André Meister

FluidFM: Combining Atomic Force Microscopy and Nanofluidics in a Universal Liquid Delivery System for Single Cell Applications and Beyond

We describe the fluidFM, an atomic force microscope (AFM) based on hollow cantilevers for local liquid dispensing and stimulation of single living cells under physiological conditions. A nanofluidic channel in the cantilever allows soluble molecules to be dispensed through a submicrometer aperture in the AFM tip. The sensitive AFM force feedback allows controlled approach of the tip to a sample for extremely local modification of surfaces in liquid environments. It also allows reliable discrimination between gentle contact with a cell membrane or its perforation. Using these two procedures, dyes have been introduced into individual living cells and even selected subcellular structures of these cells. The universality and versatility of the fluidFM will stimulate original experiments at the submicrometer scale not only in biology but also in physics, chemistry, and material science.

Nanodispenser for attoliter volume deposition using atomic force microscopy probes modified by focused-ion-beam milling

In this letter, we describe the on-demand dispensing of single liquid droplets with volumes down to a few attoliters and submicrometric spacing. This dispensing is achieved using a standard atomic force microscope probe, with a 200 nm aperture at the tip apex, opened by focused ion beam milling. The inside of the tip is used as reservoir for the liquid. This maskless dispensing, realized in ambient environment, permits the direct creation of droplet arrays. Nanoparticles, suspended in the liquid, were organized on a surface.

Nanoscale dispensing of liquids through cantilevered probes

Nanoscale dispensing is a novel technique to deposit material and create structures at dimensions of 100 nm and below. It has great flexibility in feature shape and choice of deposited material. Due to its potential low cost and lack of time consuming steps, it represents an interesting complementary tool to standard lithographic processes. The key feature of nanodispensing is deposition of liquids through an apertured scanning force microscopy probe tip. In the first experiments, liquid is manually loaded into a hollow pyramidal probe tip. Upon contact of the tip and the substrate, liquid at the end of the tip is transferred to the substrate surface. Moving the sample during contact allows to write features with sizes that can be as small as 100 nm and below, largely dependent on the aperture diameter. This approach is novel, and has recently been demonstrated in our laboratory for the first time, with feature sizes still well above 1 µm.

Parallel AFM imaging and force spectroscopy using two‐dimensional probe arrays for applications in cell biology

Atomic force microscopy (AFM) investigations of living cells provide new information in both biology and medicine. However, slow cell dynamics and the need for statistically significant sample sizes mean that data collection can be an extremely lengthy process. We address this problem by parallelizing AFM experiments using a two‐dimensional cantilever array, instead of a single cantilever. We have developed an instrument able to operate a two‐dimensional cantilever array, to perform topographical and mechanical investigations in both air and liquid. Deflection readout for all cantilevers of the probe array is performed in parallel and online by interferometry. Probe arrays were microfabricated in silicon nitride. Proof‐of‐concept has been demonstrated by analyzing the topography of hard surfaces and fixed cells in parallel, and by performing parallel force spectroscopy on living cells. These results open new research opportunities in cell biology by measuring the adhesion and elastic properties of a large number of cells. Both properties are essential parameters for research in metastatic cancer development. Copyright

Increased plasticity of the stiffness of melanoma cells correlates with their acquisition of metastatic properties.

UNLABELLED The stiffness of tumor cells varies during cancer progression. In particular, metastatic carcinoma cells analyzed by Atomic Force Microscopy (AFM) appear softer than non-invasive and normal cells. Here we examined by AFM how the stiffness of melanoma cells varies during progression from non-invasive Radial Growth Phase (RGP) to invasive Vertical Growth Phase (VGP) and to metastatic tumors. We show that transformation of melanocytes to RGP and to VGP cells is characterized by decreased cell stiffness. However, further progression to metastatic melanoma is accompanied by increased cell stiffness and the acquisition of higher plasticity by tumor cells, which is manifested by their ability to greatly augment or reduce their stiffness in response to diverse adhesion conditions. We conclude that increased plasticity, rather than decreased stiffness as suggested for other tumor types, is a marker of melanoma malignancy. These findings advise caution about the potential use of AFM for melanoma diagnosis. FROM THE CLINICAL EDITOR This study investigates the changes to cellular stiffness in metastatic melanoma cells examined via atomic force microscopy. The results demonstrate that increased plasticity is a marker of melanoma malignancy, as opposed to decreased stiffness.

Piezoresistive cantilever array for life sciences applications

Atomic Force Microscopy (AFM) techniques are used with one- or two-dimensional arrays of piezoresistive probes for parallel imaging. We present a newly designed AFM platform to drive these passivated piezoresistive cantilever arrays in air and liquid environments. Large area imaging in liquid as well as qualitative and quantitative analysis of biological cells are demonstrated by the means of piezoresistive cantilever for the first time to our knowledge. Noise limitations in topography and force resolutions of these piezolevers are quantified.

Attovial-based antibody nanoarrays.

Antibody array‐based technology is a powerful emerging tool in proteomics, but to enable global proteome analysis, antibody array layouts with even higher density has to be developed. To this end, we have further developed the first generation of a nanoarray platform, based on attoliter‐sized vials, attovials, which we have characterized and used for the detection of complement factor C1q in human serum samples. Finally, we demonstrated proof‐of‐concept for individual functionalization of the attovials with a recombinant antibody.

Concept and Demonstration of Individual Probe Actuation in Two-Dimensional Parallel Atomic Force Microscope System

A concept of an array actuator that is used to control the tip–sample separation of cantilevers in a two-dimensional (2D) probe array scanning system is proposed in this article. The feasibility of the concept is demonstrated with a 10×10 array actuator with 500 µm xy-pitches. The array actuator is made by slicing a bulk piezoceramic block. The obtained maximum actuation of a single probe was 2.19 µmp–p at ±168 Vp–p. A major issue for the actuator was the insufficient strength of the frame of the probe array chip. The demonstrated array actuator is highly compatible with previously developed parallel readout modules that use either a parallel optical beam or integrated piezoresistive deflection sensing. A large-scale 2D probe array is our ultimate target.

Piezoresistive scanning probe arrays for operation in liquids

Piezoresistive scanning probe arrays have been developed in view of operation in liquid environments. When the cantilevers are immersed in electrically conductive solutions like for instance physiological buffers, the piezoresistive sensing elements as well as the metal connections have to be passivated. For that purpose, the sensors and the metal wiring were covered with different protective coatings. Long term stability of these passivation layers was demonstrated by imaging in a buffer solution for several hours. Moreover, in view of reducing the damping and thus decreasing the hydrodynamic resistance in liquids, special truss cantilevers have been developed. It was found that this special design conferred no improvement in terms of Q-factor and resonant frequency when operated in water. In order to explain the behaviour of these probes, a theoretical model was established. The model predicted that truss structures could theoretically improve the cantilever performances in liquid, but the probes would need to be operated at high frequency, above 10 MHz.

Modeling, filtering and optimization for AFM arrays

In this paper, we present new tools and results developed for Arrays of Microsystems and especially for Atomic Force Microscope (AFM) array design. For modeling, we developed a two-scale model of cantilever arrays in elastodynamics. A robust optimization toolbox is interfaced to aid for design before the microfabrication process. A model based algorithm of static state estimation using measurement of mechanical displacements by interferometry is stated. Quantization of interferometry data processing is analyzed for FPGA implementation. A robust H ∞ filtering problem of the coupled cantilevers is solved for time-invariant system with random noise effects. Our solution allows semi-decentralized computing based on functional calculus that can be implemented by networks of distributed electronic circuits as shown in a previous paper.