Electrokinetic
concentration based on ion concentration polarization
(ICP) offers a unique possibility to increase detection sensitivity
and speed of surface-based biosensors for low-abundance biomolecules
inside a microfluidic channel. To further improve the concentration
performance, we investigated the effect of surface ion conductance
of the ion-selective conductive polymer membrane, poly(3,4-ethylenedioxythiophene)
polystyrenesulfonate (PEDOT:PSS), in a microfluidic channel. By increasing
its thickness and surface charge, we could achieve a concentration
increase of DNA by 6 orders of magnitude from an
initial concentration of 100 fM within 10 min. As for the detection
via surface hybridization on morpholino (MO) probes, DNA target concentration
as low as 10 pM was detected within 15 min. This result means an improvement
by 2 orders of magnitude in terms of the detection
limit compared with our previous developed PEDOT:PSS membrane. These
results demonstrate a potential application of the PEDOT:PSS membrane
for the ICP-enhanced detection of DNA and other biomolecules in surface-based
assays down to picomolar regimes.
PSS) was directly printed and then reversibly surface bonded onto a morpholino microarray for hybridization. Using this electrokinetic trapping concentrator, we could achieve a maximum concentration factor of ∼800 for DNA and a limit of detection of 10 nM within 15 min. In terms of the detection speed, it enabled faster hybridization by around 10-fold when compared to conventional diffusion-based hybridization. A significant advantage of our approach is that the fabrication of the microfluidic concentrator is completely decoupled from the microarray; by eliminating the need to deposit an ion-selective layer on the microarray surface prior to device integration, interfacing between both modules, the PDMS chip for electrokinetic concentration and the substrate for DNA sensing are easier and applicable to any microarray platform. Furthermore, this fabrication strategy facilitates a multiplexing of concentrators. We have demonstrated the proof-of-concept for multiplexing by building a device with 5 parallel concentrators connected to a single inlet/outlet and applying it to parallel concentration and hybridization. Such device yielded similar concentration and hybridization efficiency compared to that of a single-channel device without adding any complexity to the fabrication and setup. These results demonstrate that our concentrator concept can be applied to the development of a highly multiplexed concentrator-enhanced microarray detection system for either genetic analysis or other diagnostic assays.
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