Cooperative Optical Trapping of Polystyrene Microparticle and Protein Forming a Submillimeter Linear Assembly of Microparticle

Optical trapping of dielectric and metal particles yields different types of “optically evolving assembly” at air/solution and glass/solution interfaces. However, all these structures have in common that the trapping laser is scattered and propagated through the assembly, expanding from the focus up to a few tens of micrometers. In the present work, we fabricate a single submillimeter linear assembly of polystyrene microparticles starting from the surface of a concentrated lysozyme D2O solution. Such assembly has a three-dimensional linear structure composed of a single microparticle aggregate without folding and bending. Indeed, it is prepared along the lysozyme assembly, which is also generated by optical trapping. The cooperative trapping of the microparticle and lysozyme did not arrange as a homogeneously distributed assembly. Instead, a unique anomalously long assembly of microparticles and a densely, widely, and deeply expanded lysozyme layer were simultaneously prepared. Their morphology was reconstructed by shifting the imaging plane immediately after switching off the trapping laser. Independently, the lysozyme assembly was also confirmed by fluorescence imaging and Raman scattering spectroscopy. Thus, we consider that the described cooperative “optically evolved assembling” has a large potential to fabricate hybrid materials with applications in different fields such as colloid science, protein chemistry, and soft matter.