Real-Time Path Planning for Automating Optical Tweezers based Particle Transport Operations

Ashis Gopal Banerjee and Satyandra K. Gupta

B5: Advances in Technology 2 , Poster Presentation, GRID 2009

11:00 AM-12:00 PM, Thurgood Marshall

Optical tweezers (OT) have been developed to successfully trap and transport micro and nano scale components in a fluid medium. Components can be simply released from optical traps by switching off laser beams. Multiple optical traps can perform several operations in parallel. These characteristics make optical tweezers a very promising technology for creating directed micro and nano scale assemblies. They are useful in a large number of biological applications as well. We have explored the problem of real-time path planning for autonomous OT based transport operations. Such operations pose interesting challenges as the environment is uncertain and dynamic due to the random Brownian motion of the particles and noise in the imaging based measurements. Offline simulations are performed to gather trapping probability data that serves as a measure of trap strength and reliability as a function of relative position of the particle under consideration with respect to the trap focus, and trap velocity. Simple trapping probability models are then utilized in a stochastic dynamic programming framework to compute optimum trap locations and velocities that minimizes the total, expected transport time. A discrete version of an approximate partially observable Markov decision process algorithm is developed. Real-time performance is ensured by pruning the search space and enhancing convergence rates by introducing a non-linear value function. The algorithm is validated using 2 µm diameter silica beads in a holographic tweezer set-up. Successful runs show that the automated planner is flexible, works well in reasonably crowded scenes, and is capable of transporting a specific particle to a given goal location by avoiding collisions either by circumventing or by trapping other freely diffusing particles. This technique for transporting individual particles is now being integrated within a decoupled and prioritized framework to move multiple particles simultaneously.