"Development of a low-cost portable sequential detection sensor for quantification of fluoride and cyanide in water".

Safe drinking water monitoring requires inexpensive, on-site tools that can sensitively quantify multiple inorganic anions in complex matrices. We report an integrated, low-cost (<$80) portable fluorescence sensor with the dual-responsive coumarin probe for the quantitative sequential detection of cyanide and fluoride. The device consists of a 405 nm micro-laser as a light source along with AS7265x multispectral detector and ESP32 based microcontroller. Using this device, we achieved the LOD value of 0.08 ppm for cyanide and 0.02 ppm for fluoride with robust linear calibrations (R2 = 0.995 and 0.991, 1-10 ppm), Machine-learning regressors further compensated matrix and co-analyte effects, and pH/interference studies (common cations/anions, pH 6-8) validated field-relevant support. We employed the open-source hardware, a solvent-tuned sequential assay, and data-driven quantification, made the device as a good chemo sensor and the device is the first of this kind for portable fluorescence sensor developed for the fluoride and cyanide with the superior LOD values and it can be extendable for making of device for various toxic molecules and ions.