Abstract
The rapid growth of microfluidic cell culturing in biological and biomedical research and industry calls for fast, non-invasive and reliable methods of evaluating conditions such as pH inside a microfluidic system. We show that by careful calibration it is possible to measure pH within microfluidic chambers with high accuracy and precision, using a direct single-pass measurement of light absorption in a commercially available phenol-red-containing cell culture medium. The measurement is carried out using a standard laboratory microscope and, contrary to previously reported methods, requires no modification of the microfluidic device design. We demonstrate the validity of this method by measuring absorption of light transmitted through 30-micrometer thick microfluidic chambers, using an inverted microscope fitted with a scientific-grade digital camera and two bandpass filters. In the pH range of 7-8, our measurements have a standard deviation and absolute error below 0.05 for a measurement volume smaller than 4 nL.
Highlights
Microfluidic devices are promising for a wide range of bioapplications [1]
We demonstrate the validity of this method by measuring absorption of light transmitted through 30-micrometer thick microfluidic chambers, using an inverted microscope fitted with a scientific-grade digital camera and two bandpass filters
We demonstrate that an accurate evaluation of pH in a conventional microfluidic system is possible using only a single-pass absorption measurement and standard imaging equipment
Summary
Microfluidic devices are promising for a wide range of bioapplications [1]. Microfluidic devices designed for cell culture first appeared about a decade ago [2] and since a growing number of miniature scale bioreactors for cell culture have been reported, primarily with the aim of bringing experimental resolution closer to the single-cell level. One approach involves incorporating microelectrodes into the culture device that can be connected to off-chip analysis hardware [10] When properly calibrated, this approach can offer fast and precise measurements over a wide range of pH values. An obvious disadvantage is that electrodes embedded into a disposable chip increase fabrication complexity and call for a designed culture platform This system requires about half a microliter of fluid for the measurement [10], which is an order of magnitude larger than in some reported bioreactors [11]. Our approach offers a simple and accurate method to measure pH of commercially available culture media in microfluidic chambers (based, e.g., on PDMS or any other optically transparent material), using only nL of culture medium as the actual measurement volume. Our results show how proper image analysis and calibration allows such imaging equipment (available in most biomedical research labs) to be used directly for the measurement of variables that can be linked to spectral modifications of optical absorption, in liquids or thin solid sections, even when the level of absorption is very small (
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
