# Femtosecond Laser-Inscripted Direct Ultrafast Fabrication of a DNA Distributor Using Microfluidics
## 1 Introduction  
A femtosecond laser, which emits optical pulses with a femtosecond duration, has been used as a versatile tool for single or multiple writing processes to create lines or holes directly [1]. This laser capability has enabled the expansion of its applications to a wide range of bioengineering and biomedicine applications, such as surgery, treatment, drug screening, detection, diagnostics, drug delivery, and analysis [2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13]. There are several other advantages as follows. A femtosecond laser can be used to process a variety of materials, including glasses, semiconductor materials, and polymers [14; 15]. Complicated patterns can be generated for a micro-scale to nano-scale without using a mask [16]. An ultrafast laser process can be performed regardless of the clean room classification. In the 2010s, the femtosecond laser system has become more reliable, robust, and practical. As the heat transfer from bulk thermal conduction becomes longer than the electron-phonon interactiontime, damages from laser ablation occur due to heat diffusion into the surroundings. This has been reduced significantly with the increased stability of the high speed (femtosecond) laser process [17]. In addition, the storage of multi-photon absorption inside transparent materials has enabled it to generate three-dimensional internal micro-patterns in transparent materials [18]. The improved features of the femtosecond laser system have facilitated three-dimensional (3D) pattern-embedded micro-fabrication of soft materials as well as high quality surface micromachining. Therefore, the femtosecond laser system is suitable for use in bio-applications. Polydimethylsiloxane (PDMS) is a soft and transparent material suitable for ultrafast laser machining. PDMS is one of the most popular polymers in microfluidics and bio-applications due to its high thermal stability, low cost, and excellent biocompatibility. This has generated a lot of interest in PDMS-based laser micromachining [4]. [PERSON] et al. described the use of a Ti: sapphire laser to create a topographical structure on a flat surface of PDMS [19]. This application has extended the use of soft-lithography to rapid prototyping of the devices. [PERSON] et al. characterized the key parameters (sample speed, number of passes, and laser power) for ultrafast laser machining of micro-channels fabricated in PDMS [20]. [PERSON] et al. fabricated a low-cost, high-quality, concave PDMS micro-lens array using high-speed line-scanning of femtosecond laser pulses [21]. [PERSON] et al. reported the fabrication of solvent-tunable PDMS micro-lenses using a femtosecond laser direct writing technique through a multi-photon absorption process [22]. [PERSON] et al. presented an experimental investigation on the effects of process parameters on a medical grade PDMS elastomer processed by a laser source [23]. [PERSON] et al. presented a direct single-step process to address the challenges encountered in laser nano-patterning of transparent elastomeric membranes with and without tension [24]. [PERSON] et al. demonstrated a facile single step laser treatment process to create a superhydrophobic PDMS surface [25]. [PERSON] et al. suggested the laser-based fabrication of arrays of conical micro-wells for cell culture applications [26]. [PERSON] et al. introduced simple-to-use polyester micro-assay microfluidic platform for 3D stem cell research using laser ablation [27]. [PERSON] et al. performed the customization of femtosecond laser ablation at low energy to fabricate microfluidic channels less than 1-\(\upmu\)m wide and 2-\(\upmu\)m tall [28]. In order to generate and culture multiple 3D cell spheroids, [PERSON] et al. introduced laser-based rapid prototype techniques for PDMS multi-well chips [29]. In general, obtaining information on the size distribution of DNA in a sample solution has been challenging. Thus, in this study, we proposed a simple and quick method to evaluate the size distribution of DNA in a solution prior to performing the main experiment.