Design Considerations for Micro- and Nanopositioning: Leveraging the Latest for Biophysical Applications

Abstract

Biophysical applications ranging from fluorescence microassays to single-molecule microscopy are increasingly dependent on automated nanoscale positional control and stability. A whirlwind of motion-industry innovation has resulted in an array of new motion options offering significant improvements in application performance, reproducibility and throughput. The challenge to leverage these developments depends on researchers, engineers and motion vendors acquiring a common language of specifications and a shared understanding of the challenges posed by application needs. To assist in building this shared understanding, this article reviews today's motion technologies, beginning with a concise review of key principles of motion control focusing on applications. It progresses through illustrations of sensor/encoder technologies and servo techniques. A spectrum of classical and recent motion technologies is explored, from stepper and servo actuation of conventional microscopy stages, to advanced piezo stack nanopositioners capable of picometer precision, to novel ultrasonic resonant piezomotors and piezo-ceramic-based mechanisms capable of high-force positioning over many millimeters while providing resolutions down into the sub-nanometer range. A special emphasis is placed on the effects of integrating multiple motion technologies into an application, such as stacking a fine nanopositioner atop a long-travel stage. Examples and data are presented to clarify these issues, including important and insightful new stability measurements taken directly from an advanced optical trapping application. The important topics of software and interfacing are also explored from an applications perspective, since design-and-debugging time, synchronization capabilities and overall throughput are heavily dependent on these often-overlooked aspects of motion system design. The discussion is designed to illuminate specifications-related topics that become increasingly important as precision requirements tighten. Throughout, both traditional and novel techniques and approaches are explored so that readers are left with a solid overview of the state of the art, and an actionable perspective that readies them to discuss and evaluate specifications and vendor capabilities against practical application requirements.