|
|
Research
The
acitvity consists in the study of the electron transfer properties of metalloproteins
of different kinds (e.g. blue-copper, heme metalloproteins) at the level of
the single molecule by means of scanning probe microscopy.
Particularly, we investigate the electron transfer reaction of molecules chemisorbed
onto atomically flat electrodes (e.g. Au(111)) taking advantage of potentiostatic
control of the reaction and using electrochemical scanning tunneling microscope
as a nanoprobe.
This approach helps us to elucidate the nature of the tunneling current arising
from single redox proteins upon tuning the substrate potential to the unoccupied
molecular levels. Furthermore, it provides a unique tool to figure out the most
suitable molecules to be used in Biomolecular Electronics applications.
 |
The
representation of the X-ray structure of azurin from Pseudomonas aeruginosa.
This blue-copper protein binds to gold via a surface disulfide bridge
(Cys3Cys26).
|
|
Schematic
set-up of the electrochemical scanning tunneling microscope and energy
diagram for the molecular adsorbate spectroscopy.
|
|
 |
 |
| Comparative ECSTM and ECAFM imaging of a sample of azurins on Au(111) imaged as a function of Vs (vs SCE). The results point out the electronic nature of the features visible by STM (bright spots appears only above -125 mV) [Ultramicroscopy 89 (2001) 291]. | |
 |
ECAFM |
| ECSTM | |
Metalloproteins
are used in this research activity as active elements of hybrid nanoelectronic
devices. By exploiting both their redox properties and, when possible, chemisorption
capabilities onto metal leads, single to few molecules biomolecular devices
can be implemented.
Particularly, in single protein transistors, a gate voltage swithches the current
flow through a metalloprotein immobilized in a ~ 5 nm gap (made by state of
the art electron beam lithography) by varying the alignement of the unoccupied
molecular levels to the Fermi level of the leads.
 |
 |
 |
In case of larger gaps (10 - 80 nm), a protein (sub)monolayer is placed in between the leads by suitable chemical functionalization of the device surface (usually SiO2).
Plasmid
DNA and mitochondrial DNA (mtDNA) have been studied. MtDNA was purified from
homogenised rat liver. Our interest was to assess the damage induced by tert-butylhydroperoxide
on mtDNA. Protocols for producing high quality images of DNA deposited on mica
were developed.
Follows
the links below to see the images and a brief description of the research:
Surface functionalization
and pattering is another fundamental issue for assembling monolayers of functional
biomolecules right in the place we want (e.g. in between two planar nanoelectrodes).
We develop approaches for immobilizing different biomolecules onto surfaces
of different nature (Au, SiO2, mica, glass, metal and semiconductor oxides,
etc.) exploiting a number of different functional groups on the protein surface
(SH, SS, NH2, etc.). These methods can be of general applicability or tailored
on the specific molecule and molecular arrangement we want to obtain.
The use of optical and non conventional dip-pen lithography (based on AFM)
endows the developed methods with spatial resolution (down to 100 nm).
 |
|
The
schematic reaction used for immobilizing proteins on oxygen exposing
surfaces. The method exploits surface protein amines to form a covalent
link with the silane + glutharic dialdheyde layer [Surf. Sci. 504 (2002)
282].
|
 |
Example
of a protein (azurin) monolayer assembled by the aforementioned method.
|
 |
 |
|
Example of AFM dip-pen lithography. A square area (1 µm) of mica has been functionalized with a 3-aminopropylthriethoxysilane monolayer transferred by the AFM tip. By properly tuning the scanning speed and the load applied to the cantilever it is possible to write and read with the same tip which has been previously coated with the desired molecules. |
|
We are moving to the investigation of mechanical properties of living cells. The main tool we plan to exploit is Atomic Force Microscopy (AFM) implemented in the Force Spectroscopy approach (Force Volume). Our interest is in the elasticity spatial variation of the cell membrane and elasticity temporal variation while living cells are exposed to drugs. Also Quartz Crystal Microbalance (QCM) is used to study the viscoelasticity variation of cells during the cell cycle.
|
Atomic
Force Microscopy of a Fibroblast
|
Quartz
Crystal Microbalance of a Cellular Carpet
|
 |
 |
Top Page |
