Fabrication of MEMS Devices with Macroporous Silicon Membrane Embedded with Modulated 3D Structures for Optimal Cell Sor
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Fabrication of MEMS Devices with Macroporous Silicon Membrane Embedded with Modulated 3D Structures for Optimal Cell Sorting Natalya Tokranova, Xiaojun Feng, Steve Olson, Tang Tang, Bai Xu, James Castracane School of Nanosciences and NanoEngineering, University at Albany (SUNY), 251 Fuller Rd, Albany, New York Macroporous silicon is a type of porous silicon that has ordered arrays of channels with high aspect ratio. Macroporous silicon with ordered 3-D structures have a variety of applications such as filters for a particle separation, photonic crystals and optical shortpass filters because of their spatially periodic structures [1-3]. These structures can be prepared by the electrochemical etching (ECE) of silicon wafers in hydrofluoric acid (HF). We report here a way to fabricate macroporous silicon membranes with ordered 3D structures that have controlled periodicity and dimensions appropriate for cell sorting. The silicon 3D structures have pores with variable diameters to modulate the flow behavior and optimize cell sorting efficiency. The silicon membranes were fabricated by wet etching of n-type (100) silicon substrate (40-60 Ω cm) in potassium hydroxide (KOH) solution with isopropyl alcohol at 80 o C. The 3-D structures were prepared by the electrochemical etching (ECE) of the membranes in diluted HF using the backside illumination with modulated intensity. The thickness of the fabricated membrane has been varied from 20 to 200 µm to optimize filtration of the cells by MEMS (Micro-ElectroMechanical Systems) chips designed for biological cell sorting and cell positioning. The software packages IntelliSuite and ANSYS FLOWTRAN were used to study the mechanical strength of the membrane as well as the velocity profile and flow behavior of Newtonian fluids inside the macroporous silicon membrane. Introduction The next generation of instrumentation for bioanalysis will rely on microchip technology. The main advantages of microchips include reduced costs and reagent consumption, the possibility of parallel processing and integrated measurements, rapid sorting and precise analysis of a single biological object. The trend toward miniaturization drives the creation of smaller MEMS devices that are suitable to be used for advanced analysis of the properties of single cells. This article addresses the feasibility of using macroporous silicon membranes for particle sorting, cell positioning, and filtration. Two steps were involved in the fabrication of the porous membranes. The first was a wet etching of silicon in potassium hydroxide (KOH) solution for the membrane fabrication. The second was an electrochemical etching of silicon membranes in hydrofluoric acid (HF) for macropore formation. These wet etching methods have been widely used in silicon technology [4-7]. KOH etching is used for micromachining bulk silicon while electrochemical etching in hydrofluoric acid has been known as a technique for porous silicon formation. According to the International Union of Pure and Applied Chemistry (IUPAC) standard, th
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