Bidimensional Dynamic Magnetic Levitation: Sequential Separation of Microplastics by Density and Size.

There is a current gap in sample preparation techniques integrating the separation of microplastics according to their different material types and particle sizes. We describe herein the Bidimensional Dynamic Magnetic Levitation (2D-MagLev) technique, enabling the resolution of mixtures of microplastics sorting them by plastic type and particle size. Separations are carried out in a bespoke flow cell sandwiched between two ring magnets and connected to programmable pumps for flow control. The first separation dimension is based on sequential increases in the concentration of a paramagnetic salt (MnCl2), enabling magnetic levitation of microplastics with determined densities. The second dimension is based on increasing flow rate gradients and maintaining constant MnCl2 concentrations. This fractionates the magnetically levitating microplastics according to their different particle sizes. Microplastics are therefore collected by their increasing density, and the particles corresponding to each density are fractionated from smaller to larger size. Using polyethylene microspheres with defined density (1.03-1.13 g cm-3) and size (98-390 µm) as microplastic mimicking materials, we investigated their optimum threshold velocities for their size fractionation, potential effects of medium viscosity and sample loading, and types of flow rate gradients (linear, step). Performing a separation using a combination of step gradients in both MnCl2 concentration and flow rate, mixtures comprising microplastics of two different densities and three different particle sizes were separated. 2D-MagLev is simple, fast, versatile, and robust, opening new avenues to facilitate the study of the environmental presence and impact of microplastics.

Nanoplastic Sample Cleanup by Micro-Electromembrane Extraction across Free Liquid Membranes.

Sample preparation techniques enabling the separation and cleanup of nanoplastics removing other components present in complex sample matrices are scarce. Herein, micro-electromembrane extraction (µ-EME) has been explored for this purpose based on the extraction of nanoplastic particles across a free liquid membrane (FLM). The extraction unit is based on a perfluoroalkoxy tube sequentially filled with the acceptor solution (20 µL 5 mM phosphate buffer, pH 10.7), FLM (10 µL 1-pentanol), and donor solution (20 µL sample/standard solution). Sulfonated polystyrene beads (200 nm particle size) were selected as a model mimicking negatively charged nanoplastics. At 700 V, nanoplastics transferred from the donor solution into the FLM before moving across the FLM into the acceptor solution. Quantitative nanoplastic measurements after µ-EME were performed by injecting the acceptor solution into a capillary electrophoresis system with diode array detection. µ-EME allowed the rapid nanoplastic sample cleanup, requiring an extraction time of just 90 s and obtaining a nanoplastic transfer yield through the FLM of 60% with RSD values below 9%. The µ-EME technique enabled the efficient sample matrix cleanup of nanoplastics spiked in different tea matrices. Nanoplastic transfer yield through the FLM for black tea and flavored tea matrices were 56% and 47%, respectively, with complete sample matrix removal of UV-absorbing compounds.

Tailoring molecularly imprinted polymer on titanium-multiwalled carbon nanotube functionalized gold electrode for enhanced chlorophyll determination in microalgae health assessment.

A unique method for determining chlorophyll content in microalgae is devised employing a gold interdigitated electrode (G-IDE) with a 10-µm gap, augmented by a nano-molecularly imprinted polymer (nano-MIP) and a titanium dioxide/multiwalled carbon nanotube (TiO2/MWCNT) nanocomposite. The nano-MIP, produced using chlorophyll template voids, successfully trapped chlorophyll, while the TiO2/MWCNT nanocomposite, synthesized by the sol-gel technique, exhibited a consistent distribution and anatase crystalline structure. The rebinding of procured chlorophyll powder, which was used as a template for nano-MIP synthesis, was identified with a high determination coefficient (R2 = 0.9857). By combining the TiO2/MWCNT nanocomposite with nano-MIP, the G-IDE sensing method achieved a slightly better R2 value of 0.9892 for detecting chlorophyll in microalgae. The presented G-IDE sensor showed a significant threefold enhancement in chlorophyll detection compared with commercially available chlorophyll powder. It had a detection limit of 0.917 mL (v/v) and a linear range that spanned from 10-6 to 1 mL. The effectiveness of the sensor in detecting chlorophyll in microalgae was confirmed through validation of its repeatability and reusability.

