Fig. 1. Schematic diagram of the experimental setup（sensing system）

Fig. 2. Mode field distribution of single-mode fiber and conical fiber

Fig. 3. Sensor manufacturing process flowchart and the waist cone area of the tapered fiber

Fig. 4. Cu²⁺-II-CS synthesis protocol

Fig. 5. SEM images of CS-PVA-coated and uncoated tapered optical fibers

Fig. 6. Response of uncoated bare cone sensor to Cu²⁺ concentration solution

Fig. 7. Response of CS-PVA tapered fiber optic sensor to Cu²⁺ concentration solution

Fig. 8. Response of CS-PVA ion imprinting sensor to Cu，Cd，Fe，Co，Pb ions

Fig. 9. Repeatability experiment selective detection

Fig. 10. Response time of the CS-PVA ion-imprinted sensor