Smartphone-Based Analytical Platforms: Portable Supplementary Tools for Seawater Monitoring of Nutrients, Heavy Metals, and Emerging Contaminants

The increasing influx of nutrients, heavy metals, and emerging contaminants into marine ecosystems poses serious threats to environmental and human health. Conventional analytical techniques, however, remain largely laboratory-bound, expensive, and unsuitable for real-time field monitoring. In response, smartphone-based analytical platforms have rapidly emerged as a portable, low-cost, and user-friendly alternative for seawater analysis. Nevertheless, to the best of our knowledge, no comprehensive review has yet systematically integrated the three major pollutant categories-nutrients, heavy metals, and emerging contaminants-within the framework of smartphone-based detection specifically applied to seawater matrices. To fill this gap, this review evaluates representative studies on nutrient monitoring, heavy metal ion detection, and emerging contaminant analysis, covering literature published from 2017 to 2025. Despite substantial progress, major challenges persist, including seawater matrix interference, the tradeoff between portability and analytical performance, device-to-device variability, and the lack of standardized protocols. Future directions point toward artificial intelligence-assisted signal processing, hybrid multimodal platforms, cloud-connected monitoring networks, and commercialization. Integrating recent interdisciplinary developments, this review aims to provide a comprehensive reference and perspective regarding smartphone-based analytical platforms as a supplementary tool for routine marine environmental monitoring.