MEMS-Based Thermal and Mass-Transport Control for Microfluidic Biochemical Reagent Mixing and 2-D Gas Chromatography.

Abstract

This research demonstrates the use of microelectromechanical systems (MEMS) technology to control microscale heat and mass transfer for lab-on-a-chip biochemical assays and the analysis of complex vapor mixtures. Toward this goal, we have developed two microdevices, namely (1) a micromixer and (2) a microthermal modulator. The micromixer uses natural convection to greatly simplify the micromixing process in a microfluidic network, whereas the microthermal modulator utilizes forced convection to manipulate vapor samples in a fast, low-power consuming manner within a comprehensive 2-D gas chromatography system. In a microfluidic network, micromixing is a crucial step for biochemical analysis. A critical challenge is that the microfluidic systems need numerous chambers and channels not only for mixing but also for biochemical reactions and detections. Thus, a simple and compatible design of the micromixer element for the system is essential. Here, we demonstrate a simple, yet effective, scheme that enables micromixing and biochemical reaction in a single chamber without using any mechanical components. We accomplish this process by using natural convection in conjunction with two alternating heaters for micromixing. As a model application, we demonstrate PCR and its reagent mixing in a single microfluidic chamber. Our results will significantly simplify the micromixing and subsequent biochemical reactions. In comprehensive two-dimensional gas chromatography (GCxGC), a modulator is placed at the juncture between two separation columns to focus and re-inject eluting mixture components, thereby enhancing the resolution and the sensitivity of the analysis. Here, we present the design, fabrication, thermal operation, and initial testing of a two-stage microscale thermal modulator (µTM). The µTM contains two sequential serpentine Pyrex-on-Si microchannels (stages) that cryogenically trap analytes eluting from the first-dimension column and thermally inject them into the second-dimension column in a rapid, programmable manner with low thermal crosstalk between the two stages. A lumped heat transfer model is used to analyze the device design with respect to the rates of heating and cooling, power dissipation, and inter-stage thermal. Preliminary tests using a conventional capillary column interfaced to the µTM demonstrate the modulation of a mixture of alkanes.