Mixed poly (ethylene glycol) (PEG) and oligo (ethylene glycol) (OEG)
layers on gold as non-fouling surfaces created by backfilling
Running title: Mixed poly (ethylene glycol) (PEG) and oligo (ethylene glycol) (OEG) layers on gold as nonfouling surfaces created by backfilling
Arcot R. Lokanathana, Shuai Zhanga, Viduthalai R. Reginaa, Martin A. Colea, Ryosuke Ogakia‡, Mingdong
Donga, Flemming Besenbachera, Rikke L. Meyera, Peter Kingshottb‡
a-
The Interdisciplinary Nanoscience Centre (iNANO), Aarhus University, Ny Munkegade 120, Aarhus
8000, Denmark.
b-
Industrial Research Institute Swinburne (IRIS), Swinburne University of Technology, Burwood Road,
Hawthorn 3122, Australia.
‡
Corresponding authors:
I. Ryosuke Ogaki
Phone number: +45 8942 3556
Email: ryo@phys.au.dk
II. Peter Kingshott
Formerly at iNANO, Aarhus University, Denmark
Currently at IRIS, Swinburne University of Technology, Australia
Phone number: +61 9214 5033
Email: pkingshott@swin.edu.au
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Calculating inelastic mean free path of Au 4f photoelectron
The inelastic mean free path (IMFP) value of Au 4f photoelectron through PEG was estimated
using the scheme developed by Cumpson et al. 1 based on a quantitative structure property relationship
(QSPR). The QSPR enables the estimation of IMFP of 1 keV electron through any polymer with a
known chemical structure. To begin with, the molecular index of polymer repeat unit at the zero-order,
 , is calculated using the valence connectivity index values 1. Once ov is known, the IMFP value of
o v
photoelectrons with kinetic energy E, can be calculated by using equation S1. Cumpson et al. reported
the IMFP value for 1 keV photoelectrons through PEG using the above mentioned procedure1.
Furthermore by using equation S2, it is possible to calculate the IMFP value for electrons of kinetic
energy E, in a polymer, if the IMFP for 1 keV electrons is known 1. Thus the IMFP of Au 4f
photoelectrons with kinetic energy of 1402.6 eV (using Al kα radiation) through PEG is calculated as
3.8 nm.


3.117( O  V )  0.4207 N rings

 
 1.104 ( E KeV ) 0.79 Eqn-S1

N non H


  i ( E KeV ) 0.79 Eqn-S2
Where, λi – attenuation length of electrons of kinetic energy E keV,  take off angle of analyzer,
 – atomic connectivity index of polymer repeat unit, Nrings – number of aromatic rings, Nnon-H –
o v
number of atoms in repeat unit excluding hydrogen atoms, EKeV – kinetic energy of photoelectron. λi –
attenuation length of electrons of kinetic energy 1 keV.
2
Figure S1. XPS high resolution spectra for the SH-PEG-COOHSAM, SH-PEG-COOHSAM+SH-R and
SH-PEG-COOHSAM+SH-R-OEG3 surfaces. Figure S1a shows C 1s spectra and Figure S1b shows S2p
spectra.
Table SIa. Contact angles for water, formamide and α-bromonapthalene measured on the SH-PEGCOOHSAM, SH-PEG-COOHSAM+SH-R, SH-PEG-COOHSAM+ SH-R-OEG3, SH-R-OEG3-SAM, SH-R
surfaces.
Sample
Water
Formamide
Bromonapthalene
PEG-COOHSAM
25˚ ± 1.7
9.6˚ ± 1.1
4.8˚ ± 0.7
PEG-COOHSAM+OEG3
26.9˚ ± 1.6
12.3˚ ± 1.1
7˚ ± 0.9
PEG-COOHSAM+R
34.3˚ ± 0.7
16.8˚ ± 1
7.2˚ ± 0.9
OEG3-SAM
24.3˚ ± 1.6
13.6˚ ± 0.5
11.9˚ ± 0.4
RSAM
100.3˚ ± 1
85.3˚ ± 2.6
48.5˚ ± 2.6
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Table SIb. Lifshitz van der Waals component (Sd), electron acceptor component (S+), electron donor
component (S)of water, formamide and -Bromonapthalene.
Liquid
sd mJ/m2
s mJ/m2
s mJ/m2
Water
21.8
25.5
25.5
Formamide
39
2.28
39.6
-Bromonapthalene
44
0
0
Figure S 2 (QCM). Representative QCM plots showing the change in frequency upon exposure to 10 %
FBS, 37° C 750 l, 100 l/ min on: Au, PEG-COOHSAM, PEG-COOHSAM+R, PEG-COOHSAM+OEG3,
RSAM and OEG3-SAM. The time points of serum exposure and PBS rinse are indicated with arrows.
References
1.
P. J. Cumpson, Surface and Interface Analysis 31 (1), 23-34 (2001).
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