Nanostructured pillars based on vertically aligned carbon nanotubes as the stationary phase in micro‐CEC

Abstract

We present a micro-CEC chip carrying out a highly efficient separation of dsDNA fragments through vertically aligned multi-wall carbon nanotubes (MWCNTs) in a microchannel. The vertically aligned MWCNTs were grown directly in the microchannel to form straight nanopillar arrays as ordered and directional chromatographic supports. 1-Pyrenedodecanoic acid was employed for the surface modification of the MWCNTs' stationary phase to adsorb analytes by hydrophobic interactions. This device was used for separating dsDNA fragments of three different lengths (254, 360, and 572 bp), and fluorescence detection was employed to verify the electrokinetic transport in the MWCNT array. The micro-CEC separation of the three compounds was achieved in less than 300 s at a field strength of 66 V/cm due to superior laminar flow patterns and a lower flow resistance resulting from the vertically aligned MWCNTs being used as the stationary phase medium. In addition, a fivefold reduction of band broadening was obtained when the analyte was separated by the chromatographic MWCNT array channel instead of the CE channel. From all of the results, we suggest that an in situ grown and directional MWCNT array can potentially be useful for preparing more diversified forms of stationary phases for vertically efficient chip-based electrochromatography.

Microfluidic Systems for Biosensing

“…The H-filter allows continuous filtration of unwanted components or extraction of desired analytes from fluids without the need for a membrane filter or similar component that requires cleaning or replacement. Wu et al have developed a microcapillary electrochromatography (μCEC) chip for performing a highly efficient separation of double-stranded DNA (dsDNA) fragments through vertically aligned multi-wall carbon nanotubes (MWCNTs) in a microchannel as shown in Figure 2 [65]. This is the first report on the development of a novel stationary nanocolumn by directly growing homogeneous and vertically aligned MWCNTs in microchannels to enable improved analytical performance in capillary electrochromatography.…”

“…Other methods such as chromatography, dielectrophoresis, transverse isoelectric focusing, and ultrasonic trapping have been developed. A novel concentration method employing the dual-asymmetry electrokinetic flow (DAEKF) has been developed by Wu et al [66] for catecholamines concentration and detection in a CEEC nanochannel. The combination of asymmetry EOF and field-effect control was introduced to carry out a two-dimensional gradient shear flow exposed to a downward trailing velocity vector for the generation of a strong downward rotational flow for sample concentration (see Figure 3).…”

“…(a) Photographic overhead view of the μCEC chip (dark area in the central channel consisting of MWCNTs array, 1: sample reservoir, 2: eluent buffer/running buffer reservoir, 3: sample waste, 4: eluent buffer waste, 5: running buffer waste, D: detector), (b) The schematic arrangement of MWCNTs in μCEC channels as vertically aligned nanopillars, (c) the SEM image of a cross section (a-a’ plane) of the μCEC channel, (d) The SEM image of vertically-aligned MWCNTs directly grown in microchannel [65]. …”

“…(Region I: a 2-D shear flow, Region II: pulling effect-asymmetric electroosmotic flow (AEOF), Regions IV: pushing effect AEOF). Fluorescence image of Rhodamine B for (c) traditional EOF in a nanochannel, (d) the restacking effect by the DAEKF system in a nanochannel [66]. …”

Carbon nanotube based separation columns for high electrical field strengths in microchip electrochromatography

“…A few groups have shown CNTs grown in microfluidic channels for electrokinetic separations. [10][11][12] Goswami et al 10 used a Fe-Al catalyst to grow vertically aligned CNTs in microfluidic channels for electrochromatographic separations and solid phase extraction and showed a proof of concept separation of thiourea and tryptophan. The maximum electrical field strength was 150 V cm À1 due to limitations with bubble formation from electrolysis.…”