or column) temperature; all of these three numbers can be improved without mutual compromises. We use a mixture of five amino acids as a sample and show that we can increase the efficiency by 34%-260% and the separation speeds by 7%-10% by raising the operation temperature from 30 to 70 °C. When we use a 2 µm i.d. × 80 cm in length OT column coated with OTMS at a temperature of 70 °C, we can frequently obtain peak capacities of 700-800 within 20-30 min for separating cytochrome C digests. By increasing the column length to 160 cm, we can obtain a peak capacity of 2720 within 143 min for separating a complex peptide sample. This peak capacity is the highest peak capacity to date for one-dimensional LC separations. Importantly, heating the column is easy to implement and does not cost much, and many commercial LC systems already have compartments to control column temperatures. Running LC using a narrow OT column at an elevated temperature should broaden the applications of OT-LC in chemical and biochemical analyses.

Recent advances and applications of molecularly imprinted polymers in solid-phase extraction for real sample analysis.

Sample pretreatment is essential for the analysis of complicated real samples due to their complex matrices and low analyte concentrations. Among all sample pretreatment methods, solid-phase extraction is arguably the most frequently used one. However, the majority of available solid-phase extraction adsorbents suffer from limited selectivity. Molecularly imprinted polymers are a type of tailor-made artificial antibodies and receptors with specific recognition sites for target molecules. Using molecularly imprinted polymers instead of conventional adsorbents can greatly improve the selectivity of solid-phase extraction, and therefore molecularly imprinted polymer-based solid-phase extraction has been widely applied to separation, clean up and/or preconcentration of target analytes in various kinds of real samples. In this article, after a brief introduction, the recent developments and applications of molecularly imprinted polymer-based solid-phase extraction for determination of different analytes in complicated real samples during the 2015-2020 are reviewed systematically, including the solid-phase extraction modes, molecularly imprinted adsorbent types and their preparations, and the practical applications of solid-phase extraction to various real samples (environmental, food, biological, and pharmaceutical samples). Finally, the challenges and opportunities of using molecularly imprinted polymer-based solid-phase extraction for real sample analysis are discussed.

Performing flow injection chromatography using a narrow open tubular column.

Flow injection chromatography (FIC) or sequential injection chromatography (SIC) is a low-pressure liquid chromatography technique that uses flow injection or sequential injection hardware. Due to the constraints of this hardware, the separation resolution is low; often no more than 3-5 components are resolved. We have recently demonstrated the excellent resolving power of narrow open tubular (OT) columns for various biomolecules, and only moderate elution pressures are needed to carry out these separations. In this paper, we incorporate a narrow OT column with FIC and construct an FIC system using a pressure chamber and two injection valves to implement gradient elution. The resultant system not only improves the resolution but also reduces the system cost. When we use the system to separate peptides from trypsin-digested cytochrome C, we can resolve dozens of peptides (with resolutions of 0.5 or greater) at a speed of 12 samples per hour. When we use this system to separate a mixture containing 3 amino acids, we can base-line resolve these compounds at a speed of 1800 sample per hour.

Picoflow Liquid Chromatography-Mass Spectrometry for Ultrasensitive Bottom-Up Proteomics Using 2-µm-i.d. Open Tubular Columns.

In many areas of application, key objectives of chemical separation and analysis are to minimize the sample quantity while maximizing the chemical information obtained. Increasing measurement sensitivity is especially critical for proteomics research, especially when processing trace samples and where multiple measurements are desired. A rich collection of technologies has been developed, but the resulting sensitivity remains insufficient for achieving in-depth coverage of proteomic samples as small as single cells. Here, we combine picoliter-scale liquid chromatography (picoLC) with mass spectrometry (MS) to address this issue. The picoLC employs a 2-µm-i.d. open tubular column to reduce the sample input needed to greatly increase the sensitivity achieved using electrospray ionization (ESI) with MS. With this picoLC-MS system, we show that we can identify ∼1000 proteins reliably using only 75 pg of tryptic peptides, representing a 10-100-fold sensitivity improvement compared with the state-of-the-art liquid chromatography (LC) or capillary electrophoresis (CE)-MS methods. PicoLC-MS extends the limit of separation science and is expected to be a powerful tool for single cell proteomics.

