Conventional sensing platforms for plant health monitoring are often limited by high operating temperatures, rigid substrates, and poor compatibility with ambient, power-constrained, or biologically sensitive environments. These limitations hinder their integration into emerging platforms such as smart agriculture and plant-interfaced electronics, where mechanical flexibility, energy efficiency, and low thermal budgets are essential. This paper reports a scalable, thermally passive NO₂ sensor based on light-activated 3D TiO₂ nanoarchitectures. Fabricated via sequential glancing angle deposition, the highly ordered porous nanoarchitectures exhibit tunable broadband light scattering and defect-mediated sub-bandgap activation under ambient light. Integrated with a wireless microcontroller and mobile application, the sensor enables autonomous NO₂ monitoring in real-world conditions. Field deployment on Mentha suaveolens plants demonstrates real-time tracking of gas-induced physiological stress, establishing practical ecological relevance. This platform overcomes the key limitations of conventional sensors, offering a structurally tunable, spectrally adaptive, and fabrication-scalable solution for light-powered, bio-integrated environmental monitoring.

Lead-free halide-perovskite memristors have advanced rapidly from initial proof-of-concept junctions to centimeter-scale selector-free crossbar arrays, maintaining full compatibility with CMOS backend processes. In these highly interconnected matrices, surface passivation, strain-relief interfaces, and non-toxic B-site substitutions successfully reduce sneak currents and stabilize resistance states. The Introduction section lays out the structural and functional basis, detailing phase behavior, bandgap tunability, and tolerance-factor-guided crystal design within Ruddlesden-Popper, Dion-Jacobson, vacancy-ordered, and double-perovskite frameworks, each of which is evaluated for its ability to confine filaments and reduce crosstalk in crossbar configurations. The following sections examine the characteristics of charge transport and the dynamics of ion migration, followed by a detailed outline of chemical and mechanical stabilization strategies in response to the high current densities and heat fluxes typical of large-area crossbars. The comparison of solution, vapor, and solid-state synthesis routes focuses on aspects such as film uniformity, grain-boundary control, and compatibility with flexible or heterogeneous substrates, all evaluated against the demanding uniformity requirements of multilevel crossbar programming. The principles of resistive switching and array architecture are elaborated upon, emphasizing the three-dimensional (3D) stacking of selector-integrated vertical nanowires and hybrid photonic-memristive layers as promising approaches to enhance bandwidth and reduce energy consumption per operation. By integrating sustainable chemistry with scalable crossbar engineering, these memories are set to provide ultra-dense, energy-efficient hardware that meets the performance demands of contemporary artificial intelligence accelerators while adhering to new regulations on hazardous materials in electronic devices.