Silver nanoparticles/poly ortho-toluidine/modified carbon paste electrode as a stable anode for hydrazine oxidation in the alkaline media

Ag Nanoparticles-Modified 3D Graphene Foam for Binder-Free Electrodes of Electrochemical Sensors

Ag nanoparticles-modified 3D graphene foam was synthesized through a one-step in-situ approach and then directly applied as the electrode of an electrochemical sensor. The composite foam electrode exhibited electrocatalytic activity towards Hg(II) oxidation with high limit of detection and sensitivity of 0.11 μM and 8.0 μA/μM, respectively. Moreover, the composite foam electrode for the sensor exhibited high cycling stability, long-term durability and reproducibility. These results were attributed to the unique porous structure of the composite foam electrode, which enabled the surface of Ag nanoparticles modified reduced graphene oxide (Ag NPs modified rGO) foam to become highly accessible to the metal ion and provided more void volume for the reaction with metal ion. This work not only proved that the composite foam has great potential application in heavy metal ions sensors, but also provided a facile method of gram scale synthesis 3D electrode materials based on rGO foam and other electrical active materials for various applications.

Enzyme-free electrochemical immunosensor based on methylene blue and the electro-oxidation of hydrazine on Pt nanoparticles

Enzyme-free electrochemical sensors enable rapid, high sensitivity measurements without the limitations associated with enzyme reporters. However, the performance of non-enzymatic electrochemical sensors tends to suffer from slow electrode kinetics and poor signal stability. We report a new enzyme-free electrochemical immunosensor based on a unique competitive detection scheme using methylene blue (MB), hydrazine and platinum nanoparticles (Pt NPs). This scheme is coupled with a robust immunosandwich format employing a MB-labelled detection antibody as a non-enzymatic reporter. In the presence of the target antigen, surface-immobilized MB consumes interfacial hydrazine thereby diminishing the electro-oxidation of hydrazine on Pt NPs. Thus, the concentration of the antigen is directly proportional to the reduction in the electrochemical signal. For proof-of-concept, this sensor was used to detect Plasmodium falciparum histidine-rich protein 2 (PfHRP2), an important malaria biomarker, in unadulterated human saliva samples. Chronocoulometric measurements showed that this platform exhibits pM-range sensitivity, high specificity and good reproducibility, making it well suited for many biosensing applications including noninvasive diagnostic testing.