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Bad vibrations

How to keep the effects of environmental bounce out of your data

Ewen Callaway

Editor's note: Lab Tools aims to bring you tips on lab techniques beyond what you'd find in a published protocol and to act a springboard for readers to share further tips. Have you struggled with vibrations in your experiments, or found a solution you think other readers might benefit from? Do you have an idea for a future Lab Tools article? Tell us by posting a comment.

Whether it's an NMR or a two-photon microscope, scientists love toys - at least when they work. Sometimes the most mundane things bungle technology: environmental vibrations from cars driving by, central air conditioning, the voices of the operators, and even the ocean. As instruments become more sensitive, subsonic rumblings become more insidious, particularly for nanotechnology applications. With many instruments, such as atomic-force and electron microscopes, cutting down on vibration is essential to collecting good data. "You could spend a million or two...

When researchers suspect vibration is wreaking havoc on their data, they should identify the origin of the noise or get an environmental engineer to find it, say scientists who regularly deal with vibration. For example, Vicki Colvin, a chemist at Rice University in Houston, noticed images moving around in a circle on her transitional electron microscope. "It was like a ghost," she says. Colvin discovered that an air duct was causing the problem and spent $1.20 on a shield to divert air away from the scope. "The easiest way to get rid of vibrational noise is to stop it at its source," says Larry Cohen, a neuroscientist at Yale University.

The design of a building is critical to the vibration that reaches an instrument, says Ahmad Soueid, senior vice president at HDR Architecture in Omaha, Neb., which has designed more than a dozen nanotech laboratories. Isolating air-handling equipment from laboratories and using special joints that redirect vibration to the ground are some of the fixes his firm uses. Recently, concerns over vibration plagued a $250 million NIH facility under construction in Baltimore. Initial reports indicated the building's quivers could render confocal microscopes useless, although later measurements suggested most instruments will work with proper dampening (www.the-scientist.com/news/display/40504/).

There's no universal fix, says David Platus, president of Minus K, a company that makes high-end vibration-isolation tables (see How It Works). Solutions vary, from cheap rubber pads that rest under instruments, to the air-cushioned tables that have been around for 50 years, to tables that sense vibration and cancel it out. "The more sensitive the instrument, the better isolation you need," he says.

Electron Microscopy

User: Kurt Albertine, an anatomist at the University of Utah School of Medicine
Project: Electron microscopy of lung tissue samples
Problem: Low-frequency vibration causes double and triple images.
Solution: Albertine says the best solution for a scanning or transmission electron microscope is to put the machine on at least a one foot-thick slab of concrete. Most EM labs should be on the first floor or in the basement, he says. To further dampen vibration, users can load their microscopes on special dollies with thick rubber feet. Albertine recommends consulting with the microscope's manufacturer to find a solution. "They know their instruments, and they know how to optimize them despite a poor environment," he says.

<figcaption>Transmission electron micrographs of lung tissue: A sharply focused image (left) is unacceptably blurred when vibration is not controlled (right). Credit: Courtesy of Kurt H. Albertine and Nancy B. Chandler</figcaption>
Transmission electron micrographs of lung tissue: A sharply focused image (left) is unacceptably blurred when vibration is not controlled (right). Credit: Courtesy of Kurt H. Albertine and Nancy B. Chandler

Fluorescence Microscopy

User: Larry Cohen, a neuroscientist at Yale University
Project: Imaging calcium- and voltage-dependent fluorescent dyes in live neurons with two-photon or epifluorescence microscopes
Problem: Even the slightest shaking can compromise the millisecond-timed measurements.
Solution: Cohen was among the first light microscopists to tackle vibration, beginning in the early 1970s. He started with air tables, which remain the industry standard and cost several thousand dollars, depending on size. The tables dampen up-and-down vibration well, says Cohen, but they have more trouble with side-to-side movements. On the advice of an engineer, Cohen mounted his microscope on top of motorcycle inner tubes resting on an air table. That solved most of the problems, but vibration still got through. He next bought a $5,000 table from Minus K that uses springs and flexors tuned to an instrument's precise weight, and it has solved his problems.
Brian Salzberg, a neuroscientist at the University of Pennsylvania who did a postdoc with Cohen in the 1970s, has gone even further to quell vibration in his lab. "The engineers, bless them, cleverly located all the air-handling equipment on the roof, so the building shakes," he says. As a fix, he rests his microscope on a $10,000 active isolation table produced by Halcyonics. The table electronically senses vibrations then mechanically cancels them out. To dampen vibration transmitted through the air, Salzberg shrouds his set-up in a soundproof curtain. "That combination works very well for us," he says.
Noise can come from sources other than vibration, Cohen cautions. Shot noise, related to the movement of photons, can overshadow vibrational noise. Moreover, when imaging live animals, breaths and heartbeats add still more noise. Those are problems isolation tables won't resolve.

Selected Vibration Isolation Tables

Manufacturer Cost Pros Cons
Air tables

TMC www.techmfg.com
Newport www.newport.com

~$4,400
(3' x 4' table that can bear 200 lbs)

• Suitable for most jobs and locations, from AFM to fluorescence microscopy
• Dampens down to ~1 Hz
• Low cost

• Requires air/nitrogen tank or a compressor
• Vibrations can still be transmitted through the air or via electrical cords

Passive mechanical tables

Minus K Technology www.minusk.com

~$5,000

(table that can bear 200 lbs)

• Dampens down to ~0.5 Hz
• Low cost
• No air canisters or compressors needed

• Tables are "tuned" to a specific weight (Salzburg solves that problem by tuning to a higher mass, then removing lead weights as new equipment is added.)
• Vulnerable to vibrations that come through the air or electrical cords

Active tables

Halcyonics www.halcyonics.de
Herzan www.herzan.com

~$10,000

(table that can bear 200 lbs)

• Dampens down to 0.5 Hz
• Compensates for vibrations transmitted via air and electrical cords
• Can connect to a computer to troubleshoot a vibration issue

• Costs twice as much as air or passive mechanical tables

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