A High-Performance and Versatile Fluorometer for Chlorophyll a Monitoring

Chlorophyll a (Chl a) monitoring is vital for aquatic ecosystem assessment but is challenged by low signals and interference. Addressing this, we introduced balanced maximum entropy m-sequence modulation for Chl a fluorescence detection, developing a novel high-sensitivity sensor offered in configurations for both portable and deep-sea applications. The sensor achieved outstanding limits of detection (LOD) of 4.17 ng/L (fluorescein sodium, FS) and 4.82 ng/L (spinach-extracted Chl a), significantly surpassing commercial instruments. It also features a wide dynamic range (0–500 μg/L FS, R2 = 0.9983), excellent long-term stability with negligible drift, measured system response T90 < 24 s, and low power consumption (40 mA working/0.5 mA standby). Critically, a near 1:1 fluorescence response gain between FS and extracted Chl a under the sensor’s specific configuration was experimentally demonstrated, validating FS as a high-precision proxy standard and simplifying future calibration. Field experiments in West Lake confirmed the sensor’s ability to accurately track spatial variations consistent with the standard spectrophotometric method, achieving highly consistent quantitative results (within 3% relative error) at half sampling locations. In summary, the sensor developed in this study, due to its outstanding performance, promises to provide a reliable and efficient new tool for high-precision portable and deep-sea in situ chl a monitoring.