Manipulation of microspheres and biological cells with multiple agile VCSEL traps

A microscope-integrated vertical cavity surface emitting laser (VCSEL) array trapping system capable of independent control, rotation, and batch processing of biological cells is developed and demonstrated. The trapping system is applied for manipulation of yeast cells and PC-12 cells. In our trapping system, a single VCSEL trap serves as a collector and distributor, while an array of VCSEL traps functions like a chip, enabling parallel processing of multiple objects. The trapping system here differs from earlier VCSEL tweezers set-ups in several ways, including (1) the optical traps are mobile with the addition of a static sample holder; and (2) both a single and an array of optical traps can be controlled independently by tilting mirrors at the conjugate planes of the objective back aperture, and their relative depth can be adjusted without losing trapping power. These enhancements provide an advantage for lab-on-a-chip devices that contain microfluidics, since the background flow resulting from moving the sample plane introduces complexity and uncertainty in the velocity and force analysis on microparticles or cells. In addition, independent control of traps can offer more flexibility in multi-target manipulation. Here, we address optical design considerations for keeping stable trapping performance while multiplexing. Potential improvements based on two independently controlled VCSEL arrays are discussed and related applications are investigated.