Structural and functional imaging of 3D microfluidic mixers using optical coherence tomography

Abstract

To achieve high mixing efficiency in microfluidic devices, complex designs are often required. Microfluidic devices have been evaluated with light and confocal microscopy, but fluid-flow characteristics at different depths are difficult to separate from the en face images produced. By using optical coherence tomography (OCT), an imaging modality capable of imaging 3D microstructures at micrometer-scale resolutions over millimeter-size scales, we obtained 3D dynamic functional and structural data for three representative microfluidic mixers: a Y channel mixer, a 3D serpentine mixer, and a vortex mixer. In the serpentine mixer, OCT image analysis revealed that the mixing efficiency was linearly dependent on the Reynolds number, whereas it appeared to have exponential dependence when imaged with light microscopy. The visual overlap of fluid flows in light-microscopy images leads to an overestimation of the mixing efficiency, an effect that was eliminated with OCT imaging. Doppler OCT measurements determined velocity profiles at various points in the serpentine mixer. Mixing patterns in the vortex mixer were compared with light-microscopy and OCT image analysis. These results demonstrate that OCT can significantly improve the characterization of 3D microfluidic device structure and function.

Evaluation of Microfluidic Biosensor Development Using Microscopic Analysis of Molecular Beacon Hybridization Kinetics

“…This study showed that mixing through diffusion is efficient for stop-flow reactions in microfluidic devices. In a related study, we characterized mixing patterns in more complex microfluidic devices designed for enhancing mixing under continuous flow conditions (Xi et al, 2004).…”

“…Although the fabrication and use of microfluidic devices has been highly successful, the understanding of flow phenomena and biochemical reaction kinetics in these systems is still limited because of the lack of appropriate analysis tools. In the past, several methods have been used to characterize flow phenomena in microfluidic devices including light microscopy (Therriault et al, 2003), confocal microscopy (Liu et al, 2000;Stroock et al, 2002), laser particle velocimetry (Grant, 1997;Meinhart et al, 1999), fluorescence correlation spectroscopy (Brinkmeier et al, 1999;Dittrich and Schwille, 2002) and optical coherence tomography (Schaefer et al, 2004;Xi et al, 2004). However, few studies have investigated real-time biochemical reaction kinetics in microfluidic devices (Kamholz et al, 1999;Liu et al, 2000).…”

Optical imaging techniques in microfluidics and their applications

“…So usually OCT is not used to obtain images of the samples in the microfluidic channel. Instead, it can be used to measure the flow velocity of the fluid in microfluidic channels [34][35][36][37][38][39] A typical setup for a Doppler OCT system 38 is shown in Fig. 1(a), where the spectral domain OCT is used.…”

Characterization of microfluidic mixing and reaction in microchannels via analysis of cross-sectional patterns

“…3D-image reconstruction is a promising means to interpret a flow field exactly, so avoiding poor estimates. These techniques include magnetic-resonance imaging ͑MRI͒, 25 nuclear-magneticresonance ͑NMR͒ microscopy, [26][27][28] circular-dichroism spectra with synchrotron radiation ͑CDSR͒, 29 and optical-coherence tomography ͑OCT͒, 30,31 and the use of a deconvolution microscope, 32 laser-sheet illumination microscope, 33 confocal microscope, 34 two-photon absorption fluorescence microscope, 35 and a coherent anti-Stokes Raman scattering ͑CARS͒ microscope. 36 They have received much attention in the biological and medical fields, and their application to microfluidics is thriving.…”