A thread-based electrofluidic platform for direct transfer, separation, and pre-concentration of materials from sample swabs.

A new method and platform has been developed for direct transfer, electrophoretic separation, and pre-concentration of swabbed samples using the principles of thread-based electrofluidics. A direct electrokinetic injection has been observed for a variety of analytes ranging from small molecules to proteins. The effect of physicochemical interactions of the analyte with the swab and the thread on the transfer efficiency has been studied by exploring different swab and thread combinations. For fluorescein, using a polyurethane swab, 98% and 94% transfer efficiencies were observed on mercerised cotton and nylon thread, while only 80% transfer efficiency was observed on polyester thread, respectively. A 97% transfer of fluorescein was observed on the nylon thread when a flocked nylon swab was used, while only 47% transfer was observed when a cotton swab was used. A successful transfer has been observed for both liquid and dry samples from either pre-wetted or dry swabs in both the presence and absence of any surrounding electrolytes. The platform has been further adapted for multiplexed analysis, where a sample from a single swab was transferred onto two parallel thread systems with ca. 50% distribution between them. The method has been validated for transfer, separation, and pre-concentration of DNA from blood. It has also been successfully used to directly analyse dried blood samples using a commercial sampling device, Neoteryx Mitra.

Recent advances in miniaturization of portable liquid chromatography with emphasis on detection.

Liquid chromatography is a prominent analytical technique in separation science and chemical analysis, applied across numerous fields of research and within industrial applications. Over the past few decades, there has been a growing interest in the miniaturization of this technique, which has been particularly enabled through new miniature and portable detection technologies for in-field, at-site, and point-of-need (collectively 'out-of-lab') analyses. Accordingly, significant advances have been made in recent years in the development of miniaturized liquid chromatography with photometric, electrochemical, and mass spectrometric detection, enabling the development of field-deployable and portable instruments for various applications. Herein, recent developments in the miniaturization of detection systems for inclusion within, and/or coupling with, portable liquid chromatographic systems, are reviewed in detail together with critical comments and expected future trends in this area.

Nanomaterial-assisted thread-based isotachophoresis with on-thread solute trapping.

This research describes a nanomaterial-assisted thread-based isotachophoresis (TB-ITP) setup for the clean-up, preconcentration, and trapping of alkaloids (coptisine, berberine, and palmatine) in biological fluids, followed by their on-thread desorption electrospray ionization mass spectrometry (DESI-MS) determination. The reusable TB-ITP setup and a DESI compatible thread holder were 3D printed. A single nylon thread was employed as the ITP substrate for solute isolation and enrichment, and a short piece of graphene oxide (GO) functionalized nylon thread was tied around the main 'separation' thread as the 'trap' for the trapping of ITP focused alkaloids. Compared to the direct DESI-MS sample analysis, the sensitivity of the proposed method for the model solutes was increased up to 10-fold, benefiting from the TB-ITP focusing and enrichment strategy. This proof-of-concept use of nanomaterial-modified threads in electrofluidic separation and concentration procedures opens up a promising avenue to explore, particularly with regard to the sensitivity and selectivity of thread-based electrofluidic separation coupled with ambient ionization MS.

Small-Footprint, Field-Deployable LC/MS System for On-Site Analysis of Per- and Polyfluoroalkyl Substances in Soil.

Per- and polyfluoroalkyl substances (PFASs) are emerging environmental pollutants of global concern. For rapid field site evaluation, there are very few sensitive, field-deployable analytical techniques. In this work, a portable lightweight capillary liquid chromatography (capLC) system was coupled with a small footprint portable mass spectrometer and configured for field-based applications. Further, an at-site ultrasound-assisted extraction (pUAE) methodology was developed and applied with a portable capLC/mass spectrometry (MS) system for on-site analysis of PFASs in real soil samples. The influential variables on the integration of capLC with MS and on the resolution and signal intensity of the capLC/MS setup were investigated. The important parameters affecting the efficiency of the pUAE method were also studied and optimized using the response surface methodology based on a central composite design. The mean recovery for 11 PFASs ranged between 70 and 110%, with relative standard deviations ranging from 3 to 12%. In-field method sensitivity for 12 PFASs ranged from 0.6 to 0.1 ng/g, with wide dynamic ranges (1-600 ng/g) and excellent linearities (R2 > 0.991). The in-field portable system was benchmarked against a commercial lab-based LC-tandem MS (MS/MS) system for the analysis of PFASs in real soil samples, with the results showing good agreement. When deployed to a field site, 12 PFASs were detected and identified in real soil samples at concentrations ranging from 8.1 ng/g (for perfluorooctanesulfonic acid) to 2935.0 ng/g (perfluorohexanesulfonic acid).

