Biomedical Engineering Reference
In-Depth Information
NPs are readily employed for the sensing of Hg
2+
ions, based on
luminescence quenching through Hg
2+
-induced aggregation.
24
The
interactions between 11-MUA-Au NPs and Hg
2+
ions occur through
Hg
2+
-carboxylate bonding or Hg
2+
-Au
+
metallophilic interaction.
In the presence of 2,6-pyridinedicarboxylic acid (PDCA), the 11-
MUA-Au NPs bind to Hg
2+
, leading to a decrease in luorescence
(Fig. 9.9). In the absence of PDCA, interference from Pb
2+
and Cd
2+
ions is strong. Such interference is minimized by adding 1.0 mM PDCA
to the solution, mainly due to its strong interaction with Hg
2+
.
73
This
approach provides high sensitivity (limit of detection (LOD) = 5.0 nM)
and selectivity (at least 10-fold against Pb
2+
and Cd
2+
). This LOD
is lower than the maximum level (2.0 ppb) of mercury permitted
in drinking water by the United States Environmental Protection
Agency (EPA). This approach provides a sensitivity that is two
orders of magnitude lower than those reported for heavy metal ion
sensors based on chelation/aggregation-mediated colorimetry and
for Au NP systems based on modulation of luorescence quenching.
Furthermore, this Au NP-based nanosensor can be applied to analyses
of Hg
2+
in environmental samples. For example, the concentration of
Hg
2+
in a pond water sample determined using this 11-MUA-Au NP
sensor was 3.49 ppb, in good agreement with the value (3.20 ppb)
determined using inductively coupled plasma mass spectrometry
(ICP−MS).
Figure 9.9
(A) Fluorescence ratios [(
I
Fo
-
I
F
)/
I
Fo
] at 520 nm for the 11-
MUA-Au NPs (10 nM) measured in the absence and presence
of PDCA (1.0 mM) after the addition of 500 nM metal ions in
5 mM sodium tetraborate solutions at pH 9.2. (B) Fluorescence
response of the 11-MUA-Au NPs upon the addition of Hg
2+
ions (0, 10, 25, 50, 100, 250, 500, 750, 1000, 2500, 5000, and
10,000 nM). Inset: Plot of luorescence ratios [(
I
Fo
-
I
F
)/
I
Fo
] of
11-MUA-Au NPs at 520 nm versus log[Hg
2+
]. [Reprinted with
permission from Ref. 24].
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