How to get Force, Force Gradient and Damping with a single scan and how to image in the attractive regime in any environment. L. Costa1,3, M. S. Rodrigues1,4, J. Chevrier2,3,F. Comin1 ESRF. 6 Rue Jules Horowitz, BP 220, 38043 Grenoble, France 2 Institut Néel, 25 rue des Martyrs, BP 166, 38042 Grenoble, France 3 Université Joseph Fourier, 38041 Grenoble, France 4 CFMC-FCUL University Lisboa, 1749-016 Lisboa, Portugal 1 We developed a new Atomic Force Microscope that we called “Force Feedback Microscope” [1][5]. Avoiding the cantilever “Snap on” the surface, it gives the possibility to measure independently and simultaneously the Force, the Force gradient and the Damping between the AFM probe and the sample in both the attractive and repulsive regimes. It can work in air and liquid environments and can detect forces below the picoNewton limit. Non Contact images of biological samples in solutions can be acquired. Their visco-elastic properties can be investigated simultaneously to the acquisition of the topography in the repulsive regime. ■ WHY ANOTHER AFM ? - “When you have a new idea, few people trust you before it works” • Because the “Jump to contact” limits the non-contact imaging. • Because, despite the many efforts that have been made to extend the FM-AFM to the liquid environment [2], the huge decrease of the Q-factor and the presence of thermal noise at the cantilever resonance still limits the AFM sensitivity in such ambient. ■ EXPERIMENTAL SET-UP-“A direct measurement of atomic forces” An adapted feedback control keeps the distance xt between the AFM probe and an optical fibre constant, counteracting via an actuator every kind of force acting on the probe. The actuator is the lever itself: displacing the base of the cantilever with a Piezoelectric element, the counteracting force is applied to the tip. A • Because at present AFM cannot be applied to the observation of fine structures on living cell membranes, as the membranes are extremely soft compared with available cantilevers. Thus, it is necessary for AFMs to have the ability of non-contact imaging in liquids [3]. • Because, as suggested by the emerging multi-frequency techniques, the recording of nano-mechanical properties of biological samples while acquiring imagesgives access to a lateral resolution below 10nm with a surprising gain in the acquisition time compared to Force-Volume method [4]. ■ NEW FORCE CURVES - “Attractive forces are now accessible” Mica in deionised water Black – Complete force curve with the FFM Blue-Red – Approach-Retract force curve including the range of force not accessible in conventional static Mode Green line – Tip sample distance where jump to contact would occur in static mode No jump to contact: short - range attractive forces are now accessible and can be used as set point to perform microscopy. A Fsample/probe A fibered Fabry-Pérot interferometer measures the instantaneous position of the cantilever B OPERATION MODE: Ffeedback = - Fsample/probe ■ FORCE, FORCE GRADIENT, DAMPING simultaneously “An oscillation small enough is imposed to the tip around its equilibrium position” ■ NEW IMAGING “Choose your STRATEGIES - set-point” SETPOINT RECORDING FORCE TOPOGRAPHY FORCE GRADIENT DAMPING FORCE GRADIENT TOPOGRAPHY FORCE DAMPING DAMPING TOPOGRAPHY FORCE FORCE GRADIENT LIPIDS on Mica in Solution – Image acquired at constant repulsive Force of 50 pN Approach – Retract in conventional Static Mode The force in blue is obtained integrating the measured Stiffness The force in red is the real time force measured ■ FFM IN THE ATTRACTIVE REGIME Topography Ffeedback B P r o t ei n Buffer : s TB K & OPT 2 0m M N HE P E S 5 mM M g Cl 2 Complete characterisation of the interaction ■ FFM IN THE REPULSIVE REGIME P r o t ei n Buffer : s O P TN 2 0m M HE P E S 5 mM M gC l 2 Topography Max 19.9 nm Max 0.002 N/m Force gradient Min -0.019 N/m Min 0.0 nm Force gradient Max 0.02 N/m Min 0.08 μKg/s REFERENCES: “We've learned from experience that the truth will come out” Richard P. Feynman 1974 Achieve chemical resolution in air and liquid environment during topography data acquisition : Non-Contact AFM. Min 0.11 μKg/s • Non contact AFM of living cells [1] M. S. Rodrigues, L. Costa, J. Chevrier and F. Comin, “Measurement of the complete force curve at the nanoscale”, arxiv, 1205:19332 (2012) [2] T. Fukuma, K. Kobayashi, K. Matsushige and H. Yamada, "True molecular resolution in liquid by frequency-modulation atomic force microscopy", Appl. Phys. Lett., vol. 86, 193108 (2005) [3] T. Ando, T. Uchihashi, T. Fukuma, “High-speed atomic force microscopy for nano-visualization of dynamic biomolecular processes”, Progress in Surface Science, vol. 83, pp.337-437 (2008) [4] A. Raman, S. Trigueros, A. Cartagena, A. P. Z. Stevenson, M. Susilo, E. Nauman and S. Antoranz Contera, “Mapping nanomechanical properties of live cells using multi-harmonic atomic force microscopy”, Nature Nanotech., vol. 6, pp. 809-815 (2011) We acknowledge support from the project ANR-09-NANO-042-02 PianHo [5] Patent B11187 (2011.) “Dispositif de mesure de force atomique”, E.S.R.F, Université Joseph Fourier ■ NEXT STEPS Damping Min -0.001 N/m Max 1.13 μKg/s Force Force gradient Elasticity • High speed non-contact measurements of organic materials, proteins, DNA, polymers. Max 6.19 μKg/s Damping Topography