Weighing of biomolecules, single cells and single nanoparticles in fluid

• Published in: Nature Vol. 446; no. 7139; pp. 1066 - 1069
• Main Authors: Carlson, Greg, Burg, Thomas P, Godin, Michel, Foster, John S, Knudsen, Scott M, Shen, Wenjiang, Manalis, Scott R, Babcock, Ken
• Format: Journal Article
• Language: English
• Published: London Nature Publishing 26.04.2007; Nature Publishing Group
• Subjects: Bacteria - chemistry; Bacteria - isolation & purification; Biological Products - analysis; Biological Products - chemistry; Cells - chemistry; Cellular biology; Colloids - analysis; Colloids - chemistry; Density measurement; Exact sciences and technology; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Mass and density; Measurement techniques; Measurements common to several branches of physics and astronomy; Mechanical instruments, equipment and techniques; Metrology, measurements and laboratory procedures; Microfluidics - instrumentation; Microfluidics - methods; Micromechanical devices and systems; Molecular Weight; Nanoparticles; Nanoparticles - analysis; Nanoparticles - chemistry; Nanotechnology; Pathogens; Physics; Proteins - analysis; Proteins - chemistry; Quartz; Research methodology; Silicon; Solutions - chemistry; Vacuum; Weight measurement; Nanoparticles; Biological compound; Nanomechanical devices; Particle suspension; Response functions; Resonators; Animal cells; Nanotechnology
• ISSN: 0028-0836; 1476-4687; 1476-4679
• DOI: 10.1038/nature05741

Nanomechanical resonators enable the measurement of mass with extraordinary sensitivity. Previously, samples as light as 7 zeptograms (1 zg  =  10-21 g) have been weighed in vacuum, and proton-level resolution seems to be within reach. Resolving small mass changes requires the resonator to be light and to ring at a very pure tone-that is, with a high quality factor. In solution, viscosity severely degrades both of these characteristics, thus preventing many applications in nanotechnology and the life sciences where fluid is required. Although the resonant structure can be designed to minimize viscous loss, resolution is still substantially degraded when compared to measurements made in air or vacuum. An entirely different approach eliminates viscous damping by placing the solution inside a hollow resonator that is surrounded by vacuum. Here we demonstrate that suspended microchannel resonators can weigh single nanoparticles, single bacterial cells and sub-monolayers of adsorbed proteins in water with sub-femtogram resolution (1 Hz bandwidth). Central to these results is our observation that viscous loss due to the fluid is negligible compared to the intrinsic damping of our silicon crystal resonator. The combination of the low resonator mass (100 ng) and high quality factor (15,000) enables an improvement in mass resolution of six orders of magnitude over a high-end commercial quartz crystal microbalance. This gives access to intriguing applications, such as mass-based flow cytometry, the direct detection of pathogens, or the non-optical sizing and mass density measurement of colloidal particles.