On-Chip Trace Detection of Heavy Metal Ions in Extreme-Deep Seawater Using CMOS-Integrated Low-Noise Transimpedance Amplifiers

Electrochemical techniques are widely employed for detecting trace heavy metal ions in environmental samples by measuring redox reaction currents. While conventional benchtop electrochemical workstations provide high signal fidelity for higher concentrations, their bulky and discrete components face scalability and noise limitations, restricting their ability to detect trace concentration heavy metal ion of deep-sea samples. To address these limitations, we developed a custom-designed, low-noise, multi-channel complementary metal-oxide-semiconductor (CMOS) transimpedance amplifier integrated circuit (IC) with vertically integrated on-chip electrodes. This system achieves an extremely-low noise level of 273.9 fA _RMS and reduces the electrochemical reaction (ECR) area to just 1 mm², enabling sensitive detection of heavy metals in the wide range of 0.05–500 µg/L. We validated the system’s performance by detecting Cd²⁺ and Pb²⁺ in real seawater samples collected from a depth of 8,448 meters in the Mariana Trench, achieving concentrations of 0.859 µg/L for Cd²⁺ and 0.921 µg/L for Pb²⁺. Compared to inductively coupled plasma-mass spectrometry (ICP-MS), our system demonstrated excellent agreement for Cd²⁺ (0.10% deviation) and reasonable consistency for Pb²⁺ (28.0% deviation), reflecting its selectivity for free ions. Our work provides a robust, portable, and miniaturized solution for trace heavy metal detection under extreme conditions and complex environmental backgrounds, paving the way for advanced in situ oceanic monitoring technologies.