Theoretical and numerical analysis of temperature gradient focusing via Joule heating

Abstract

We present a detailed theoretical and numerical analysis of temperature gradient focusing (TGF) via Joule heating-an analytical species concentration and separation technique relying upon the dependence of an analyte's velocity on temperature due to the temperature dependence of a buffer's ionic strength and viscosity. The governing transport equations are presented, analyzed, and implemented into a quasi-1D numerical model to predict the resulting temperature, velocity, and concentration profiles along a microchannel of varying width under an applied electric field. Numerical results show good agreement with experimental trials presented in previous work. The model is used to analyze the effects of varying certain geometrical and experimental parameters on the focusing performance of the device. Simulations also help depict the separation capability of the device, as well as the effectiveness of different buffer systems used in the technique. The analysis provides rule-of-thumb methodology for implementation of TGF into analytical systems, as well as a fundamental model applicable to any lab-on-a-chip system in which Joule heating and temperature-dependent electrokinetic transport are to be analyzed.

Joule heating effects on electrokinetic focusing and trapping of particles in constriction microchannels

“…It is noted that similar microchannels have also been demonstrated to implement the so-called temperature gradient focusing of ionic species via JH of the background buffer solution [29][30][31][32].…”

Recent progress of online sample preconcentration techniques in microchip electrophoresis

“…In the capillary format, however, the combination with different chemical operation units is more difficult than the microfluidic devices. To solve this problem, a tapered microchannel on a PDMS chip is applied to TGF for the formation of the gradient of Joule heating [107,108]. By using a single channel device without applying pressure, the concentration of FITC-labeled BSA is increased to at least 200-fold within 2 min.…”

Bioanalytical separations using electric field gradient techniques

“…Joule heating as a means of generating a temperature gradient, as opposed to an external source, was modeled by various groups [87,89]. Joule heating occurs when an electric field is applied along the length of a conducting medium [97].…”

“…Although Joule heating is an appealing option for many TGF devices because of its speed, simplicity, and low power requirements, runaway heating is often a problem. A quasi-1-D numerical model was generated by Sommer et al [87] to account for thermal behavior and species transport in a microchannel. Various channel geometries were also examined to enhance device performance; narrow channels performed faster separations with higher concentrations but were less stable due to runaway heating.…”