Designing a smartphone in-built, wireless, ultrasensitive hybrid heterostructure-based sensor is challenging, but it is potentially crucial for achieving efficient electrochemical responses related to real-time food safety monitoring. Herein, the pioneering design of a few-layered MXene-tagged NiCoMn-layered double hydroxide (LDH)/amorphous sulfide (MXe/NiCoMn-LDH/S) hollow spheres were fabricated and tagged onto a laser-induced graphene (LIG) electrode for smartphone-based electrochemical detection of nitrite (NO₂ ^-). Benefiting from the unique structural and compositional advantages of MXe/NiCoMn-LDH/S integrated on a flexible LIG electrode platform, the sensor achieved a linear detection range from 0.90 to 25 µM, and a low detection limit of 0.21 µM, along with a high sensitivity of 11.88 µA µM^-1 cm^-2. Additionally, using the LSV, the sensor demonstrated a wider linear range from 10 to 860 µM with a detection limit of 7.38 µM and sensitivity of 1.15 µA µM^-1 cm^-2. It also demonstrated strong anti-interference capability against various organic and inorganic substances, along with excellent reproducibility, repeatability, and reusability, as well as outstanding stability over 30 days. The proposed point-of-care electrochemical system, featuring a portable and affordable LIG electrode design, along with compact smartphone integrity, highlights its advantages over traditional benchtop potentiostats in real-time water quality monitoring in rural and low-resource areas.

Current research on supercapacitors focuses on achieving high specific energy by expanding the voltage window and improving specific capacitance through advanced electrode design. This study presents a new type of pseudocapacitive integrated electrode developed by decorating α-Fe2O3 nanoparticles onto NH4V3O8 multiwalled nanotubes using a simple and efficient method. α-Fe2O3 stores energy through conversion reactions, while NH4V3O8 facilitates intercalation-based storage. The difference in work function between α-Fe2O3 nanoparticles and NH4V3O8 multiwalled nanotubes generates a built-in electric field at the heterointerface, as confirmed by density functional theory calculations. This built-in electric field enables simultaneous operation at both positive and negative potentials, thereby supporting sulfate ion conversion and sodium ion intercalation. These mechanisms are validated by in situ Raman and ex situ X-ray photoelectron spectroscopy analyses. Owing to the coexistence of multiple energy storage mechanisms and the presence of a built-in electric field, the assembled full cell delivers a high specific energy (79 Wh/kg), specific power (5996 W/kg), and a broad voltage window of 2.2 V. These findings emphasize the effectiveness of the integrated electrode design and represent a significant advancement toward realizing next-generation energy storage technologies for a wide array of applications, ranging from portable electronics to expansive renewable power infrastructures.