270182 Temperature Measurement in a Microfluidic Device for Insulator-Based Dielectrophoretic Applications

Monday, October 29, 2012: 9:45 AM
408 (Convention Center )
Asuka Nakano, Kathleen Bush and Alexandra Ros, Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ

Temperature Measurement in a Microfluidic Device for Insulator-based Dielectrophoretic Applications

Asuka Nakano, Kathleen Bush, Alexandra Ros

Department of Chemistry and Biochemistry, Arizona State University, Tempe AZ, 85287

Direct current (DC) insulator-based dielectrophoresis (iDEP) has been used with cells and biomolecules such as DNA and proteins for separation, pre-concentration, and fractionation. Unlike the other existing analytical techniques, DEP response is governed by a particle's polarizability in an inhomogeneous electric field. This additional parameter space facilitates improved separation in a gel-free environment, which is of particular importance for more complex samples such as disease markers found in body fluids. DC iDEP has potential to be used as an alternative to AC iDEP since DC iDEP does not require electrokinetic and/or pressure pumps necessary in AC iDEP experiments.

The application of large DC voltage in iDEP results in heat generation known as Joule heating within the microfluidic device.  This phenomenon is of great interest due to its influence on protein migration1 as well as protein stability.  In this work we present a means to measure fluid temperature in microfluidic systems by implementing fluorescent microscopy that enables dual color detection with an optical splitter and a CCD camera. Our previous work demonstrated DEP streaming of monomeric immunoglobulin G (IgG) due to positive DEP, however, unlike DNA and cells, the mechanisms of protein polarization remain less understood. Furthermore, additional electroosmotic and electrophoretic forces interplay with DEP resulting in complex protein migration behavior.  Fluid temperature due to Joule heating is another factor, which has not been thoroughly investigated experimentally in iDEP. Therefore our study provides novel information to develop iDEP devices for separation, concentration, and fractionation.

In this work, we demonstrate a way to quantify the fluorescence emission ratio of two dyes2: Rhodamine B (RhB), a temperature sensitive dye, and Rhodamine 110 (Rh110), a temperature insensitive dye, using the same device developed for our IgG DEP experiments. While the emission intensity of RhB is proportional to the local temperature, it is biased by variations in the illuminating fluorescence light intensity. To eliminate the potential bias, we employed the two dye system and performed quantitative analysis by referencing the RhB fluorescence intensity with the Rh110 fluorescence intensity. Experiments were performed under the same buffer conditions and applied potentials to mimic the conditions of successful iDEP protein streaming. Over a period of 30 minutes, we tracked the change in temperature as well as temperature variations in different locations around the post regions and within the reservoirs.

Our preliminary experiments show that there is no significant temperature rise either within the channel or the reservoir despite minor challenges associated with these dyes such as photobleaching and non-specific adsorption of RhB to the PDMS surface. Our results demonstrate that the effects of Joule heating are small, which can be explained by two reasons. First, the temperature does not increase significantly within the channel since the bulk liquid is consistently refreshed by electrokinetic flow thus minimizing an increase in temperature. Second, the temperature within the reservoir does not vary to a large extent owing to the large solution volumes (~70 µL). Even though Joule heating is present, heat is dissipated causing the solution to remain at room temperature.

In addition to DC iDEP, our scope can be further expanded to temperature measurement within a channel with smaller structures and constrictions (i.e. nano-posts). With combination of AC iDEP, the nanostructures have potential to create larger DEP force and to immobilize proteins via DEP (DEP trapping). Thus, it is of importance to measure temperature fluctuations since a larger Joule heating effect is expected with such small constrictions.  Our study therefore provides valuable information of the micro- and nano-environment, in which protein iDEP experiments are performed leading to more profound understanding of protein iDEP.

References

(1)    Chaurey, V.; Polanco, C.; Chou, C.-F.; Swami, N. S. Biomicrofluidics 2012, 6, 012806–14.

(2)    Ross, D.; Locascio, L. E. Anal. Chem. 2002, 74, 2556–2564.

 


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