Biomedical Engineering Reference
In-Depth Information
0.2-3.0 μM Sudan IV. The RLS approach provides LODs of 3.2, 3.0, 3.2,
and 2.9 nM, for Sudan I, II, III, and IV, respectively, which are about
3000-fold more sensitive than with simple absorbance detection. A
similar strategy has been employed to determine the concentration
of ferulic acid, with an LOD of 15.2 nM.
68
Unlike reduction,
oxidation of Ag NPs can be applied to detection of analytes that are
capable of oxidizing Au NPs. As the size of the Ag NPs decreases, a
decrease in RLS signal occurs, which is proportional to the analyte
concentration. An example of this approach is the determination
of chlorine dioxide in ammonia-ammonium nitrate solution (pH
9.1).
69
The RLS signal of Ag NPs at 470 nm decreases with increasing
concentration of chlorine dioxide over the range of 1.1-185.0 ng/mL,
with a correlation coeficient of 0.9995. This method is simple, rapid,
sensitive (LOD 0.50 ng/mL), and cost-effective for the determination
of chlorine dioxide in drinking water.
Figure 8.12
RLS signals based on visual detection of Sudan IV using
a portable laser pointer (653 nm, 2.0 mW, up) and a light
emitting diode (458 nm, 0.5 mW, down) as irradiated light
sources. Concentrations: AgNO
3
, 4.5 × 10
-4
M; NaOH, 8.0 ×
10
-3
M; NH
3
·H
2
O, 0.02%; Sudan IV (from left to right, mM), 0,
0.1, 0.2, 0.4, 0.6, 1.2, and a real sample of cayenne oil. Triton
X-100, 0.012%. Reprinted from Ref. 67 with permission. See
also Color Insert.
8.3.2.2 Biopolymers
Ag NPs are not as popular as Au NPs for the determination of
biopolymers, mainly because they deteriorate through some types
of reactions. For this reason, Ag NPs are usually used to improve
detection sensitivity after selective capture of analytes of interest
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