Golden Scales: Nanoscale Mass Sensor from Berkeley Can Be Used to Weigh Individual Atoms and Molecules

July 29, 2008

There's a new "gold standard" in the sensitivity of weighing scales. Using the same technology with which they created the world's first fully functional nanotube radio, researchers with Berkeley Lab and the University of California (UC) at Berkeley have fashioned a nanoelectromechanical system (NEMS) that can function as a scale sensitive enough to measure the mass of a single atom of gold.

Alex Zettl, a physicist who holds joint appointments with Berkeley Lab's Materials Sciences Division (MSD) and UC Berkeley's Physics Department, where he is the director of the Center of Integrated Nanomechanical Systems, led this research. Working with him were members of his research group, Kenneth Jensen and Kwanpyo Kim.

"For the past 15 years or so, the holy grail of NEMS has been to push them to a small enough size with high enough sensitivity so that they might resolve the mass of a single molecule or even single atom," Zettl said. "This has been a challenge even at cryogenic temperatures where reduced thermal noise improves the sensitivity. We have achieved sub-single-atom resolution at room temperature!"

The new NEMS mass sensor consists of a single carbon nanotube that is double-walled to provide uniform electrical properties and increased rigidity. One tip of the carbon nanotube is free and the other tip is anchored to an electrode in close proximity to a counter-electrode. A DC voltage source, such as from a battery or a solar cell array, is connected to the electrodes. Applying a DC bias creates a negative electrical charge on the free tip of the nanotube. An additional radio frequency wave "tickles" the nanotube, causing it to vibrate at a characteristic "flexural" resonance frequency.

When an atom or molecule is deposited onto the carbon nanotube, the tube's resonant frequency changes in proportion to the mass of the atom or molecule, much like the added mass of a diver changes the flexural resonance frequency of a diving board. Measuring this change in frequency reveals the mass of the impinging atom or molecule.

"Getting nanotubes to vibrate is fairly easy," said Jensen. "The difficult part is detecting those small vibrations. We accomplished this by field-emitting, or spraying, electrons from the tip of the nanotube and detecting the resulting electrical current."

Using their NEMS mass sensor, Zettl, Jensen and Kim were able to weigh individual gold atoms and measure masses as small as two fifths that of a gold atom at room temperature and in just a little more than one second of time. A gold atom has a mass of 3.25 x 10-25 kilograms, which means that there are about 3 million million million million gold atoms in a single kilogram.

While there have been other NEMS that function as mass sensors before, most of these previous devices were fashioned from silicon, and none had achieved the magical single-atom resolution at room temperature. The carbon nanotube mass sensor of Zettl's group is a thousand times smaller by volume than typical NEMS resonators - measuring only about a billionth of a meter in diameter and 200 billionths of a meter in length.

"Carbon nanotubes are the ideal material for this purpose and their small size makes them sensitive enough to resolve single atoms even at room temperature," Jensen said.

While scientists already have the ability to measure the mass of individual atoms through a complex technique known as mass spectrometry, this new carbon nanotube NEMS mass sensor offers some distinct advantages and opens the door to new possibilities, as Jensen explained.

"Unlike mass spectrometry, our device does not require the ionization of neutral atoms or molecules that can destroy samples such as proteins. Also unlike mass spectrometers, our carbon nanotube mass sensor becomes more sensitive at higher mass ranges, which makes it more suitable for measuring large biomolecules like DNA. Finally, our device is small enough so that, in time, it could be incorporated onto a chip."

Zettl, Jensen and Kim described their NEMS mass sensor in a paper published in the journal Nature Nanotechnology, entitled: "An atomic-resolution nanomechanical mass sensor." This research was supported by the U.S. Department of Energy's Office of Science, Basic Energy Sciences Program's Materials Sciences and Engineering Division, and by the National Science Foundation within the Center of Integrated Nanomechanical Systems.

