Advances in Paper-Based Ammonia Sensors in Environment: Sustainable Materials, Nanotechnology Integration, and Smart Analytical Platforms

This review provides a comprehensive analysis of recent developments in sustainable paper-based sensors for ammonia detection, emphasizing their potential as low-cost, portable, and environmentally benign alternatives to conventional analytical techniques. It systematically evaluates principal sensing strategies including colorimetric, electrochemical, and chemiresistive modalities that utilize natural dyes, engineered nanomaterials, and conductive polymers to achieve enhanced sensitivity and rapid signal transduction. With operational lifespans of 30 to 45 days, colorimetric platforms based on plant extracts and anthocyanins can detect as little as 0.5 mg L−1 in aqueous medium, which makes them ideal for low-cost, disposable applications. WS2–PANI hybrids and CNT/PPy/Pt are examples of chemiresistive nanocomposite sensors that exhibit ppb-level detection (down to 5 ppb) in gaseous environments, fast response–recovery periods (less than 45 s and about 80 s, respectively), and stability for more than 60 days in ambient humidity. Advances in fabrication methodologies such as additive manufacturing and three-dimensional microstructured platforms have facilitated the creation of mechanically flexible devices with capabilities for smartphone-based signal acquisition and real-time analytical performance across diverse application domains. These include environmental surveillance, food quality assessment, occupational safety, and clinical diagnostics, wherein sensor efficacy approaches or surpasses that of standard instrumentation. The review also addresses critical limitations such as analyte selectivity and temporal stability, and explores emerging directions involving integration with internet of things frameworks, use of fully biodegradable substrates, and simultaneous detection of multiple chemical targets. The collective progress reflects a paradigm shift toward the deployment of accessible and ecologically responsible sensing technologies aligned with global health and environmental sustainability objectives.