Electrokinetic Extraction of Doxorubicin from Biological Fluids by Polymer Inclusion Membrane Sampling Probe.

A polymer inclusion membrane (PIM) based sampling probe was developed for electrokinetic extraction of drugs from biological fluids. The probe was fabricated by dip-coating a nonconductive glass capillary tube in a homogeneous PIM solution for three cycles. The PIM solution comprised cellulose triacetate (CTA), 2-nitrophenyl octyl ether (NPOE), and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [EMIM][NTf2] in a ratio of 5:4:2. The developed probe electrokinetically extracted doxorubicin from human plasma, human serum, and dried blood spot (DBS). The practicability and reliability of the electrokinetic extraction were evaluated by LC-MS/MS to quantify the desorption of extracted doxorubicin. Under the optimized conditions, a quantification limit of 0.2-2 ng/mL was achieved for the three biological samples. The probe was further integrated into a portable battery-powered device for safe low-voltage (36 V) electrokinetic extraction. The developed technique is envisioned to provide a more efficient analytical workflow in the laboratory.

Biphasic Magnetic Levitation to Detect Organic Pollutants on Microplastics.

Microplastics have the potential to adsorb organic pollutants due to their lipophilic nature. Evaluating the distribution of multiple organic pollutants in different types of microplastics coexisting in a sample is a strenuous and challenging analytical task. Here, we report position-dependent microplastic trapping in a biphasic medium comprising a paramagnetic aqueous donor phase containing the mixed microplastics and a diamagnetic organic acceptor phase. Depending on the relative height of the sample container positioned in a magnetic field, the selective density-dependent trapping of microplastics is achieved. Concurrently, the organic pollutants adsorbed on the microplastics are desorbed in the organic acceptor phase, which is easily solidified, separated, and transferred for organic pollutant determination by high-performance liquid chromatography. This facilitates analytical studies involving multiple organic pollutants distributed in solid heterogeneous mixtures.

Magnetism-Assisted Density Gradient Separation of Microplastics.

A versatile method for the efficient separation of different types of microplastics from particle mixtures is presented. Magnetism-assisted density gradient separation (Mag-DG-Sep) relies on a bespoke separation cell connected to a gradient pump and located between two like-pole-facing neodymium magnets. In Mag-DG-Sep, particle mixtures initially sunk in water are subjected to a gradient of increasing concentration of MnCl2, enabling the sequential suspension and collection of particles with different densities. The suspension process is assisted by the paramagnetism of the MnCl2 solution placed between the two magnets, which contributes to focusing the ascending particles from the bottom of the separation cell to the outlet, thus enhancing the resolution of the separation process. To demonstrate the concept, a mixture of polyethylene (PE) polymer particles with a similar size range (180-212 µm) but different densities (ca. 0.98, 1.025, 1.08, and 1.35 g cm-3) was selectively separated in a single Mag-DG-Sep run. These particles were also efficiently separated when mixed with other types of particles, such as glass or soil. A generic linear MnCl2 gradient can be directly applied for sample screening covering a broad range of densities (0.98-2.20 g cm-3), while steps can be introduced in the gradient, increasing the separation resolution of particles with close densities (1.025-1.08 g cm-3). As a proof-of-concept application, Mag-DG-Sep facilitated sample preparation of microplastics present in a soil sample prior to their examination by attenuated total reflection Fourier-transform infrared spectroscopy.

Isotachophoresis for rapid transformation of Escherichia coli.

