High selective, sensitive, paper-based probe for Cu(II) detection: Aprospective form Nano-scale turn-on to Micro-scale turn-off states

A new fluorimetric-based method has been developed for detection of Cu(II) usingneocuproine-based carbon quantum dots (CQDs). When Cu(II) is adsorbed onto the surface of theCQDs, it interacts with the functional groups, resulting in either an increase or decrease influorescence emission depending on the concentration of Cu(II). This is the first reported methodthat can detect Cu(II) at both nano-molar and micro-molar levels with two different phenomena,means that ۰.۰۰۱-۰.۱ μM addition of Cu(II) caused the enhancemnet of CQDs’ FL emissionintensity whereas the ۱-۱۰ μM addition of Cu(II) led the FL emission of CQDs to quench. Thisfascinating phenomena can turn this sensing probe into promising platform for real-worldapplications. A low-cost, easy-to-use, highly selective and sensitive CQD-based sensing systemshowed a limit of detection (LOD) of ۰.۰۰۱ μM and a dynamic range of ۰.۰۰۱-۱۰ μM. The sensingpotential of the system on human serum sample has also been tested, showing the recovery of ۹۹.۸-۱۰۳.۴% along with the RSD of <%۶. Surprisingly, the measured concentration of cupric ions inhuman plasma after ۲-۱۰ μM cupric ions addition was found to be ۲۲.۱۵۷ μM, which isastonishingly well fit in the range of cupric concentration in the plasma of healthy individuals ۱.The findings indicate that the CQD-based sensor possesses high accuracy and precision towardCu(II) detection, indicating good potential for practical use.