Surface-Charge Induced Ion Depletion and Sample Stacking near Single Nanopores in Microfluidic Devices

Abstract

We report integrated nanopore/microchannel devices in which single nanopores are isolated between two microfluidic channels. The devices were formed by sandwiching track-etched conical nanopores in a poly(ethylene terephthalate) membrane between two poly(dimethylsiloxane) microchannels. Integration of the nanopores into microfluidic devices improves mass transport to the nanopore and allows easy coupling of applied potentials. Electrical and optical characterization of these individual nanopores suggests double layer overlap is not required to form an ion depletion region adjacent to the nanopore in the microchannel; rather, excess surface charge in the nanopore contributes to the formation of this ion depletion region. We used fluorescent probes to optically map the ion depletion region and the stacking of fluorescein near the nanopore/microchannel junction, and current measurements confirmed formation of the ion depletion region.

Interconnected ordered nanoporous networks of colloidal crystals integrated on a microfluidic chip for highly efficient protein concentration

“…Obviously, the concentration is a dynamic balance between electroosmotic and electrophoretic transport. This enrichment mechanism is consistent with the ''surface-charge induced ion depletion effect (SCIIDE)'' proposed by Jacobson and his co-workers [42] and can well explain why longer enrichment time is required in the case of samples with lower concentration (e.g. 100 ng/mL, inset in Fig.…”

Optofluidic in situ maskless lithography of charge selective nanoporous hydrogel for DNA preconcentration

“…To alleviate these limitations, various techniques have been reported in a form of miniaturized system. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] The conventional way to enhance the sensitivity of detection is to increase the copy number of DNA by the chemical amplification through polymerase chain reaction ͑PCR͒. [1][2][3] However, various components are necessary in PCR chemistry, such as enzymes and primers as well as precise temperature control.…”

“…[4][5][6][7][8][9][10][11][12][13][14][15][16][17] Sample preconcentration exploits various sample characteristics, including electric charge, size, mobility, and affinity. [4][5][6][7][8][9][10][11][12][13][14][15][16][17] DNA has the unique property of having a uniform charge to size ratio, making charge selective preconcentration efficient. Among the preconcentration techniques using the electric property of DNA, the electrokinetic trapping technique has received much attention due to its high sensitivity and easy miniaturization.…”

“…Electrokinetic trapping usually utilizes a charged nanochannel ͑or nanoporous membrane͒ between microchannels, allowing for enrichment of counterions along the structure while excluding coions. [11][12][13][14][15][16][17] The local electric field gradient and concentration polarization are induced when an electric field is applied across the charged nanochannel so that sample preconcentration can be achieved. 17 The electrokinetic trap-ping technique does not suffer from overall device size, since the preconcentration occurs in the immediate proximity of the ion depleted boundary, and has shown a high efficiency for concentrating charged biomolecules.…”

“…For example, multistep lithography and etching steps are required for a monolithic nanochannel fabrication between microchannels 11 and the incorporation of a charged nanoporous membrane between microchannels by manual alignment does not ensure reproducible characteristics. 12 These issues stimulated research efforts for developing easy fabrication methods, which include the in situ charge selective nanoporous hydrogel fabrication by photopolymerization 17 ͑Fig. 1͒.…”