Nanopositioning Solutions for Next Generation Sequencing

Sample Motion

The design team of a Next-Generation Sequencing platform usually selects one of the two primary methodologies within fluorescence microscopy for imaging in two axes: field-sequential imaging or constant velocity imaging.  In the first method, individual fields of view are acquired sequentially; in the other, the imaging is performed continuously, during constant velocity scanning.  The architectural decision of how and when to move the sample with an XY stage into the optical field of view (FOV) determines the platform’s motion requirements and behavior.

Field-sequential Imaging

In field-sequential imaging, the sequence of events is move, stop, image, and repeat. The motion platform must move the sample within the field of view, remain stationary during image acquisition and then quickly move the sample to the next FOV.  The motion platform is a combination of precise mechanical and efficient control solutions that allows the sequencing instrument to move the sample with minimal system resonance.  Key performance metrics are move and settle time, as well as position jitter during image acquisition.  Depending on the optical system, any sub-micron motion (jitter) during image acquisition may cause blurring of the image.  For example, the image quality of a system using a 0.80 NA objective may degrade as the camera detects unwanted motion as small as several hundred nanometers at short-wavelengths.

While field-sequential imaging typically translates into a lower cost system, a portion of the time spent moving (and settling) can lead to lower overall throughput.  The timing diagram shows how sample illumination and camera image capture time occurs while the stage is maintaining position.  While the nanopositioning stage is moving to the next field of view for imaging, the previously captured image can be transferred in parallel with the stage move.  Depending on the transfer rate and amount of data either the camera or the stage can limit instrument throughput.  Dover Motion has industry leading approaches and tools for optimizing step and settle time.

Laser Autofocus

Optical-based autofocusing relies on sending a laser diode beam down through the objective where it reflects off the sample or a nearby glass surface. This continuous tracking laser autofocus method provides the highest performance but can be considerably more expensive to implement.  This architecture allows the Z-axis stage to be driven by the digital laser autofocus.  Dover Motion has been building high-performance, direct drive Z nanopositioing stages for many years with thousands of systems in the field, many of which operate around the clock.  Our newest stage is our DOF-5 nanopositioning stage for objective focusing.  Customers who use the DOF-5 notice the following benefits:

• Fast, accurate, and repeatable 100nm moves
• Integrated optical linear encoder with 1.25nm or 5nm resolution
• Internal, high performance servo drive and control with reduced cabling
• Direct connection to Autofocus systems for easy integration

Fluorescence Imaging

While the sequencing process may vary between platforms and companies, all optical-based instruments are looking for specific light wavelengths associated with the four bases of DNA: Adenine (A), Cytosine (C), Guanine (G) and Thymine (T).  During sample preparation, a different color fluorescent tag is bound to indicate which of the four bases is present. These instruments rely on precision optical filters, commonly on a rotary indexer or linear array.  Often referred to as “filter cubes”, these assemblies contain an excitation filter, an emission filter, and occasionally a beam splitter.  Each one of these four cubes must be quickly and accurately moved into the FOV in order to pick up the minimal number of photons being emitted by the fluorophore.  We have a robust history of working with optical and fluorescence imaging .  The experts at Dover Motion are consulted on optical architecture options where we work with our customers to design a system with the highest performance and throughput. For example, our expertise provides the following benefits:

• Cost-effective options for both rotary or linear indexing architectures
• Multiple technologies to support a range of price and performance requirements
• Custom design experience for unique filter changing needs.

Other Capabilities

Dover Motion provides collaborative solutions for motion control that enable NGS platforms to focus on what they do best: large scale DNA and RNA sequencing.  Our engineers and designers have both deep understanding of our core technologies and in a wide range of ancillary application technologies.  We are well versed in automated microscopy, control theory, fluorescence microscopy, vibration control, optimizing servo tuning and structural resonances.  Collaborating with our experts enable NGS platforms to decrease instrument development time and prevent system challenges before they arise.

Here are some examples of where Dover Motion’s expertise can be of value to NGS system engineers:

• Preventing cables, tubing and temperature control elements from hindering platform motion.
• Best practices for other controlled systems such as temperature control.
• Normalizing the sample plan to the optical beam path, either scheduled or dynamically.
• Vibration control best practices including managing the consequences of isolation.
• Advanced methods to further reduce step and settle time.
• Controlling the filter rotary indexer or linear array.

Building the Right Precision Motion Control System

Dover Motion offers a variety of standard products for your precision motion control needs, and we also specialize in collaborating with our clients to configure the right motion solution for their unique application. With more than 50 years of experience in the life sciences, diagnostics, and factory automation industries, we understand your needs and industry and can provide you the flexibility you need to hit your cost and schedule targets.