Facile synthesis of metal-organic framework-derived SiW12@Co3O4 and its peroxidase-like activity in colorimetric assay.

Over the past few years, artificial enzymes have attracted enormous attention due to their high stabilities and cost-effective productions. In this work, metal-organic framework-derived SiW12@Co3O4 was synthesized in large quantities by stirring the mixture at ambient temperature and calcination. The obtained SiW12@Co3O4 exhibited a highly inherent peroxidase-like activity and excellent stability. Kinetic studies demonstrated that the synthesized SiW12@Co3O4 had a strong binding affinity to 3,3',5,5'-tetramethylbenzidine (TMB), stronger than HRP had. Specifically, the peroxidase-like activity of SiW12@Co3O4 in an aqueous solution was well maintained after incubation at an elevated temperature, at an extreme pH and for a long time. A SiW12@Co3O4-based method was further developed for H2O2 and one-pot glucose detection with good sensitivity and reliability. The facile synthesis approach is expected to facilitate the practical use of metal-organic frameworks and their derivatives as enzyme mimics in the future.

Ultrafast Gradient Separation with Narrow Open Tubular Liquid Chromatography.

Separation speed and resolution are two important figures of merit in chromatography. Often, one gains the speed at the cost of the resolution, and vice versa. Scientists have employed short-packed columns for ultrafast separations but encountered challenges such as limited mobile phase velocity, extra-column effect caused band broadening, and column packing difficulty. We have recently demonstrated ultrahigh resolutions of narrow open tubular liquid chromatography (NOTLC); this allows us to trade some of the resolution for speed. In this work, we explored NOTLC for ultrafast LC separations. We used a 2.7 cm (effective length) narrow open tubular (NOT) column and showed a baseline separation of 6 amino acids in less than 700 ms. Ways to further increase the speed were discussed. Using short narrow open tubular (NOT) columns to perform ultrafast separation we overcame the challenges from using short packed columns. To demonstrate the feasibility of using this ultrafast separation technique for practical applications, we separated complex protein digests; peptides were nicely resolved in ∼1 min.

Experimentally Validating Open Tubular Liquid Chromatography for a Peak Capacity of 2000 in 3 h.

The advancements in life science research mandate effective tools capable of analyzing large numbers of samples with low quantities and high complexities. As an essential analytical tool for this research, liquid chromatography (LC) encounters an ever-increasing demand for enhanced resolving power, accelerated analysis speed, and reduced limit of detection. Although theoretical studies have indicated that open tubular (OT) columns can produce superior resolving power under comparable elution pressures and analysis times, ultrahigh-resolution and ultrahigh-speed open tubular liquid chromatography (OTLC) separations have never been reported. Here we present experimental results to demonstrate the predicted potential of this technique. We use a 2 µm i.d. × 75 cm long OT column coated with trimethoxy(octadecyl)silane for separating pepsin/trypsin digested E. coli lysates and routinely produce exceptionally high peak capacities (e.g., 1900-2000 in 3-5 h). We reduce the column length to 2.7 cm and exhibit the capability of OTLC for ultrafast separations. Under an elution pressure of 227.5 bar, we complete the separation of six amino acids in ∼800 ms and resolve these compounds within ∼400 ms. In addition, we show that OTLC has low attomole limits of detection (LOD) and each separation requires samples of only a few picoliters. Importantly, no ultrahigh elution pressures are required. With the ultrahigh resolution, ultrahigh speed, low LOD, and low sample volume requirement, OTLC can potentially be a powerful tool for biotech research, especially single cell analysis.

Smartphone assisted immunodetection of HIV p24 antigen using reusable, centrifugal microchannel array chip.

