Multiplexed proteomic sample preconcentration device using surface-patterned ion-selective membrane

Abstract

In this paper, we report a new method of fabricating a high-throughput protein preconcentrator in poly(dimethylsiloxane) (PDMS) microfluidic chip format. We print a submicron thick ion-selective membrane on the glass substrate by using standard patterning techniques. By simply plasma-bonding a PDMS microfluidic device on top of the printed glass substrate, we can integrate the ion-selective membrane into the device and rapidly prototype a PDMS preconcentrator without complicated microfabrication and cumbersome integration processes. The PDMS preconcentrator shows a concentration factor as high as approximately 10(4) in 5 min. This printing method even allows fabricating a parallel array of preconcentrators to increase the concentrated sample volume, which can facilitate an integration of our microfluidic preconcentrator chip as a signal enhancing tool to various detectors such as a mass spectrometer.

Figure 1

Concept of the single-step integration of ion-selective membrane into PDMS preconcentrator by plasma bonding.

Figure 2

Schematics of PDMS precconcentrator with surface-patterned Nafion membrane on the glass substrate and its operation. The middle channel is loaded with a sample and the side channel is filled with a buffer solution. For preconcentration, a potential difference applied across the middle and the side channel in combination with an electrokinectic flow.

Figure 3

Fabrication of PDMS preconcentration device via surface-patterned ion-selective membrane using (a) micro-stamping technique and (b) micro-flow patterning in microchannel.

Figure 4

(a) Optical images of the PDMS preconcentrator chip. All the microchannels were 50 μm deep and 50 μm wide. Scanning electron microscope images of a Nafion patterned glass (b) before and (c) after PDMS bonding. The thickness of the Nafion membrane on glass was 191 nm.

Figure 5

Preconcentration factor and size of the depletion region as a function of voltage difference.

Figure 6

Preconcentration of β-Phycoerythrin protein versus electrokinetic trapping time. This result shows that we can achieve a preconcentration factor of ~ 10⁴ in 5 min. Fluorescence images of 4 nM protein shown next to the graph indicate an increase of the concentrated plug in size and concentration with trapping time.

Figure 7

(a) Array of 10 single preconcentrators, (b) magnified view of a single preconcentrator with electrical configuration and (c) fluorescence images of single preconcentrators in the array.