Electrochemically etched nanoporous silicon membrane for filtration of biological fluids

Many biological fluids require filtration during its processing, either to separate the various components in the fluid or to remove unwanted or harmful contaminants from the medium. Challenges arise in the filtration process as the masses to be filtered appear in various sizes. Conventional filtration method requires lengthy and timely repeated processes. A simple solution to this problem is the isolation of the unwanted masses via sequenced filtration using precisely sized nanoporous silicon membrane. Porous silicon has found various applications in microelectronics and microelectromechanical systems (MEMS) including MEMS packaging and isolation layer. Recent advancements in MEMS fabrication have enabled the production of nanoporous silicon membrane for isolation of components in biological fluids. Aside from effectively separating various components in biological fluids such as blood and enzyme solutions, nanoporous silicon membrane could be utilized to selectively remove harmful contaminants in the aforementioned fluids via multiple filtration process. Whether the intended mass to be separated from the medium is a fluid component or harmful contaminants, the mass is selectively filtered using silicon membrane with precisely controlled nanosized pores. The membrane was fabricated by initial KOH etching on <;100>; silicon. A 10x10 array, each having a square dimension of 200 μm x 200 μm and membrane thickness of approximately 800 nm was produced after patterning and 480 minutes of etching in 35 % KOH solution at 80 οC. The array was then dipped in HF:H₂O:C₂H₅OH (2:3:5) electrolyte solution and elecetrochemically etched with the silicon membrane as the anode to produce nanopores throughout the thickness of the membranes. It is observed that applying DC current between 100 mA and 200 mA for 5 seconds varies the pore size between 1.5 nm and 3.5 nm. For the stipulated etch time, increment of 10 mA in app- - lied current increases the average pore size by approximately 2.0 A. On the other hand, variation in electrolyte solution concentration varies the area ratio of pores to matrix, with 12 % HF (12:38:50) electrolyte solution produces a 1:1 ratio between pores and silicon matrix. Due to the simple and cheap fabrication process, porous silicon membrane envisage a promising method for development of an economical system used in precisely controlled nanofiltration applications.