Comparing polyelectrolyte multilayer-coated PMMA microfluidic devices and glass microchips for electrophoretic separations

Abstract

There is a continuing drive in microfluidics to transfer microchip systems from the more expensive glass microchips to cheaper polymer microchips. Here, we investigate using polyelectrolyte multilayers (PEM) as a coating system for PMMA microchips to improve their functionality. The multilayer system was prepared by layer-to-layer deposition of poly(diallyldimethylammonium) chloride and polystyrene sulfonate. Practical aspects of coating PMMA microchips were explored. The multilayer buildup process was monitored using EOF measurements, and the stability of the PEM was investigated. The performance of the PEM-PMMA microchip was compared with those of a standard glass microchip and a PEM-glass microchip in terms of EOF and separating two fluorescent dyes. Several key findings in the development of the multilayer coating procedure for PMMA chips are also presented. It was found that, with careful preparation, a PEM-PMMA microchip can be prepared that has properties comparable--and in some cases superior--to those of a standard glass microchip.

Fig. 1

a. Schematic of a single lane on the ACLARA lab card. The reservoir abbreviations are sample (A), buffer (B), sample waste (C), and buffer waste (D). The distances from the reservoirs of the injection channel to the separation channel are 14 mm for A to E and 4 mm for C to F. The injection channel is a 0.25 mm offset T design (E to F). The distance from reservoir B to the intersection of E is 8 mm. The distance from reservoir D to the intersection of F is 44 mm. b. Schematic of in-house PMMA microchip. The reservoir abbreviations are sample (A), buffer (B), sample waste (C), and buffer waste (D). The distances from the reservoirs to the center of the intersection (E) are 4 mm for A, B, and C and 39 mm for D (separation channel). Channel width and depth were 100 µm and 80 µm, respectively.

Fig. 2

Image of typical clog formation at the sample reservoir in an ACLARA microchip.

Fig. 3

Electroosmotic flow of the microchannel vs. the layer number. The positive EOF values indicate that the EOF is flowing toward the cathode (normal polarity) and the negative EOF values indicate that the EOF is flowing toward the anode (reverse polarity).

Fig. 4

Electropherogram showing separation of (1) fluorescein and (2) FITC on a PEM-PMMA microchip. Note that the time shown includes a 100 s gap between the run time and the time the detection system started. Separation conditions as detailed in the Experimental section.