Counter-pressure-assisted ITP with electrokinetic injection under field-amplified conditions for bacterial analysis

Investigation of on-line electrokinetic enrichment strategies for capillary electrophoresis of extracellular vesicles

This work explores strategies for electrokinetic preconcentration of extracellular vesicles (EVs) that are potential source of biomarkers for different diseases. The first approach that led to successful preconcentration of EVs is based on large volume sample stacking (LVSS), allowing an enrichment factor of 7 for CE of EVs with long-end injection (using a capillary with an effective length of 50 cm). Attempts were also made to perform multiple cycles of LVSS, field amplified sample stacking (FASS) and field amplified sample injection (FASI), to improve EVs preconcentration performance. The focus was then put on development of capillary isotachophoresis under high ionic strengths (IS) for electrokinetic enrichment of slow migrating EVs having heterogeneous mobilities. This approach relies on the use of extremely high concentrations of the terminating electrolyte (TE) to slow down the mobility of TE co-ions, rendering them slower than those of EVs. The limit of detection for intact EVs using the developed ITP-UV method reached 8.3 × 108 EVs/mL, allowing an enrichment of 25 folds and a linear calibration up to 4 × 1010 EVs/mL. The ITP-UV and ITP-LIF approaches were applied to provide the electrokinetic signature of EVs of bovine milk and human plasma as well as to visualize more specifically intravesicular fluorescently labelled EVs. The investigation of these strategies shredded light into the challenges still encountered with electrokinetic preconcentration and separation of heterogeneous EVs sub-populations which are discussed herein based on our results and other attempts reported in the literature.

Isotachophoretic quantification of total viable bacteria on meat and surfaces

BACKGROUND

The quantification of microbes, particularly live bacteria, is of utmost importance in assessing the quality of meat products. In the context of meat processing facilities, prompt identification and removal of contaminated carcasses or surfaces is crucial to ensuring the continuous production of safe meat for human consumption. The plate count method and other traditional detection methods are not only labour-intensive but also time-consuming taking 24-48 h.

RESULTS

In this report, we present a novel isotachophoretic quantification method utilizing two nucleic acid stains, SYTO9 and propionic iodide, for the detection of total viable bacteria. The study employed E. coli M23 bacteria as a model organism, with an analysis time of only 30 min. The method demonstrated a limit of detection (LOD) of 184 CFU mL-1 and 14 cells mL-1 for total viable count and total cell count, respectively. Furthermore, this new approach is capable of detecting the microbial quality standard limits for food contacting surfaces (10 CFU cm-2) and meat (1.99 × 104 CFU cm-2) by swabbing an area of 10 × 10 cm2.

SIGNIFICANCE

In contrast to the culture-based methods usually employed in food processing facilities, this isotachophoretic technique enables easy and rapid detection (<30 min) of microorganisms, facilitating crucial decision-making essential for maintaining product quality and safety.

Performance evaluation of commercially available swabs for environmental monitoring: Uptake and release efficiency

Safety and the quality of products rely on proper cleanliness procedures and good manufacturing practices in the production environment. The use of swabs for the collection of samples from surfaces has been a common practice in industries, medicine and forensic studies. To accommodate these different purposes, many varieties of swabs have been introduced into the market, and it is important to assess the performance of these swabs before incorporating into an environmental monitoring procedure. The overall effectiveness of a swab is determined by two factors: the number of bacteria that a swab can uptake from a surface and the number of picked-up bacteria the swab can elute into a releasing buffer. This study evaluated the uptake efficiency and release efficiency of four different commercially available swabs: CleanFoam (Texwipes, USA), FLOQSwabs (Copan diagnostic Inc., USA), Hydraflock swabs (Puritan medical products, USA), and Cotton swabs. Cotton swabs showed the highest uptake efficiency (96.5 ± 1.9%), whereas CleanFoam swabs (57.9 ± 20.3%) showed the least. Both flocked (FLOQSwabs and Hydraflock) swabs showed over 80% uptake efficiency. Releasing efficiency of swabs was tested with eight different releasing buffers. Cotton swabs displayed the lowest release efficiency with most of the tested releasing buffers. When employed with Tris HEPES, Tris MOPS, Tris TAPS, FLOQSwabs, and Hydraflock swabs exhibited releasing efficiency of over 75%. The overall efficiency of the swabs was determined using TAPS as the releasing buffer and the values obtained were 80.4 ± 9.8%, 54.7 ± 16.9%, 35.0 ± 12.7% and 25.2 ± 6.9% for Hydraflock swabs, FLOQSwabs, Cotton swabs and Cleanfoam swabs, respectively.

Isotachophoresis: Theory and Microfluidic Applications

Isotachophoresis (ITP) is a versatile electrophoretic technique that can be used for sample preconcentration, separation, purification, and mixing, and to control and accelerate chemical reactions. Although the basic technique is nearly a century old and widely used, there is a persistent need for an easily approachable, succinct, and rigorous review of ITP theory and analysis. This is important because the interest and adoption of the technique has grown over the last two decades, especially with its implementation in microfluidics and integration with on-chip chemical and biochemical assays. We here provide a review of ITP theory starting from physicochemical first-principles, including conservation of species, conservation of current, approximation of charge neutrality, pH equilibrium of weak electrolytes, and so-called regulating functions that govern transport dynamics, with a strong emphasis on steady and unsteady transport. We combine these generally applicable (to all types of ITP) theoretical discussions with applications of ITP in the field of microfluidic systems, particularly on-chip biochemical analyses. Our discussion includes principles that govern the ITP focusing of weak and strong electrolytes; ITP dynamics in peak and plateau modes; a review of simulation tools, experimental tools, and detection methods; applications of ITP for on-chip separations and trace analyte manipulation; and design considerations and challenges for microfluidic ITP systems. We conclude with remarks on possible future research directions. The intent of this review is to help make ITP analysis and design principles more accessible to the scientific and engineering communities and to provide a rigorous basis for the increased adoption of ITP in microfluidics.

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.