Suppression of Apparent Fluid Flow in Capillary Isotachophoresis without Recourse to Capillary Coating

Abstract

This manuscript describes a new analytical methodology that allows one to stop the apparent fluid flow in uncoated fused silica capillaries. This method, which requires neither capillary coating nor buffer additive, is based on the use of a 22% polyethylene oxide gel which is placed at the anodic end of the capillary. Its high viscosity precludes its penetration into the capillary and the apparent electro-osmotic pumping effect is stopped. To avoid sample depletion in the gel, the concentration of the background electrolyte in the gel has to be at least 10-fold higher than that of the background electrolyte. This method was applied to isotachophoretic experiments performed in unmodified silica capillaries and at high alkaline pHs. The sharpness of the zone boundaries was perfectly conserved. The separation voltages recorded during the isotachophoretic processes demonstrate a very good stability of the system preventing fluctuations of the analyte migration times between runs. This approach can be virtually applied at any pH value of the background electrolyte, in the presence of organic solvents or surfactants. Using this methodology, it has been possible to detect underivatized Amyloid-β peptide 1-40, one of the potential Alzheimer's disease biomarkers, at lower concentrations than ever previously achieved using UV detection.

Recent Electrokinetic and Microfluidic Strategies for Detection of Amyloid Beta Peptide Biomarkers: Towards Molecular Diagnosis of Alzheimer's Disease

“…[48] Under electroosmotic‐flow (EOF) suppression conditions (i. e. elimination of the bulk liquid motion normally occurred under application of a high voltage over a silica capillary possessing negative surface charges), the target Aβ peptides were trapped between two anions, OH − in TE and CH 3 COO − in LE, during their electrophoretic migrations to the detector. This stacking method allowed to quantify Aβ 1 ‐ 40 down to 700 nM just with UV detection [48] . To further improve the detection limit, a multiple‐electrokinetic preconcentration concept was developed [49] .…”

“…1 nM Monitoring of the interaction between nanoparticles and the Aβ peptides [42][43][44][45][46] CE-LIF [41] Immunoprecipitation and off-line labelling Aβ1-42/Aβ1-38 0.1 nM Discrimination between AD patients and healthy persons [41] CE-LIF [47] Immuno-enrichmenton-bead fluorescent labelling -thermal elution Aβ1-42, Aβ1-40, Aβ1-38 0.1 nM Discrimination between AD patients and healthy persons [47] ITP-UV [48] -Aβ1-40 700 nM -Multiple-ITP-UV [49] -Aβ1-40 50 nM -ITP-MS [50] Off-line fluorescent labelling of peptides Aβ1-40, Aβ1-42, Aβ1-38 0.1 nM Discrimination between AD patients and healthy persons [50] Multiple LVSEP-LIF [51] Off-line fluorescent labelling of peptides [51] MCE-UV [52] - Biosensors [54,55] Sandwich immunoassay Aβ 1-42 0.5 μM Proof of concept Immuno-enrichment on magnetic beads prior to CE-UV [60] -Aβ 1-42 and Aβ 1-40 sub μM range -Immuno-enrichment on magnetic beads and fluorescent labelling prior to CE-LIF [41,52,[61][62][63]47] -Aβ 1-38, Aβ 1-40, and Aβ 1-42 sub nM ranges Discrimination between AD patients and healthy persons [41,52,[61][62][63]47] Immunoassay in microfluidic droplets [57] Single-step immunoassay using functionalized magnetic beads Magneto-CE [59] Immuno-capture and chemical elution of labelled peptides inside a CE microchannel peptides in biofluids in particular. The first CE method for separation and ultraviolet (UV) detection of Aβ peptides was communicated in 2008.…”

Recent advances in enhancing the sensitivity of electrophoresis and electrochromatography in capillaries and microchips (2014–2016)

“…Oukacine and Taverna reported a method that suppressed fluid flow by using a 22% w/v polyethylene oxide gel in the outlet vial . Due to the high viscosity of the gel, it physically prevented liquid from exiting the capillary effectively causing the capillary to become closed at that end.…”

Recent developments in capillary and microchip electroseparations of peptides (2013–middle 2015)

“…Anionic CITP with leading electrolyte (LE) composed of 43.4 mM CH 3 COOH, 194.4 mM NH 4 OH, pH 9.9, and terminating electrolyte (TE) containing 392 mM NH 4 OH, pH 11.4, in FS capillaries with EOF suppressed by high‐viscous 22% polyethylene oxide gel placed at the anodic capillary end was applied to analysis of underivatized Aβ peptide 1–40 . The method allowed detection of this Alzheimer's disease biomoarker at lower concentration than ever previously achieved by CE with UV‐detection.…”