A nanomechanical mass sensor with yoctogram resolution

Nanomechanical resonators have been used to weigh cells, biomolecules and gas molecules, and to study basic phenomena in surface science, such as phase transitions and diffusion. These experiments all rely on the ability of nanomechanical mass sensors to resolve small masses. Here, we report mass sensing experiments with a resolution of 1.7?yg (1?yg?=?10(-24)?g), which corresponds to the mass of one proton. The resonator is a carbon nanotube of length ～150?nm that vibrates at a frequency of almost 2?GHz. This unprecedented level of sensitivity allows us to detect adsorption events of naphthalene molecules (C(10)H(8)), and to measure the binding energy of a xenon atom on the nanotube surface. These ultrasensitive nanotube resonators could have applications in mass spectrometry, magnetometry and surface science.     

Zeptogram-scale nanomechanical mass sensing

Very high frequency (VHF) nanoelectromechanical systems (NEMS) provide unprecedented sensitivity for inertial mass sensing. We demonstrate in situ measurements in real time with mass noise floor approximately 20 zg. Our best mass resolution corresponds to approximately 7 zg, equivalent to approximately 30 xenon atoms or the mass of an individual 4 kDa molecule. Detailed analysis of the ultimate sensitivity of such devices based on these experimental results indicates that NEMS can ultimately provide inertial mass sensing of individual intact, electrically neutral macromolecules with single-Dalton (1 amu) resolution.     

Single-protein nanomechanical mass spectrometry in real time

Nanoelectromechanical systems (NEMS) resonators can detect mass with exceptional sensitivity. Previously, mass spectra from several hundred adsorption events were assembled in NEMS-based mass spectrometry using statistical analysis. Here, we report the first realization of single-molecule NEMS-based mass spectrometry in real time. As each molecule in the sample adsorbs on the resonator, its mass and position of adsorption are determined by continuously tracking two driven vibrational modes of the device. We demonstrate the potential of multimode NEMS-based mass spectrometry by analysing IgM antibody complexes in real time. NEMS-based mass spectrometry is a unique and promising new form of mass spectrometry: it can resolve neutral species, provide a resolving power that increases markedly for very large masses, and allow the acquisition of spectra, molecule-by-molecule, in real time.     

Cantilever sensor for nanomechanical detection of specific protein conformations

A fast, label-free, and multiplexed method based on piezoresistive cantilevers is reported for the detection of specific protein conformations at the nanoscale level. The ligand-binding domain of the human oestrogen receptor (ERalpha-LBD) is used as the experimental model system, and ERalpha-LBD with or without oestradiol (E2) is detected using the conformation-specific peptides alpha/betaI (Ser-Ser-Asn-His-Gln-Ser-Ser-Arg-Leu-Ile-Glu-Leu-Leu-Ser-Arg, which recognizes E2-bound ER) and alpha/betaII (Ser-Ala-Pro-Arg-Ala-Thr-Ile-Ser-His-Tyr-Leu-Met-Gly-Gly, which recognizes E2-free ER). Target-specific signals are obtained in situ at protein concentrations of 2.5-20 nM. The in-build electrical readout of the piezoresistive cantilevers provides a convenient alternative to the conventional optical detection, and the presented method offers the possibility of detecting protein conformational changes using miniaturized microarrays.     

Prion protein detection using nanomechanical resonator arrays and secondary mass labeling

Nanomechanical resonators have shown potential application for mass sensing and have been used to detect a variety of biomolecules. In this study, a dynamic resonance-based technique was used to detect prion proteins (PrP), which in conformationally altered forms are known to cause neurodegenerative diseases in animals as well as humans. Antibodies and nanoparticles were used as mass labels to increase the mass shift and thus amplify the frequency shift signal used in PrP detection. A sandwich assay was used to immobilize PrP between two monoclonal antibodies, one of which was conjugated to the resonator's surface while the other was either used alone or linked to the nanoparticles as a mass label. Without additional mass labeling, PrP was not detected at concentrations below 20 microg/mL. In the presence of secondary antibodies the analytical sensitivity was improved to 2 microg/mL. With the use of functionalized nanoparticles, the sensitivity improved an additional 3 orders of magnitude to 2 ng/mL.     

