Smartphone-based optical and spectroscopic sensors for food safety monitoring: principles, applications, and future directions.

Food safety monitoring increasingly requires analytical tools that are rapid, portable, and accessible beyond centralized laboratories. In this context, smartphone-based optical and spectroscopic sensors have emerged as highly promising platforms because they combine image acquisition, signal processing, data transmission, and user-friendly interfaces within a compact and widely available device. This review critically summarizes recent advances in smartphone-enabled food safety sensing, with emphasis on the underlying optical principles, hardware integration strategies, analytical workflows, and application scenarios. We discuss the major sensing modalities currently adapted to smartphone platforms, including colorimetric, fluorescence, chemiluminescence, and Raman/surface-enhanced Raman scattering approaches, and examine how camera modules, illumination control, add-on optics, 3D-printed attachments, and app-based processing pipelines influence analytical performance. Recent applications are organized by target class, covering pesticide residues, heavy metals, mycotoxins, adulterants, microbial pathogens, and spoilage-related markers. Across these categories, smartphone-assisted systems have demonstrated strong potential for decentralized screening, field deployment, and point-of-need decision support. However, the transition from laboratory demonstrations to practical deployment remains constrained by unresolved issues related to analytical standardization, validation under realistic food conditions, and integration of smartphone hardware with reliable data-processing workflows. Emerging trends indicate that future progress will be driven by artificial intelligence-assisted analysis, multimodal sensing, sustainable substrates, smart packaging integration, and connectivity with cloud- and traceability-based digital food systems. Overall, smartphone-based optical and spectroscopic sensors are evolving from low-cost imaging tools into increasingly sophisticated analytical platforms with the potential to bridge laboratory-grade detection and real-world food safety surveillance.