Miniature Multiwavelength Deep UV-LED-Based Absorption Detection System for Capillary LC.

A new miniature deep UV absorbance detector has been developed using low-cost and high-performance LEDs, which can be operated in both scanning (230 to 300 nm) and individual wavelength (240, 255, and 275 nm) detection modes. The detector is mostly composed of off-the-shelf components, such as LEDs, trifurcated fiber optic assembly, a capillary Z-type flow cell, and photodiodes. It has been characterized for use with a standard capillary LC system and was benchmarked against a standard variable wavelength capillary LC detector. The detector shows very low levels of stray light (<0.4%), utilization of up to 99.0% of the effective path length of the flow cell, a wide dynamic range (0.5 to 200 µg/mL for sulfamethazine, carbamazepine, and flavone), and low noise levels (at 300 µAU level). The detector was applied within a miniaturized LC system.

Thread-based isoelectric focusing coupled with desorption electrospray ionization mass spectrometry.

The combination of a thread-based electrofluidic analytical device and desorption electrospray ionization mass-spectrometry (DESI-MS) was investigated for the separation and concentration of proteins. The combination delivered a low-cost novel approach for sample pretreatment and target focusing, with direct "on-thread" ambient mass spectrometry detection. For this purpose, a platform for thread-based isoelectric focusing (TB-IEF) was 3D-printed, optimised, and applied to the separation and focusing of three model proteins. Successful separation and focusing was achieved within 30 min. The TB-IEF device was coupled with DESI-MS by direct exposure of the focused solutes on the dried thread to the DESI source. As a proof-of-concept, a 10-fold increase in the DESI-MS response for insulin was achieved following the TB-IEF preconcentration, whilst simultaneously isolating the target solutes from their sample matrix.

Porogens and porogen selection in the preparation of porous polymer monoliths.

Porogens are key components required for the preparation of porous polymer monoliths for application in separation science. Porogens determine the stability, selectivity, and permeability of polymer monoliths. This review summarizes the role of porogens in the preparation of porous polymer monoliths with a focus on clear understanding of effect of porogens on morphological properties, porosity, surface area, mechanical stability, and permeability of monoliths, particularly targeting the field of separation science. This review also includes the use of different types of porogens with the focus on various approaches used to set criteria for their systematic selection, including porogen-free techniques recently used for synthesis of porous monoliths. It discusses the current state-of-the-art applications of porogens in column preparation as well as where the future developments in this field may be directed.

3D Printed Liquid Cooling Interface for a Deep-UV-LED-Based Flow-Through Absorbance Detector.

Ultraviolet (UV)-light-emitting diodes (LEDs) are now widely used in analytical absorbance-based detectors; as compared to conventional UV lamps, they offer lower cost, faster response time, and higher photon conversion efficiency. However, current generation deep-UV-LEDs produce excess heat when operated at normal operating currents, which affects output stability and reduces their overall performance and lifespan. Herein a 3D printed liquid cooling interface has been developed for a deep-UV-LED-based optical detector, for capillary format flow-through detection. The interface consists of a circular channel that is tightly wrapped around the LED to provide active liquid cooling. The design also facilitates easy plug-and-play assembly of the various essential components of the detector: specifically, a 255 nm UV-LED, a capillary Z-cell, and a broadband UV photodiode (PD). The unique liquid cooling interface improved the performance of the detector by reducing the LED temperature up to 22 °C, increasing the spectral output up to 34%, decreasing the required stabilization time by up to 6-fold, and reducing the baseline noise and limits of detection (LODs) by a factor of 2. The detector was successfully used within a capillary HPLC system and could offer a miniaturized, rapidly stabilized, highly sensitive, and low-cost alternative to conventional UV detectors.

Ion-Exchange Based Immobilization of Chromogenic Reagents on Microfluidic Paper Analytical Devices.

