Spectroscopic Transduction in Miniaturized Lab-on-a-Chip Devices: Functional Nanomaterials and Edge AI Integration for Real-Time in Situ Environmental Monitoring of Heavy Metals, Pesticides, and Marine Pollutants

monitoring of heavy metals, pesticides, marine pollutants, and ocean acidification proxies has exposed the limitations of conventional laboratory-based spectroscopic methods, which suffer from slow turnaround, high costs, and poor adaptability to remote environments. This critical review surveys advances from 2023-2026 in microfluidic lab-on-a-chip (LOC) platforms that integrate functional nanomaterials with spectroscopic transduction (primarily fluorescence, absorbance, surface-enhanced Raman scattering (SERS), surface plasmon resonance (SPR), and quantum dot-based optical detection) and edge-deployable AI. Emphasis is placed on how nanomaterials enhance spectroscopic signals within microfluidic channels while addressing laminar flow control, passive mixing, antifouling, and stability in high-salinity and high-pressure marine matrices. The convergence with lightweight, hardware-aware AI/ML for on-chip denoising, drift compensation, multiplexing, and anomaly detection is examined under strict power and memory constraints. Ocean acidification monitoring requiring high-precision spectrophotometric pH and total alkalinity (TA) measurements serves as a rigorous benchmark for Arctic, open-ocean, and buoy deployments. Performance metrics, matrix interferences, autonomy limitations, and scalability barriers of these spectroscopic LOC systems are critically evaluated, with a forward-looking roadmap toward autonomous, IoT-enabled, and biodegradable spectroscopic microfluidic platforms for sustainable environmental monitoring.