Permanent gold nanoparticle coatings on polyelectrolyte multilayer modified capillaries for open-tubular capillary electrochromatography

Multilayer coatings based on gold nanoparticles and polymers with bovine serum albumin as a functional layer for the chiral separation in capillary electrochromatography

In this study, we developed physically adsorbed multi-layer coatings using poly-l-lysine or poly(diallyldimethylammonium chloride) and gold nanoparticles, which were functionalized with bovine serum albumin for the chiral separation in electrochromatography. The approach involves sequentially depositing positively charged polymers and negatively charged citrate-stabilized gold nanoparticles. By repeating this modification cycle, we created two- and four-layer coatings, which were sequentially functionalized with albumin forming three- and five-layer coatings that were finally applied for the separation of enantiomers of dl-tryptophan. The formed coatings exhibit stability across a pH range of 2-10 and feature a dense, uniform surface, as confirmed by scanning electron microscope images. The number of layers impacted nanoparticle deposition density, with five-layer coatings being denser than three-layer ones. Five-layer coatings enable baseline separation of dl-tryptophan enantiomers, whereas three-layer coatings require the presence of albumin in the background electrolyte for separation. Therefore, increasing the number of layers and gold nanoparticles density enhances albumin active center concentration on capillary walls, improving the separation of dl-tryptophan enantiomers. The five-layer coatings can be easily fabricated and possess good repeatability of analytes migration time.

Open-tubular Capillary Electrochromatography with Janus Structured Au-Fe3O4 Nanoparticles Coating as Stationary Phase

A novel Au-Fe₃O₄ nanoparticles-based capillary column was fabricated by magnetic approach for open-tubular capillary electrochromatography (OT-CEC). The bifunctional dumbbell-like Janus Au-Fe₃O₄ nanoparticles (Au-Fe₃O₄ NPs) were prepared through a hydrothermal synthesis strategy, and the morphology was characterized by transmission electron microscopy (TEM). Multilayers Au-Fe₃O₄ NPs were easily coated onto the inner surface of silica capillary by an external magnetic field to generate an Au-Fe₃O₄ NPs-based column. Compared with a bare capillary, the modified surface exhibited more stable and suppressed electroosmotic mobility. The column showed good separation efficiency for neutral analytes in the OT-CEC separation mode, with theoretical plate numbers of up to 79705 per meter for naphthalene. The successful separation of dihydroxy benzene isomers and proteins demonstrated that the column exhibits a reasonable separation performance. The reproducibility of the Au-Fe₃O₄ NPs capillary was studied, with relative standard deviations (RSD) for day-to-day and column-to-column less than 1 and 1.75%, respectively.

Preparation of a thiols β-cyclodextrin/gold nanoparticles-coated open tubular column for capillary electrochromatography enantioseparations

Inspired by the distinct chemical and physical properties of nanoparticles, here a novel open-tubular capillary electrochromatography column was prepared by electrostatic assembly of poly(diallydimethylammonium chloride) onto the inner surface of a fused-silica capillary, followed by self-adsorption of negatively charged SH-β-cyclodextrin/gold nanoparticles. The formation of the SH-β-cyclodextrin/gold nanoparticles coated capillary was confirmed and characterized by scanning electron microscopy and energy dispersive spectrometry. The results of scanning electron microscopy and energy dispersive spectrometry studies indicated that SH-β-cyclodextrin/gold nanoparticles were successfully coated on the inner wall of the capillary column. The performance of the SH-β-cyclodextrin/gold nanoparticles coated capillary was validated by the analysis of six pairs of chiral drugs, namely zopiclone, carvedilol, salbutamol, terbutaline sulfate, phenoxybenzamine hydrochloride, and ibuprofen. Satisfactory enantioseparation results were achieved, confirming the use of gold nanoparticles as the support could enhance the phase ratio of the open-tubular capillary column. Additionally, the stability and reproducibility of the SH-β-cyclodextrin/gold nanoparticles coated capillary column were also investigated. Then, this proposed method was well validated with good linearity (≥0.999), recovery (90.0-93.5%) and repeatability, and was successfully used for enantioseparation of ibuprofen in spiked plasma samples, which indicated the new column's potential usage in biological analysis.

