High-Resolution Micro-object Separation by Rotating Magnetic Chromatography.

The development of new technologies for the separation, selection, and isolation of microparticles such as rare target cells, circulating tumor cells, cancer stem cells, and immune cells has become increasingly important in the last few years. Microparticle separation technologies are usually applied to the analysis of disease-associated cells, but these procedures often face a cell separation problem that is often insufficient for single specific cell analyses. To overcome these limitations, a highly accurate size-based microparticle separation technique, herein called "rotating magnetic chromatography", is proposed in this work. Magnetic nanoparticles, placed in a microfluidic separation channel, are forced to move in well-defined trajectories by an external magnetic field, colliding with microparticles that are in this way separated on the basis of their dimensions with high accuracy and reproducibility. The method was optimized by using fluorescein isothiocyanate-modified polystyrene particles (chosen as a reference standard) and then applied to the analysis of cancer cells like Hep-3B and SK-Hep-1, allowing their fast and high-resolution chromatographic separation as a function of their dimensions. Due to its unmatched sub-micrometer cell separation capabilities, RMC can be considered a break-through technique that can unlock new perspectives in different scientific fields, that is, in medical oncology.

A reciprocating magnetic field assisted on-line solid-phase extraction coupled with liquid chromatography-tandem mass spectrometry determination of trace tetracyclines in water.

A reciprocating magnetic-field-assisted on-line solid-phase extraction (RMF-SPE) method coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been developed for continuous enrichment of trace chemicals in water samples. Under the assist of the reciprocating magnetic field, carboxyl-modified magnetic nanoparticles (CMNPs) were applied to prepare microcolumn with even dispersion by periodical motion, instead of traditional compaction as extraction sorbents. When water sample passed through the extraction region, dynamic sorbents generates an advantage of countless contacts between sorbents and targets without blocking for high efficient extraction. In this study, the on-line RMF-SPE method was established and evaluated by determination of tetracyclines (TCs) from water samples as analysis models, including oxytetracycline, tetracycline, demeclocycline, metacycline, chlortetracycline, and doxycycline. Experimental conditions have been investigated such as flow rate, reciprocating speed, elution time, and so on. The method showed high relative recovery (95.4-111.1%) and good repeatability with RSD from 2.9 to 11.8% for the 200 mL water sample. The linearity range, limits of detection (LODs), and limits of quantification (LOQs) were 0.5-200 µg L-1 (chlortetracycline) and 0.1-200 µg L-1 (other TCs), 12.0-74.1 ng L-1, and 40.1-247 ng L-1, respectively. More importantly, the high enrichment factors in a range of 204 (chlortetracycline) to 276 (demeclocycline) indicate that a small amount of dynamic sorbents (only 10 mg) give full play to extraction attributing to the reciprocating movement, especially for trace analysis and continuous extraction, which is significant for water samples from sea, river and domestic waste.

Open-tubular radially cyclical electric field-flow fractionation (OTR-CyElFFF): an online concentric distribution strategy for simultaneous separation of microparticles.

An open-tubular radially cyclical electric field-flow fractionation technique which achieves the online separation of microparticles in a functional annular channel is proposed in this study. The system was set up by using a stainless steel tube and a platinum wire modified with ionic liquid/mesoporous silica materials as the external and internal electrodes. The feasibility for online separation of various particles was experimentally demonstrated. Particles in the channel were affected by a radial electric field and field-flow fractionation (FFF). On the cross section, different particles showed distinctive migration distances depending on their own properties and the different magnitudes of forces being exerted. The same kind of particles form an annular distribution within the same annulus while different particles form annular distributions at varied concentric annuli through electrophoresis. Under a laminar flow of FFF, different sizes of particles formed a conical arrangement within the annular separation channel. With the joint influence of electric field and flow field, different trajectories were obtained and the particles were eventually separated. Voltage, frequency and duty cycle value are the main parameters affecting the separation of particles. By adjusting these parameters, particles migrate in a zigzag trajectory on one side of the electrodes (mode I) and reach both sides of the electrodes (mode II). Six polystyrene particles were completely separated with high resolution within several minutes. Our system offers numerous advantages of label-free, high-resolution and online separation without tedious operations, and it is a promising tool for the effective separation of various micro-objects.

Magnetic separation coupled with high-performance liquid chromatography-mass spectrometry for rapid separation and determination of lignans in Schisandra chinensis.

Despite the strong antihepatotoxic, antioxidant, and antitumor properties of lignans from Schisandra chinensis, their applications in new drug development, bioscience and functional foods, etc. are limited because of their low abundance and complex coextractions. In this study, a magnetic separation method has been developed based on polyethylenimine-modified magnetic nanoparticles to rapidly and effectively separate and purify the lignans from S. chinensis crude extracts through cation-π interaction and electrostatic adsorption. The magnetic nanoparticles were characterized by transmission electron microscopy, vibrating sample magnetometry, Fourier transform infrared spectroscopy, and X-ray diffraction. Polyethylenimine-modified magnetic nanoparticles showed a spherical-shaped morphology and the average size was about 10 nm with superparamagnetism. Under the pH 7.4, polyethylenimine modified magnetic nanoparticles can remove a lot of coextracts. The range of detection limits and quantification limits was 0.27-0.34 and 0.89-1.13 ng/mL, respectively. Compared with other common methods, the magnetic separation method proposed in this study is much simpler and more effective through both strong cation-π interaction and electrostatic interaction.