Synthesis of boronate-decorated polyethyleneimine-grafted porous layer open tubular capillaries for enrichment of polyphenols in fruit juices

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.

Recent applications and chiral separation developments based on stationary phases in open tubular capillary electrochromatography (2019–2022)

Capillary electrochromatography (CEC) plays a significant role in chiral separation via the double separation principle, partition coefficient difference between the two phases, and electroosmotic flow-driven separation. Given the distinct properties of the inner wall stationary phase (SP), the separation ability of each SP differs from one another. Particularly, it provides large room for promising applications of open tubular capillary electrochromatography (OT-CEC). We divided the OT-CEC SPs developed over the past four years into six types: ionic liquids, nanoparticle materials, microporous materials, biomaterials, non-nanopolymers, and others, to mainly introduce their characteristics in chiral drug separation. There also added a few classic SPs that occurred within ten years as supplements to enrich the features of each SP. Additionally, we discuss their applications in metabolomics, food, cosmetics, environment, and biology as analytes in addition to chiral drugs. OT-CEC plays an increasingly significant role in chiral separation and may promote the development of capillary electrophoresis (CE) combined with other instruments in recent years, such as CE with mass spectrometry (CE/MS) and CE with ultraviolet light detector (CE/UV).

Terpolymeric platform with enhanced hydrophilicity via cysteic acid for serum intact glycopeptide analysis

A new polymeric (methyl methacrylate/ethylene glycol dimethacrylate/1,2-epoxy-5-hexene) base/matrix has been fabricated and decorated with zwitterionic hydrophilic cysteic acid (Cya) for the enrichment of intact N-glycopeptides from standards and biological samples. Terpolymer-Cya provides good enrichment efficiency, improved hydrophilicity, and selectivity by virtue of better surface area (2.09 × 10² m²/g) provided by terpolymer and the zwitterionic property offered by cysteic acid. Cysteic acid-functionalized polymeric hydrophilic interaction liquid chromatography (HILIC) sorbent enriches 35 and 24 N-linked glycopeptides via SPE (solid phase extraction) mode from tryptic digests of model glycoproteins, i.e., immunoglobulin G (IgG) and horseradish peroxidase (HRP), respectively. Zwitterionic chemistry of cysteine helps in achieving higher selectivity with BSA digest (1:200), and lower detection limit down to 100 attomoles with a complete glycosylation profile of each standard digest. The recovery of 81% and good reproducibility define the application of terpolymer-Cya for complex samples like a serum. Analysis of human serum provides a profile of 807 intact N-linked glycopeptides via nano-liquid chromatography-tandem mass spectrometry (nLC-MS/MS). To the best of our knowledge, this is the highest number of glycopeptides enriched by any HILIC sorbent. Selected glycoproteins are evaluated in link to various cancers including the breast, lung, uterine, and melanoma using single-nucleotide variances (BioMuta). This study represents the complete idea of using an in-house developed strategy as a successful tool to help analyze, relate, and answer glycoprotein-based clinical issues regarding cancers.

Construction of PEGylated boronate-affinity-oriented imprinting magnetic nanoparticles for ultrasensitive detection of ellagic acid from beverages

Molecularly imprinted polymers (MIPs) can exhibit antibody-level affinity for target molecules. However, the nonspecific adsorption of non-imprinted regions for non-target molecules limits the application range of MIPs. Herein, we fabricated PEGylated boronate-affinity-oriented ellagic acid-imprinting magnetic nanoparticles (PBEMN), which first integrated boronate-affinity-oriented surface imprinting and sequential PEGylation for small molecule-imprinted MIPs. The resultant PBEMN possess higher adsorption capacity and faster adsorption rate for template ellagic acid (EA) molecules than the non-PEGylated control. To prove the excellent performance, the PBEMN were linked with hydrophilic boronic acid-modified/fluorescein isothiocyanate-loaded graphene oxide (BFGO), because BFGO could selectively label cis-diol-containing substances by boronate-affinity and output ultrasensitive fluorescent signals. Based on a dual boronate-affinity synergy, the PBEMN first selectively captured EA molecules by boronate-affinity-oriented molecular imprinted recognition, and then the EA molecules were further labeled with BFGO through boronate-affinity. The PBEMN linked BFGO (PBPF) strategy provided ultrahigh sensitivity for EA molecules with a limit of detection of 39.1 fg mL^-1, resulting from the low nonspecific adsorption of PBEMN and the ultrasensitive fluorescence signal of BFGO. Lastly, the PBPF strategy was successfully employed in the determination of EA concentration in a spiked beverage sample with recovery and relative standard deviation in the range of 96.5 to 104.2% and 3.8 to 5.1%, respectively. This work demonstrates that the integration of boronate-affinity-oriented surface imprinting and sequential PEGylation may be a universal tool for improving the performance of MIPs.