Distance-based detection methods, as used in development of microfluidic paper analytical devices (µPADs), rely on the dynamic formation of a colored band along the length of the paper microfluidic channels. The color change is driven by the reaction of chromogenic reagents (typically water-insoluble) that are bound to the paper, thus not subject to being washed away by the sample flow along the detection channel. Here, we introduce the use of an anion-exchange filter paper (as a replacement for standard, unmodified filter paper) for distance-based detection in µPADs, in order to immobilize the water-soluble anionic reagents upon the paper detection channels based on ion-exchange interactions of the oppositely charged paper (protonated tertiary amine groups) and the anionic groups of the reagents. The ion-exchange (IE) paper was initially characterized and its properties were compared with standard cellulose paper. The IE paper was shown to be capable of strong retention of anionic reagents exhibiting acidic functional groups (carboxylic, sulfonic), which become deprotonated and negatively charged when in contact with the IE paper. The effect of the ionic strength (10-250 mM Cl-) and pH (1-13) on the immobilization of the investigated reagents were also determined. The IE-µPADs were then modified with anionic chromogenic reagents and applied to distance-based determination of total calcium (LOD = 0.03 mM) and total acidity (LOD = 2.5 mM) content in serum and wine samples, respectively. The detailed mechanisms of the developed assays on the IE paper are also discussed. We propose that IE-µPADs represent a useful new addition to the distance-based detection toolbox and considerably enhance the applicability of such a detection method.

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. Under the right conditions OT-LC columns have the potential to offer superior column efficiency, higher overall peak capacity, and higher column permeability compared to packed capillary and monolithic columns. However, such advantages are highly dependent upon column format and dimensions, and to date in liquid chromatography the advantages of open tubular format columns have been most widely discussed and applied in the field of proteomics. In this review we have focused on the wider variety of separation mechanisms and applications which can be achieved following the modification of the inner wall of the capillary with a thin-layer stationary phase. In particular the latest advances in stationary phase development and formation, together with new column formats and dimensions are reviewed. Detection options for OT-LC are also discussed and recent advances in this area highlighted. Finally, this review summarises existing applications of OT-LC and illustrates the future potential for this technique.

Recent strategies to enhance the performance of polymer monoliths for analytical separations.

This review summarizes recent developments made in the incorporation of functional materials into organic polymer monoliths, together with new monolithic forms and formats, which enhance their application as supports and stationary phase materials for sample preparation and chromatographic separations. While polymer monoliths are well-known supports for the separation of large molecules, recent developments have been made to improve their features for the separation of small molecules. The selectivity and performance of organic polymer monoliths has been improved by the incorporation of different materials, such as metal-organic frameworks, covalent organic frameworks, or other types of nanostructured materials (carbon nanohorns, nanodiamonds, polyoxometalates, layered double hydroxides, or attapulgite). The surface area of polymer monoliths has been significantly increased by polymer hypercrosslinking, resulting in increased efficiency when applied to the separation of small molecules. In addition, recent exploration of less conventional supports for casting polymer monoliths, including photonic fibres and 3D printed materials, has opened new avenues for the applications of polymer monoliths in the field of separation science. Recent developments made in these topics are covered, focusing on the strategies followed by the authors to prepare the polymer monoliths and the effect of these modifications on the developed analytical applications.

Investigating the Effect of Column Geometry on Separation Efficiency using 3D Printed Liquid Chromatographic Columns Containing Polymer Monolithic Phases.

Effect of column geometry on the liquid chromatographic separations using 3D printed liquid chromatographic columns with in-column polymerized monoliths has been studied. Three different liquid chromatographic columns were designed and 3D printed in titanium as 2D serpentine, 3D spiral, and 3D serpentine columns, of equal length and i.d. Successful in-column thermal polymerization of mechanically stable poly(BuMA-co-EDMA) monoliths was achieved within each design without any significant structural differences between phases. Van Deemter plots indicated higher efficiencies for the 3D serpentine chromatographic columns with higher aspect ratio turns at higher linear velocities and smaller analysis times as compared to their counterpart columns with lower aspect ratio turns. Computational fluid dynamic simulations of a basic monolithic structure indicated 44%, 90%, 100%, and 118% higher flow through narrow channels in the curved monolithic configuration as compared to the straight monolithic configuration at linear velocities of 1, 2.5, 5, and 10 mm s-1, respectively. Isocratic RPLC separations with the 3D serpentine column resulted in an average 23% and 245% (8 solutes) increase in the number of theoretical plates as compared to the 3D spiral and 2D serpentine columns, respectively. Gradient RPLC separations with the 3D serpentine column resulted in an average 15% and 82% (8 solutes) increase in the peak capacity as compared to the 3D spiral and 2D serpentine columns, respectively. Use of the 3D serpentine column at a higher flow rate, as compared to the 3D spiral column, provided a 58% reduction in the analysis time and 74% increase in the peak capacity for the isocratic separations of the small molecules and the gradient separations of proteins, respectively.

