Engineering light-driven micromotors with fluorescent dye coatings for easy detection and tracking

Micromotors are the backbone of material research as they are small-sized, self-propelled, intelligent systems capable of performing multiple tasks ranging from biomedicine to environmental monitoring. One of the primary obstacles the field faces is the live detection and differentiation of individual units through a complex environment. In this study, we demonstrate a facile approach for designing light-activated dye-tagged micromotors on a large scale. Both rod and sphere shaped micromotors made of titanium dioxide (TiO2)/copper oxide (Cu2O)-silica are designed to self-propel under the illumination of low-intensity UV/Visible light in aqueous peroxide medium. The micromotors were modified with site-specific coatings of different dyes, such as Alq3, Alizarin, Zinc Phthalocyanine, etc. The fabrication of micromotors and coating with dyes was performed using a simple and versatile physical vapor deposition-based glancing angle deposition (GLAD) technique. The fluorescent dyes help to detect the motion and position of micromotors independently. Moreover, they also help to identify the swimming direction as well as differentiate the micromotors in a complex medium consisting of similar configurations of other particles (bacteria and passive fluorescent particles). Light provides full control over the dynamics as well as the fluorescent nature of micromotors. To present the versatility of our design scheme, micromotors of different shapes, materials, and dye coatings are designed and explored for fluorescence-based observations. The simplistic design approach with easy-to-load multiple fluorescent dyes at specific locations is an interesting feature that makes the micromotors suitable candidates for various microfluidic and lab-on-a-chip studies, including biological or fluorescent samples.