The Use of Modified Fe3O4 Particles to Recover Polyphenolic Compounds for the Valorisation of Olive Mill Wastewater from Slovenian Istria

Olive mill waste water (OMWW), a by-product created during the processing of olive oil, contains high amounts of polyphenolic compounds. If put to further use, these polyphenolic compounds could be a valuable resource for the speciality chemical industry. In order to achieve this, isolation of the polyphenolic compounds from OMWW is needed. Several techniques for this process already exist, the most widely used of which is adsorption beds. This research describes new ways of collecting polyphenolic compounds by using unmodified iron oxide (Fe₃O₄) particles and Fe₃O₄ modified with silica gel (Fe₃O₄@C18), citric acid (Fe₃O₄@CA), and sodium dodecyl sulphate (Fe₃O₄@SDS). This approach is superior to adsorption beds since it can be used in a continuous system without clogging, while the nano-sized shapes create a high surface area for adsorption. The results of this study show that, if used in a loop system of several adsorption and desorption cycles, (un)modified Fe₃O₄ has the potential to collect high concentrations of polyphenolic compounds. A combination of different modifications of the Fe₃O₄ particles is also beneficial, as these combinations can be tailored to allow for the removal of specific polyphenolic compounds.

PEGylation of boronate-affinity-oriented surface imprinting magnetic nanoparticles with improved performance

High specific selectivity is the continuous goal of exploit glycoprotein-imprinted materials. Boronate-affinity-oriented surface imprinting can limit the heterogeneity of imprinted cavities, and PEGylation can reduce the nonspecific adsorption of imprinted materials towards non-target molecules. However, there are no reports on the integration of the above two advantages. Herein, we first integrated the boronate-affinity-oriented surface imprinting and PEGylation, and fabricated PEGylated boronate-affinity-oriented surface imprinting magnetic nanoparticles (PBSIMN) with horseradish peroxidase (HRP) as a model glycoprotein template. The successful synthesis of PBSIMN was demonstrated in detail by various characterization. Compared with non-PEGylated control, the PBSIMN showed greater adsorption capacity for HRP, and faster adsorption rate. To evaluate the improved performance, the PBSIMN was linked with hydrophilic boronic acid-modified/fluorescein isothiocyanate-loaded graphene oxide (BFGO), and used for the detection of HRP in real samples. Because PEGylation led to decrease of non-specific binding on PBSIMN, the proposed strategy provided ultrahigh sensitivity with limit of detection of 6.0 fg mL^-1 for HRP, which were an order of magnitude lower than the non-PEGylated counterparts. When spiked with 0.05, 0.5 and 5.0 mg mL^-1, recoveries of HRP were in the range of 97.4%-101.8% with relative standard deviation (RSD) no more than 5.4% for mouse serum, and between 98.2% and 103.2% with RSD no more than 5.0% human serum. This work indicates that the boronate-affinity-oriented surface imprinting and PEGylation can improve the performance of imprinted materials.

Boronate-modified polyethyleneimine dendrimer as a solid-phase extraction adsorbent for the analysis of luteolin via HPLC

Luteolin (LTL) is a flavonoid containing a cis-diol, which has significant anti-inflammatory, anti-allergic, anti-diabetic, anti-cancer and neuroprotective activities. In this work, a silver modified boric acid affinity polyvinyl imine (PEI) dendritic adsorbent (PPEI-Ag@CPBA) was prepared on polystyrene (PS) for the rapid recognition and selective separation of LTL. A thin layer of polydopamine (PDA) was formed on the surface of the substrate by self-polymerization, and a PDA-coated PS material (PS@PDA) was obtained. PEI with sufficient active amino groups was grafted onto PS@PDA to obtain a PEI-modified material (PS@PDA@PEI), then AgNO3 was reduced with NaBH4, and PS@PDA@PEI was embedded on Ag. Finally, PPEI-Ag@CPBA was obtained through the condensation reaction of PEI with 4-carboxyphenyl boric acid (CPBA). The adsorption conditions were optimized, the optimal pH and the optimum amount of adsorbent were determined, and the maximum adsorption capacity was found to be 2.49 mg g-1. This method has been successfully applied to the selective identification of LTL in peanut shell samples, and provides a practical platform for the detection of LTL in complex substrates.

In-tube solid-phase microextraction: Current trends and future perspectives

In-tube solid-phase microextraction (IT-SPME) was developed about 24 years ago as an effective sample preparation technique using an open tubular capillary column as an extraction device. IT-SPME is useful for micro-concentration, automated sample cleanup, and rapid online analysis, and can be used to determine the analytes in complex matrices simple sample processing methods such as direct sample injection or filtration. IT-SPME is usually performed in combination with high-performance liquid chromatography using an online column switching technology, in which the entire process from sample preparation to separation to data analysis is automated using the autosampler. Furthermore, IT-SPME minimizes the use of harmful organic solvents and is simple and labor-saving, making it a sustainable and environmentally friendly green analytical technique. Various operating systems and new sorbent materials have been developed to improve its extraction efficiency by, for example, enhancing its sorption capacity and selectivity. In addition, IT-SPME methods have been widely applied in environmental analysis, food analysis and bioanalysis. This review describes the present state of IT-SPME technology and summarizes its current trends and future perspectives, including method development and strategies to improve extraction efficiency.