A frequent limitation of electroporation (EP) and chemical transformation (CT) are the need of tedious and time-consuming procedures for inducing transformation competence, the substantial number of cells required, and the low transformation yields typically achieved. Here, we show a new and rapid electrokinetic method for transformation of small number of noncompetent Escherichia coli TOP10 cells (2-3 × 105 ) at room temperature. Escherichia coli TOP10 cells and plasmid DNA are sequentially injected into a 50 µm ID capillary and focused into 11.5 nL by isotachophoresis (ITP) induced by application of high DC voltage (-16 kV). Through ITP, a large excess of plasmid DNA is brought in contact with the cell surface, with the contact time adjusted by application of a counter-pressure (1.3 psi) opposing the ITP movement. The transformation rate was more than 1000-fold higher compared to EP and CT at survival rates greater than 60%.

An Open Microfluidic Chip for Continuous Sampling of Solute from a Turbulent Particle Suspension.

High solids content complicates in situ analysis of chemical processing, biological suspensions, and environmental streams. In most cases, analytical methods require at least one pre-treatment step of a small volume of sample before a particle-free fluid can be analyzed. We have developed a continuous in situ sampler that can "sip" particle-free solution from a turbulent high solids content stream (a slurry). An open microfluidic chip with an extended slit opening shields the internal laminar flow from the turbulence outside. Unlike other open chips, our chip does not require close proximity to a solid surface and operates in turbulent environments for hours without maintenance. Two applications are demonstrated: monitoring FeIII in a stirred slurry of mixed ore particles at high solids loading (4 %wt) and paracetamol tablet dissolution profiles for two different formulations.

The influence of electrolyte concentration on nanofractures fabricated in a 3D-printed microfluidic device by controlled dielectric breakdown.

A three-dimensional-printed microfluidic device made of a thermoplastic material was used to study the creation of molecular filters by controlled dielectric breakdown. The device was made from acrylonitrile butadiene styrene by a fused deposition modeling three-dimensional printer and consisted of two V-shaped sample compartments separated by 750 µm of extruded plastic gap. Nanofractures were formed in the thin piece of acrylonitrile butadiene styrene by controlled dielectric breakdown by application voltage of 15-20 kV with the voltage terminated when reaching a defined current threshold. Variation of the size of the nanofractures was achieved by both variation of the current threshold and by variation of the ionic strength of the electrolyte used for breakdown. Electrophoretic transport of two proteins, R-phycoerythrin (RPE; <10 nm in size) and fluorescamine-labeled BSA (f-BSA; 2-4 nm), was used to monitor the size and transport properties of the nanofractures. Using 1 mM phosphate buffer, both RPE and f-BSA passed through the nanofractures when the current threshold was set to 25 µA. However, when the threshold was lowered to 10 µA or lower, RPE was restricted from moving through the nanofractures. When we increased the electrolyte concentration during breakdown from 1 to 10 mM phosphate buffer, BSA passed but RPE was blocked when the threshold was equal to, or lower than, 25 µA. This demonstrates that nanofracture size (pore area) is directly related to the breakdown current threshold but inversely related to the concentration of the electrolyte used for the breakdown process.

In-Syringe Electrokinetic Protein Removal from Biological Samples prior to Electrospray Ionization Mass Spectrometry.

Here, an electrokinetic extraction (EkE) syringe is presented allowing for on-line electrokinetic removal of serum proteins before ESI-MS. The proposed concept is demonstrated by the determination of pharmaceuticals from human serum within minutes, with sample preparation limited to a 5× dilution of the sample in the background electrolyte (BGE) and application of voltage, both of which can be performed in-syringe. Signal enhancements of 3.6-32 fold relative to direct infusion of diluted serum and up to 10.8 fold enhancement, were obtained for basic and acidic pharmaceuticals, respectively. Linear correlations for the basic drugs by EkE-ESI-MS/MS were achieved, covering the necessary clinical range with LOQs of 5.3, 7.8, 6.1, and 17.8 ng mL-1 for clomipramine, chlorphenamine, pindolol, and atenolol, respectively. For the acidic drugs, the EkE-ESI-MS LOQs were 3.1 µg mL-1 and 2.9 µg mL-1 for naproxen and paracetamol, respectively. The EkE-ESI-MS and EkE-ESI-MS/MS methods showed good accuracy (%found of 81 % to 120 %), precision (≤20 %), and linearity (r>0.997) for all the studied drugs in spiked serum samples.