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.

Rapid screening of inorganic and organic anions in liquid by-products from hydrothermal treatment of biomass by capillary electrophoresis.

A simple and rapid capillary electrophoresis method with capacitively coupled contactless conductivity detection (CE-C4 D) for the simultaneous determination of inorganic and organic anions in liquid product obtained from the hydrothermal treatment of biomass residues is presented. Under the optimal analytical conditions, limits of detection ranged from 1.8 to 9.4 µM for most target solutes and 53 µM for citrate. Relative standard deviations were below 0.5% for migration times and within 0.6-6.5% for peak areas for all solutes. The proposed method was successfully applied for the rapid determination and screening of inorganic and organic anions in liquid product produced following differing hydrothermal treatment temperatures for banana and pineapple biomass, and the contribution of organic acid formation to acidity in the liquid was evaluated. CE-C4 D could be a suitable method for the optimization or tailoring of HTT conditions for desired liquid product composition, and additionally for determination of the best variety(s) of biomass to use in such processes.

Separation of superparamagnetic magnetite nanoparticles by capillary zone electrophoresis using non-complexing and complexing electrolyte anions and tetramethylammonium as dispersing additive.

Separations of bare superparamagnetic magnetite nanoparticles (BSPMNPs, approx. 11 nm diameter) was performed using non-complexing (nitrate) and complexing (chloride, citrate and phosphate) electrolyte ions with additions of tetramethylammonium hydroxide (TMAOH), which is commonly applied to control the synthesis of stable iron oxides. The use of TMAOH as a background electrolyte (BGE) additive for capillary electrophoresis (CE) separations provided for the first time electropherograms of BSPMNPs exhibiting symmetrical and highly reproducible peaks, free of spurious spikes characteristic of nanoparticle clusters. Consequently, accurate determination of the electrophoretic effective mobility of BSPMNPs was possible, yielding a value of -3.345E-08 m2 V-1 s-1 (relative standard deviation (RSD) of 0.500%). The obtained mobilities of BSPMNPs in the presence of various electrolyte ions show that the degree of complexation with the surface of BSPMNPs follows the order chloride < citrate < phosphate, correlating with the stabilities of Fe(III) complexes with the respective anions. Finally, bare and carboxylated iron oxide nanoparticles were successfully separated in only 10 min using 10 mM Tris-nitrate containing 20 mM of TMAOH as electrolyte. Our findings show that simple and rapid CE experiments are an excellent tool to characterise and monitor properties and interactions of iron oxide nanoparticles with other molecules for surface modification purposes.

Miniaturized capillary ion chromatograph with UV light-emitting diode based indirect absorbance detection for anion analysis in potable and environmental waters.

A miniaturized, flexible, and low-cost capillary ion chromatography system has been developed for anion analysis in water. The ion chromatography has an open platform, modular design, and allows for ease of modification. The assembled platform weighs ca. 0.6 kg and is 25 × 25 cm in size. Isocratic separation of common anions (F- , Cl- , NO2- , Br- , and NO3- ) could be achieved in under 15 min using sodium benzoate eluent at a flow rate of 3 µL/min, a packed capillary column (0.150 × 150 mm) containing Waters IC-Pak 10 µm anion exchange resin, and light-emitting diode based indirect UV detection. Several low UV light-emitting diodes were assessed in terms of sensitivity, including a new 235 nm light-emitting diode, however, the highest sensitivity was demonstrated using a 255 nm light-emitting diode. Linear calibration ranges applicable to typical natural water analysis were obtained. For retention time and peak area repeatability, relative standard deviation values ranged from 0.60-0.95 and 1.95-3.53%, respectively. Several water samples were analysed and accuracy (recovery) was demonstrated through analysis of a prepared mixed anion standard. Relative errors of -0.36, -1.25, -0.80, and -0.76% were obtained for fluoride, chloride, nitrite, and nitrate, respectively.

Micro-Capillary Coatings Based on Spiropyran Polymeric Brushes for Metal Ion Binding, Detection, and Release in Continuous Flow.

