Advanced gas sensors via nanoscale structure engineering and fabrication strategies

Recent progress in nanoscale materials engineering has reshaped the field of gas sensing, transforming it from empirical material substitution into a design discipline that links fabrication, structure, and performance. This review provides a comprehensive overview of fabrication strategies for nanostructured gas sensors, categorized into three main fabrication processes: wet, dry and hybrid dry-wet fabrication approaches. Wet-synthesis techniques including hydrothermal growth, sol-gel processing, and electrospinning enable the formation of nanowires, nanosheets, and porous networks with a high surface area, controlled morphology, and rich defect chemistry that enhance gas adsorption and charge transfer. Dry-fabrication methods such as physical vapor deposition, plasma etching, and atomic layer deposition provide precise dimensional control, wafer-scale reproducibility, and excellent compatibility with integrated electronic platforms, facilitating scalable and uniform device construction. Hybrid dry-wet fabrication strategies integrate the structural versatility of wet chemistry with the deterministic precision of dry processing to produce hierarchical and conformal nanostructures that optimize gas-solid interactions and enable high-performance device integration. Through a comparative analysis of the recent literature, this review correlates fabrication parameters with the resulting nanostructural features such as porosity, crystallinity, and junction density, and discusses their influence on sensing metrics including sensitivity, selectivity, response and recovery dynamics, and long-term stability. Emerging trends in low-power operation, reproducible array fabrication, and integration with flexible and CMOS-compatible substrates are also highlighted, reflecting the ongoing transition of gas sensors toward intelligent, networked, and application-ready systems. By establishing a process-aware framework that links fabrication design with functional performance, this review aims to guide the rational development of next-generation nanostructured gas sensors for environmental, industrial, and healthcare applications.