Multimaterial 3D Printed Fluidic Device for Measuring Pharmaceuticals in Biological Fluids.

Multimaterial 3D printing provides a unique capability for the creation of highly complex integrated devices where complementary functionality is realized using differences in material properties. Using a single and automated print process, microfluidic devices were fabricated containing (i) an optically transparent structure for fluorescence detection, (ii) electrodes for electrokinetic transport, (iii) a primary membrane to remove particulates and macromolecules including proteins, and (iv) a secondary membrane to concentrate small molecule targets. The device was used for the simultaneous extraction and concentration of small molecule pharmaceuticals from urine, which was followed by an on-chip electrophoretic separation of the concentrated targets for quantitative analysis. Owing to the high level of functional integration inside the device, manual handling was minimal and restricted to the introduction of the sample and buffer solutions. The 3D printed sample-in/answer-out device allowed the direct quantification of ampicillin-a small molecule pharmaceutical-in untreated urine within 3 min, down to 2 ppm. These results demonstrate the potential of 3D printing for on-demand fabrication of disposable, functionally integrated devices for low-cost point-of-collection (POC) diagnostics.

In-Syringe Electrokinetic Ampholytes Focusing Coupled with Electrospray Ionization Mass Spectrometry.

A 25 µL analytical glass syringe has been used for isoelectric focusing (IEF) utilizing the stainless-steel needle and plunger as electrodes. The generation of protons and hydroxyl ions at the electrodes facilitated a neutralization reaction boundary (NRB) mechanism to focus different amphoteric compounds, such as hemoglobin, bovine serum albumin, R-phycoerythrin, and histidine, within minutes. After optimization of different experimental parameters affecting the IEF process and the coupling of the IEF syringe with electrospray ionization mass spectrometry (ESI-MS), a BGE composed of NH4Ac, 1.0 mM, pH 4.0, in 70.0% (v/v) acetonitrile was used for the IEF of histidine. A voltage of -200 V was applied for 5.0 min to accomplish the IEF and increased to -400 V during the infusion to ESI-MS at a flow rate of 4.0 µL/min. The coaxial sheath liquid consisting of 0.2% (v/v) formic acid was added at 4.0 µL/min. The detection limit was found to be 2.2 µg/mL and a nonlinear quadratic fit calibration curve was constructed for histidine over the range of 4.0-64.0 µg/mL with a correlation coefficient ( r) = 0.9998. The determination of histidine in spiked urine samples as relevant for the diagnosis of histidinemia was demonstrated by the IEF syringe-ESI-MS system with accuracy from 88.25% to 102.16% and a relative standard deviation less than 11%.

Recent advances in enhancing the sensitivity of electrophoresis and electrochromatography in capillaries and microchips (2016-2018).

One of the most cited limitations of capillary and microchip electrophoresis is the poor sensitivity. This review continues to update this series of biannual reviews, first published in Electrophoresis in 2007, on developments in the field of online/in-line concentration methods in capillaries and microchips, covering the period July 2016-June 2018. It includes developments in the field of stacking, covering all methods from field-amplified sample stacking and large-volume sample stacking, through to isotachophoresis, dynamic pH junction, and sweeping. Attention is also given to online or in-line extraction methods that have been used for electrophoresis.

Preconcentration by solvent removal: techniques and applications.

