An iron oxide/reduced graphene oxide (ION-RGO) nanocomposite has been fabricated to functionalize a low-cost electrochemical nitrite sensor realized by light-scribed reduced graphene oxide (LRGO) electrodes on a PET substrate. To enhance the stability and adhesion of the electrode, the PET substrate was modified by RF oxygen plasma, and a thin layer of the cationic poly (diallyl dimethyl ammonium chloride) was deposited. Raman spectroscopy and scanning electron microscopy coupled to energy-dispersive X-ray spectroscopy (SEM-EDX) reveal that the light-scribing process successfully reduces graphene oxide while forming a porous multilayered structure. As confirmed by cyclic voltammetry, the LRGO electrochemical response to ferri-ferrocyanide and nitrite is significantly improved after functionalization with the ION-RGO nanocomposite film. Under optimized differential pulse voltammetry conditions, the LRGO/ION-RGO electrode responds linearly (R2 = 0.97) to nitrite in the range of 10–400 µM, achieving a limit of detection of 7.2 μM and sensitivity of 0.14 µA/µM. A single LRGO/ION-RGO electrode stands for 11 consecutive runs. The novel fabrication process leads to highly stable and reproducible electrodes for electrochemical sensors and thus offers a low-cost option for the rapid and sensitive detection of nitrite.

In this work, we developed and evaluated a Prussian blue (PB)/reduced graphene oxide (RGO) nanocomposite electrode for high-performance symmetric supercapacitors. The nanocomposite was synthesized through the co-precipitation of Fe(II) and [Fe(CN)6]4− ions in the presence of graphene oxide (GO), followed by the deposition of ultrathin films onto indium tin oxide (ITO) substrates via layer-by-layer (LbL) assembly using poly(diallyldimethylammonium chloride) (PDAC) as the polycation. The optimized electrode architecture, obtained by carefully controlling the film composition and number of deposited layers, exhibited a high specific capacitance of 487.1 F g−1 and excellent cycling stability, retaining 77.7% of its initial capacitance after 5,000 charge–discharge cycles. This enhanced electrochemical performance is attributed to the synergistic combination of electric double-layer capacitance (EDLC) and pseudocapacitive charge-storage mechanisms, which emerge from the intimate integration of PB and RGO within the nanocomposite structure rather than from the individual components alone. The technological potential of the ITO/PB/RGO/PDAC electrodes was further demonstrated in a symmetric supercapacitor assembled using filter paper soaked in KCl solution as both electrolyte reservoir and separator. The assembled device was capable of repeatedly powering a red LED (1.8 V) after charging with an external power source, highlighting the practical applicability of the proposed electrode design for energy-storage systems.