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

Abstract

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 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.

Multimodal biophotonic workstation for live cell analysis

“…The setup that is incorporated here uses two beam-coupling in a photorefractive barium titanate crystal to achieve background suppression and quantitative phase-measurements in a mapping area of 0 j p [12]. Due to these working characteristics, DynPCM provides a high Signal-to-Noise-Ratio, even for pure phase-objects [13]. In this experiment, the focus is on the novelty filtering capability of the setup.…”

Depth-resolved velocimetry of Hagen–Poiseuille and electro-osmotic flow using dynamic phase-contrast microscopy

“…Using a two-wavelength setup, phase measurements up to several π have been demonstrated. With this phase resolution, it is possible to observe mixing processes of fluids with a very small refractive index difference using DynPCM [24].…”