Towards microfluidic-based optical encryption using superhydrophobic surfaces created by femtosecond laser ablation

Although superhydrophobic surfaces have been extensively studied in the past, few studies have achieved optical encryption through the manipulation of droplets combined with the surface superhydrophobic properties. We present here our work in using femtosecond laser ablation to create micro-/nano-structures on polydimethylsiloxane (PDMS) substrate surfaces, enabling them to become superhydrophobic. Directional transport tracks to steer droplet motions were designed on the processed PDMS surface utilizing a high-contrast difference in surface wettability; self-cleaning property using the droplets was also verified on the substrate surface. Moreover, using a surface with designed high-contrast regions to trap droplets, magnetic-assisted manipulation of nanoparticles enabled in-situ reversible optical imaging/encryption. Our simple method for creating high-contrast surface wettability regions holds great potential for fostering a wide range of innovative applications such as droplet-based microfluidics as well as new optical encryption devices.