Abstract
Stop-flow lithography (SFL) is a microfluidic-based particle synthesis method, in which photolithography with a two dimensional (2D) photomask is performed in situ within a microfluidic environment to fabricate multifunctional microstructures. Here, we modified the SFL technique by utilizing an adjustable electrostatic-force-modulated 3D (EFM-3D) mask to continuously fabricate microlens structures for high-throughput production. The adjustable EFM-3D mask contains a layer filled with a UV-absorbing liquid and transparent elastomer structures in the shape of microlenses between two conductive glass substrates. An acrylate oligomer stream is photopolymerized via the microscope projection photolithography, where the EFM-3D mask was set at the field-stop plane of the microscope, thus forming the microlens structures. The produced microlens structures flow downstream without adhesion to the polydimethysiloxane (PDMS) microchannel surfaces due to the existence of an oxygen-aided inhibition layer. Microlens structures with variations in curvature and aperture can be produced by changing objective magnifications, controlling the morphology of the EFM-3D mask through electrostatic force, and varying the concentration of UV-light absorption dyes. We have successfully demonstrated to produce microlens structures with an aperture ranging from 50 μm to 2 mm and the smallest focus spot size of 0.59 μm. Our proposed method allows one to fabricate microlens structures in a fast, simple and high-throughput mode for application in micro-optical systems.
Highlights
Stop-flow lithography (SFL) technique [1], which was first proposed by Professor Doyle’s group, has been intensively used in the fabrication of various complex or multifunctional microstructures with applications that range from mechanical to biomedical engineering, such as synthesis of colloidal, glass, and silicon microcomponents [2,3], nonspherical superparamagnetic particles [4,5], cell-laden microgel particles [6,7], and multifunctional encoded particles for biomolecule analysis [8,9]
An acrylate oligomer stream is photopolymerized via the microscope projection photolithography, where the electrostatic-force-modulated 3D (EFM-3D) mask was set at the field-stop plane of the microscope
A shadow mask placed onto the EFM-3D mask defines the shape and size of the substrate of the produced microlens structures
Summary
Stop-flow lithography (SFL) technique [1], which was first proposed by Professor Doyle’s group, has been intensively used in the fabrication of various complex or multifunctional microstructures with applications that range from mechanical to biomedical engineering, such as synthesis of colloidal, glass, and silicon microcomponents [2,3], nonspherical superparamagnetic particles [4,5], cell-laden microgel particles [6,7], and multifunctional encoded particles for biomolecule analysis [8,9] This technique combines the advantages of microscope projection photolithography and microfluidics to continuously form morphologically complex particles. Our previous work [14]
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