Optical Trapping, Cell Manipulation, And Robotics

ABSTRACT A new type of analytical and preparative cytometric instrument was developed. The instrument combines image analysis and machine vision with single cell and chromosome manipulation by means of optical trapping. A proof-of- principle instrument, OCAM, has the ability to locate and analyze biological particles inside an enclosed manipulation chamber, as well as the ability to move and position particles according to preprogrammed protocols. Preliminary re­ sults and potential biological applications of such a microrobot are discussed. 1. INTRODUCTION The last twenty years have seen the development of two major classes of high-performance analytical instruments. These are: (i) video microscope-based image processing workstations; and (ii) flow cytometers. Traditionally, the two classes have been characterized by widely differing capabilities and, therefore, applications. Thus, image processing mi­ croscopes have been capable of analyzing biological particles at low speed but with high resolution, whereas flow cy­ tometers have been capable of zero-resolution imaging at very high speeds. Moreover, flow cytometers have naturally lent themselves to preparative applications (flow sorting), while imaging instruments, fitted with mechanical micro- manipulators, have seen only limited preparative use.Current developments in the field of cytometric instrumentation suggest that the distinction between imaging and flow instruments is beginning to disappear. Indeed, one-dimensional imaging (scanning) flow cytometers are already in use, and several imaging flow cytometers are being developed which will provide images of moderate but useful reso­ lution. The discovery of optical trapping by Ashkin l in the late 60s, and especially the recent technical developments in optical trapping as applied to biological problems 2*3*4, have opened up a completely new range of applications for imaging instruments as preparative and manipulation devices. The robotic optical trapping manipulator described in this article is a good example of the spectrum of capabilities inherent in instrumentation based on optical trapping.For many reasons, optical trapping as a means for manipulating microscopic biological particles, is far superior to mechanical micromanipulators. Indeed, optical trapping can easily be achieved in a completely enclosed chamber, thus preventing crosscontamination between the sample and the laboratory environment and allowing one to control very ac­ curately and over extended periods of time the physical and chemical parameters of the biological sample. Further­ more, the absence of mechanical devices makes possible the use of manipulation chambers with very fine structural de­ tails, such as microscopic compartments and interconnecting channels. The presence of such chamber structures opens up new possibilities for the separation and processing of individual biological particles.The potentially complex structure of the manipulation chamber, together with the ability of the instrument to im­ age, analyze, separate, and position biological panicles inside the chamber, can only be used efficiently if appropriate analysis and control software is available to replace a human operator. When endowed with such software, an optical manipulator becomes a true microscopic robot, in the sense that it processes visual (video) information to determine the detailed way in which to execute some predetermined task. It is particularly this combination of imaging, optical trapping, machine vision, and robotics that makes our instrument the first of what we see as a new class of analytical and preparative cytometric instrumentation.This article begins with a brief discussion of the physics and history of optical trapping. This is followed by a dis­ cussion of our current instrument, OCAM, and of its user interface and control software. We present preliminary re­ sults demonstrating the ability of the instrument to manipulate live cells and chromosomes, following which we dis­ cuss current and future applications of a robotic optical trapping cell manipulator in biology and biotechnology.