Preparation and application of immunoaffinity in-tube solid phase microextraction column with oriented antibody-immobilized porous layer open tubular capillary for high sensitive quantification of serum extracellular domain of human epidermal growth factor receptor 2 levels

Human epidermal growth factor receptor 2 (HER2) gene expresses a transmembrane glycoprotein that is over-expressed in 15-30% breast, 3% lung, and other several digestive cancers. So HER2 is a good biomarker for tumor diagnostic and treatment monitoring. Clinically, detection of HER2 often employs invasive approaches with tissue samples, which at large extent limit its universal application. Shedding of the extracellular domain (ECD) of the HER2 (HER2-ECD) into the circulation has led to the development of a serum test of HER2-ECD as an additional approach to probe the HER2 overexpression. However, few methods were developed due to the high sensitivity required by the serum HER2-ECD determination. In this work, we prepared a novel immunoaffinity in-tube solid phase microextraction (IT-SPME) sorbent for selective enrichment of HER2-ECD. Two clinical available monoclonal antibodies against to HER2, trastuzumab and pertuzumab, were selected as immunoaffinity ligands. Porous layer open tubular capillary with oriented antibody immobilization were fabricated and systematically optimized to afford a higher extraction capacity. The capacity was reached to 120.4 μg/m, which is more than 1000 times higher than that obtained by a common method (directly antibody immobilization on a naked capillary). After sample extraction and enrichment by the IT-SPME, the eluent were determined by a particle-enhanced turbidimetric immunoassay (PETIA). Sensitive quantification of HER2-ECD by the PETIA was thereby accomplished. HER2-ECD concentrations in 82 clinical serum samples were determined by the developed IT-SPME/PETIA method, and the results were well-correlated with that by the clinical used chemiluminescence immunoassay (CLIA). Besides, the IT-SPME/PETIA method was found providing 5 times higher sensitivity than the CLIA, and 500 times higher than the PETIA without IT-SPME. The results indicate that the developed method is suitable for high-sensitive quantification of HER2-ECD in clinical samples.

Capillary electrophoresis-immobilized enzyme microreactors for acetylcholinesterase assay with surface modification by highly-homogeneous microporous layer

We propose a new capillary electrophoresis (CE)-based open-tubular immobilized enzyme microreactor (OT-IMER) and its application in acetylcholinesterase (AChE) assays. The IMER is fabricated at the capillary inlet (reactor length of ∼1 cm) with the inner surface modified by a micropore-structured layer (thickness of ∼220 nm, pore size of ∼15-20 nm). The use of IMER accomplishes the enzymatic reaction and separation/detection of the products in the same capillary within 3 min. The feasibility of the proposed method is evaluated via online analysis of the activity and inhibition of AChE enzymes. Such method exhibits good reproducibility with relative standard deviation (RSD) of less than 4% for 20 runs, and the enzyme remains over 82% of the initial activity after usage of 7 days. The IMERs are successfully applied to detect the organophosphorus pesticide, paraoxon, in three types of vegetable juice samples with a limit of detection of as low as 61 ng mL^-1. Results show that the spiked samples are in the range of 89.6-105.9% with RSD less than 2.7%, thereby indicating its satisfactory level of accurate and reliable analysis of real samples by using the proposed method. Our study indicates that, with combination of advantages of both porous-layer capillary and CE OT-IMER, the proposed method is capable to enhance enzymatic reactions and to achieve rapid analysis with simple instrumentation and operation, thus would pave the way for extensive application of CE-based IMERs in a variety of bioanalysis.

In-tube solid-phase microextraction capillary column packed with mesoporous TiO2 nanoparticles for phosphopeptide analysis

In this study, an in-tube solid-phase microextraction column packed with mesoporous TiO₂ nanoparticles, coupled with MALDI-TOF-MS, was applied to the selective enrichment and detection of phosphopeptides in complex biological samples. The mesoporous TiO₂ nanoparticles with high specific surface areas, prepared by a sol-gel and solvothermal method, were injected into the capillary using a slurry packing method with in situ polymerized monolithic segments as frits. Compared with the traditional solid-phase extraction method, the TiO₂ -packed column with an effective length of 1 cm exhibited excellent selectivity (α-casein/β-casein/BSA molar ratio of 1:1:100) and sensitivity (10 fmol of a β-casein enzymatic hydrolysis sample) for the enrichment of phosphopeptides. These performance characteristics make this system suitable for the detection of phosphorylated peptides in practical biosamples, such as nonfat milk.

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.