Ultrasensitive nanoelectromechanical mass detection

Abstract

We describe the application of nanoelectromechanical systems ͑NEMS͒ to ultrasensitive mass detection. In these experiments, a modulated flux of atoms was adsorbed upon the surface of a 32.8 MHz NEMS resonator within an ultrahigh-vacuum environment. The mass-induced resonance frequency shifts by these adsorbates were then measured to ascertain a mass sensitivity of 2.53 ϫ10 Ϫ18 g. In these initial measurements, this sensitivity is limited by the noise in the NEMS displacement transducer; the ultimate limits of the technique are set by fundamental phase noise processes. Our results and analysis indicate that mass sensing of individual molecules will be realizable with optimized NEMS devices. © 2004 American Institute of Physics. ͓DOI: 10.1063/1.1755417͔ Nanoelectromechanical systems ͑NEMS͒ are emerging as strong candidates for a host of important applications in semiconductor-based technology and fundamental science. The minuscule active masses of NEMS, in particular, render them extremely sensitive to added mass-a crucial attribute for a wide range of sensing applications.Resonant mass sensors with high mass sensitivities have been employed in many diverse fields of science and technology. Among the most sensitive are those based on the acoustic vibratory modes of crystals, 2,3 thin films, 4 and micron-sized cantilevers. [5][6][7][8] In all of these, the vibratory mass of the resonator, its resonance frequency, and quality factor (Q) are central in establishing its mass sensitivity. In this letter, we demonstrate attogram-scale inertial mass sensing using high-frequency NEMS, and discuss how even greater sensitivity will be obtainable with such devices.9 This provides a concrete initial demonstration of the potential that nanoscale mechanical devices offer for sensing and ultimately weighing individual molecules.These initial experiments were carried out in an ultrahigh vacuum ͑UHV͒ environment within the apparatus depicted in Fig. 1͑a͒. This system allows the operation of a NEMS resonator ͑transduced magnetomotively 10 ͒ while a pulsed, weak flux of Au atoms is directed upon it. The Au atoms are generated by a thermal evaporation source and travel ballistically toward the NEMS within the apparatus. The mass flux, F, of the evaporator is measured by a calibrated quartz crystal monitor and modulated by a shutter; both are in the vicinity of the evaporator. The resonator temperature is regulated at TϷ17 K, both to ensure unity adsorbate sticking probability 11 and to allow careful monitoring of the resonator temperature fluctuations ͑see Fig. 3͒. Then, with knowledge of the exposed NEMS surface area, S ͑determined from careful scanning electron microscopy measurements͒, we can determine the exact mass 12 of the adsorbed Au atoms on the NEMS as ⌬m(t) Ϸ͐ 0 t SF(r QCM /r NEMS ) 2 dt. In this system, the geometric factor, (r QCM /r NEMS ) 2 Ϸ5ϫ10 Ϫ3 . We employed nanomechanical doubly clamped SiC beam resonators such as the ones shown in Fig. 1͑b͒ as the sensor elements in these experiments. The beams are embedded with...

Integrated MEMS/NEMS Resonant Cantilevers for Ultrasensitive Biological Detection

“…In ultrahigh vacuum, the resonant cantilevers even showed the mass resolution as high as attogram level [10]. However, these previously reported results were generally obtained in laboratories, with an off-sensor optical position sensing detection (PSD) of AFM mode used [11,12]. For portable bio/chemical sensing applications, there is a recent trend to integrate the sensing and actuating elements into the cantilever for onchip dynamic detection [6,13,14].…”

“…Differently, the dynamic detecting method employs the cantilever as a resonator. Induced by specific mass adsorbate, a shift in the resonant frequency is read out as the sensing signal [7][8][9][10][11].…”

Platinum composite nanowires for ultrasensitive mass detection

“…1 The vibrational frequencies of such NEMSs are highly sensitive over a wide mass range with minuscule active masses. As such, they are favorable candidates for the detection of a single molecule, which would require a mass sensitivity in the range of zeptogram to attogram (10 À21 -10 À18 g), 2 NEMSs have a strong potential in a wide range of applications, such as in force sensing 3 and mass resonator, 2,4 as well as in the study of quantum vibration 5 and other fundamental physical phenomena. 6 To achieve ultra-high mass sensitivity, various low dimensional structures 2,[7][8][9][10][11][12] have been subjected to detailed investigations.…”

“…Thus, the minimum detectable mass is about 0.4 attogram (1attogram ¼ 10 À18 g). 4 If the small mass is attributed to a slight increase in the length of the wire, resulting in a small increase in the aspect ratio, for the FEB-CVD Pt composite nano-resonator, the decrement in the resonant vibration frequency is calculated to be 253 kHz. This would mostly account for the large reduction in the resonance frequency (about 8.9% in frequency reduction), which is in good agreement with our experimental data of about 8.1% in frequency reduction.…”

Cantilever based mass sensor with hard contact readout

“…1 Cantilever based mass sensing, relying on a resonant frequency shift induced by the added mass, 2 has a potential for very high mass resolution as demonstrated by the reported detection of masses in the 10 −18 g range. 3 The resonant frequency shift can be detected using optical 3 or electronic 4 detection methods. Most high-resolution systems, however, rely on optical detection.…”