Surface Wettability and Electrical Resistance Analysis of Droplets on Indium-Tin-Oxide Glass Fabricated Using an Ultraviolet Laser System

Abstract

Indium tin oxide (ITO) is widely used as a substrate for fabricating chips because of its optical transparency, favorable chemical stability, and high electrical conductivity. However, the wettability of ITO surface is neutral (the contact angle was approximately 90°) or hydrophilic. For reagent transporting and manipulation in biochip application, the surface wettability of ITO-based chips was modified to the hydrophobic or nearly hydrophobic surface to enable their use with droplets. Due to the above demand, this study used a 355-nm ultraviolet laser to fabricate a comb microstructure on ITO glass to modify the surface wettability characteristics. All of the fabrication patterns with various line width and pitch, depth, and surface roughness were employed. Subsequently, the contact angle (CA) of droplets on the ITO glass was analyzed to examine wettability and electrical performance by using the different voltages applied to the electrode. The proposed approach can succeed in the fabrication of a biochip with suitable comb-microstructure by using the optimal operating voltage and time functions for the catch droplets on ITO glass for precision medicine application. The experiment results indicated that the CA of droplets under a volume of 20 μL on flat ITO substrate was approximately 92° ± 2°; furthermore, due to its lowest surface roughness, the pattern line width and pitch of 110 μm exhibited a smaller CA variation and more favorable spherical droplet morphology, with a side and front view CA of 83° ± 1° and 78.5° ± 2.5°, respectively, while a laser scanning speed of 750 mm/s was employed. Other line width and pitch, as well as scanning speed parameters, increased the surface roughness and resulted in the surface becoming hydrophilic. In addition, to prevent droplet morphology collapse, the droplet’s electric operation voltage and driving time did not exceed 5 V and 20 s, respectively. With this method, the surface modification process can be employed to control the droplet’s CA by adjusting the line width and pitch and the laser scanning speed, especially in the neutral or nearly hydrophobic surface for droplet transporting. This enables the production of a microfluidic chip with a surface that is both light transmittance and has favorable electrical conductivity. In addition, the shape of the microfluidic chip can be directly designed and fabricated using a laser direct writing system on ITO glass, obviating the use of a mask and complicated production processes in biosensing and biomanipulation applications.

Graphene and graphene–cellulose nanocrystal composite films for sustainable anodes in biophotovoltaic devices

“…38 The Q Y values of the graphene and graphene-CNC lms were 13.9 ± 2.7°and 64.0 ± 1.7°(n = 3, P = 0.0001), respectively, showing that graphene lms are more hydrophilic than graphene-CNC lms. The Q Y value of ITO was found to be 96.7 ± 1.3°, consistent with a previous study that reported 92 ± 2°, 39 suggesting that the ITO glass is slightly hydrophobic.…”

Progress in Non-Traditional Processing for Fabricating Superhydrophobic Surfaces

“…Constructing a superhydrophobic surface can effectively alleviate the problem of its inability to resist corrosion and easy freezing during use [ 95 , 96 ]. It can also be given special functions such as self-cleaning, lubrication, and drag reduction.…”

Perspective Coatings Based on Structured Conducting ITO Thin Films for General Optoelectronic Applications

“…Coatings 2024, 14, 178 3 of 16 potentially interesting technical decision for microfluidics applications (as an alternative to ITO with UV treatment [45], patterned ITO [46], or ITO coated on a PET film [47]).…”