Analytical Chemistry Chemical Cytometry Quantitates Superoxide
Analytical Chemistry Chemical Cytometry Quantitates Superoxide
Analytical Chemistry Chemical Cytometry Quantitates Superoxide
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Table 3. Film Thickness Measurements on PPF<br />
Substrates Modified with CP Films with and without<br />
Overprinting of a NP Layer a<br />
film thickness/nm b<br />
sonication solvent and time CP region CP/NP region<br />
H2O (5 min) 1.6 ± 0.3 2.2 ± 0.3<br />
H2O (5 min) 1.4 ± 0.3 2.1 ± 0.2<br />
H2O (5 min) + ACN (30 min) 1.7 ± 0.6 2.1 ± 0.3<br />
H2O (5 min) + ACN (30 min) 1.5 ± 0.4 2.0 ± 0.2<br />
a Samples were prepared in duplicate. b AFM line profiles are shown<br />
in Figure S-7 (Supporting Information).<br />
Figure 6. SEM images of surfaces that were immersed in 10 mM<br />
CBD/0.1 H2SO4 for 30 min and subsequently printed with (a) ABD/<br />
0.5 M HCl and (b) 0.5 M HCl inks. After printing, the surfaces were<br />
immersed in Au nanoparticle solution for 40 min.<br />
was demonstrated by printing the secondary modifiers NP and<br />
AP.<br />
CP + NP on PPF. NP groups were printed onto a base CP<br />
film grafted spontaneously to PPF at OCP. Two ∼3.0 × 1.5 mm 2<br />
PPF samples were immersed in 10 mM CBD/0.1 M H2SO4<br />
solution for 30 min to form the base films. One half of each<br />
sample was then printed with a nonpatterned stamp using<br />
NBD/1 M H2SO4 ink. Cyclic voltammetry (Figure S-6, Supporting<br />
Information) confirmed that NBD had reacted in the<br />
expected manner giving an NP layer.<br />
AFM depth profiling measurements of printed and unprinted<br />
sections (Table 3) show that printing increases the film thickness,<br />
consistent with attachment of NP to the CP layer. The magnitude<br />
of the increase (∼0.4-0.7 nm) corresponds to the addition of a<br />
submonolayer of NP groups on top of the CP film. However, NP<br />
is also expected to couple within the CP film, and hence, the<br />
concentration of printed NP groups may be higher than indicated<br />
by film thickness data.<br />
To test the stability of the printed layers, the samples were<br />
sonicated in ACN for 30 min and the AFM measurements were<br />
repeated. The data in the lower part of Table 3 indicate that the<br />
film thicknesses did not change significantly, consistent with<br />
covalent attachment both to the substrate surface and between<br />
the base and printed layers.<br />
CP + AP on PPF. In the second example of the buildup<br />
printing approach, AP groups were patterned onto a spontaneously<br />
grafted layer of CP groups using a patterned stamp with ABD/<br />
0.5 M HCl ink. A blank was also prepared on a CP layer by printing<br />
with blank 0.5 M HCl ink. The printed surfaces were immersed<br />
for 40 min in a solution of Au nanoparticles and then sonicated in<br />
H 2O for 30 s prior to analysis by SEM. Figure 6 shows the SEM<br />
images where the assembled Au nanoparticles clearly reveal the<br />
patterned immobilization of AP (Figure 6a) in comparison with<br />
the control (Figure 6b).<br />
The buildup approach for preparing patterned two- or multicomponent<br />
surfaces should be applicable to all substrates at which<br />
grafting from aryldiazonium salt solutions proceeds spontaneously<br />
at OCP. However, the requirement that the second aryldiazonium<br />
cation be reduced by the substrate places some limitations on<br />
the nature and thickness of the base film and also on the<br />
aryldiazonium cation derivative. For strongly reducing substrates<br />
(such as zinc), it should be possible to print even relatively difficultto-reduce<br />
aryldiazonium cations onto thick base films. On the<br />
other hand, printing on less-reducing substrates (such as Au) is<br />
likely to be successful only with easily reduced aryldiazonium salt<br />
derivatives on thin base films. In the examples above, the base<br />
films were formed by spontaneous grafting from a aryldiazonium<br />
salt solution. There is no reason why MCP, electrografting, and/<br />
or other classes of modifiers cannot be used. Methods such as<br />
electro-oxidation of primary amines 47 or arylhydrazines; 48 electroreduction<br />
of iodonium, 49,50 sulfonium 51 salts, or vinylic compounds;<br />
52 photolytic or thermal grafting of alkenes and alkynes; 53-56<br />
or photografting of arylazides 57 would greatly widen the range of<br />
functionalities that could be added to the surface.<br />
CONCLUSION<br />
Microcontact printing using aryldiazonium salt inks has been<br />
applied to carbon, metal, and semiconductor substrates to give<br />
stable, covalently attached, thin films. The thickness and the<br />
morphology of the printed film appear to depend on the potential<br />
driving force for reduction of the aryldiazonium cation by the<br />
substrate. Aminophenyl and carboxyphenyl groups in printed<br />
layers retain the ability to form amide bonds with solution species<br />
and, consequently, provide useful tethers for more complex<br />
surface structures.<br />
Microcontact printing using aryldiazonium salts is applicable<br />
to all substrate-diazonium salt combinations for which surface<br />
modification proceeds spontaneously at open circuit potential in<br />
solution. The variable film thickness and roughness, which is<br />
substrate- and film-dependent, may be a limitation for some<br />
potential applications; however, compared with other methods for<br />
patterning layers using aryldiazonium salts, microcontact is low<br />
cost and simple to implement with no requirement for electrochemical<br />
capability. Tightly defined patterns with feature sizes<br />
tens of micrometers upward can be routinely prepared, and<br />
(47) Barbier, B.; Pinson, J.; Desarmot, G.; Sanchez, M. J. Electrochem. Soc. 1990,<br />
137, 1757–1764.<br />
(48) Malmos, K.; Iruthayaraj, J.; Pedersen, S. U.; Daasbjerg, K. J. Am. Chem.<br />
Soc. 2009, 131, 13926–13927.<br />
(49) Vase, K. H.; Holm, A. H.; Norrman, K.; Pedersen, S. U.; Daasbjerg, K.<br />
Langmuir 2007, 23, 3786–3793.<br />
(50) Vase, K. H. j.; Holm, A. H. k.; Pedersen, S. U.; Daasbjerg, K. Langmuir<br />
2005, 21, 8085–8089.<br />
(51) Vase, K. H.; Holm, A. H.; Norrman, K.; Pedersen, S. U.; Daasbjerg, K.<br />
Langmuir 2008, 24, 182–188.<br />
(52) Palacin, S.; Bureau, C.; Charlier, J.; Deniau, G.; Mouanda, B.; Viel, P.<br />
ChemPhysChem 2004, 5, 1469–1481.<br />
(53) Lasseter, T. L.; Cai, W.; Hamers, R. J. Analyst 2004, 129, 3–8.<br />
(54) Ssenyange, S.; Anariba, F.; Bocian, D. F.; McCreery, R. L. Langmuir 2005,<br />
21, 11105–11112.<br />
(55) Sun, B.; Colavita, P. E.; Kim, H.; Lockett, M.; Marcus, M. S.; Smith, L. M.;<br />
Hamers, R. J. Langmuir 2006, 22, 9598–9605.<br />
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<strong>Analytical</strong> <strong>Chemistry</strong>, Vol. 82, No. 16, August 15, 2010<br />
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