Microfluidics based bioimaging with cost-efficient fabrication of multi-level micrometer-sized trenches

Abstract

Microfluidic devices, through their vast applicability as tools for miniaturized experimental setups, have become indispensable for cutting edge research and diagnostics. However, the high operational cost and the requirement of sophisticated equipment and clean room facility for the fabrication of these devices make their use unfeasible for many research laboratories in resource limited settings. Therefore, with the aim of increasing accessibility, in this article, we report a novel, cost-effective micro-fabrication technique for fabricating multi-layer microfluidic devices using only common wet-lab facilities, thereby significantly lowering the cost. Our proposed process-flow-design eliminates the need for a mastermold, does not require any sophisticated lithography tools, and can be executed successfully outside a clean room. In this work, we also optimized the critical steps (such as spin coating and wet etching) of our fabrication process and validated the process flow and the device by trapping and imaging Caenorhabditis elegans. The fabricated devices are effective in conducting lifetime assays and flushing out larvae, which are, in general, manually picked from Petri dishes or separated using sieves. Our technique is not only cost effective but also scalable, as it can be used to fabricate devices with multiple layers of confinements ranging from 0.6 to more than 50 $\mu$m, thus enabling the study of unicellular and multicellular organisms. This technique, therefore, has the potential to be adopted widely by many research laboratories for a variety of applications.

FIG. 1.

Flow chart of the fabrication process for a multilayer device followed in this article.

FIG. 2.

Optimization of spin-coated films and wet chemical etching on the glass substrate: (a) Coated thickness of PMMA films on glass slides as a function of spin speeds for different concentrations of etch resist. (b) Etch depth of the trench on masked glass slides as a function of etching time for different etchant solutions.

FIG. 3.

Three dimensional representation of the two-step device: (a) and (b) Perspective view and a (c) top view. 1 and 2 are the inlet ports for food and worms, respectively, and 3 is the outlet port for food/progeny. Regions I and III represent the first step of the device with 8  $\mu$m depth, and region II represents the second step (forming the middle trench) with 50  $\mu$m depth, respectively. (These are representative images and are not to scale.) (d) Surface profile of the trench obtained after 2 min etching using a BHF with an IPA solution. (e) Average surface profile (in black) of five different x-axis profiles of the etched glass slide with multistep channels. (f) Microscopy image of the two-step device with inlet/outlet ports punched onto the PDMS block.

FIG. 4.

Results of numerical simulations. (a) 3D design of the fluid chamber. (b) Combined view of velocity profiles along different axes. (c)–(e) Velocity (mm s ${}^{-1}$) profiles in the center of the worm chamber along the (c) XZ plane, (d) the XY plane, and (e) the YZ plane.

FIG. 5.

(a) Arrangement of the microfluidic device with attached tubings on the microscope stage for the image acquisition of live C. elegans. (b) Microscopy image of the complete microfluidic device with adult worms, eggs, and progeny inside the trenches (adult worms only in region II and eggs and small progeny are in region II and region III). (c) Image of the device with worms trapped inside the middle channels, i.e., in region II. (d) and (e) Live adult worms trapped inside the square trench and unable to cross the barrier (height barrier of the first step) in the device.