Nanoporous Silver-based Surface Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) technology is a powerful tool for the identification of biological and chemical analytes due to its high sensitivity, well-resolved bands, low water interference, which makes SERS be widely used in analytical chemistry, biomedical diagnostics.Nanoporous metals, prepared by dealloying, have received extensive attention due to their good stability, uniform surface morphology and quasi-periodic structure. The surface plasman resonance of these nanoporous metals has been exploited and tried to be used as SERS substrates.In this paper, nanoporous silver, prepared by dealloying Ag-Al alloy, is used as SERS active substrate. Its electromagnetic field coupling with silver nanoparticles has been studied. Moreover, a highly sensitive and selective SERS-based thrombin apasensor has been developed. The details are summarized as follows:1. Tuning the electromagnetic field coupling between nanoporous silver and silver nanoparticles connected by hybridized oligonucleotideOn monolithic nanoporous silver (NPS), via DNA hybridization, we constructed an NPS/DNA-Cy5/silver nanoparticle (Ag NP) sandwich to investigate its SERS effect. In this sandwich, no chemical enhancement contributes to the SERS signal of Cy5. As compared with NPS, the present substrate exhibits particularly strong electromagnetic (EM) field enhancement. At the same Ag NPs surface loading, the SERS intensity decreases exponentially with increasing the length of double-stranded DNA (dsDNA). A larger pore size of NPS leads to weaker EM enhancement within the sandwich, but the relative intensity is not sensitive to the sizes and it is determined by the length of dsDNA. 2. SERS-base thrombin aptasensorThrombin plays an important physiological function in vivo, so its sensitive detection is of great significance. A bifunctional molecule,4-aminothiophenol, was used as connecting molecule. After diazotization of the amino group, it could be form a covalent bond with histidine residuel on the surface of thrombin and made the thrombin to be bound to the surface of silver nanoparticle. Meanwhile, the aptamer of thrombin was immobilized on the surface of nanoporous silver through Ag-S bond self-assembly. Via the specific reaction between thrombin and its aptamer, a thrombin aptasensor was constructed. A N=N bond as Raman marker was fallen into a hot spot formed between nanoposous silver and silver nanoparticle, and its Raman signal selectively enhanced. With increasing the thrombin concentration the intensity of the marker increased linearly over a range of1pM-l nM with a detection limit of ca.0.01pM. Moreover, this assay could distinguish thrombin from other non-target proteins, and therefore presented high selectivity.