Non-invasive pressure sensing in microfluidic chips using laser interferometry

Precision fluid pressure detection in microfluidics is challenging due to the restricted accessibility for integration of pressure sensors. We propose an adapted geometric laser interferometry technique capable of sensing changes in fluid pressure within the microfluidic chips noninvasively. In the past, similar interferometric approaches have been proposed for pressure determination in microfluidic devices; in this study, we experimented a different setup. We allowed a helium-neon laser beam to propagate through the air filled microchannels. We then captured the interference of the reflected waves from the microchip using a high-resolution camera sensor as bright and dark fringes, for applied pressures of 1-10 psi. These fringes shift with changes in air pressure inside the microchannels, and they (fringe shift) are interpreted as related to the changing air index of refraction and density. The use of optical interferometry for microfluidic pressure measurements is limited at this point; however, it is highly promising.