Compact Microfluidic Platform with LED Light-Actuated Valves for Enzyme-Linked Immunosorbent Assay Automation

Abstract

Lab-on-a-chip devices incorporating valves and pumps can perform complex assays involving multiple reagents. However, the instruments used to drive these chips are complex and bulky. In this article, a new wax valve design that uses light from a light emitting diode (LED) for both opening and closing is reported. The valves and a pumping chamber are integrated in lab-on-a-foil chips that can be fabricated at low cost using rapid prototyping techniques. A chip for the implementation of enzyme-linked immunosorbent assays (ELISA) is designed. A porous nitrocellulose material is used for the immobilization of capture antibodies in the microchannel. A compact generic instrument with an array of 64 LEDs, a linear actuator to drive the pumping chamber, and absorbance detection for a colorimetric readout of the assay is also presented. Characterization of all the components and functionalities of the platform and the designed chip demonstrate their potential for assay automation.

Keywords: lab-on-a-chip; lab-on-a-foil; microfluidic ELISA; wax valve.

Figure A1

Circuit for LED row-column addressing.

Figure A2

Microscope images of valves with the bottom polyester layer removed (a) after opening, and (b) after closing. Scale bars are 250 µm; (c) SEM image of an open valve with the bottom polyester layer removed; (d) SEM image of an open valve from the tunnel entrance side.

Figure A3

Dependence of the volume displaced by the pumping chamber on the relative position of the actuator.

Figure A4

Images of the chip at different steps of an assay-like test. The black arrows indicate the open valves.

Figure A5

Images of the pump before and after an assay.

Figure 1

(a) A 3D illustration of the valve structure; (b) Cross-sectional representation of the valve opening; (c) Two different configurations of the wax valve; (d) Complete fluidic schematic of the ELISA chip.

Figure 2

Schematic illustration of (a) the pumping system, and (b) the absorbance measurement system.

Figure 3

(a) Valve with wax-loading port full of wax; (b) Penetration of the wax inside the channel by capillarity; (c) Formation of the wax barrier on top of the heater. Bottom drawings are cross-sectional illustrations of the process.

Figure 4

(a) Chip; (b) Instrument; (c) Chip on the instrument; (d) Optical microscope images before and after opening and closing a reservoir valve. Arrows indicate the direction of the flow (a white piece of paper was interposed between the valve and the LED during image captures for improved visualization). Scale bars are 200 µm; (e) Black field optical microscope image of an open reservoir valve. The liquid has been removed to enhance the visualization of the tunnel. Scale bars are 500 µm; (f) Priming valve before and after opening (the LED outline can be seen underneath the valve through the transparent polyester films). Scale bars are 200 µm.

Figure 5

(a) Calibration of the flow rate vs. actuator velocity; (b) Calibration of the pressure vs. actuator displacement (all valves closed). Dashed lines are guides to the eye.

Figure 6

(a) Absorbance measurement for oxidized TMB. Comparative with a plate reader; (b) Photodiode output voltage signal for different dye solutions (and different activated LEDs) in relation to the values obtained for deionized water. The concentration of dyes is the same used for the reagents; (c) Calibration of the pressure measurement based on the compression of air in a dead-end channel.

Figure 7

(a) Photodiode signals for two TNFα concentrations; (b) Absorbance response to different TNFα concentrations. Each data point is the average of three measurements obtained from three separate chips. The mean absorbance value of the blanks has been subtracted from the absorbance values obtained for all other TNFα concentrations.