# A Low-Cost Laser-Prototyped Microfluidic Device for Separating Cells and Bacteria
## 1 Introduction  
Separating bacteria and other impurities from cells is an essential step in various biomedical applications, including cell culture, drug discovery, and diagnostics [1; 2]. Impurities such as bacteria, viruses, and other microorganisms can interfere with the desired biological processes and contaminate the final product, leading to inaccurate results and potential harm to the end user [3]. Therefore, effective separation techniques are crucial for ensuring the purity and safety of cell-based products. Microfluidics is a rapidly developing field that has revolutionized cell separation techniques [4; 5; 6; 7]. Microfluidic devices use tiny channels and chambers to manipulate fluids and particles at the microscale level, allowing for precise and efficient separation of cells from other impurities [8; 9]. Microfluidic-based cell separation techniques offer several advantages over conventional methods, including reduced sample size, higher purity, and faster separation times [10; 11]. There are two primary approaches to microfluidic cell separation: passive and active [12; 13; 14; 15]. Passive methods rely on physical differences in cell size, shape, or deformability to separate cells, whereas active methods use external forces to manipulate cells. Some of the mainstream active methods are dielectrophoresis (DEP), electrophoresis, acoustic separation, optical tweezers, and magnetophoresis [16; 17; 18]. The DEP method applies an electric field to cells, allowing for their separation based on their electrical properties [19]. Cells with different dielectric properties experience different forces and are separated based on their response to the electric field. However, DEP and other electric field-based methods rely on the sample and medium conductivity and dielectric properties, and these methods can be detrimental to delicate biological samples due to Joule heating [20]. In acoustic-based methods, acoustic waves are used to separate cells based on their size, shape, and compressibility [2; 21; 22]. Cells experience different forcesbased on their acoustic properties, which allows for their manipulation [23]. While acoustic methods are gentler towards biological samples due to their inherited biocompatibility characteristics, acoustic systems may require bulky and expensive external equipment for functioning. Similarly, magnetic and optical methods can be quite complex and expensive due to the required external peripheral equipment [24; 25; 26]. Passive methods include inertial focusing, deterministic lateral displacement, hydrodynamic filtration, and viscoelastic separation [27; 28; 29; 30]. [PERSON] et al. presented the asymmetrical deterministic lateral displacement (DLD) method for enhancing the separation and throughput of red blood cells (RBCs) [31]. The researchers propose a new approach by changing the ratio of lateral-gap to downstream-gap, which allows for efficient separation of non-uniformly shaped and sized RBCs while maintaining a high throughput. The study introduces the concept of the separation index (SI) as a means to compare the separation efficiency across various DLD devices. The SI is shown to have an index of over 95%, indicating the effectiveness of the asymmetrical DLD gap-size method. Passive methods including filtration-based approaches are more prone to problems depending on the cell size variations due to their lacking dynamic adjustability. One of the most promising microfluidic-based passive cell separation techniques is called inertial focusing [32; 33; 34]. In this method, cells are separated based on their size and shape as they flow through microchannels under the influence of fluid forces [35]. This technique is particularly useful for applications such as cell-based assays and clinical diagnostics, where high purity and efficiency are essential. Inertial cell separation methods are a group of microfluidic techniques that utilize the physical properties of cells, such as their size, shape, and deformability, to sort and separate them from other cells or impurities.