Method for Microfluidic Whole-Chip Temperature Measurement Using Thin-Film Poly(dimethylsiloxane)/Rhodamine B

Abstract

A novel method is presented for on-chip temperature measurements using a poly(dimethylsiloxane) (PDMS) thin film dissolved with Rhodamine B dye. This thin film is sandwiched between two glass substrates (one of which is 150 microm thick) and bonded to a microchannel molded in a PDMS substrate. Whole-chip (liquid and substrate) temperature measurements can be obtained via fluorescent intensity visualization. For verification purposes, the thin film was tested with a tapered microchannel subjected to Joule heating, with resulting axial temperature gradients comparing well with numerical simulations. Errors induced by the definite film thickness are discussed and accounted for during experimental and analytical analysis. Alternative validation using the traditional in-channel Rhodamine B injection method was also attempted. The thin film has several advantages over traditional methods. First, false intensity readings due to adsorption and absorption of Rhodamine B into PDMS channels are eliminated. Second, whole-chip temperature measurements are possible. Third, separation of working liquid from Rhodamine B dye prevents possible electrophoresis effects.

Thermometry at the nanoscale

“…The temperature mapping on microfluidic devices using dyes as fluorescent thermometers was also considered by Samy et al 17 and, more recently, by Jung et al 15 RhB was incorporated in PDMS and SU8 polymer matrices and the temperature was determined from the optically active thin layer covering the microfluidic device. Samy et al 17 used an intermediate substrate between the fluid and the sensing layer, while Jung et al A quite different dye-based luminescent molecular thermometer able to map the temperature gradient on a fluid was recently developed by Feng et al 21 It consisted of a pyrene-containing triarylboron molecule, DPTB, showing temperature-dependent green to blue luminescence with quantum yield greater than 0.64 over the temperature range 223-373 K, that was dissolved in MOE. The temperature can be determined by the blueshift of the broad emission spectra, ascribed to the thermal equilibrium between twisted intramolecular charge transfer and local excited state of the DPTB molecule.…”

Microwave Dielectric Heating of Fluids in Microfluidic Devices

“…The general trend of all three curves is similar. The difference between the curve of Samy et al, 2008 and the other two authors can be explained by the different physical medium and local environment used in the measurements.…”

“…The RhB solution has been employed: to examine in-channel temperature and flow profiles at a T-shaped microchannel intersection during electrokinetic pumping (Erickson et al, 2003) and to characterize the temperature field resulting from resistive microheaters embedded in a poly(dimethylsiloxane) (PDMS) microchip (Fu et al, 2006). Even though the RhB has been primarily used for temperature measurement in aqueous environment, the absorbed RhB dye molecules in a PDMS thin film can be used for whole chip temperature measurement (Samy et al, 2008). The calibration equations used for computing temperature using fluorescent dyes relate the fluorescence intensity at an unknown temperature to the intensity at only one particular reference temperature.…”

“…to fit the measured IRT(T) for different values of T. Table 1 includes the values of A0 to A3 that were reported by Fu et al, 2006;Ross et al, 2010;and Samy et al, 2008. The temperatures T0 given by eqn.…”

Evaluation of Microvalves Developed for Point-of-Care Testing Devices Using Shape-Memory Polymers

“…In addition, the heating power of the microvalve was calculated from the applied voltage and the resistance of the microheater. 2.3 Temperature measurement by LIF spectroscopy Measuring the temperature of a very small amount of liquid is not straightforward, and a promising approach to addressing this issue is to use the temperature-dependent fluorescence intensity of dyes [14][15][16][17][18][19]. Generally, fluorescence intensity decreases with increasing temperature owing to the increase in collision frequency between dye and solvent molecules, and this phenomenon is called "temperature quenching".…”