Paper AS2+BI-ThM6
Nanoarrayed Biomolecular Recognition followed by AFM

Thursday, November 12, 2009, 9:40 am, Room K

The use of nanoarrayed surfaces in the field of biomolecular recognition is very promising for the improvement of bio-detection performance. Atomic Force microscope (AFM)  is widely used to produce and characterize nanoarrayed surfaces and to carry out studies in the biological field. This work presents the study and characterization by AFM measurements of the fabrication steps of nanoarrayed surfaces based on organothiols (carboxylic and Polyethylene oxide) and the study of an immunoassay performed on these surfaces. The immunoassay was based on the bio-recognition between Human IgG/anti-Human IgG.

The nanoarray was fabricated by plasma colloidal lithography following the procedure developed in our lab. AFM studies of the process of nanoarray fabrication showed that during lithographic process, the etching step is crucial for the final the characteristics of the surface and that the process originates a good chemical nano-contrast.

The AFM analysis of the bio-interaction was performed after Human IgG immobilisation and anti-Human IgG recognition steps. The nanoarray was incubated with Human IgG solution resulting in an increase of height on the nano areas.  The AFM image demonstrates that IgG molecules are adsorbed mainly on the border between the two organothiols. The preferential disposition of proteins on the borders of the two different materials with hydrophobic and hydrophilic groups was already reported and associated to the fact that the proteins tend to adsorb where they can find better accommodation. In our case, this effect can be explained by the fact that having the carboxylic spots with hydrophilic character the IgG hydrophobic groups are better accommodated on the border between the two materials, leading to higher adsorption on the boundaries. After the Human IgG incubation, the surface was blocked with BSA and the following step consisted in the immobilisation of anti-Human IgG. After this step, a height increase on the border of the COOH nano area is detected by AFM. The increase is about the double of the initial with Human IgG. This is an indication that the anti Human IgG binds specifically with the Human IgG already on the surface. The distribution on the borders of the nano-area can explain the better efficiency of the nano-patterns in biomolecular recognition as already described on different studies. The preferential proteins immobilisation on the nano areas boundaries seems to improve the binding efficiency of the immobilised Human IgG bio-detector by a better availability of the binding sites on the surface and reduction of steric hindrance.