A closed-loop control SLM-based holographic optical tweezers system for manipulating multiple microparticles and cells on a microfluidic chip

Manipulation of individual microparticles is facing a challenge in low efficiency for trapping and sorting of multiple cells and physical collision interaction at the microscale. To aim higher efficiency and stability of manipulation, this paper proposes a closed-loop control holographic optical tweezers (HOT) system for manipulating multiple microparticles on a microfluidic chip. The adaptive algorithm of holographic patterns based on liquid crystal spatial light modulator (LC-SLM) for producing multiple optical traps were firstly made, demonstrating that Weighted Gerchberg-Saxton (GSW) algorithm could obtain higher trap uniformity among four algorithms. Then, the optical force calculation shows that the maximum transverse radiation pressure on a micropaticle occurs at several microns in an optical trap center (like “donut region”). More importantly, the flowchart and delay time of the closed-loop control HOT system were fully analyzed and optimized, the optical trap estimation time by compensator (95 ms ± 9 ms) dominated the trapping process, in comparison to image acquisition time (from 3.1 ms to 14.5 ms), transmission time (1.7 ms), processing time (22.1 ms), holographic algorithm time (15.2 ms), and SLM response time (14 ms). In addition, the recognition of adhesive microparicles was made to effectively isolate into individual particles and trap them. Finally, the closed-loop control HOT system was self-built, and multiple particles (polystyrenes, yeast and Rhizopus cells) were highly efficiently manipulated for the position, orientation, and interaction of multiple particles via utilizing real-time feedback from optical force measurements and adaptive algorithm adjustments and optimizing the trapping conditions, overcoming the challenges of particle instability. This work enhances the accuracy and reliability of optical trapping and opens new avenues for micro-manipulation applications in biomedicine, material science, and lab-on-a-chip technologies.