Silver/ions hybrids

Villamo, O., Barboiu, C., Barboiu, M., Yau-Chun-Wan, W. and Hovnanian, N. (2002) Hybrid organic-inorganic membranes containing a fixed thioether complexing agent for the facilitated transport of silver ions. Journal of Membrane Science, 204, 97-110. 

Taton et al. used gold nanoparticles functionalized with thiol-modified oligonucleotides to detect the presence of its complementary sequence hybridized on a transparent substrate (Fig. 13.9).16 In comparison to conventional fluorophore probes, this technique is three times more sensitive in discriminating an oligonucleotide sequence with a single basepair mismatch. In addition, signal amplification by reduction of silver ions on the nanoparticles drastically increased the sensitivity of... 

Figure 13.9 The assembly of oligonucleotide-functionalized Au nanoparticles on an Au surface via DNA hybridization and signal enhancement by reduction of silver ions on the nanoparticles for DNA array detection.16...

Table I shows that the silver-palladium alloys do indeed perform better than the co-precipitates. Silver ions are obviously extracted more rapidly from the physical mixture of silver and palladium in the co-precipitate than from the alloy, but that this improvement is still not enough for a high level of security in critical hybrid circuits.

The formation of the vinyl cation-silver ion complex in the slow step of the reaction is consistent with the observation of an inverse secondary deuterium kinetic isotope effect, because the terminal C—H bond undergoes a hybridization change from sp to sp in the rate-determining step of the reaction. 

A second mechanism was also proposed to account for the kinetic dependence on the concentration of CD3COOD (equation 117). In this mechanism, the deuterated acetic acid supplies the which adds to the silver ion-Tz complex in the rate-determining step of the reaction. This slow step also has the appropriate hybridization change from sp to sp at the terminal acetylenic carbon and would lead to the inverse isotope effect that is observed. 

An interesting detection approach combining enzymatic electrochemical detection and silver precipitation is that reported by Martinez-Paredes et al. [40]. They used the enzyme alkaline phosphatase (AP) to catal3 e the dephosphorylation of the substrate 3-indoxyl phosphate thus producing a compound able to reduce silver ions in solution into a metallic deposit localized where the enzymatic label is attached. The deposited silver is then electrochemically stripped into solution and measured by anodic stripping voltammetry (ASV). The DNA hybridization assay was... 

Silver enhancement is based on the reduction of silver ions from one solution (usually the enhancer) by another (the initiator) in the presence of Au-NPs [77]. The reduction reaction causes silver to build up preferentially on the surface of the Au-NPs, giving rise to a core-shell structure. An illustrative example is the work from Bonanni etal. [78]. They used streptavidin-coated Au-NPs and silver enhancement kits to amplify the impedimetric signal generated in a biosensor detecting the DNA hybridization event. The scheme displaying the sensor preparation procedure is shown in Fig. 4.13. A good reproducibility was achieved (RSD lower than 8.5%), the detection limit being 11.8 pmol. 

Hybridization step is carried out at room temperature in 2 x SSC buffer by dropping a 40 pL aliquot of the biotinylated target for 1 hour and rinsing with Tris buffer pH 7.2. After that 40 pLofSx 10 M S-AP are dropped on the electrode for 1 hour. Then the electrode is rinsed with Tris buffer pH 9.8 and enzymatic reaction with 3-lP and silver ions, and detection step is carried out as mentioned in previous sections. 

On the basis of the previous DNA assay, the Mirkin group has developed a silver staining method to enhance the sensitivity. In the sandwich-type format, thiol-modified oligonucleotides were attached to the soUd support These oligonucleotides and the DNA targets hybridized with the DNA functionalized AuNPs. The reduction of the added silver ions was catalyzed by the AuNPs. The concentration of the DNA target was proportional to that of silver, which was visualized with a flatbed scanner. This method was... 

Wu, J., Chumbimuni-Torres, K.Y, Galik, M. et al. (2009) Potentiomettic detection of DNA hybridization using enzyme-induced metallization and a silver ion selective electrode. Ana/. Chem., SI (24), 10007-10012. 

To test for silver migration, a constant DC voltage is applied between a silver-filled adhesive and a nearby conductor, such that the adhesive is the anode, and the voltage gradient between the conductors is on the order of 1 volt/ mil. Moisture vapor condensed on the intervening surface can permit silver ions to migrate toward the cathode and form a conductive path of metallic silver which short-circuits the device. Migration has traditionally been more of a problem in hybrid than in monolithic ICs, because the adhesive fillet may approach other conductors on the hybrid substrate. 

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