Reminder: CBM seminar: Monday, 7 July 2008, 11 AM

Cristina Leonesi cristina.leonesi at
Fri Jul 4 09:32:27 CEST 2008

Dear All, 

You are kindly invited to the next CBM seminar: 

Imaging and force spectroscopy by AFM on DNA 

Dr. Giovanni Di Santo 

Laboratoire de Physique de la Matière Vivante, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne – Switzerland 

giovanni.disanto at 

Moderator: Dr. Stefano Prato, APE Research srl 

Monday, 7 July 2008, 11 AM 

Meeting Room CBM, Q building, 1st floor 

AREA Science Park, Basovizza (TS) 


Atomic force microscopy (AFM) is a powerful tool for determining the topography of native biomolecules at subnanometer resolution. A custom made AFM conceived for vacuum and low temperatures (77 K) experiments has been developed in order to increase the resolution on soft samples. Starting from a first prototype working in contact mode, we implemented dynamic modes (tapping, non-contact) on the aim to reduce possible sample damaging due to strong tip-sample interactions. Technical solutions to improve the functionality of the microscope will be described. 

Non Contact mode provides high signal stability and the needed sensitivity to visualize DNA details on the single molecule scale. In this mode of operation, also known as Frequency Modulation AFM, Frequency shift ( D f) versus separation (Z) curves lead to a detailed comprehension of the tip-sample interaction providing quantitative measurements of both force and interaction potential. We present D f vs Z curves taken on DNA molecules deposited on mica substrates. The high resolution force measurements on soft specimens like APTES functionalized mica has returned adhesion forces less than 1 nN. The experimental conditions permit to evaluate the net interaction between the sample and a sharp tip. The single point spectroscopy measurements indicate that FM-AFM can easily detect differences in interaction forces between sample and substrate opening the possibility to evaluate local interaction at the molecular scale. 
For information: info at 

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