Cation-selective electropreconcentration

Abstract

A cation-selective microfluidic sample preconcentration system is described. The cation sample was electropreconcentrated using a reversed-direction electroosmotic flow (EOF) and an anion-permselective filter, where an electric double layer (EDL) overlap condition existed. The anion-permselective filter between microchannels was fabricated by three different methods: 1) extending a positively charged, nanoporous, polymer membrane by photopolymerization of poly(diallyldimethylammonium chloride) (PDADMAC); 2) etching a nanochannel and then coating it with a positively-charged monomer, N-[3-(trimethoxysilyl)propyl]-N'-(4-vinylbenzyl)ethylenediamine hydrochloride (TMSVE); and, 3) etching a nanochannel and then coating it with a positively-charged, pre-formed polymer, polyE-323. The EOF direction in the microchannel was reversed by both TMSVE and polyE-323 coatings. The cation-selective preconcentration was investigated using charged fluorescent dyes and tetramethylrhodamine isothiocyanate (TRITC)-tagged peptides/proteins. The preconcentration in the three different systems was compared with respect to efficiency, dependence on buffer concentration and pH, tolerable flow rate, and sample adsorption. Both TMSVE- and polyE-323-coated nanochannels showed robust preconcentration at high flow rates, whereas the PDADMAC membrane maintained anion-permselectivity at higher buffer concentrations. The TMSVE-coated nanochannels showed a more stable preconcentration process, whereas the polyE-323-coated nanochannels showed a lower peptide sample adsorption and robust efficiency under a wide range of buffer pHs. The system described here can potentially be used for the preconcentration of cationic peptides/proteins on microfluidic devices for subsequent analyses.

Development of a low flow‐resistive charged nanoporous membrane in a microchip for fast electropreconcentration

“…In addition, the poly‐SS membrane has an advantage over Nafion membrane in terms of in‐situ fabrication based on photopolymerization , which means it can be conveniently fabricated in any location inside a microfluidic chip. The poly‐SS membrane results in anion‐selective preconcentration contrary to the previously reported poly‐DADMAC (poly‐diallyldimethylammonium chloride) which showed cation‐selective preconcentration .…”

“…The preconcentrated plug sample concentration was estimated from fluorescence intensities of standard fluorescein solutions filled in the microchip (Fig. A) . Potentials applied at S, W, and D reservoirs were 250, 0, and 160 V, respectively.…”

Electropreconcentration‐induced local pH change

“…To the contrary, in case of cation‐selective electropreconcentration, where all micro‐ and nanochannel surface charges are positive, EOF directions are reversed (i.e. toward anode) and anions are continuously extracted through the nanochannel as cation samples are stacked near the micro‐ and nanochannel interface . Then, we can expect decrease in hydronium concentration in the preconcentrated sample plug and corresponding pH increase.…”

“…A), counter‐ions (cations in this case) to the channel surface charge can continuously flow through the EDL‐overlapped charge‐selective nanochannel, while co‐ion (anions in this case) flow is suppressed in the sample channel. Because the charge neutrality should be maintained and counter‐ions continuously flow, the co‐ion concentration in the sample channel is limited by the counter‐ion concentration in the buffer, which limits the maximum co‐ion sample concentrating factor, and therefore, the preconcentration is co‐ion selective . In this condition, the electric field applied to the sample channel redistribute co‐ions based on their electrophoretic mobilities with higher mobility ions toward the sample reservoir and lower mobility ions toward the micro‐nanochannel interface.…”

Development of a conductivity-based photothermal absorbance detection microchip using polyelectrolytic gel electrodes

“…They have been applied in cytometry/velocimetry measurements,[33,34] as a micromixer,[35] for electroporation,[36] logic gate,[37] and sample preconcentration. [38–40] One advantage of PGEs compared to metal electrodes is the ease of microchip fabrication. Whereas the metal electrodes are deposited on the cover slip and require careful alignment over the microchannels, the PGEs can be photopolymerized in-situ post-bonding.…”