Direct laser writing of photoresponsive colloids for microscale patterning of 3D porous structures

Porous-walled 3D structures such as microscale rectangular cavities that exhibit size-selective permeability were created by harnessing the power of multi-photon direct laser writing of photoresponsive colloids. The photoresponsive microspheres were formed by grafting a copolymer brush 55 nm thick onto silica colloids with 927 nm diameter. It is found that by the laser scanning confocal microscopy (LSCM) images, the photoresponsive colloidal species exhibit a marked change in reflectivity after being photoswitched from the spirobenzopyran (SP) to the merocyanine (MC)-form through direct laser writing. The porous nature of the patterned microcavity is demonstrated by introducing a fluorescent dye into the surrounding fluid, which diffuses into the interior of the cavity. Direct laser writing of photoresponsive colloidal species enables patterning of 3D structures of near arbitrary geometry with controlled feature size, roughness, and porosity.