Large scan area high-speed atomic force microscopy using a resonant scanner.

A large scan area high-speed scan stage for atomic force microscopy using the resonant oscillation of a quartz bar has been constructed. The sample scanner can be used for high-speed imaging in both air and liquid environments. The well-defined time-position response of the scan stage due to the use of resonance allows highly linearized images to be obtained with a scan size up to 37.5 mum in 0.7 s. The scanner is demonstrated for imaging highly topographic silicon test samples and a semicrystalline polymer undergoing crystallization in air, while images of a polymer and a living bacteria, S. aureus, are obtained in liquid.

Power gain exhibited by motile mechanosensory neurons in Drosophila ears.

In insects and vertebrates alike, hearing is assisted by the motility of mechanosensory cells. Much like pushing a swing augments its swing, this cellular motility is thought to actively augment vibrations inside the ear, thus amplifying the ear's mechanical input. Power gain is the hallmark of such active amplification, yet whether and how much energy motile mechanosensory cells contribute within intact auditory systems has remained uncertain. Here, we assess the mechanical energy provided by motile mechanosensory neurons in the antennal hearing organs of Drosophila melanogaster by analyzing the fluctuations of the sound receiver to which these neurons connect. By using dead WT flies and live mutants (tilB(2), btv(5P1), and nompA(2)) with defective neurons as a background, we show that the intact, motile neurons do exhibit power gain. In WT flies, the neurons lift the receiver's mean total energy by 19 zJ, which corresponds to 4.6 times the energy of the receiver's Brownian motion. Larger energy contributions (200 zJ) associate with self-sustained oscillations, suggesting that the neurons adjust their energy expenditure to optimize the receiver's sensitivity to sound. We conclude that motile mechanosensory cells provide active amplification; in Drosophila, mechanical energy contributed by these cells boosts the vibrations that enter the ear.

High-Q dynamic force microscopy in liquid and its application to living cells.

We present a new dynamic force microscopy technique for imaging in liquids in the piconewton regime. The low quality factor (Q) of the cantilever is increased up to three orders of magnitude by the implementation of a positive feedback control. The technique also includes a phase-locked loop unit to track the resonance of the cantilever. Experiments and computer simulations indicate that the tip-sample forces are below 100 pN, about two orders of magnitude lower than in conventional tapping mode atomic force microscopy. Furthermore, the spectroscopic ability is greatly enhanced. Either the phase shift or the resonant frequency shows a high sensitivity to variations in either the energy dissipation or conservative interactions between the tip and the sample, respectively. The potential of this technique is demonstrated by imaging living cells.

Chemical sensors and biosensors in liquid environment based on microcantilevers with amplified quality factor.

A new technique is presented for bio/chemical sensors, based on microcantilevers, for detection in liquid environment. The low quality factor of the cantilever in liquid is increased up to three orders of magnitude by using Q-control. This enables AC detection that is immune to the long-term drift of the DC cantilever response in liquids, and to temperature variations. This technique has been applied for the detection of ethanol in aqueous solution by using the microbalance method, and for antibody/antigen recognition by the surface stress method. The results show the feasibility and very high sensitivity of these novel devices.

Modeling of cylindrically tapered cantilevers for transverse dynamic force microscopy (TDFM).

In transverse dynamic force microscopy a cylindrically tapered cantilever is mounted perpendicularly to the sample surface and set into transversal oscillation. The dynamics of the cantilever has been studied using the continuum mechanical model with discrete element analysis. A viscoelastic model has been used to describe the tip-sample interaction. In this way an in-phase and an out-of-phase component of the force has been extracted from the experimental data. Two different techniques, involving two experimental setups and two corresponding data analysis routines, have been developed to calculate the two components of the force at different tip-sample separations. In one case the change in resonant frequency and corresponding oscillation amplitude is measured whereas in the second case the usual way of recording amplitude and phase signal at a fixed driving frequency is applied. The results from these two methods are shown to be completely consistent and produce almost identical force curves.