A Simple Opto-Fluidic Switch Detecting Liquid Filling in Polymer-Based Microfluidic Systems

Abstract

A novel detection scheme for detection of liquid levels and bubbles in microfluidic systems, using the principle of total internal reflection (TIR) is presented. A laser beam impinges on the side walls of a channel which are inclined at 45°. In an unfilled channel of such a "V-groove", TIR deflects the beam by 900 into a simple light detector. Upon the presence of liquid, the refractive index in the channel changes, thus eliminating deflection by TIR. The detection principle is robust, requiring no calibration, and tolerating alignment errors of the laser larger than the width and depth of the microfluidic channels. The machining of the V-groves can seamlessly be integrated into common polymer microfabrication schemes such as injection molding.

Optical non-contact localization of liquid-gas interfaces on disk during rotation for measuring flow rates and viscosities

“…unprecedented dynamic recordings of flow rates and viscosities during rotation are enabled by a line laser and linear image sensor in contrast to the static scanning principle of our previous work. 22 The spatial resolution could be further increased by using a linear image sensor featuring a pixel pitch ,50 mm. This would improve the measuring precision because the meniscus could be pinpointed more accurately.…”

“…To this end, we previously presented a technique based on TIR on the channel wall to localize liquid-gas interfaces in microchannels at rest. 22 In this contribution, we present its implementation on a centrifugal microfluidic platform. [23][24][25][26][27][28] Our technique is based on linear illumination and detection elements allowing quasi-continuous meniscus detection (e.g.…”

The centrifugal microfluidic Bio-Disk platform

“…To tackle this problem, we elaborated an optical guidance based on the total internal reflection at polymer-air interface of V-grooves incorporated the backside of the substrate (figure 15, right) [61][62][63]. Under perpendicular incidence, the beam is deflected by 90 • into the plane of the substrate to probe the measurement chamber.…”

TIR-Based Dynamic Liquid-Level and Flow-Rate Sensing and its Application on Centrifugal Microfluidic Platforms

“…Figure 5 demonstrates the capability of the system to measure the dynamic viscosity of low-viscosity liquids. The unprecedented dynamic recordings of the flow rates and viscosities during rotation are enabled by the linear optical elements in contrast to the static scanning principle of our previous work [3]. The previously described glycerol solutions are used to highlight the correlation between the measured viscosities and the reference viscosities.…”

“…To this end, we recently presented a technique based on TIR on the channel wall to localize liquid-gas interfaces in microchannels at rest [3].…”