Abstract
A temperature sensor that uses temperature-sensitive fluorescent dyes is developed. The droplet sensor has a diameter of 40 μm and uses 1 g/L of Rhodamine B (RhB) and 0.5 g/L of Rhodamine 110 (Rh110), which are fluorescent dyes that are dissolved in an ionic liquid (1-ethyl-3-methylimidazolium ethyl sulfate) to function as temperature indicators. This ionic liquid is encapsulated using vacuum Parylene film deposition (which is known as the Parylene-on-liquid-deposition (PoLD) method). The droplet is sealed by the chemically stable and impermeable Parylene film, which prevents the dye from interacting with the molecules in the solution and keeps the volume and concentration of the fluorescent material fixed. The two fluorescent dyes enable the temperature to be measured ratiometrically such that the droplet sensor can be used in various applications, such as the wireless temperature measurement of microregions. The sensor can measure the temperature of such microregions with an accuracy of 1.9 °C, a precision of 3.7 °C, and a fluorescence intensity change sensitivity of 1.0%/K. The sensor can measure temperatures at different sensor depths in water, ranging from 0 to 850 μm. The droplet sensor is fabricated using microelectromechanical system (MEMS) technology and is highly applicable to lab-on-a-chip devices.
Highlights
The temperature control of microfluidic channels is essential for lab-on-a-chip experiments, such as capillary electrophoresis [1]
The sensor fluorescence intensity was defined as the difference between the maximum and minimum gray values, which weredenoted by IRhB for Rhodamine B (RhB) and IRh110 for Rhodamine 110 (Rh110)
The droplet sensor has a diameter of 40 μm and uses Rhodamine B and Rhodamine 110 fluorescent dyes dissolved in an ionic liquid (1-ethyl-3-methylimidazolium ethyl sulfate) as temperature indicators
Summary
The temperature control of microfluidic channels is essential for lab-on-a-chip experiments, such as capillary electrophoresis [1] The temperature in these microfluidic channels is typically measured by imaging temperature-sensitive materials dissolved in liquids. Fluorescent dyes (or thermochromic liquid crystals), and more recently quantum dots, have been used as temperature-sensitive materials because their photoemission intensities are temperature dependent [2,3,4,5,6,7,8]. This method is versatile, and possesses several drawbacks. The dye could not interact with the chemicals in the solution because the droplets were sealed by the chemically stable film
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