*Communication* **Fabrication of Transparent and Flexible Digital Microfluidics Devices**

**Jianchen Cai <sup>1</sup> , Jiaxi Jiang <sup>2</sup> , Jinyun Jiang <sup>1</sup> , Yin Tao <sup>1</sup> , Xiang Gao <sup>1</sup> , Meiya Ding <sup>1</sup> and Yiqiang Fan 2,\***


**Abstract:** This study proposed a fabrication method for thin, film-based, transparent, and flexible digital microfluidic devices. A series of characterizations were also conducted with the fabricated digital microfluidic devices. For the device fabrication, the electrodes were patterned by laser ablation of 220 nm-thick indium tin oxide (ITO) layer on a 175 µm-thick polyethylene terephthalate (PET) substrate. The electrodes were insulated with a layer of 12 µm-thick polyethylene (PE) film as the dielectric layer, and finally, a surface treatment was conducted on PE film in order to enhance the hydrophobicity. The whole digital microfluidic device has a total thickness of less than 200 µm and is nearly transparent in the visible range. The droplet manipulation with the proposed digital microfluidic device was also achieved. In addition, a series of characterization studies were conducted as follows: the contact angles under different driving voltages, the leakage current density across the patterned electrodes, and the minimum driving voltage with different control algorithms and droplet volume were measured and discussed. The UV–VIS spectrum of the proposed digital microfluidic devices was also provided in order to verify the transparency of the fabricated device. Compared with conventional methods for the fabrication of digital microfluidic devices, which usually have opaque metal/carbon electrodes, the proposed transparent and flexible digital microfluidics could have significant advantages for the observation of the droplets on the digital microfluidic device, especially for colorimetric analysis using the digital microfluidic approach.

**Keywords:** digital microfluidics; lab-on-a-chip; ITO; PET
