Interaction of silver colloids with phosphatidylglycerol

Interaction of silver colloids with phosphatidylglycerol monolayers.
Yvette Tran a, Sophie Bernard b, Philippe Fontaine c, Michel Goldmann b,c.
a
b
ESPCI - LPM. 10 rue Vauquelin. 75231 Paris cedex 05. France.
GRPB. Université René Descartes. 45, rue des Saints-Pères. 75270 Paris cedex 06. France.
c
LURE. Bat. 209D. Centre Universitaire Paris-Sud. 91405 Orsay cedex. France.
Silver colloids are currently used as active surfaces for analytical applications of SERS
(Surface-Enhanced Raman Scattering) [1] and could be required to support SERS from
phospholipid monolayers. Colloidal sols are prepared according to Lee and Meisel’s method
described in reference [2]. We have investigated the effect of silver colloids on
phosphatidylglycerol PG by varying two factors : the density of colloidal particles in the
subphase and the chain length of phosphatidylglycerol. The compression isotherms
(particularly the LE-LC phase transition) are modified with the concentration of colloids, and
the effect is more important for shorter chains (see figures below). With fluorescence
microscopy, rounded domains are observed over pure water in contrast with dendritic
structures over colloids-containing subphases [3]. If there is clearly a morphological change at
mesoscopic scales, we have also found a change in the microscopic structure of the
monolayer using grazing incidence X-ray diffraction. It was observed for both DMPG (L-α
dimyristoyl-PG with C14:0 chains) and DPPG (L-α dipalmitoyl-PG with C16:0 chains). The
DMPG hydrocarbon tails assume a perpendicular average orientation on the layer plane and
form a hexagonal lattice over pure water whereas the tails are tilted toward their next-nearest
neighbors over colloidal subphases. The chain tilt increases with the density of colloidal
particles. The same was observed for DPPG monolayers even though the C16 tails are already
tilted over colloids-free subphases. Furthermore, X-ray reflectivity measures give additional
information since the concentration profile perpendicularly to the layer plane is determined
with this technique. Indeed, there might be none adsorption of silver colloids on
phosphatidylglycerol monolayers.
50
50
-3
10 M Ag
40
40
-4
10 M Ag
-5
5 10 M Ag
30
30
-5
2.5 10 M Ag
-5
20
10 M Ag
M A
Mg A g
5 10
-4
-5
10 10
0
0
40 50
60 70
80
90 100 110 120 130
2
Molecular area (Å )
Compression isotherms of DMPG (C14:0)
monolayer over colloids-free and colloidscontaining subphases. T = 25°C.
[2]
[3]
10
20
pure
Surface pressure (mN/m )
water
pure water(mN/m )
Surface pressure
[1]
Mg A g
M-4 A
10
10
30
-3
30
40 50
60 70
80
90 100 110 120 130
2
Molecular area (Å )
Compression isotherms of DPPG (C16:0)
monolayer over colloids-free and colloidscontaining subphases. T = 25°C.
Bernard S., Schwaller M.A., Moiroux J., Lévi G., Aubard J., J. Raman Spectrosc. 1996, 27, 539-547.
Quélin X., Bernard S., Rouaï L., Aubard J., Louis G., Gadenne P., Phys. Stat. Sol. 1999, 175, 399-403.
Lee P.C., Meisel D., J. Phys. Chem. 1982, 986, 3391-3396.
Tran Y., Bernard S., Peretti P., Eur. Phys. J. AP 2000 (sous-presse).