Calorimetry is the science of measuring heat. For more than 200 years now, calorimetry has advanced and various types of calorimeters have been developed for diverse applications. The development of microfabrication and microfluidics led to the advent of chip calorimeters, miniaturized calorimeters built and integrated as chips. Chip calorimeters, as labelfree biosensors, have many advantages due to their small sample volume and high-throughput capability. In this review, techniques for realizing chip calorimeters are discussed in terms of their major functional components: insulation, fluid handling, and thermometry. Recent trends in the development of chip calorimeters are also discussed, along with several application areas. New fabrication techniques can provide higher sensitivity and easier, more reliable sample handling for chip calorimeters, which would enable new application areas, such as the study of single cell metabolism.
Inertial microfluidics utilizes fluid inertia from high flow velocity to manipulate particles and fluids in 3D. Acquiring a 3D information of particle positions and complex flow patterns within microfluidic devices requires 3D imaging techniques such as confocal microscopy, which are often expensive and slow. Here, we report on a prism-mirror-embedded microfluidic device that allows simultaneous imaging of the top and side view of the microchannel for a high-speed, low-cost 3D imaging. The microprism mirrors are fabricated and integrated into a microfluidic system using conventional microfabrication techniques including wet etch and soft lithography. This inexpensive high quality prism mirror provides a highly reflective, smooth mirror surface with precise 45 reflection angle, enabling 3D measurement of inertial migration of microparticles in a rectangular channel at speeds in excess of 10 000 frame/s. V
We present a simple but effective method to measure the pressure inside a deformable microchannel using laser scattering in a translucent Scotch tape. Our idea exploits the fact that the speckle pattern generated by a turbid layer is sensitive to the changes in the optical wavefront of an impinging beam. A change in the internal pressure of a channel deforms the elastic channel, which can be detected by measuring the speckle patterns of a coherent laser beam that has passed through the channel and the Scotch tape. We demonstrate that with a proper calibration, internal pressure can be remotely sensed with the resolution of 0.1 kPa within a pressure range of 0-3 kPa after calibration.
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