A 3D hierarchical Mn ₃ O ₄ nanoflake structure supported on nitrogenated reduced graphene oxide (NrGO), with excellent oxygen reduction in alkaline medium, was developed by electrodeposition. High performance is attributed to poor nanoflake crystallinity and strong nanoflake–NrGO coupling.

We show that a partially reduced graphene oxide electrocatalyst, synthesized by electrochemical reduction of graphene oxide (GO), displays significantly enhanced catalytic activity towards the oxygen reduction reaction (ORR) in alkaline solutions compared to the starting GO. The electrochemical partial reduction of GO was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. Electrochemical impedance spectroscopy (EIS) verified the enhanced electron transfer ability of the electrochemically reduced graphene oxide (ErGO) compared to GO. The resultant ErGO electrode showed enhanced capacitance and an ORR onset potential of −0.11 V vs. Ag/AgCl, similar to that of a nitrogen doped reduced graphene oxide (NrGO) electrode produced by a hydrothermal process. However the ErGO exhibited considerably lower electron transfer numbers (2.0–3.3 at a potential range of −0.4 V to −1.0 V) indicating that although both catalysts operate under combined 4e ⁻ and 2e ⁻ ORR processes, ErGO follows a more predominant 2e ⁻ pathway. The ORR process in ErGO has been linked to the presence of quinone functional groups, which favour the 2e ⁻ ORR pathway.

We report a self-sufficient microfluidic paper-based lateral flow immunoassay device (μLFD) for highly sensitive detection of the thyroid-stimulating hormone (TSH). Fabrication of the paper microchannels involves engraving the nitrocellulose membrane with a CO₂ laser to create narrow flow paths, which constrain the fluid flow over the test zone. The proposed microchannel modified devices were studied for detection of the TSH using gold nanoparticles as labels. The effect of such microchannel modified LFDs has led to an improvement in sensitivity by nine times and the limit of detection by 6.6 times due to the slow flow rate of the sample compared with the traditional LFD. In addition, the binding of gold nanoparticles over the test line is more uniform in the case of the μLFD, thus minimizing leading-edge effects, resulting in more accurate quantitative analysis. The proposed strategy offers great potential for multiplex detection of biomarkers with increased sensitivity without introducing any hydrophobic materials to the LFD.