A stand-alone and portable microfluidic platform for quantitative multi-step assays

C. Parent, N. Verplanck, J- L. Achard, F. Boizot, R. Charles, Y. Fouillet
CEA-LETI,
France

Keywords: microfluidic, lab on a chip, mutli step assays, quantitative assays

Summary:

This paper reports an automated platform for quantitative multi-step assays composed of two main components: a microfluidic chip using collapsible chambers pneumatically actuated and a portable instrument to automate the fluidic operations. To achieve a complete biological assay on a microfluidic chip, major fluidic operations such as volume calibration, fluid transfer, mixing, aliquoting have to be implemented. Moreover, for a quantitative assay, our strategy is to integrate a dilution range to generate an internal calibration. Standards solutions at different concentrations are prepared in the chip to perform a calibration curve and to compare the sample measurement to this curve. This multi-step long process has to be controlled as precisely as in laboratory. This purpose is achieved with a solution using an array of collapsible chambers and microvalves. (Figure 1-A). The device is composed by a hyper elastic membrane (Ecoflex, Smooth on) positioned between two Cyclic Olefin Copolymer (COC) micro milled credit card format cards. The membrane is actuated through the pneumatic layer to shift the chambers and valves between two states (Figure 1-B). To close the chambers, compressed air is injected through the pneumatic layer. Then, fluid is transferred where pressure is released. This method is more adapted to control discrete volumes than continuous flow [1] and handles a high range of volume (from ┬ÁL to mL) compared to digital microfluidic using PDMS [2]. Another issue is to carry out the operations in parallel to limit the number of actuators and to simplify the automaton. An X-Y architecture is used to actuate each column of valves or chambers simultaneously. As examples of quantitative and multi-step assays, a glucose assay and a homogeneous ELISA test have been conducted using this architecture and this technology (Figure 3-5). Reagents are injected in the Y direction and mixed in the X direction. Valves are closed between the chambers to avoid contaminations. These tests have validated essential fluidic operations such as volumes calibration, aliquoting and mixing. These architectures integrate dilutions to calibrate the tests (dilutions factors up to 64). In a few steps, eight dilutions are achieved in parallel. The stretchable chambers offer a complete filling and emptying which produces precise volumes (Figure 2-4). The X-Y architecture is versatile and is currently used to validate heterogeneous ELISA tests which include washing steps. An instrument compatible with these microfluidic chips has been developed (Figure 6). The portable instrument is 10 x 14 x 24 cm (height x width x depth). The main components operated by an Arduino mega microcontroller include micropumps, pressure sensors and solenoids valves. The inputs and the outputs are standardized to use the same instrument for different microfluidic chips. The user can select and start a protocol through the touch screen. The combination of this technology and this architecture offers the possibility to perform multi-step and quantitative assays in a stand-alone and portable platform. 1.S. K. W. Dertinger et al, 2001 2.E. C. Jensen et al, Lab Chip, 2013