Label-free analysis of microfluidic mixing processes by dynamic phase contrast microscopy

Frank Holtmann, Mathias Eversloh, Cornelia Denz
2009 Journal of Optics. A, Pure and applied optics  
We demonstrate a dynamic phase contrast microscope based on photorefractive holographic interferometry. This system allows us to quantify concentration changes during micro-mixing processes by measuring the change of the optical path length. Therefore, no labelling processes with dyes or tracers are needed. The obtained interferograms are evaluated by an intensity analysis of every pixel, resulting in a high lateral resolution of about one micrometre, and the possibility of real-time phase
more » ... eal-time phase determination. Due to the interferometric nature of the method the phase measurement is unambiguous for optical phase changes in the interval of zero to π radians. We present the expansion of the phase measurement range by a two-wavelength method, allowing us to resolve concentration changes down to 4 × 10 −6 mol cm −3 and quantify concentrations up to 10 −3 mol cm −3 . The result is an optimization of the resolution by a factor of two and of the dynamic range by a factor of six in comparison to the single-wavelength technique.
doi:10.1088/1464-4258/11/3/034014 fatcat:w6vbmwi4dbcybog7aeykbiljka