A novel method for in-situ temperature measurements of microfluidic devices using thin-film poly(dimethylsiloxane) (PDMS) saturated with Rhodamine B dye is reported. Rhodamine B is commonly injected into the working fluid for on-chip temperature field visualization of glass and silicon based microfluidic devices since its fluorescent intensity is temperature dependent. However, such a visualization method results in unreliable temperature measurements for polymeric devices such as PDMS due to high absorption and adsorption. Thus, an inexpensive temperature measurement technique was developed in which a thin PDMS layer (∼30 μm) is fabricated and submersed for several days into a Rhodamine B solution. To prevent backward diffusion of the dye into the working fluid during operation, a glass barrier (∼150 μm) is bonded between the thin film and the PDMS mold containing the microchannel design. Temperature measurements are made by utilizing standard method of measuring changes in the normalized fluorescent intensity. For verification purposes, a new calibration curve is developed and the thin film is tested with a tapered microchannel subjected to joule heating. The resulting temperature field along the axial direction of the channel for different input power compares well with numerical simulations. Errors in temperature measurement due to the current design are discussed.

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