Abstract
We report the application of a microfluidic device for semi-contact temperature measurement in picoliter volumes of aqueous media. Our device, a freely positionable multifunctional pipette, operates by a hydrodynamic confinement principle, i.e., by creating a virtual flow cell of micrometer dimensions within a greater aqueous volume. We utilized two fluorescent rhodamines, which exhibit different fluorescent responses with temperature, and made ratiometric intensity measurements. The temperature dependence of the intensity ratio was calibrated and used in a model study of the thermal activation of TRPV1 ion channels expressed in Chinese hamster ovary cells. Our approach represents a practical and robust solution to the specific problem of measuring temperature in biological experiments in vitro, involving highly localized heat generation, for example with an IR-B laser.
Highlights
Accurate temperature determination is a key issue in many experimental studies within the fields of physics, chemistry and biology
Many applications involving microfluidic chips depend on temperature measurement and control, mostly performed on flows confined to fluidic channels of micro- to millimeter dimensions
The specific features of the multifunctional pipette provide a remedy to some significant issues of fluorescence based temperature sensing: the virtual flow cell is unaffected by absorption of the dye to the device walls [29], and the fast exchange of rhodamine solutions counteracts fluorescence photobleaching, which has a detrimental effect on the intensity measurements
Summary
Accurate temperature determination is a key issue in many experimental studies within the fields of physics, chemistry and biology. Many microscopy experiments in the life sciences utilize fluorescence or confocal imaging as standard techniques, the additional fluorescence intensity measurements for such a thermosensor does not pose any additional challenge or expense Such systems exhibit disadvantages, including the absorption of the fluorescent dye by the channel walls, most notable in polydimethylsiloxane (PDMS) based microfluidic devices, which hinders accurate fluorescence measurement, or the degradation of the fluorophore by photobleaching [19,22]. The specific features of the multifunctional pipette provide a remedy to some significant issues of fluorescence based temperature sensing: the virtual flow cell is unaffected by absorption of the dye to the device walls [29], and the fast exchange of rhodamine solutions counteracts fluorescence photobleaching, which has a detrimental effect on the intensity measurements. Due to the dual dye/single wavelength intensity ratio measurement, the device needs calibration only once for a given pair of dye concentration values used in the microfluidic devices
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