Finite size effect on nanomechanical mass detection: the role of surface elasticity

Nanomechanical resonators have recently been highlighted because of their remarkable ability to perform both sensing and detection. Since the nanomechanical resonators are characterized by a large surface-to-volume ratio, it is implied that the surface effect plays a substantial role on not only the resonance but also the sensing performance of nanomechanical resonators. In this work, we have studied the role of surface effect on the detection sensitivity of a nanoresonator that undergoes either harmonic vibration or nonlinear oscillation based on the continuum elastic model such as an elastic beam model. It is shown that the surface effect makes an impact on both harmonic resonance and nonlinear oscillations, and that the sensing performance is dependent on the surface effect. Moreover, we have also investigated the surface effect on the mechanical tuning of resonance and sensing performance. It is interestingly found that the mechanical tuning of resonance is independent of the surface effect, while the mechanical tuning of sensing performance is determined by the surface effect. Our study sheds light on the importance of the surface effect on the sensing performance of nanoresonators.     

An atomic force microscope tip designed to measure time-varying nanomechanical forces

Tapping-mode atomic force microscopy (AFM), in which the vibrating tip periodically approaches, interacts and retracts from the sample surface, is the most common AFM imaging method. The tip experiences attractive and repulsive forces that depend on the chemical and mechanical properties of the sample, yet conventional AFM tips are limited in their ability to resolve these time-varying forces. We have created a specially designed cantilever tip that allows these interaction forces to be measured with good (sub-microsecond) temporal resolution and material properties to be determined and mapped in detail with nanoscale spatial resolution. Mechanical measurements based on these force waveforms are provided at a rate of 4 kHz. The forces and contact areas encountered in these measurements are orders of magnitude smaller than conventional indentation and AFM-based indentation techniques that typically provide data rates around 1 Hz. We use this tool to quantify and map nanomechanical changes in a binary polymer blend in the vicinity of its glass transition.     

Clamped-free double-walled carbon nanotube-based mass sensor

In this study, we investigate the vibrations of the cantilever double-walled carbon nanotube (DWCNT) with attached bacterium on the tip in the view of developing the sensor. This sensor will be able to help to identify the bacterium or virus that may be attached to the DWCNT. Four cases are considered; these are light or heavy bacteria attached to either inner or outer nanotube. The problem is solved by the finite difference method.     

Full-wafer fabrication by nanostencil lithography of micro/nanomechanical mass sensors monolithically integrated with CMOS

Wafer-scale nanostencil lithography (nSL) is used to define several types of silicon mechanical resonators, whose dimensions range from 20?μm down to 200?nm, monolithically integrated with CMOS circuits. We demonstrate the simultaneous patterning by nSL of ～2000 nanodevices per wafer by post-processing standard CMOS substrates using one single metal evaporation, pattern transfer to silicon and subsequent etch of the sacrificial layer. Resonance frequencies in the MHz range were measured in air and vacuum. As proof-of-concept towards an application as high performance sensors, CMOS integrated nano/micromechanical resonators are successfully implemented as ultra-sensitive areal mass sensors. These devices demonstrate the ability to monitor the deposition of gold layers whose average thickness is smaller than a monolayer. Their areal mass sensitivity is in the range of 10(-11)?g?cm(-2)?Hz(-1), and their thickness resolution corresponds to approximately a thousandth of a monolayer.     

Nanobeam sensor for measuring a zeptogram mass

Single-walled carbon nanotubes (SWCNTs) have attracted intense interest in recent years due to their suitability for a wide range of applications, such as nano-sensors and nano-actuators. The primary objective of this paper is presenting a simplified nonlocal finite element model to investigate the potential application of CNTs as a nanomechanical mass sensor. Nonlocal differential elasticity of Eringen is exploited to reveal the long-range interactions between atoms. The CNT resonator is proposed as a bridge Euler–Bernoulli nanobeam with attached mass. An efficient finite element model is developed to discretize the nanobeam domain and solve the equation of motion numerically. The effect of nonlocal parameter on vibration characteristics is discussed and compared with published works. The effects of added mass on the nonlocal frequency shift percentage and higher vibrational modes are discussed in details. Numerical results show that the mass sensitivity of the nanotube sensor is in the zeptogram range.     

An integrated magnetotransistor sensor

The initial voltage offset between the collectors in integrated circuits, including an npn-type dual-collector lateral bipolar magnetotransistor, formed in a well, and polysilicon resistors, is investigated experimentally. The choice of the switching circuit of the magnetotransistor determines the mode of operation and its effect on the offset. The initial offset between the voltages on the collectors is less than 1 mV, which enables the relative value of the useful signal in a weak magnetic field to be increased. Translated from Izmeritel’naya Tekhnika, No. 4, pp. 50–54, April, 2009.     

