Tunable LSPR of silver/gold bimetallic nanoframes and their SERS activity for methyl red detection.

Ag/Au bimetallic nanostructures have received much attention in surface-enhanced Raman scattering (SERS). However, the synthesis of this nanostructure type still remains a challenge. In the present research, Ag/Au nanoframes were synthesized via a simple room temperature solution phase chemical reduction method using pre-synthesized triangular Ag nanoplates as templates in the presence of appropriate amounts of HAuCl4. Controlling experimental parameters was applied for understanding of the growth mechanism. The galvanic exchange reaction resulted in a uniform deposition of the Au shell on the Ag nanoplates and the Ag core was removed which generated triangular hollow nanoframes. It is found that the amount of HAuCl4 added to the growth solution played a key role in controlling the Ag/Au nanoframes. The resultant silver/gold nanoframes with average size of 50 nm were applied in detecting methyl red (MR) in the solution-phase using an excitation wavelength laser of 532 nm. The SERS signal was greatly enhanced owing to the tunable plasmonic peaks in the visible region (400-650 nm). The limit of detection (LOD) of MR in diluted solution was 10-6 M. The enhancement factor (EF) was about 8 × 104 toward 10-5 M of MR. Interestingly, the linear dependence between the logarithm of the SERS signal intensity (log I) and the logarithm of the MR concentration (log C) occurred in the range from 10-6 to 10-4 M. Our work promises the application of Ag/Au nanoframes as a chemical sensor in detecting MR molecules at low concentration with high performance.

A label-free and highly sensitive DNA biosensor based on the core-shell structured CeO2-NR@Ppy nanocomposite for Salmonella detection.

A core-shell cerium oxide nanorod@polypyrrole (CeO2-NR@Ppy) nanocomposite-based electrochemical DNA biosensor was studied for Salmonella detection. The core-shell CeO2-NR@Ppy nanocomposite was prepared by in situ chemical oxidative polymerization of pyrrole monomer on CeO2-NRs, which provided a suitable platform for electrochemical DNA biosensor fabrication. The immobilization of ss-DNA sequences onto nanocomposite-coated microelectrode was performed via covalent attachment method. DNA biosensor electrochemical responses were studied by cyclic voltammetry and electrochemical impedance spectroscopy with [Fe (CN)6]3-/4- as redox probe. Under optimal conditions, DNA biosensor response showed good linearity in the range of 0.01-0.4 nM with sensitivity of 593.7â€¯Ω·nM-1·cm-2. The low limit of detection and limit of quantification for the DNA biosensor were 0.084 and 0.28 nM, respectively. The proposed DNA biosensor also showed good results when used in detecting actual Salmonella samples.

Biosensor based on nanocomposite material for pathogenic virus detection.

This paper introduces a DNA biosensor based on a DNA/chitosan/multi-walled carbon nanotube nanocomposite for pathogenic virus detection. An easy, cost-effective approach to the immobilization of probe DNA sequences on the sensor surface was performed. Cyclic voltammograms were used to characterize the probe DNA sequence immobilization. Complementary sequence hybridization was examined by electrochemical impedance spectroscopy. Results revealed that the developed DNA sensor can detect a target DNA concentration as low as 0.01×10(-12) M. The sensitivity of the prepared sensor was 52.57 kΩ/fM. The reusability and storage stability of the DNA sensor were also investigated. Results showed that the electron-transfer resistance decreased to approximately 35% after 8 weeks and to approximately 80% after 12 weeks of storage.