Etude de différentes méthodes de biofonctionnalisation pour la ...

ill. Etudes du film Lan gmuir-Blodgett ehzymatique
The addition of ODA at the air-water interface alters strongly the shape of the curve. Firstly, the
surface pressure starts to increase much earlier, meaning that enzymes are more prone to be
adsorbed. Secondly, whatever the enzyme concentration chosen for the mixed ODNenzyme film,
a
plateau at a the surface pressure of 26 mN m
is reached after 600 mm, but here also, the kinetics of
adsorption depends strongly of the enzyme concentration, Thirdty, a different behavior in the evolution
of the surface pressure is observed for the highest concentration (8 mgi1): the surface pressure rose
to near 29.4 mN m' at 80 mm, and decreased back to 26 mN m after 600 min as if a relaxation
phenomenon occurred.
If ODA is replaced by stearic acid (SAc), the surface pressure started to rise only after 60mm and a
plateau is reached at a surface pressure of 14,8 mN m'. Clearly, these results show that when SA is
used, enzymes are less prone to be adsorbed.
31. Pressure area (it-A) isotherms
a) ODA monolayer vs pH
ODA used to form the Langmuir monolayer at the air-water interface was known since 193019, The
stearylamine monolayers could be formed under a wide range of conditions.
For example, figure 2 shows surface pressure-area isotherms for ODA obtained at different pH: 11,
8.07 and 7.5. pH 11 was reached by the addition of small quantïties of NaOH, while the lower pH
values were obtained by the addition of NH4NO3. As we can see, the ODA monolayers change sharply
as the subphase pH is altered. On strongly alkaline solutions (pH=11), the m-A curve resembles
closely the curves obtained by Adam2° with highly condensed monolayers. On the contrary ,
for the
lowest value of pH, the monolayers are in an expanded state. lt also appears for pressures close to
42 mN m, a kink for the lowest value of pH which could be attributed to a LE-LC transition.
The apparent surface area per molecule, extrapolated to O mN rn'1 from the linear portion of
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