Competitive aptasensor with gold nanoparticle dimers and magnetite nanoparticles for SERS-based determination of thrombin.

It is known that the intensity of surface-enhanced Raman scattering (SERS) of monomeric gold nanoparticles (GNPs) is insufficient for ultrasensitive analysis. The authors describe dimeric GNPs for use in a competitive SERS and aptamer based assay for thrombin. The reagent 1,2-bis(4-pyridyl) ethylene serves as both the coupling agent and the Raman reporter on the GNP dimers. In the presence of thrombin, the hybridization of two aptamers, one attached to the GNP dimers, the other to magnetic nanoparticles, is competitively prevented. This method takes advantage of the unique "hot spots" of the GNP dimers to amplify the Raman signal. This results in an ultra-sensitive thrombin assay when compared to assays using GNP monomers. The limit of detection is as low as 1 fM of thrombin. The Raman intensity, best measured at 1612 cm-1, increases linearly in the 1 fM to 10 nM thrombin concentration range. The method was applied to the determinaiton of thrombin in spiked simulated body fluid and human serum. Graphical abstract This method takes advantage of the unique "hot spots" of the gold nanoparticle dimers to amplify the Raman signal. The dimers are linked to the magnetic nanoparticles via an aptamer. The use of both competitive displacement and magnetic separation greatly improves the sensitivity of the thrombin assay.

Detection of microRNA using a polydopamine mediated bimetallic SERS substrate and a re-circulated enzymatic amplification system.

A surface-enhanced Raman scattering (SERS) method is described for the determination of microRNA that is associated with various forms of cancer. The substrate consists of functionalized gold-silver bimetallic structure, and the sensitivity is strongly enhanced by making use of a re-circulated enzymatic amplification system (REAS). Poly-dopamine acts as both a reductant and a protective of the substrates. It was employed to link the gold core and silver satellite. The unique "hot spots" consisting of a Au@PDA@Ag nanocomposite improve the Raman signal and sensitivity. The reductive feature of PDA can prevent the susceptible oxidation of metallic silver to maintain the high Raman activity. To improve the sensitivity of the assays, a re-circulated enzymatic amplification system was developed in which the nicking endonuclease triggers the nucleic acid reaction system to enter an amplified cycle. By integrating the bimetallic nanosubstrate and magnetic separation into the REAS, microRNA can be detected by SERS (best at the Raman band of 1586 cm-1) with a limit of detection as low as 0.2 fM. In our perception, the assay provides an exciting new avenue to study the expression of tumor genes. Thus, it holds vast promise in cancer diagnosis. Graphical abstract Schematic presentation of the SERS method based on poly-dopamine mediated bimetallic SERS substrate and re-circulated enzymatic amplification.

A novel SERS-based magnetic aptasensor for prostate specific antigen assay with high sensitivity.

The accurate and highly sensitive detection of prostate specific antigen (PSA) is particularly important, especially for obese men and patients. In this report, we present a novel aptamer-based surface-enhanced Raman scattering (SERS) sensor that employs magnetic nanoparticles (MNPs) core-Au nanoparticles (AuNPs) satellite assemblies to detect PSA. The high specific biorecognition between aptamer and PSA caused the dissolution of the core-satellite assemblies, thus the concentration of functionalized AuNPs (signal probes) existing in the supernatant was on the rise with the continual addition of PSA. The aptamer-modified MNPs were used as supporting materials and separation tools in the present sensor. With the assistance of magnet, the mixture was removed from the supernatant for the concentration effects. It was found that the corresponding SERS signals from the supernatant were in direct correlation to PSA concentrations over a wide range and the limit of detection (LOD) was as low as 5.0pg/mL. Excellent recovery was also obtained to assess the feasibility of this method for human serum samples detection. All of these results show a promising application of this method. And this novel sensor can be used for the accurate and highly sensitive detection of PSA in clinic samples in the future.

A novel SERS nanoprobe based on the use of core-shell nanoparticles with embedded reporter molecule to detect E. coli O157:H7 with high sensitivity.

The authors report on a surface-enhanced Raman scattering (SERS) nanoprobe for the specific detection of Escherichia coli O157:H7 (E. coli O157:H7). Gold nanoparticles (AuNPs) were coated with a thick silica shell, and the Raman reporter (4,4'-dipyridyl) was embedded between gold nanoparticle and silica shell. This technique prevents any external effects on the AuNPs from the environment and avoids any interaction between the Raman reporter and possible impurities. Compared to the SERS nanoprobe of the conventional AuNP/AgNP type, the present nanoprobe can be applied in complex biochemical circumstances without aggregation because of its excellent stability. The SERS nanoprobeis stable for up to 50 h. The probe was applied to the SERS detection of E. coli O157:H7 by exploiting the Raman band peaking at 1612 cm-1 of 4,4'-dipyridyl (DP). The limit of detection is as low as 10 CFU·mL-1. The technique was successfully employed to the detection of E. coli O157:H7 in real samples, achieving recoveries between 95.5 and 114.8%. Graphical abstract A novel surface-enhanced Raman scattering (SERS) nanoprobe based on the silica encapsulated gold nanoparticles (SEGNs) combining with the functionalized magnetic nanoparticles (MNPs), detecting E. coli O157:H7 with high sensitivity and specificity.