Advances in nanoparticle-enhanced paper sensor for detecting toxic metals in water.

Toxic metals in water pose a serious threat to public health and the environment, especially in regions with limited access to advanced laboratory infrastructure. Traditional methods for detecting toxic metals, such as atomic absorption spectrometry (AAS) and inductively coupled plasma mass spectrometry (ICP-MS), are accurate but expensive, complex, and unsuitable for on-site use. In contrast, paper-based analytical devices (PADs) offer a low-cost, and user-friendly alternative, especially in resource-limited areas. Recent advancements have significantly improved PAD performance, especially through the integration of nanoparticles and the use of enhanced colorimetric and electrochemical detection methods. These improvements have enabled faster, more sensitive detection while maintaining simplicity and field readiness. This review explores key advancements in PAD technology from 2015 to 2025 including advances in sensitivity, nanoparticle functionalization, and smartphone-based readouts. Unlike previous reviews, this study presents a comparative analysis of PAD detection mechanisms, evaluates commercialization and regulatory challenges, and explores emerging trends such as smartphone integration and microextraction techniques. By addressing these aspects, this review highlights key advancements and optimization strategies to enhance the stability, selectivity, and practical implementation of PADs for water quality monitoring.