In situ immobilization of sulfated-β-cyclodextrin as stationary phase for capillary electrochromatography enantioseparation

In this work, a novel sulfated-β-cyclodextrin (S-β-CD) coated stationary phase was prepared for open-tubular capillary electrochromatography (OT-CEC). The capillary was developed by attaching polydopamine/sulfated-β-cyclodextrin (PDA/S-β-CD) onto the gold nanoparticles (AuNPs) coated capillary which was pretreated with polydopamine. The results of scanning electron microscopy (SEM) and energy dispersive X-ray analysis spectroscopy (EDS) indicated that polydopamine/sulfated-β-cyclodextrin was successfully fixed on the gold nanoparticles coated capillary. To evaluate the performance of the prepared open tubular (OT) column, the enantioseparation was carried out by using ten chiral drugs as model analytes. Under the optimal conditions, salbutamol, terbutaline, trantinterol, tulobuterol, clorprenaline, pheniramine, chlorpheniramine, brompheniramine, isoprenaline and tolterodine were baseline separated with the resolution (Rs) values of 3.25, 1.76, 2.51, 1.89, 3.17, 2.17, 1.99, 1.72, 2.01 and 3.20, respectively. Repeatability of the column was studied, with the relative standard deviations for run-to-run, day-to-day and column-to-column lower than 5.7%.

Multi-lumen capillary based trypsin micro-reactor for the rapid digestion of proteins

In this work we evaluated a novel microreactor prepared using a surface modified, high surface-to-volume ratio multi-lumen fused silica capillary (MLC). The MLC investigated contained 126 parallel channels, each of 4 μm internal diameter. The MLC, along with conventional fused silica capillaries of 25 μm and 50 μm internal diameter, were treated by (3-aminopropyl)triethoxysilane (APTES) and then modified with gold nanoparticles, of ∼20 nm in diameter, to ultimately provide immobilisation sites for the proteolytic enzyme, trypsin. The modified capillaries and MLCs were characterised and profiled using non-invasive scanning capacitively coupled contactless conductivity detection (sC4D). The sC4D profiles confirmed a significantly higher amount of enzyme was immobilised to the MLC when compared to the fused silica capillaries, attributable to the increased surface to volume ratio. The MLC was used for dynamic protein digestion, where peptide fragments were collected and subjected to off-line chromatographic evaluation. The digestion was achieved with the MLC reactor, using a residence time of just 1.26 min, following which the HPLC peak associated with the intact protein decreased by >70%. The MLC reactors behaved similarly to the classical in vitro or in-solution approach, but provided a reduction in digestion time, and fewer peaks associated with trypsin auto-digestion, which is common using in-solution digestion. The digestion of cytochrome C using both the MLC-IMER and the in-solution approach, resulted in a sequence coverage of ∼80%. The preparation of the MLC microreactor was reproducible with <2.5% RSD between reactors (n = 3) as determined by sC4D.

Advances in covalent organic frameworks in separation science

Covalent organic frameworks (COFs) are a new class of multifunctional crystalline organic polymer constructed with organic monomers via robust covalent bonds. The unique properties such as convenient modification, low densities, large specific surface areas, good stability and permanent porosity make COFs great potential in separation science. This review shows the state-of-the art for the application of COFs and their composites in analytical separation science. COFs and their composites have been explored as promising sorbents for solid phase extraction, potential coatings for solid phase microextraction, and novel stationary phases for gas chromatography, high-performance liquid chromatography and capillary electrochromatography. The prospects of COFs for separation science are also presented, which can offer an outlook and reference for further study on the applications of COFs.

