3D Hydrodynamic Focusing in Microscale Optofluidic Channels Formed with a Single Sacrificial Layer.

Erik S Hamilton,Aaron R Hawkins,Vahid Ganjalizadeh,Holger Schmidt,Joel G Wright

doi:10.3390/mi11040349

Erik S Hamilton, Aaron R Hawkins + Show 3 more

Open Access

https://doi.org/10.3390/mi11040349

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Abstract

Optofluidic devices are capable of detecting single molecules, but greater sensitivity and specificity is desired through hydrodynamic focusing (HDF). Three-dimensional (3D) hydrodynamic focusing was implemented in 10-μm scale microchannel cross-sections made with a single sacrificial layer. HDF is achieved using buffer fluid to sheath the sample fluid, requiring four fluid ports to operate by pressure driven flow. A low-pressure chamber, or pit, formed by etching into a substrate, enables volumetric flow ratio-induced focusing at a low flow velocity. The single layer design simplifies surface micromachining and improves device yield by 1.56 times over previous work. The focusing design was integrated with optical waveguides and used in order to analyze fluorescent signals from beads in fluid flow. The implementation of the focusing scheme was found to narrow the distribution of bead velocity and fluorescent signal, giving rise to 33% more consistent signal. Reservoir effects were observed at low operational vacuum pressures and a balance between optofluidic signal variance and intensity was achieved. The implementation of the design in optofluidic sensors will enable higher detection sensitivity and sample specificity.

Highlights

The optofluidic detection of particles in liquid waveguide channels has recently grown in significance [1,2,3,4,5,6,7]
Fluorescent beads representing molecules of interest were analyzed to find 33% more consistent signal with focusing
The reservoir effects were observed at low operational vacuum pressures and an optimal detection scheme was used to maximize signal consistency while maintaining high signal intensity

Summary

Introduction

The optofluidic detection of particles in liquid waveguide channels has recently grown in significance [1,2,3,4,5,6,7]. The intersecting of solid-core waveguides with liquid-core waveguides enables light-matter interaction, such as fluorescence generation for single molecule detection. This is especially interesting for identification of particles in liquid, such as disease pathogens [8,9,10,11,12,13,14]. Fluid that is in the center of the channel flows faster than fluid at the walls This means fluorescent particles, being distributed evenly through a channel, would spend different amounts of time in perpendicular excitation light beams as they flow past excitation points introducing variation in excitation times and fluorescent signal generation.

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