Biomedical Engineering Reference
In-Depth Information
The experimental concentration ratios (
C
X
/C
tot
) can be converted into weight percentages of
model compounds (Genet et al., 2008, Rouxhet & Genet, 2011), using the carbon
concentration specific to each compound (Table 3).
Density
(g.cm
-3
)
Proteins
0.312
*
0.273
*
43.5 1.4
Silane
0.5 0.333 27.3 0.9
Polysaccharides
0.833 - 37.0 1.5
Hydrocarbons
- - 71.4 0.9
* Data computed from the amino acid sequence of glucose oxidase on the basis of ProtParam tool
available on the ExPASy molecular biology server (http://us.expasy.org).
Table 3. Chemical composition of organic compounds (molar concentration ratio of elements
and concentration of carbon) and their densities.
Carbon concent.
(mmol.g
-1
)
O/C
N/C
Results, presented in Table 4, show the often dominating presence of hydrocarbon-like
compounds and polysaccharides, for all samples. Both compounds are due to adventitious
contamination which may originate from adsorption from air, as always observed for high
surface energy solids (Caillou et al., 2008; Mantel et al., 1995),
but also from aqueous media
(Landoulsi et al., 2008a). They may be taken as a global way to reflect the amount of
compounds which contain hydrocarbon chains and oxygen, such as esters, but excluding
proteins and silane. The concentration of
silane deduced for non-silanized samples is non
negligible but highly variable, and may also be attributed to contamination. A drastic
increase of silane concentration is observed for all silanized samples (Table 4).
(wt. %)
Thickness (nm)
Pr
Sl
PS
HC
at θ
= 0°
at θ = 60°
nat
2.9
5.8
29.5
61.7
3.6
2.2
+BS
(8.5)
6.1
28.3
57.1
3.2
2.1
+Gox
16.3
0.0
24.7
59.0
3.2
2.3
+BS+Gox
(7.3)
12.3
35.5
44.9
3.3
2.2
sil
0.0
29.0
22.2
48.8
3.8
2.7
sil+BS
(10.8)
25.5
25.2
38.5
3.9
2.8
sil+Gox
35.2
20.0
24.3
20.5
3.9
2.9
sil+BS+Gox
24.4
22.9
22.5
30.2
4.1
2.8
* The data between brackets are protein equivalent of BS products and have no physical meaning.
Table 4. Chemical composition (weight %) of the organic adlayer present on stainless steel
samples, as deduced from XPS data and expressed in terms of classes of molecular
compounds*. Thickness of the organic adlayer deduced from measurements at
photoelectron collection angle
θ
= 0° and 60°.
The Gox treatment leads to a marked increase of the protein concentration on nat sample
and a much stronger increase on sil sample. This may be attributed to physical adsorption