Preconcentration is the aspect of analytical method development covering the need to improve detection sensitivity. This review collects the advances in a diversity of approaches to achieve preconcentration by solvent removal. Evaporation in microfluidic and paper-based devices is reported in a variety of forms and later compared to membrane-assisted evaporation. Sample partitioning in an immiscible fluid is also described. The reported methodologies highlight the need to achieve good control of the gas-liquid interface to obtain accurate results. A comprehensive comparison of different strategies is presented here discussing their benefits and drawbacks as well as the research needs in this area. Graphical abstract ᅟ.

In-Transit Electroextraction of Small-Molecule Pharmaceuticals from Blood.

An electrokinetic platform was developed for extracting small-molecule pharmaceuticals from a dried blood spot. Through the exclusion of liquid reagents and use of low field strength (6 V cm-1 ), the electroextraction of a drug from a dried blood spot, deposited on a polymer inclusion membrane (PIM), could be realised while in transit in the mail. In transit sample preparation provides a potential solution to in situ sample degradation and may accelerate the workflow upon arrival of a patient sample at the analytical facility. The electroextraction method was enabled through our discovery of the use of 15-20 µm thin PIMs as electrophoretic separation medium in absence of liquid reagents. Here, a PIM consisting of cellulose triacetate as polymer base, 2-nitrophenyl octyl ether as plasticizer and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide as carrier was used. The PIM, was packaged with two 12 V batteries to supply the separation voltage. A blood spot containing berberine chloride was deposited and dried before the applying the separation potential, allowing for the electroextraction while the packaged device was shipped in internal mail. Upon arrival in the analytical laboratory, the PIM was analysed using a fluorescence microscope with photon multiplier tube, quantifying the berberine extracted away from the sample matrix. This platform represents a new opportunity for processing clinical samples during transport to the laboratory, saving time and manual handling to accelerate the time to result.

Low-Cost Passive Sampling Device with Integrated Porous Membrane Produced Using Multimaterial 3D Printing.

Multimaterial 3D printing facilitates the rapid production of complex devices with integrated materials of varying properties and functionality. Herein, multimaterial fused deposition modeling (MM-FDM) 3D printing was applied to the fabrication of low-cost passive sampler devices with integrated porous membranes. Using MM-FDM 3D printing, the device body was produced using black polylactic acid, with Poro-Lay Lay-Felt filament used for the printing of the integrated porous membranes (rubber-elastomeric polymer, porous after removal of a water-soluble poly(vinyl alcohol) component). The resulting device consisted of two interlocking circular frames, each containing the integrated membrane, which could be efficiently sealed together without the need for additional O-rings, and prevented loss of enclosed microparticulate sorbent. Scanning electron microscopy (SEM) analysis of the purified composite filament confirmed the porous properties of the material, an average pore size of ∼30 nm. The printed passive samplers with various membrane thicknesses, including 0.5, 1.0, and 1.5 mm, were evaluated for their ability to facilitate the extraction of atrazine as the model solute onto the internal sorbent, under standard conditions. Gas chromatography-mass spectrometry was used to determine the uptake of atrazine by the device from standard water samples and also to evaluate any chemical leaching from the printed materials. The sampler with 0.5 mm thick membrane showed the best performance with 87% depletion and a sampling rate of 0.19 Ld-1 ( n = 3, % RSD = 0.59). The results obtained using these printed sampling devices with integrated membranes were in close agreement to devices fitted with a standard poly(ether sulfone) membrane.

Precise, accurate and user-independent blood collection system for dried blood spot sample preparation.