Micro-capillaries, capable of light-regulated binding and qualitative detection of divalent metal ions in continuous flow, have been realised through functionalisation with spiropyran photochromic brush-type coatings. Upon irradiation with UV light, the coating switches from the passive non-binding spiropyran form to the active merocyanine form, which binds different divalent metal ions (Zn2+, Co2+, Cu2+, Ni2+, Cd2+), as they pass through the micro-capillary. Furthermore, the merocyanine visible absorbance spectrum changes upon metal ion binding, enabling the ion uptake to be detected optically. Irradiation with white light causes reversion of the merocyanine to the passive spiropyran form, with simultaneous release of the bound metal ion from the micro-capillary coating.

Direct Production of Microstructured Surfaces for Planar Chromatography Using 3D Printing.

Through optimization of the printing process and orientation, a suitably developed surface area has been realized upon a 3D printed polymer substrate to facilitate chromatographic separations in a planar configuration. Using an Objet Eden 260VS 3D printer, polymer thin layer chromatography platforms were directly fabricated without any additional surface functionalization and successfully applied to the separation of various dye and protein mixtures. The print material was characterized using gas chromatography coupled to mass spectrometry and spectroscopic techniques such as infrared and Raman. Preliminary studies included the separation of colored dyes, whereby the separation performance could be visualized optically. Subsequent separations were achieved using fluorescent dyes and fluorescently tagged proteins. The separation of proteins was affected by differences in the isoelectric point (pI) and the ion exchange properties of the printed substrate. The simple chromatographic separations are the first achieved using an unmodified 3D printed stationary phase.

Geometrical Alignment of Multiple Fabrication Steps for Rapid Prototyping of Microfluidic Paper-Based Analytical Devices.

Three main fabrication steps for microfluidic paper-based analytical devices (µPADs) were fully integrated with accurate geometrical alignment between the individual steps in a simple and rapid manner. A wax printer for creating hydrophobic barriers was integrated with an inexpensive (ca. $300) electronic craft plotter/cutter for paper cutting, followed by colorimetric reagent deposition using technical pens. The principal shortcoming in the lack of accurate and precise alignment of the features created by these three individual fabrication steps was addressed in this work by developing appropriate alignment procedures during the multistep fabrication process. The wax printing step was geometrically aligned with the following cutting and plotting (deposition) steps in a highly accurate and precise manner using optical scanning function of the plotter/cutter based on registration marks printed on the paper using the wax printer and scanned by the plotter/cutter. The accuracy and precision of alignment in a two-dimensional plane were quantified by cutting and plotting cross-shaped features and measuring their center coordinates relative to wax printed reference lines. The average accuracy along the X- and Y-axis was 0.12 and 0.16 mm for cutting and 0.19 and 0.17 mm for plotting, respectively. The potential of this approach was demonstrated by fabricating µPADs for instrument-free determination of cobalt in waters using distance-based readout, with excellent precision (%RSD = 5.7) and detection limit (LOD) of 2.5 ng and 0.5 mg/L (mass and concentration LODs, respectively).

Comparing Microfluidic Performance of Three-Dimensional (3D) Printing Platforms.

Three-dimensional (3D) printing has emerged as a potential revolutionary technology for the fabrication of microfluidic devices. A direct experimental comparison of the three 3D printing technologies dominating microfluidics was conducted using a Y-junction microfluidic device, the design of which was optimized for each printer: fused deposition molding (FDM), Polyjet, and digital light processing stereolithography (DLP-SLA). Printer performance was evaluated in terms of feature size, accuracy, and suitability for mass manufacturing; laminar flow was studied to assess their suitability for microfluidics. FDM was suitable for microfabrication with minimum features of 321 ± 5 µm, and rough surfaces of 10.97 µm. Microfluidic devices >500 µm, rapid mixing (71% ± 12% after 5 mm, 100 µL/min) was observed, indicating a strength in fabricating micromixers. Polyjet fabricated channels with a minimum size of 205 ± 13 µm, and a surface roughness of 0.99 µm. Compared with FDM, mixing decreased (27% ± 10%), but Polyjet printing is more suited for microfluidic applications where flow splitting is not required, such as cell culture or droplet generators. DLP-SLA fabricated a minimum channel size of 154 ± 10 µm, and 94 ± 7 µm for positive structures such as soft lithography templates, with a roughness of 0.35 µm. These results, in addition to low mixing (8% ± 1%), showed suitability for microfabrication, and microfluidic applications requiring precise control of flow. Through further discussion of the capabilities (and limitations) of these printers, we intend to provide guidance toward the selection of the 3D printing technology most suitable for specific microfluidic applications.