Biomedical Engineering Reference
In-Depth Information
regions observed in the calibration curve of the imprinted composite, Fig. 4C ,curve
(b), are attributed to the existence of two types of TNT-binding sites. Whereas the
reflectance changes at the lower TNT concentrations of 10 fM
<
[TNT]
<
5pM
correspond to the association of (4) to the imprinted
-donor sites of the matrix, the
reflectance changes observed at the higher TNT concentrations, 100 pM
p
<
[TNT]
<
m
M, which are also observed for the non-imprinted matrix, curve (b), are
attributed to the association of TNT to the non-imprinted bis-aniline
10
p
-donor bridges
as well as to the excess of thioaniline
-donor units modifying the Au NPs in the
composites. The calibration curves also reveal a difference of approximately two
orders of magnitude in the inflection points between the imprinted and non-imprinted
Au NPs matrices. The lower inflection point associated with the imprinted matrix
originates from the existence of nonoptimal, partially fitting binding sites for TNT
molecules, which are presumably formed during the imprinting process.
To further exemplify the use of
p
-donor-acceptor interactions for imprinting
the bis-aniline-cross-linked Au NPs matrices, the herbicide, N , N 0 -dimethyl-4,4 0 -
bipyridinium dichloride, methyl viologen (MV 2+ ), (5), was imprinted, and sensed,
by similar methodology [ 57 ]. In this case, the electropolymerization process
involved the direct imprint of MV 2+ in the composite due to the highly solubility
of (5) itself. Figure 4D depicts the sensograms obtained for analyzing (5) on the
(5)-imprinted and non-imprinted matrices, and the respective calibration curves are
presented in Fig. 4E . A striking difference in the performance of the two matrices is
observed, with a 10 3 -fold lower detection limit by the imprinted matrix, 1 nM, as
compared to the non-imprinted composite, 1
p
M, highlighting, once again, the
important contribution of the imprinting process to the sensing paradigm.
m
2.2
Ionic Interactions in Molecularly Imprinted Au NPs
Matrices for Sensing
A second class of sensing platforms based on bis-aniline-cross-linked Au NPs
composites implementing ionic interactions between the analyte (or its imprint
analog) and the bis-aniline bridging units as an associative driving force for imprinting
was developed. Using this methodology, sensitive sensors for a variety of nitro
Fig. 4 (continued) (a-j: 10 pM-5 m M TNT) on the non-imprinted Au NPs matrix. II—injection of
increasing concentrations of TNT ( a - f : 10 fM-5 pM TNT) on the picric acid-imprinted Au NPs
matrix. (C) The calibration curves derived for the measurements in (B). (D) Sensograms, at
y ¼ 62.0 o , corresponding to MV 2+ analysis on: I—the MV 2+ -imprinted Au NPs matrix ( a - n :
1 nM-20 m MMV 2+ ), and II—the non-imprinted matrix ( a 0 - e 0 : 1-20 m MMV 2+ ). (E) The calibra-
tion curves derived for the measurements in (D). All measurements were performed in a 0.1 M
HEPES buffer solution (pH ¼ 7.2). Parts A-C - Adapted with permission from ref. 50. Copyright
2009, American Chemical Society. Parts D, E - reprinted with permission from ref. 57. Copyright
2010 American Chemical Society
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