An integrated immunodetection platform employing a simple, reusable, centrifugal microchannel array chip and a smartphone as detection unit was developed. The applicability of the platform to the detection of HIV p24 antigen was demonstrated. The microchip was made of polycarbonate and contained 4 × 8 zigzag microchannels. After the monoclonal antibody of HIV p24 was adsorbed onto the channel surfaces, HIV p24 was introduced into the microchannel to react with the antibody. A biotin linked polyclonal antibody was then brought in to react with HIV p24, and SP80 (containing streptavidin and horseradish peroxidase) was introduced to react with the biotin. Finally, a solution containing 3,3',5,5'-tetramethylbenzidine and other reagents was passed through the above channels, horseradish peroxidase catalyzed the oxidation of tetramethylbenzidine (to 3,3',5,5'- tetramethylbenzidine diamine) forming a dark color. The color intensity, indicating HIV p24 antigen quantity, was then photographed via a smartphone, and the color of each microchannel was processed via a computer to determine the HIV p24 antigen concentration. Under the optimized conditions, limits of detection (LODs) of 0.17 ng/ml and 0.11 ng/ml were obtained for p24 antigen in a buffer solution and human serum, respectively. Channel washing/rinsing was implemented via a centrifugal force. An economic portable centrifugal device that could accommodate up to 4 microchips was assembled, and multi-step solution loading and rinsing involved in this sandwich immunoassay were performed conveniently. The microchip could be reused after a simple regeneration process. The low-cost polycarbonate microchip and centrifugal device together with the simple but efficient operation make the method a promising tool for HIV screening in resource limited areas.

On-column and gradient focusing-induced high-resolution separation in narrow open tubular liquid chromatography and a simple and economic approach for pico-gradient separation.

We have recently obtained extraordinarily high efficiencies and sharp peaks using narrow open tubular (OT) columns for liquid chromatographic separations. On-column focusing is commonly observed in liquid chromatography, but this effect alone could not satisfactorily explain the sharpness of these peaks. In this work we investigated the reasons that could have led to the peak sharpness. We hypothesized initially that analytes confined in a narrow OT column might have significantly reduced analyte diffusivities and the reduced diffusivities consequently resulted in the peak sharpness. This hypothesis was invalidated immediately after we measured the diffusion coefficients and did not notice any noticeable diffusivity increases of the analytes inside such columns. We then designed an experiment and revealed a "re-focusing effect". Investigation of this re-focusing effect eventually led us to the observation of a gradient focusing caused by the composition difference between the eluent and the sample matrix. It was this gradient focusing that had contributed primarily to the peak sharpness. On the basis of this insightful understanding, we further developed a simple and economic approach to perform pico-gradient narrow open tubular liquid chromatographic separations.

Cam-based vibration-counter-balanced laser-induced fluorescence scanner for multiplexed capillary detection.

Laser-induced fluorescence (LIF) rotary scanners have been successfully used for multiplexed capillary detection. However, these scanners have a limitation that the capillaries have to be assembled in a circular format, which can be inconvenient for certain applications. A linear LIF scanner works well for flat parallel capillary arrays, but motor accelerations/decelerations (for direction changes) and scanning head vibrations introduce high instrumental noises. The number of capillaries that can be scanned by a linear scanner is limited because of the above constraints. We have constructed a cam-based scanner in an attempt to address these issues. A cam-based scanner eliminates the motor accelerations/decelerations but not the scanning head vibrations. In this work, we attach a second scanning head to the cam on the opposite side of the first scanning head to counter-balance the mechanical vibrations. With this modification, we improve the limit of detection by more than 3 times (from 69 pM to 20 pM fluorescein). We also increase the capillary number capacity by more than 6 times; the total number of capillaries that can be scanned is 426 if 150-µm-o.d. capillaries are used or 320 if 200-µm-o.d. capillaries are used. To demonstrate the utility of this instrument, we assemble a 99-capillary array on one capillary holder and perform capillary electrophoresis of two fluorescent dyes; separations in all capillaries are successfully monitored simultaneously. We also apply it for detecting fluorescently labeled proteins resolved by 24 s-dimension capillaries in a chip-capillary hybrid device; two-dimensional separation results are nicely produced.

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.

Monolith columns for liquid chromatographic separations of intact proteins: A review of recent advances and applications.

In this article we survey 256 references (with an emphasis on the papers published in the past decade) on monolithic columns for intact protein separation. Protein enrichment and purification are included in the broadly defined separation. After a brief introduction, we describe the types of monolithic columns and modes of chromatographic separations employed for protein separations. While the majority of the work is still in the research and development phase, papers have been published toward utilizing monolithic columns for practical applications. We survey these papers as well in this review. Characteristics of selected methods along with their pros and cons will also be discussed.