Etude de différentes méthodes de biofonctionnalisation pour la ...

I/I. Etudes du film Lan gmuir-Blodgett enzymatique
In the first part, it has been found that for the mixed Langmuir film at the air-water interface, a
transition occurred between 35 and 43 mN m1. lt was assumed that during this transition, proteins
were expulsed from the air water interface and pushed under the polar heads of ODA monolayers.
Such a phenomenon was time dependent. To confirm this assumption, in this second part Atomic
Force Microscopy (AFM) and ATR-FTIR have been employed to study the structure of such mixed
Langmuir-Blodgett films for dipping pressure of both 30 and 40 mN m' on solid substrates.
For the characterization of LB films, AFM is an interesting tool since it could give access to the
molecular architecture, Indeed few papers have dealt with this technique applied to the
characterization of
mixed LB films and the most representative ones concern the study of mixed
Langmuir-Blodgett films constituted of behenic acid and glucose oxidase1'23. For example, Alexandre1
et al. have reported that for the study at the microscopic scale of such a system, the structure of the
mixed films appeared to be heterogeneous, enzyme aggregates being dispersed randomly on the
substrate and these aggregates covered by a behenic acid monolayer in which defects have been
observed.
ATR-FTIR is also an important analytical tool for the study of only a few deposited monolayers due
to its very high sensitivity. Although several works have been devoted to the study of Self Assembled
Monolayers (SAMs)4'5, curiously, only a few concern the study of mixed Langmuir-Blodgett films.
Nevertheless Ancelin et al., have shown how ATR-FTIR can be used to analyse the details of
molecular order, conformation, and interactions of two layers of mixed Langmuir-Blodgett films of fatty
acid and glucose oxidase as a function of dipping pressure6.
Silica plates with low rms were used for the AFM measurements as this type of surface is also
used for microsensor applications, while germanium ATR prisms were used for the ATR-FTIR
measurements. The reason why the ATR experiments have been conducted with germanium is the
high refractive index of this crystal and also the possible accessibility to the spectral windows of the
Si-O-Si band at 1100 cm.
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