An accurate and precise 3 µL blood collection and dispensing system is presented for the preparation of dried blood spot (DBS) samples. Using end-to-end glass capillaries in conjugation with pre-punched DBS pads, a blood micro collection system was developed to eliminate the haematocrit dispersion, widely associated with DBS technology, while providing better levels of accuracy and precision during sample preparation. This methodology is compared to traditional micro-volume blood collection systems, such as a pipette and a digitally controlled analytical syringe. Results showed that % of recovery for the capillary methodology was closer to 100% across the three haematocrit (HCT) levels tested and when prepared by two users (98 to 100% for capillaries, 78 to 104% for pipette and 93 to 97% for digital syringe) attesting a higher accuracy. Additionally, by taking advantage of the capillary action mechanism to collect and dispense autonomously the desired volume of blood onto the DBS pad, coefficients of variation between two individuals were significantly lower than with standard methodologies (capillaries-0.05 to 0.77%, pipette-12.71 to 18.53% and digital syringe-0.72 to 1.77%). This alternate aspiration and dispensing methodology could be used by different users without compromising accuracy or precision when handling low volumes of blood during the pre-analytical steps. Graphical abstract Comparison of novel capillary dispensing methodology for dried blood spot sample preparation with pipette and digital syringe methodologies through accuracy and precision measurements of caffeine.

Correction to: Precise, accurate and user-independent blood collection system for dried blood spot sample preparation.

The authors would like to call the reader's attention to the following: The instrument they used to measure the volumetric precision of the dispensing devices is not called "VMS" but "PCS®".

Using Printing Orientation for Tuning Fluidic Behavior in Microfluidic Chips Made by Fused Deposition Modeling 3D Printing.

Fluidic behavior in microfluidic devices is dictated by low Reynolds numbers, complicating mixing. Here, the effect of the orientation of the extruded filament on the fluidic behavior is investigated in fused deposition modeling (FDM) printed fluidic devices. Devices were printed with filament orientations at 0°, 30°, 60°, and 90° to the direction of the flow. The extent of mixing was observed when pumping yellow and blue solutions into the inlets of a Y-shaped device, and measuring the extent of mixing of two colored solutions under different angles and at flow rates of 25, 50, and 100 µL/min. Fluidic devices printed with filament extruded at 60° to the flow showed the highest mixing efficiency, but results obtained at 30° suggested more complex fluid movement, as the measured degree of mixing decreased along the fluidic channel at higher flow rates. To explore this, a device with -37° filament orientation on the top surface was designed to align with the direction of the first fluid input channel and +37° on the bottom surface of the channel to align with the direction of the second fluidic input. Results indicated a rotational movement of the fluids down the microchannel, which were confirmed by computational fluid dynamics. These results demonstrate the impact of the filament extrusion direction on fluidic behavior in microfluidic devices made by FDM printing. Two chips with laminar flow (0° filament direction) or mixing flow (+37/-37° filament direction) were used to perform isotachophoresis and colorimetric detection of iron in river water, respectively, demonstrating the simplicity with which the same device can be tuned for different applications simply by controlling the way the device is printed.

One-Step Fabrication of a Microfluidic Device with an Integrated Membrane and Embedded Reagents by Multimaterial 3D Printing.

One of the largest impediments in the development of microfluidic-based smart sensing systems is the manufacturability of integrated, complex devices. Here we propose multimaterial 3D printing for the fabrication of such devices in a single step. A microfluidic device containing an integrated porous membrane and embedded liquid reagents was made by 3D printing and applied for the analysis of nitrate in soil. The manufacture of the integrated, sealed device was realized as a single print within 30 min. The body of the device was printed in transparent acrylonitrile butadiene styrene (ABS) and contained a 400 µm wide structure printed from a commercially available composite filament. The composite filament can be turned into a porous material through dissolution of a water-soluble material. Liquid reagents were integrated by briefly pausing the printing before resuming for sealing the device. The devices were evaluated by the determination of nitrate in a soil slurry containing zinc particles for the reduction of nitrate to nitrite using the Griess reagent. Using a consumer digital camera, the linear range of the detector response ranged from 0 to 60 ppm, covering the normal range of nitrate in soil. To ensure that the sealing of the reagent chamber is maintained, aqueous reagents should be avoided. When using the nonaqueous reagent, the multimaterial device containing the Griess reagent could be stored for over 4 days but increased the detection range to 100-500 ppm. Multimaterial 3D printing is a potentially new approach for the manufacture of microfluidic devices with multiple integrated functional components.