Analytical Chemistry Chemical Cytometry Quantitates Superoxide
Analytical Chemistry Chemical Cytometry Quantitates Superoxide
Analytical Chemistry Chemical Cytometry Quantitates Superoxide
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Figure 4. SEM images of (a-d) Si samples patterned by printing<br />
with (a) NBD/1 M H2SO4, (b)1MH2SO4, (c) ABD/0.5 M HCl, and (d)<br />
0.5 M HCl inks; (e, f) Cu samples patterned by printing with (e) NBD/1<br />
MH2SO4 and(f)1MH2SO4 inks.<br />
Table 2. Film Thicknesses for NA Layer Coupled to CP<br />
Film and Associated Controls<br />
surface film thickness/nm a<br />
PPF-CP 1.0 ± 0.3<br />
PPF-CP/SOCl2/NA 2.0 ± 0.5<br />
PPF-CP/NA 1.0 ± 0.4<br />
PPF-H2SO4/SOCl2/NA 0.4 ± 0.2<br />
a<br />
AFM line profiles are shown in Figure S-4 (Supporting Information).<br />
NA + CP on PPF. CP groups were printed on PPF using<br />
nonpatterned stamps and CBD/1 M H2SO4 ink. The films were<br />
activated by immersion in SOCl2 for 30 min and then transferred<br />
to a 20 mM NA/ACN solution at room temperature for<br />
24 h to promote coupling of NA groups to the CP layer via the<br />
formation of amide bonds. These samples are denoted PPF-CP/<br />
SOCl2/NA. Controls were also prepared: PPF-CP blanks were<br />
obtained by printing CP films onto PPF without subsequent<br />
activation or immersion in NA/ACN; for PPF-CP/NA blanks,<br />
only the activation step was omitted; and for PPF-H2SO4/<br />
SOCl2/NA, blanks were prepared by printing PPF with blank<br />
1MH2SO4, followed by “activation” and immersion in NA/<br />
ACN. Prior to their analysis, all samples and controls were<br />
sonicated for 5 min in ACN.<br />
AFM depth profiling results are shown in Table 2, and cyclic<br />
voltammograms of the modified surfaces and typical AFM line<br />
profiles are shown in Figures S-3 and S-4 (Supporting Information).<br />
Activation of the CP film and reaction with NA increased the film<br />
thickness from 1.0 ± 0.3 to 2.0 ± 0.5 nm, consistent with the<br />
coupling of NA groups to the CP layer. When the activation step<br />
7032 <strong>Analytical</strong> <strong>Chemistry</strong>, Vol. 82, No. 16, August 15, 2010<br />
Figure 5. AFM image of VACNTs tethered to a patterned AP layer<br />
on PPF.<br />
was omitted, there was no change in film thickness, confirming<br />
that NA does not physisorb to the CP film. Interestingly, a thin<br />
surface layer of NA was detected electrochemically (Figure S-3,<br />
Supporting Information) and by AFM measurements on the<br />
PPF-H2SO4/SOCl2/NA controls. The measured thickness (0.4<br />
± 0.2 nm) of this film is less than expected for a monolayer of<br />
NA groups (0.8 nm), indicating a submonolayer coverage. We<br />
assume that NA couples directly to a low concentration of<br />
carboxylate functionalities on the (otherwise) bare PPF surface.<br />
SWCNT + AP on PPF. This second example of the utility of<br />
printed films as tethers is based on recent work in which we<br />
assembled and characterized vertically aligned carbon nanotube<br />
(VACNT) forests on AP films electrografted to PPF. 46 To test<br />
whether printed AP films could be used similarly, PPF surfaces<br />
were patterned using ABD/0.5 M HCl ink and then immersed in<br />
a DMSO solution (2 mL) of cut SWCNTs (0.2 mg mL -1 ) and N,N′dicyclohexylcarbodiimide<br />
(1 mg mL -1 )for24hat65°C. These<br />
conditions promote formation of amide bonds between surfaceimmobilized<br />
AP groups and carboxylate groups at the cut ends<br />
of the SWCNTs. The resultant surfaces were sonicated in<br />
acetone for 10 s and then in isopropyl alcohol for 10 s prior to<br />
imaging by AFM. The image shown in Figure 5 (and the SEM<br />
image in Figure S-5, Supporting Information) is similar to those<br />
previously obtained for VACNTs on electrografted AP tether<br />
layers. 46<br />
These examples demonstrate that MCP yields tether layers<br />
with their usual reactivity, and hence, the method can be used to<br />
prepare patterned substrates which form the basis of more<br />
complex structures.<br />
Buildup MCP Patterning of Two-Component Surfaces.<br />
Two- or multicomponent films in which secondary modifiers are<br />
patterned on top of a continuous base film have potential<br />
applications in sensing, where (for example) the base film is<br />
tailored to reduce nonspecific interactions with the analyte while<br />
the patterned secondary modifiers act either as tethers for<br />
attachment of recognition species or as the recognition elements<br />
themselves. This “buildup” method relies on the ability of the<br />
substrate to reduce the secondary modifiers by electron transfer<br />
across the base film. Reduction of the printed secondary modifier<br />
generates radicals which couple to the base film. Hence, a<br />
covalently coupled structure spontaneously forms in a single,<br />
simple step requiring no additional reagents. The buildup method<br />
(46) Garrett, D. J.; Flavel, B. S.; Shapter, J. G.; Baronian, K. H. R.; Downard,<br />
A. J. Langmuir 2010, 26, 1848–1854.