Etude de différentes méthodes de biofonctionnalisation pour la ...

Ill. Etudes du film Lan gmuir-Blodgett enzymatique
A delay between the spreading of ODA and the outset of the isotherm recording of 180 min and 10
hours for mixed film and pure enzyme film respectively is required, in order to allow the enzyme
adsorption-desorption equilibrium to be reached at the air-water interface as shown in the previous
section.
Curve 1 shows the TE-A isotherm obtained with ODA at the natural pH of 5.5. The apparent surface
area per molecule, extrapolated to O mN m from the linear portion of the compression curve was
about 19 A2 per molecule. The monolayers seem to be in a condensed state. The collapse surface
pressure is reached for surface pressure higher than 60 mN m1. The lack of an LE-LC transition in this
case means that we are below the triple point temperature21.
For pure enzyme, the t-A isotherm shows a slight inflection between 18 mN rn1 and 23 mN m
which could be attributed to the orientation or/and the deformation of the enzyme.
For the mixed film, the apparent molecular areas were greater than pure ODA when surface
pressures are less than 45 mN m1, while they become lower than that of pure ODA when surface
pressures are more than 45 mN m
For a surface pressure of 35 mN m, a transition can be observed. Such transition may indicate a
rearrangement towards a higher order, an expulsion of the enzyme molecules from the interface
towards the bulk, or a coverage of enzyme molecules by the ODA film.
As soon as the interfacial pressure reach 40 mNm, the slope of the isotherm increase significantly
but stays, all the same, always less than that of pure ODA.
3.3. Monolayer stability
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