Lawrence Berkeley National Laboratory

---

---

	Sensor Sweep (Stony Man) by Don Pendleton (Author) As the free world stands united against the ruthless onslaught of global terrorism, a covert, action-ready force known only to the President operates behind the scenes, on red alert. A crack cybernetics team works tirelessly assessing and fielding intelligence to the commandos on the hellgrounds of a grim, high-stakes war. Stony Man's dedication to the values of freedom and justice remain the core of its efforts to defend and protect. Four freighters, armed with missiles to be launched from mobile systems at four unidentified targets, have left port in South Africa. The payload is a lethal chemical agent and the resulting death toll would be incalculable. For Stony Man, it means the speed, skill and intelligence of its operatives will be pushed to the limits in a race to stop those who...
	Sensitive Mass Sensor Formed From Nanotube.: An article from: Nanoparticle News by Business Communications Company, Inc. (Publisher) This digital document is an article from Nanoparticle News, published by Business Communications Company, Inc. on October 1, 2004. The length of the article is 607 words. The page length shown above is based on a typical 300-word page. The article is delivered in HTML format and is available in your Amazon.com Digital Locker immediately after purchase. You can view it with any web browser. Citation Details Title: Sensitive Mass Sensor Formed From Nanotube. Publication: Nanoparticle News (Magazine/Journal) Date: October 1, 2004 Publisher: Business Communications Company, Inc. Volume: 7 Issue: 9 Page: NA Distributed by Thomson...
	HONEYWELL LAUNCHES NEW MASS AIRFLOW AND HUMIDITY SENSORS.(Brief Article): An article from: Sensor Business Digest by Vital Information Publications (Publisher) This digital document is an article from Sensor Business Digest, published by Vital Information Publications on October 1, 2000. The length of the article is 1454 words. The page length shown above is based on a typical 300-word page. The article is delivered in HTML format and is available in your Amazon.com Digital Locker immediately after purchase. You can view it with any web browser. Citation Details Title: HONEYWELL LAUNCHES NEW MASS AIRFLOW AND HUMIDITY SENSORS.(Brief Article) Publication: Sensor Business Digest (Newsletter) Date: October 1, 2000 Publisher: Vital Information Publications Volume: 9 Issue: 10 Page: NA Article Type: Brief Article Distributed by Thomson...
	An absorbance-based micro-fluidic sensor for diffusion coefficient and molar mass determinations [An article from: Analytica Chimica Acta] by A.D. McBrady (Author), R. Chantiwas (Author), A.K. Torgerson (Author), Grudpa (Author) This digital document is a journal article from Analytica Chimica Acta, published by Elsevier in 2006. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser. Description: The H-Sensor reported herein is a micro-fluidic device compatible with flow injection analysis (FIA) and high performance liquid chromatography (HPLC). The device detects analytes at two separate off-chip absorbance flow cells, providing two simultaneous absorbance measurements. The ratio of these two absorbance signals contains analyte diffusion coefficient information. A theoretical model for the sensing mechanism is presented. The model relates the signal Ratio to analyte diffusion coefficient. The model is...
	Handbook of Modern Sensors: Physics, Designs, and Applications by Jacob Fraden (Author) The Handbook's coverage of sensors is extensive, ranging from simple photodiodes to complex devices containing components in combination. It offers hard-to-find reference data on the properties of numerous materials and sensing elements and emphasizes devices that are less well-known, whose technology is still being refined, and whose use permits the measurement of variables that were previously inaccessible.
	Optical Sensors: Industrial, Environmental and Diagnostic Applications (Springer Series on Chemical Sensors and Biosensors) by Ramaier Narayanaswamy (Editor), Otto S. Wolfbeis (Editor) This interesting book covers latest aspects of a highly sophisticated technology; results treated in critical detail; demonstrates applicability of this technology to practical problems in process control, biochip methods, clinical analysis, environmental sciences
	Mass flow sensor by Ronald Cohn Jesse Russell (Author) High Quality Content by WIKIPEDIA articles! A mass air flow sensor is used to find out the mass flowrate of air entering a fuel-injected internal combustion engine. The air mass information is necessary for the engine control unit (ECU) to balance and deliver the correct fuel mass to the engine. Air changes its density as it expands and contracts with temperature and pressure. In automotive applications, air density varies with the ambient temperature, altitude and the use of forced induction, which means that mass flow sensors are more appropriate than volumetric flow sensors for determining the quantity of intake air in each piston stroke. (See stoichiometry and ideal gas law.) This book was created using print-on-demand technology.
	Biological and Medical Sensor Technologies (Devices, Circuits, and Systems) by Krzysztof Iniewski (Editor) Biological and Medical Sensor Technologies presents contributions from top experts who explore the development and implementation of sensors for various applications used in medicine and biology. Edited by a pioneer in the area of advanced semiconductor materials, the book is divided into two sections. The first part covers sensors for biological applications. Topics include: Advanced sensing and communication in the biological world DNA-derivative architectures for long-wavelength bio-sensing Label-free silicon photonics Quartz crystal microbalance-based biosensors Lab-on-chip technologies for cell-sensing applications Enzyme biosensors Future directions for breath sensors Solid-state gas sensors for clinical diagnosis The second part of the book deals with sensors for medical...
	Fluid Mechanics, Heat Transfer, and Mass Transfer: Chemical Engineering Practice by K. S. Raju (Author) This broad-based book covers the three major areas of Chemical Engineering. Most of the books in the market involve one of the individual areas, namely, Fluid Mechanics, Heat Transfer or Mass Transfer, rather than all the three. This book presents this material in a single source. This avoids the user having to refer to a number of books to obtain information. Most published books covering all the three areas in a single source emphasize theory rather than practical issues. This book is written with emphasis on practice with brief theoretical concepts in the form of questions and answers, not adopting stereo-typed question-answer approach practiced in certain books in the market, bridging the two areas of theory and practice with respect to the core areas of chemical engineering. Most...
	Surface Plasmon Resonance Based Sensors (Springer Series on Chemical Sensors and Biosensors) by Jiri Homola (Editor) This is a comprehensive treatment of the field of SPR sensors, in three parts. Part I introduces principles of surface plasmon resonance bio-sensors, electromagnetic theory of surface plasmons, theory of SPR sensors and molecular interactions at sensor surfaces. Part II examines the development of SPR sensor instrumentation and functionalization methods. Part III reviews applications of SPR biosensors in the study of molecules, and in environmental monitoring, food safety and medical diagnostics.