Assembly of micro-/nano- materials with optoelectronic tweezers and freeze-drying

This work reports the use of optoelectronic tweezers (OET) and freeze-drying to assemble a variety of micro-/nano- materials into topographical micro-patterns, which can be transferred on to alternative substrates. It is demonstrated that polystyrene microparticles, metallic microparticles and graphene nanosheets can be assembled into fine micro-patterns with high precision and the assembled micro-patterns can be well preserved on the surface of OET device after removing the liquid medium via freeze-drying. The assembled micro-patterns can be transferred onto different substrates and used as anti-counterfeiting labels, corporate or exhibition logos, and laboratory instruction demos. This micro-assembly method is easy-to-use and applicable for objects made of different materials, suggesting utility for many microfabrication and micromanipulation applications in the future.