Rapid warning microanalyzer for heavy metals monitoring in natural waters

A warning microanalyzer for the rapid monitoring of different heavy metals in water using Carbon Dots (CDs) as selective optical reagents is presented. The synthesized CDs have different surface functionalization and exhibit selective fluorescence quenching by heavy metal ions, that combined with the use of microfluidics, provide sensitivity, ease of automation and reproducibility to the method. Moreover, they present maximum excitation wavelengths around 350 nm, allowing multiparametric analysis with a single light source. Although quantum yields range from 16 % to 78 % depending on the type of CDs, enough sensitivity is achieved for each heavy metal using the same measurement conditions of the optical detection system (lock-in modulating frequency, signal amplitude and measurement frequency). The microanalyzer is composed of a Cyclic Olefin Copolymer (COC) analytical microsystem, a flow management system, and a miniaturized customized optical detection system. In this paper, we demonstrate that our proposed system can be used as a toxicity control system by selectively measuring five different heavy metal ions (Co²⁺, Cu²⁺, Hg²⁺, Ni²⁺, and Pb²⁺) with detection limits ranging from 2 to 12 ppb. Spiked tap water samples were analyzed, giving recoveries from 98 % to 134 %. Polluted samples containing four of the five heavy metal ions studied (Co²⁺, Cu²⁺, Ni²⁺, and Pb²⁺) were also analyzed with no significant differences observed between both methods, the proposed microanalyzer and the reference method (ICP-OES).