Electrochemically prepared oxygen and sulfur co-doped graphitic carbon nitride quantum dots for fluorescence determination of copper and silver ions and biothiols.

Although great advances have been achieved in synthesis of fluorescent graphitic carbon nitride quantum dots (g-C3N4-dots), it is still challenging to develop g-C3N4-dots with high fluorescence quantum yield (FLQY) and multiple sensing functionalities. Herein, the oxygen and sulfur co-doped graphitic carbon nitride quantum dots (OS-g-C3N4-dots) with high FLQY of 33.9% were firstly synthesized by a simple electrochemical "tailoring" process. It was found that OS-g-C3N4-dots could specifically bind copper ions (Cu2+) and silver ions (Ag+), accompanied with a dramatic "turn-off" fluorescence response. With the help of different masking agents, OS-g-C3N4-dots are able to selectively detect Cu2+ and Ag+. Furthermore, the generated OS-g-C3N4-dots/Ag+ displayed a "turn-on" fluorescent response specific to biothiols (HCy, Cys and GSH). Therefore, the multiple functional sensing platforms based on "ON-OFF-ON" fluorescence response of OS-g-C3N4-dots for the detection of Cu2+, Ag+ and biothiols were constructed. Under the optimal conditions, the detection limits of Cu2+, Ag+, HCy, Cys and GSH were as low as 7.0 × 10-10 M, 2.0 × 10-9 M, 1.0 × 10-8 M, 1.0 × 10-8 M and 8.4 × 10-9 M, respectively. Moreover, the prepared platforms could be successfully applied to the determination of Cu2+, Ag+ and biothiols in practical samples and exhibited excellent sensitivity and selectivity.