Biomedical Engineering Reference
In-Depth Information
by calf intestine alkaline phosphatase (CIAP) and peptide
phosphorylation by protein kinase A (PKA) are representative. In the
absence of the enzymes, unreacted ATP protects Ag NPs from salt-
induced aggregation whereas in the presence of the enzymes, the
reaction product of ATP (i.e., adenosine for CIAP and ADP for PKA)
cannot (see Fig. 3.13). The colors of Ag colloidal solutions containing
ATP in the absence and presence of CIAP are yellow and pale red,
respectively, after the addition of 15 μL of 0.5 M NaCl. A similar
strategy is also useful for the determination of PKA activity using
a phosphorylation of the PKA substrate H-Leu-Arg-Arg-Ala-Ser-
Leu-Gly-OH (peptide 1) (see Fig. 3.13). When PKA phosphorylates
1 mol of peptide 1, 1 mol of ATP is consumed to form 1 mol of ADP.
As a result, the color of the Ag NP solution changes from yellow to
yellowish brown in the presence of PKA. This approach provides
LODs of 1 and 0.022 unit/mL for CIAP and PKA, respectively.
(B)
(A)
(C)
Figure 3.13 Enzymatic reactions with (A) CIAP and (B) PKA and (C) an Ag
NP-based enzyme colorimetric assay.
3.5 Summary
In this chapter, we present Au and Ag NP-based colorimetric
assays for the determination of various analytes, including DNA,
antigens, and proteins. Au NPs offer advantages such as high molar
extinction coeficients, simple preparation and bioconjugation, and
biocompatibility and thus are the most popular nanomaterials for
colorimetric assays. After suitable bioconjugation, functionalized Au
NPs provide high sensitivity and selectivity for many biomolecules.
 
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