Enantioselective open-tubular capillary electrochromatography using a β-cyclodextrin–gold nanoparticles–polydopamine coating as a stationary phase

A novel β-cyclodextrin–gold nanoparticles–polydopamine modified open tubular column was prepared for the chiral separation of enantiomers in capillary electrochromatography.

Capillary electrophoresis methods for microRNAs assays: a review

MicroRNAs (miRNAs) are short noncoding RNAs that conduct important roles in many cellular processes such as development, proliferation, differentiation, and apoptosis. In particular, circulating miRNAs have been proposed as biomarkers for cancer, diabetes, cardiovascular disease, and other illnesses. Therefore, determination of miRNA expression levels in various biofluids is important for the investigation of biological processes in health and disease and for discovering their potential as new biomarkers and drug targets. Capillary electrophoresis (CE) is emerging as a useful analytical tool for analyzing miRNA because of its simple sample preparation steps and efficient resolution of a diverse size range of compounds. In particular, CE with laser-induced fluorescence detection is a promising and relatively rapidly developing tool with the potential to provide high sensitivity and specificity in the analysis of miRNAs. This paper covers a short overview of the recent developments and applications of CE systems in miRNA studies in biological and biomedical areas.

Preparation and characterization of lysine-immobilized poly(glycidyl methacrylate) nanoparticle-coated capillary for the separation of amino acids by open tubular capillary electrochromatography

In this study, poly(glycidyl methacrylate) (PGMA) nanoparticles (NPs) were prepared and chemically immobilized for the first time onto a capillary inner wall for open tubular capillary electrochromatography (OTCEC). The immobilization of PGMA NPs onto the capillary was attained by a ring-opening reaction between the NPs and an amino-silylated fused capillary inner surface. Scanning electron micrographs clearly demonstrated that the NPs were bound to the capillary inner surface in a dense monolayer. The PGMA NP-coated column was then functionalized by lysine (Lys). After fuctionalization, the capillary can afford strong anodic electroosmotic flow, especially in acidic running buffers. Separations of three amino acids (including tryptophan, tyrosine and phenylalanine) were performed in NP-modified, monolayer Lys-functionalized and bare uncoated capillaries. Results indicated that the NP-coated column can provide more retention and higher resolution for analytes due to the hydrophobic interaction between analytes and the NP-coating. Run-to-run and column-to-column reproducibilities in the separation of the amino acids using the NP-modified column were also demonstrated.

A survey of place-exchange reaction for the preparation of water-soluble gold nanoparticles

Water-soluble gold nanoparticles (AuNPs) have gained considerable attention because they offer a myriad of potential applications, especially in the fields of biology and medicine. One method to prepare such gold nanoparticles is through the well-known Murray place-exchange reaction. In this method, precursor gold nanoparticles, bearing labile ligands and with very good size distribution, are synthesized first, and then reacted with a large excess of the desired ligand. We report a comparison of the reactivity of several known precursor gold nanoparticles (citrate-stabilized, pentanethiol-stabilized, tetraoctylammonium bromide-stabilized, and 4-dimethylaminopyridine-stabilized) to several biologically relevant ligands, including amino acids, peptides, and carbohydrates. We found that citrate-stabilized and 4-dimethylaminopyridine-stabilized gold nanoparticles have broader reactivities than the other precursors studied. Citrate-stabilized gold nanoparticles are more versatile precursors because they can be prepared in a wide range of sizes and are very stable. The hydrophobic pentane-stabilized gold nanoparticles made them "inert" toward highly water-soluble ligands. Tetraoctylammonium bromide-stabilized gold nanoparticles exhibited selective reactivity, especially for small, unhindered and amphiphilic ligands. Depending on the desired ligand and size of AuNPs, a judicious selection of the available precursors can be made for use in place-exchange reactions. In preparing water-soluble AuNPs with biologically relevant ligands, the nature of the incoming ligand and the size of the AuNP should be taken into account in order to choose the most suitable place-exchange procedure.