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Precise design and operational control of the polymerase chain reaction process is key to the performance of on-chip DNA analysis. This research is dedicated to understanding the fluid flow and heat transfer mechanisms occurring in continuous flow PCR chips from the engineering point of view. In this work, a 3-dimensional model was developed to simulate the electrical potential field, the flow field, and the temperature field in an electroosmosis-based continuous flow PCR chip. On the basis of the simultaneous solution to this model, the effects of the channel/chip size, the chip material, and the applied voltage difference on the temperature distribution and control are discussed in detail. The importance of each heat transfer mechanism for different situations is also discussed. It was found that if a larger chip thickness or a material with a lower heat conductivity was used, the temperature in the microfluidic PCR chip would decrease dramatically. The effects of the applied electrical field strength and flow velocity on the temperature distribution, however, are negligible for microchannels with a small cross-sectional area. With bigger channels, the flow direction will affect the temperature distribution in the channel because heat convection will dominate heat transfer. [ABSTRACT FROM AUTHOR]

The precise control of the loaded and dispensed sample amount in crossing microchannels is key to the performance of many lab-on-a-chip devices. The fundamental understanding of the complicated electrokinetic phenomena in such crossing type microchannels therefore is necessary. In the literature, a few theoretical models studying the transport phenomena in similar crossing microchannels did not consider the spatial gradients of conductivity due to its complexity. However, the spatial gradients of electrical conductivity of buffer solution often exist in many applications (i.e. pumping a large number of unknown species and stacking the interested sample species) and it was demonstrated that the presence of the conductivity gradients has significant influences on the on-chip microfluidic injection processes. A new theoretical model was developed in this paper to study the transport phenomena in crossing microchannels with the consideration of a large range of spatial gradient of electric conductivity. This developed model was used to simulate the potential field, flow field, and concentration field of the injection processes where the conductivity of the sample-carrying buffer differs significantly from that of the driving buffer. The transport phenomena are found to be very sensitive to the conductivity difference between the sample-carrying buffer and the driving buffer. The developed model here can be employed to find the optimal voltages for controlling the dispensed sample size and to provide guidance for designing such a crossing microchannel in lab-on-a-chip devices. [Copyright &y& Elsevier]

Non-invasive contactless simultaneous sensing and heating of individual droplets would allow droplet microfluidics to empower a wide range of applications. However, it is challenging to realize simultaneous sensing and heating of individual droplets as the resonance frequency of the droplet fluid, which is decided by its permittivity, must be known so that energy is only supplied at this frequency for droplet heating with one resonator. To tailor the energy transfer in real-life heating applications, the droplet has to be sensed first to identify its corresponding resonance frequency, which is used to dynamically tune the frequency for supplying the required energy for heating this particular droplet. To achieve this goal, two resonators are needed, with one for sensing and one for heating. Integrating multiple resonators into one typical microfluidic device limits placement of the resonators to be as close as possible, which would raise the concern of crosstalk between them. The crosstalk would result in inaccurate sensing and heating. This study focuses on numerically and experimentally investigating the effect of influencing parameters on the crosstalk between two adjacent resonators with the ultimate goal of providing guidance for multiplexing the resonators in a typical microfluidic device. ANSYS HFSS is used to perform the electromagnetic analysis based on the finite element method. Experimental studies are conducted on a microfluidic chip integrated with two resonators to validate the numerical results. An optimal distance between two resonators is suggested, with the recommendation for the resonator size and heating power towards simultaneous sensing and heating of individual droplets. [ABSTRACT FROM AUTHOR]

Polydimethylsiloxane (PDMS) is a widely used material for microfluidic devices due to its low cost, superior optical properties and fast iterative design process. Its softness however creates challenges for the device design and operation because part of the applied pressures contributes to deform chips instead of controlling the flow. The resulting dynamic behaviour is often ignored in passive microfluidic that focuses on the static behaviour of the chip, however, can cause low accuracy to active microfluidic that actuates flow frequently. Therefore, understanding the dynamic behaviour of microfluidic devices due to material compliance is of fundamental and practical importance. In this study, the microfluidic chip compliance is carefully considered by separating it from the sample tubing compliance. The capacitance is retrieved by assuming a symmetric RC circuit based on the experimentally determined time constant and chip resistance. The experimental capacitance is compared to a theoretical formula for chip designs with different height-to-width ratios and height-to-length ratios and for various fluids. The accuracy is within one order of magnitude that is much closer than previous approximations. [ABSTRACT FROM AUTHOR]