AuNP-protein hybrids

An application of biomolecule-nanoparticle hybrid supramolecular assemblies is the sensitive detection of p53, a tumor suppressor protein, by AuNP streptavidin conjugates capped with multiple ferrocene molecules.26 As shown in Figure 8.6, a mixed monolayer of double-stranded DNA and 1-hexanethiol on an Au electrode is used to capture p53, which binds to DNA containing the consensus site sequence. Subsequent conjugation of the captured p53 with biotin allowed for attachment of... 

Among noble-metal nanoparticles, AuNPs have been the most extensively used in electrochemical biosensor applications. This is because the biochemical activity of the labeled receptor biomolecules (i.e., proteins and DNA among others) is retained when AuNPs are coupled to them (25-27). Particularly, AuNPs have been successfully used as electroactive label in the detection of DNA sequences, based on the highly specific hybridization of complementary strands of DNA (2, 5, 28-31). 

In addition to the solution-phase protein detection assays such as biobarcode assays, a surface-based protein detection method was developed by Niemeyer and Ceyhan (70). In this work, a biotin-labeled antibody was conjugated to DNA using streptavidin as a tinker molecule. This conjugate was hybridized to complementary DNA-AuNPs and antibody-functionalized AuNPs. These particles are allowed to form a sandwich structure with a target protein and a second antibody immobilized on a flat surface. This was followed by a silver enhancement step catalyzed by the AuNPs which resulted in a LOD of 50 fmol (200 pM). This method is conceptually similar to the corresponding surface-based scanometric detection of DNA. Further work demonstrated a similar protein detection scheme without the silver enhancement (71). Instead, multiple layers of secondary DNA-AuNPs were used to increase signal enhancement [LOD = 0.1 finol (2 pM)]. 

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