Efficient and visual monitoring of cerium (III) ions by green-fluorescent carbon dots and paper-based sensing.

An efficient strategy for the synthesis of excitation-independent carbon nanodots has been provided. This functional nano-scale particle has been assembled by using citric acid and urea as raw materials through a microwave irradiation process in the absence of further surface modifications. The achieved nanomaterial demonstrates intensive green emissions and can be dispersible in aqueous environment. In particular, cerium (III) ion is able to quench its fluorescence emission intensity selectively and an "on-off" change has been observed. A good linearity between the concentration range of 10-6 -10-4  M has been realized and the detection limit is determined to be 0.7 μM. More importantly, we report a color-evolution based paper sensor for effective monitoring of Ce3+ by incorporating fluorescent nanoprobe onto the cellulose paper substrate.