Ultrasonically driven nanomechanical single-electron shuttle

The single-electron transistor is the fastest and most sensitive electrometer available today. Single-electron pumps and turnstiles are also being explored as part of the global effort to redefine the ampere in terms of the fundamental physical constants. However, the possibility of electrons tunnelling coherently through these devices, a phenomenon known as co-tunnelling, imposes a fundamental limit on device performance. It has been predicted that it should be possible to completely suppress co-tunnelling in mechanical versions of the single-electron transistor, which would allow mechanical devices to outperform conventional single-electron transistors in many applications. However, the mechanical devices developed so far are fundamentally limited by unwanted interactions with the electrical mechanisms that are used to excite the devices. Here we show that it is possible to overcome this problem by using ultrasonic waves rather than electrical currents as the excitation mechanism, which we demonstrate at low temperatures. This is a significant step towards the development of high-performance devices.     

Novel microcantilever design for versatile mass sensor application

This study presents a new microcantilever design for versatile mass sensor application. The novel comb-type cantilever provides a sensitive microcantilever structure for normal sensor application, and its sensing responses are compared with those of a commercial cantilever. While the comb-type cantilever has a similar total surface area to the commercial cantilever, there is a distinct difference in the design of the regional surface area. The results for a static charge interaction, used to compare the sensitivity of normal sensor applications, show a significant resonant frequency change for the comb-type cantilever when compared with that for the commercial cantilever, indicating the importance of the large surface area in the highly sensitive cantilever region. Thus, a schematic structure of a microcantilever for fabricating a highly sensitive mass sensor is proposed.     

An improved cylindrical magnetometer sensor

An improved cylindrical flux-gate magnetometer sensor element has been constructed by electrodepositing permalloy films on solid copper rod substrates with the magnetic easy-axis in the axial direction. The cylindrical films were fabricated by a three-bath electrodeposition process which resulted in a film composition of 81% Ni and 19% Fe adjusted to zero magneto-striction. The optimum ambient field during deposition was determined to be 17.5 Oe in the axial direction. Hysteresis in the resulting Longitudinal Magnetization Characteristic was minimized by tapering the edges of the films.     

Imaging nanoparticles in cells by nanomechanical holography

Nanomaterials have potential medical applications, for example in the area of drug delivery, and their possible adverse effects and cytotoxicity are curently receiving attention. Inhalation of nanoparticles is of great concern, because nanoparticles can be easily aerosolized. Imaging techniques that can visualize local populations of nanoparticles at nanometre resolution within the structures of cells are therefore important. Here we show that cells obtained from mice exposed to single-walled carbon nanohorns can be probed using a scanning probe microscopy technique called scanning near field ultrasonic holography. The nanohorns were observed inside the cells, and this was further confirmed using micro Raman spectroscopy. Scanning near field ultrasonic holography is a useful technique for probing the interactions of engineered nanomaterials in biological systems, which will greatly benefit areas in drug delivery and nanotoxicology.     

Entanglement generated in a nanomechanical oscillator system

We consider a Fabry–Perot cavity with one fixed mirror and a movable perfectly reflecting mirror. Applying a linearised fluctuation analysis, we derive the quantum fluctuations and correlation matrix between the cavity and nanomechanical oscillator. We investigate the continuous-variable (CV) entanglement and squeezing between the cavity and nanomechanical oscillator. It is found that high intensity of entanglement and squeezing between the cavity and nanomechanical oscillator can be achieved.     

DNA nanomechanical switches under folding kinetics control

Existing DNA nanodevices operate at equilibrium under changes in solution composition. We propose an alternative DNA switch design that can be driven and maintained out of equlibrium, under fixed chemical conditions. Moderate cooling rate after heat denaturation drives the switch to its lowest energy conformation, while rapid cooling (>100 degrees C/ms) locks the molecule in a unique alternative conformation that is retained over weeks at room temperature. This reversible process is probed using fluorescent energy transfer. DNA switches operating out of equilibrium should be more amenable to nanotechnology applications and scalable integration.     

An automotive engine oil viscosity sensor

For the evaluation of the condition of automotive engine oil, the oil's viscosity is one of the most important parameters. Using microacoustic viscosity sensors, an oil-viscosity measurement can be performed on-board. In this contribution, we discuss the behavior of the viscosity of engine oil, its temperature dependence, and the resulting representation in terms of output signals of microacoustic viscosity sensors. These considerations are illustrated by means of measurement results obtained for used oil samples, which have been obtained from test cars and fresh oil samples out of different viscosity classes. Finally, the detection of the viscosity increase due to soot contamination is demonstrated.